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Cleistogamy, the production of open (chasmogamous, CH) and closed (cleistogamous, CL) floral forms by one species, is present in soybean [Glycine max (L.) Merr.]. Soybean cultivars that originated from high latitudes generally have a strong tendency to produce CL flowers. The first objective of this study was to determine varietal differences in cleistogamy. The second objective was to observe morphological differences between CH and CL flowers. A total of 32 and 31 soybean cultivars (maturity groups 00 to II) were grown in fields at Tsukuba and Sapporo, Japan, respectively, in 2005. Flowers that were fertilized up to 5 d after anthesis were classified into either CH or CL. Frequency of CL flowers ranged from 0.0 to 100.0% in Tsukuba and 6.7 to 100.0% in Sapporo. Cultivars from Russia and Hokkaido generally had a high frequency of CL flowers, whereas those from the Tohoku region had a lower frequency. Average of mean temperatures for 1 wk before anthesis was negatively correlated with frequency of CL flowers. Growth chamber experiments were conducted using CL cv. Severnaya 4 and a CH cv. Toyosuzu under constant temperatures of 25[degrees]C to eliminate temperature effects. Frequency of CL flowers in Severnaya 4 and Toyosuzu was 33.7 and 92.8%, respectively, suggesting involvement of genetic factors. At the same developmental stage, CL flowers had shorter sepal, petal, and stamen than CH flowers. There was no distinct morphological change in floral organs between CH and CL flowers except for length of the organs. doi: 10.2135/cropsci2009.02.0108

Stress during tassel formation can reduce tassel size and cause insufficient pollen production in seed production. When stresses affect plant development, component compensation for grain yield is known to occur in some crops. Tassel component compensation for pollen production has not been previously reported. Chilling was imposed on two dent maize (Zea mays L.) inbreds (103 and 113 relative maturity [RM]) at the initiation of tassel formation, a critical period for maximizing pollen production. The 103 RM inbred showed limited response to chilling stress. The 113 RM inbred produced 60% fewer branches resulting in 45% fewer spikelets and 43% fewer pollen grains per tassel when chilling was applied during branch meristem initiation. For the same inbred, 42% fewer spikelets and 29% fewer pollen grains per tassel were produced when chilling was applied during spikelet meristem initiation. Chilling stress during meiosis of microsporogenesis did not decrease pollen production per anther. A decrease in the percentage of starch-filled pollen grains was found only in the lower florets on the lowest branch. The effect of decreased branch or spikelet production on total pollen production was not compensated by subsequent production of spikelets, florets, anthers, or pollen grains per anther. Susceptibility of pollen production to chilling stress during tassel formation varies among modern dent inbreds, although plasticity in the tassel for pollen yield was not observed.

Cytoplasmic male sterility (CMS), a maternally inherited trait characterized as an inability to produce functional pollen, is an important biological system for economically producing hybrid seed to enhance crop yield and studying cytoplasmic and nuclear gene interactions. In cultivated tetraploid cotton (Gossypium hirsutum L.), male fertility in two systems CMS-D2 and CMS-D8 is restored by two restorer genes [Rf.sub.1] and [Rf.sub.2], respectively. The objectives of the present study were to identify additional molecular markers for the two restorer genes and to determine their chromosomal location in the cotton genome. Two backcross ([BC.sub.1][F.sub.1]) populations were developed with D2 and D8 restorers containing their respective cytoplasms as female in crosses with the same Upland cotton maintainer as male and recurrent parent. One pentatricopeptide repeat (PPR)-based target region amplified polymorphism (TRAP) marker was developed to be tightly linked to the [Rf.sub.1] gene with a genetic distance of 0.8 cM, while three more simple sequence repeat (SSR) markers (NAU2232-550/650, NAU2232-750/850, and NAU 2801-250) were identified to be closely linked to [Rf.sub.2]. Using two common SSR markers, a consensus linkage group was constructed to include both [Rf.sub.1] and [Rf.sub.2] loci that were anchored in a 14.0-cM region by the two PPR gene-based markers. Based on four chromosome-anchored SSR markers, [Rf.sub.1] and [Rf.sub.2] were localized on chromosome D5 within a genetic distance of 1.4 cM, providing an incentive for further investigations of this [Rf.sub.1]/[Rf.sub.2]-containing region.

Poa is a complex genus taxonomically and genetically. As a result, relatively little information exists for this economically important genus with regards to reproductive mode and variability in chromosome number. We examined apomixis frequency and ploidy levels in 83 Poa accessions representing 33 species from the National Plant Germplasm System using flow cytometric techniques. In reproductive mode analysis, we analyzed at least three preparations of 50 seeds each from the accessions. In ploidy level analysis, at least three plants of each accession were analyzed. Sixty percent of the species had at least one apomictic or facultative apomictic accession; 40% were sexual. Thirty-three percent of the species had no sexual accessions. Autonomous apomixis was newly identified in P. bactriana and P. bulbosa in addition to it being previously reported in P. nervosa. Poa annua and P. trivialis were identified as obligate sexual, and P. nervosa as obligate apomictic. Two of four P. palustris accessions exhibited facultative apomixis. Ploidy levels among sexually reproducing Poa accessions ranged from 2n = 2x = 14 to 2n = 12x = 84, with most accessions between 2n = 3x = 21 to 2n = 8x = 56. Among apomictic accessions, ploidy levels ranged from 2n = 3x = 21 to 2n = 10x = 70, with most between 2n = 4x = 28 and 2n = 10x = 70. These results emphasize the wide variability in Poa, both among and within species.

Paspalum plicatulum Michx. is a wild forage grass species. The common races are tetraploid and apomictic, while sexual diploid representatives have been reported sporadically. Objectives of this study were to induce sexual 4x individuals from sexual diploids, determine the capacity for hybridization with other apomictic 4x species closely related with P. plicatulum, and thus create a tetraploid sexual material cross compatible with apomictic 4x species of the Plicatula group of Paspalum. Two induced tetraploid plants were recovered from germinating 2x seeds treated for 24 h with colchicine. Bivalent and quadrivalent chromosomes were the most common association at meiosis in these autotetraploids. Embryological analysis and progeny tests using molecular markers revealed that both induced tetraploids reproduced sexually. Single-seed screening by flow cytometry confirmed full sexual reproduction. These plants retained the high self-incompatibility system of the diploids, but set seed after reciprocal crosses and when crossed with pollen of apomictic 4x P. guenoarum Arechav. of the Plicatula group. Both sexual 4x plants constitute the foundational material for plant improvement through gene exchange and selection in apomictic 4x P. plicatulum and possibly in several apomictic species of the Plicatula group.

Maturity classification is an important concept to provide the best allocation of resources for soybean [Glycine max (L.) Merr.] research and commercialization. A similar maturity group system used in North America is being used for some seed companies in Brazil and needs research to improve its use. This study evaluated the maturity stability of 48 midwestern and 40 southern Brazilian commercial cultivars ranging from North American maturity groups VI to VIII at 15 locations. Relative maturity groups were attributed to all cultivars. All trials were planted in the first half of November. The effect of location was very important in influencing the number of days to maturity, number of days to flowering and reproductive growth period (RGP). The genotype x environment interaction, although statistically significant, was much lower than the individual effects of environment and genotype for all traits and regions. Genotype x latitude and genotype x altitude, considering also years of evaluation, were generally low or nonsignificant. A recommended list was developed of the most stable genotypes and, consequently, of the most suitable check genotypes for each maturity group classification in the southern and midwestern regions. Results indicate that the use in Brazil of a maturity group system similar to that used in North America to classify soybean genotypes is an efficient method for describing relative maturity on a broad environmental basis.

The coexistence between genetically modified (GM) and non-GM maize (Zea mays L.) fields is subjected to regulation in several countries. A strategy to reduce cross-pollination from GM to non-GM fields was evaluated, on the basis of reducing the flowering coincidence by sowing at separate times. The trial included narrow plots in which transgenic maize was sown before, simultaneously, and after adjacent non-GM maize. A three-week delay between GM and non-GM sowing dates resulted in flowering delays below 5 d for early sowings, but up to 10 to 15 d for late sowings. Cross-pollination was monitored by xenia effect and validated by real-time PCR. The combined effect of flowering delay and distance from the pollen source was evaluated. Cross-pollination dramatically decreased with distance between pollen source and receptor. Flowering delay interacted with distance to the pollen donor source and further reduced GM pollen flow in all cases. Thus, it acted as a regulatory factor. A flowering delay of 92.9 growing degree units (GDU) (7 d in our experimental conditions) was enough to reduce the adventitious presence of GM kernels in non-GM maize plots down to residual values. This study illustrates the possibility of improving coexistence through temporal separation of flowering dates on the basis of appropriate delays in sowing dates.

Spikelet number per panicle is a major target trait for improving rice (Oryza sativa L.) yield in upland fields and is strongly affected by water stress. The rice panicle consists of rachis branches and spikelets, in which preflowering spikelet abortion often occurs. We investigated the effect of timing and intensity of water stress at the early reproductive stage on the morphology of rice panicles in field and pot experiments. In the field experiment, water stress caused high rates of preflowering spikelet abortion, and spikelet number was reduced by 48% on average. Pot experiments revealed the effects of water stress on panicle morphology were dependent on the developmental stage, and water stress at the meiosis stage (10-20 d before heading) induced the highest frequency of preflowering spikelet abortion. At the meiosis stage, a mild water stress (no visible effect and less than 20% reduction in biomass production) was sufficient to cause a considerable increase in secondary rachis branch abortion (70%) and resulted in a 40 to 45% reduction in spikelet number per panicle. Reduction in plant water status under drought conditions was related to preflowering spikelet abortion, suggesting that the drought avoidance mechanism is effective for maintaining spikelet number in upland rice.

Sorghum (Sorghum bicolor L. Moench) grown in semiarid regions is often exposed to short periods of high-temperature (HT) stress during reproductive development. Objectives of this research were (i) to quantify the effects of short episodes of HT stress during reproductive development on physiological, growth, and yield processes of grain sorghum and (ii) to identify the stage(s) most sensitive during the reproductive development phase to HT stress. Plants of hybrid DK-28 E were grown in growth chambers at daytime maximum/nighttime minimum optimum temperature (OT) of 32/22[degrees]C until 29 d after sowing. Thereafter, plants were exposed to OT or HT (40/30[degrees]C) or were reciprocally transferred at 10-d intervals (10 d before flowering, 0, 10, 20, and 30 d after flowering [DAF]) from OT to HT and vice versa. Transferred plants remained in the new temperature regime for 10 d before being returned to their original temperature regime. Continuous HT stress delayed panicle emergence and decreased plant height, seed set, seed numbers, seed yield, seed size, and harvest indices but did not influence leaf photosynthesis. Exposure to short (10-d) periods of HT stress at flowering and 10 d before flowering caused maximum decreases in seed set and seed yield, and HT stress during postflowering stages (10, 20, and 30 DAF) decreased seed yield, with a larger reduction at early stages of seed development.

A strong vernalization requirement can increase the amount of time needed per breeding cycle for cool season grasses, and the presence of awns can be an eye irritant to grazing livestock. Our objective was to identify awnless tetraploid (2n = 4x = 28) Elymus accessions capable of flowering quickly and consistently in the greenhouse. A total of 244 accessions, encompassing 27 Elymus species and subspecies, were evaluated during three different time periods in the greenhouse at Ardmore, OK. Heading date of accessions ranged from 53 to 90 d after planting, with 175 accessions representing 20 species or subspecies, flowering within 90 d of planting in the greenhouse. Eighty-eight accessions, representing 11 species or subspecies, were awnless or awnletted (i.e., awns

Apomixis--asexual reproduction through seed--orovides a convenient means to faithfully propagate even heterozygous genotypes and hence expIoit heterosis, in several naturally apomictic, warm-season forage grasses. Inheritance of apomixis has been shown to be monogenic dominant in at least four economically important panacoid grasses Previously proposed breeding schemes for apomicts do not provide a means to accumulate genes contributing to nonadditive, heterotic effects over cycles of selection and recombination. Following the development of successful brachiariagrass [Brachiaria (Trin.) Griseb] cultivars by ecotype selection, artificial hybridization of brachiariagrasses began in the late 1980s with the development of a sexual tetraploidized biotype of the natural diploid, sexual ruzigrass (Brachiaria ruziziensis Germain and Evrard). A breeding scheme--recurrent selection for specific combining ability designed to accumulate nonadditive effects, originally proposed for sexual maize (Zea mays L.), is suggested as an appropriate scheme for improvement of apomictic tropical grasses, Recurrent selection on specific combining ability or interpopulation selection schemes such as reciprocal recurrent selection should be appropriate for other asexually propagated crops.

Cassava (Manihot esculenta Crantz) is a vitally important food source for many people in developing tropical countries. There are significant opportunities for improving the compositional qualities and pest resistance of cassava, and modern biotechnology is expected to play an important role in these improvements. The testing and development of genetically modified cassava will of course be subject to regulatory review, and experimental field trials must be performed in a fashion that prevents gene flow from the regulated plants. Methods to ensure reproductive isolation will be derived from a fundamental understanding of the biology of the crop. A current and comprehensive document on cassava reproductive biology is not yet available but is essential to guide regulators and scientists in planning and evaluating measures for reproductive isolation of confined field trials. This paper compiles a current view of the reproductive biology of cassava for use in experimental design and regulation of confined field trials. With the current state of knowledge on gene flow and seed dormancy in cassava, three methods for reproductive isolation of regulated experimental plots may currently be recommended: (i) removal of flower buds before flowering, (ii) destruction of plants before flowering, and (iii) floral bagging to contain pollen and seed. Areas for further research in cassava biology and biosafety are suggested.

CERES-Maize simulates kernel set as a sourcelimited process based on average plant growth rate during the lag phase after flowering. Yet the number of kernels formed by maize (Zea mays L.) also depends on timely interaction between male and female flowers, which can limit formation of reproductive sinks under some conditions. Failure to account for sink-limited kernel set may contribute to simulation error observed under conditions that affect dynamics of pollen shed or silking, but do not alter crop growth rate. We developed algorithms for a Flowering Model to simulate sink-limited kernel set from flowering dynamics. This model was calibrated against kernel production in hybrid seed production fields and then linked to CERES-Maize. The Modified CERES-Maize was calibrated against two years of field data involving three hybrids, eight population densities, and seven N levels. Integrating the capacity to simulate sinklimited kernel set with source-limited kernel set increased simulation accuracy dramatically, relative to original CERES-Maize. For 13 commercial fields tested, Modified CERES-Maize decreased simulation error for kernels per plant from 17.1 to 2.3%, improved P between measured and simulated values from 0.77 to 0.87, and decreased simulation error indicators mean error, root mean square error, and mean square deviation by 85, 40, and 64%, respectively. Modified CERES-Maize accounts for a much greater range of variability in the biological processes controlling kernel set.

Bahiagrass (Paspalum notatum Flugge) is one of the major forage grasses used for beef cattle production in the southern USA. Description of the reproductive characteristics of bahiagrass germplasm is needed for genetic improvement of this forage crop. The objective was to determine and compare the mode of reproduction of diploid and tetraploid germplasm of bahiagrass. Reproductive behavior was determined by embryo sac observations and a series of controlled pollination studies in the greenhouse and field in 2004 and 2005. Two sexual diploid populations ('Pensacola' and 'Tifton 9') were not different in self- or cross-fertility, indicating that the general fertility of the crop was not affected by phenotypic mass selection. Sexual diploids, as a group, were determined to be primarily cross-pollinated, with low but variable levels of self-fertility. A group of 20 artificially induced tetraploids was determined to be primarily sexual and cross-pollinated. Fertility of these autotetraploids was lower than the original diploids. Two selected sexual tetraploids produced similar amounts of seed when self- or cross-pollinated. In contrast, six other tetraploids, including the cultivars Argentine and Wilmington, the experimental hybrid Tifton 7, and three plant introductions 315732, 315733, and 315734 reproduced primarily by apomixis. The sexual or apomictic expression, the general fertility, and other agronomic characteristics of these groups of tetraploids define their usefulness for genetic improvement research.

Duration of the reproductive phase (DRP) is critical for soybean [Glycine max (L.) Merr.] yield. Manipulation of this phase may benefit breeding for higher yield. The soybean E-gene series control time to flowering and maturity through a photoperiod-mediated response. It is possible that E-genes and photoperiod may control the DRP. Two 2-yr studies were conducted with the objective to assess whether the DRP is influenced by either or both E-gene alleles and post-flowering photoperiod. In a planting-date experiment, the main plots were two planting dates, and sub plots were 15 E-gene near-isogenic lines (NILs) in two genetic backgrounds. In a daylength-extension experiment, seven E-gene NILs were planted to synchronize flowering date. Two photoperiods treatments were imposed after flowering: (i) ambient and (ii) ambient plus 3-h incandescent daylength extension. Early planting and daylength extension exposed plants to a longer post-flowering photoperiod, and resulted in an increase in the DRP. When exposed to the same post-flowering photoperiod, the DRP was positively related to the number of dominant E-gene alleles. Both E-genes and post-flowering photoperiod controlled the DRP and this was in addition to the known impact of E-genes on time to flowering. Hence, E-genes control time to maturity through both their effect on time to flowering and through their effect on the DRP. The results of this study underline the importance of time of flowering for determination of the DRP.

Synchronous pollination improves maize (Zea mays L.) kernel set, but the physiological reasons behind this response are yet unclear. We registered ovary fresh weight evolution at three floret positions along the ear (base, middle and tip) of plants subjected to natural (NP) or synchronous (SP) pollination during two growing seasons. Synchronous pollination of ears bagged before silking was performed five days after silking (DAS). Ovary weight increased exponentially at all floret positions (P [less than or equal to] 0.01), but a lag in this trait was detected among those at the base and middle of SP ears. At each sampling date, florets along the ear differed (P < 0.01) in ovary weight, but differences were larger for NP than for SP plants. At pollination of each floret position, however, the range in ovary weight was smaller in NP ears (ca. 4 to 5 mg [ovary.sup.-1]) than in SP ears (4 to 9 mg [ovary.sup.-1]). Contrarily, just pollinated ovaries at the tip of the ear of NP plants (i.e. on ca. 4-5 DAS) experienced the high growth rate of those already pollinated at the base (ca. 0.7 mg [d.sup.-1] for the former and ca. 3.7 mg [d.sup.-1] for the latter). The range in ovary growth rate along the ear was drastically reduced under synchronous pollination on 5 DAS (ca. 0.55 mg d 1 for the base and ca. 0.47 mg [d.sup.-1] for the tip). The larger the tip-to-base ratio in ovary growth rate, the larger the number of kernels set per plant ([r.sup.2] = 0.94; P = 0.03).

Soybean [Glycine max (L.) Merr.] seed protein is deficient in the essential sulfur-containing amino acids, methionine, and cysteine. Transgenic approaches to increase coding for these amino acids have not been particularly fruitful. Little is known about the relative importance of S stored in vegetative tissues for seed protein synthesis. This study was conducted to secure data on sulfur (S) uptake, distribution, and mobilization patterns in the reproductive phase of soybean grown under S sufficient conditions. Soybean plants were grown in hydroponic culture and pulsed with 3sS labeled S[O.sub.4] at several discrete stages during the reproductive phase of development. Sequential harvest of plants indicated where and how S is stored and mobilized during reproduction in soybean. Leaves supplied developing soybean seed with approximately 20% of its S requirement. Distribution of newly acquired S within plants changed through reproductive development; however, leaves mobilized S with a similar efficiency through R5.5. Expanding leaves take up disproportionately large quantities of S; however, leaf tissue seems dependent on newly acquired S, and is unable to utilize stored S[O.sub.4]. Pods play an important role in S storage and mobilization to seed. In contrast to the leaf fraction, expanding pods were able to utilize stored S. Pods and seeds seem dependent on mobilized S. This study demonstrates that developing soybean seeds are dependent on S that has been mobilized from other plant tissues., SOYBEAN SEED is an important source of dietary protein for humans and livestock; however, its protein contains low concentrations of the essential amino acids methionine and cysteine (Food and Agricultural [...]

Sorghum [Sorghum bicolor (L.) Moench] breeders have long recognized the importance of exotic germplasm and noncultivated sorghum races as sources of valuable genes for genetic improvement. The genus Sorghum consists of 25 species classified as five sections: Eu-sorghum, Chaetosorghum, Heterosorghum, Para-sorghum, and Stiposorghum. Species outside the Eu-sorghum section are sources of important genes for sorghum improvement, including those for insect and disease resistance, but these have not been used because of the failure of these species to cross with sorghum. An understanding of the biological nature of the incompatibility system(s) that prevent hybridization and/or seed development is necessary for the successful hybridization and introgression between sorghum and divergent Sorghum species. The objectives of this study were to determine the reason(s) for reproductive isolation between Sorghum species. The current study utilized 14 alien Sorghum species and established that pollen-pistil incompatibilities are the primary reasons that hybrids with sorghum are not obtained. The alien pollen tubes showed major inhibition of growth in sorghum pistils and seldom grew beyond the stigma. Pollen tubes of only three species grew into the ovary of sorghum. Fertilization and subsequent embryo development were not common. Seeds with developing embryos aborted before maturation, apparently because of breakdown of the endosperm. Abbreviations: EBN, endosperm balance number., SORGHUM is a major cereal crop of marginal rainfall areas of the tropics, with selected varieties widely grown in temperate regions. Recent annual grain sorghum yields have exceeded 61 000 [...]

The extent of pollen-mediated gene flow (PMGF) in wheat (Triticum spp. L) as a function of distance from a pollinator source has been measured in recent field studies. Wheat is primarily self-pollinated; however, some cross-pollination can occur depending on biological, agronomic, and environmental factors. The complexity of these interactions restricts attempts to develop a workable mechanistic model; therefore, we pursued an entirely empirical modeling approach. We fit a simple empirical regression model to all available observed data and then used it to make general predictions about the effects of field size, blending at harvest, and isolation distances on PMGF in wheat. The empirical model was derived by fitting a least squares regression line to the gene flow data when plotted as the logarithm of PMGF versus the square root distance from the edge of the source field. Linear behavior was observed when either the maximum or mean PMGF was plotted in this manner. A 'General Wheat Model' (GWM) of this same mathematical form is given which provides a conservative ('high-end') prediction of PMGF in the general case: PMGF (%) = [10.sup.-(0.2)[square root of x]], where PMGF is the percent gene flow at a particular point in the field (without blending), and x is the distance (m) from the edge of the source field. The GWM was used to show that the effect of source field size is minimal for sources of 10 ha or larger, where asymptotic levels of PMGF are obtained. The model was also applied to show that harvest-blending produces PMGF at the field level 10 to 50 times lower than the highest level observed at the edge of the receptor field. Significantly, isolation buffers of 0 to 10 m were predicted by the GWM to have only a minimal impact on harvest-blended PMGF, when the receptor field had an overall width of 100 m or greater. Without any isolation buffers, the harvest-blended PMGF between neighboring commercial-sized (>10 ha) fields was less than 0.1% (well below commercial thresholds for foreign material in wheat seed and grain). This is also well below any existing standards for labeling the presence of approved biotech traits in food or seed distributed or sold as conventional. Abbreviations: α, empirical factor relating percent gene flow to distance from source; GWM, General Wheat Model; Log10, logarithm base 10; [P.sub.o], percent gene flow immediately adjacent to the source; PMGF, pollen-mediated gene flow., POLLEN-MEDIATED GENE FLOW is the transfer and incorporation of genetic information between distinct plant populations when cross-pollination occurs. PMGF is a natural biological process that occurs to some degree in [...]

Nod factors, also known as lipo-chitooligosaccharides (LCOs), are signal molecules produced by rhizobia during rhizobia-legume symbiosis. These Nod factors often must be purified, sterilized, and stored before use in research experiments. Therefore, we evaluated the influence of purification, sterilization, and storage methods on degradation and biological activity of Nod factor comprised primarily of Nod BjV(C18:1 MeFuc). During filter sterilization, various types of filters affected the amount of LCO recovered: polyestersulfone (67.7%), cellulose acetate (54.9%), nylon (48.1%), polytetrafluoroethylene (38.0%), and mixed cellulose ester (31.8%). During autoclaving (durations of 15 to 30 min) ~30% of the LCO was lost. LCO degraded faster when stored at 23 ± 2°C (room temperature) than at 4 ± 1°C (refrigerator); after 16 mo, 74% of the LCO was recovered following room temperature storage and 84% following refrigerator storage. The biological activity (root hair deformation and stimulation of soybean seed germination) of LCO (10 7 M) obtained from autoclaved and stored samples were not different from that of freshly prepared LCO; no reduction in biological activity was found. Abbreviations: LCO, lipo-chitooligosaccharide., SUCCESSFUL ESTABLISHMENT of the nitrogen fixing rhizobia-legume symbiosis requires a complex exchange of signal molecules between the symbionts. Nod factors are the bacteria-to-plant signals and they are produced by bacteria [...]

Common buckwheat (Fagopyrum esculentum Moench; Polygonaceae) embryos accumulate six fagopyritols in two unique series: fagopyritol A1, fagopyritol A2, fagopyritol A3, fagopyritol B1, fagopyritol B2, and fagopyritol B3. Fagopyritol A1 is isosteric to a putative insulin mediator believed to be deficient in subjects with noninsulin dependent diabetes mellitus (NIDDM) and polycystic ovary syndrome (PCOS). Fagopyritols accumulate during seed development, and accumulation is enhanced in response to cooler temperatures. The objective was to test the hypothesis that seed maturation at cooler temperature enhances fagopyritol accumulation, improves seed quality, and increases yield of desirable fagopyritols for dietary treatment of NIDDM and PCOS. Seeds from buckwheat plants grown at 15, 22, or 30°C were harvested at 8, 12, 16, 20, and 28 d after pollination (DAP) and analyzed for soluble carbohydrates in the embryos. Remaining seeds were dried and tested for germination and seedling growth. Embryo dry weight increased rapidly between 8 and 12 DAP at 30°C, 12 and 16 DAP at 22°C, and 16 and 20 DAP at 15°C. Seed dry weight declined (-0.86 mg per 1°C) when maturation temperature increased. Total soluble carbohydrates remained constant across seed maturation temperatures, but the composition of carbohydrates changed in response to different maturation temperatures. Fagopyritol A1 and fagopyritol B1 were highest in seeds matured at 15°C, whereas fagopyritol A2, fagopyritol B2, fagopyritol A3, raffinose, and stachyose were higher in seeds matured at 30°C. At harvest, seeds matured at 30°C had highest germination. Cool temperatures during buckwheat seed maturation can result in increased seed size and yield of fagopyritol A1 and fagopyritol B1 in embryos for nutritional and medicinal applications. Abbreviations: DAP, days after pollination; DGMI, digalactosyl myoinositol; DW, dry weight; FW, fresh weight; NIDDM, noninsulin dependent diabetes mellitus; PCOS, polycystic ovary syndrome; RFOs, raffinose family oligosaccharides; RH, relative humidity., ORIGINATING in northeast Asia, southern Siberia, and northern China, common buckwheat (Polygonaceae family) is one of 18 recognized natural species of Fagopyrum and is the most important from economical, agricultural, [...]

Molecular tools have not identified the gene(s) governing apomixis nor have they been used to successfully transfer the trait to important, sexually reproducing food crops. Several molecular studies addressing apomixis in grasses have used interspecific and intergeneric hybrids. The failure to recover specific [F.sub.1] genotypes from these wide crosses can be caused by unfavorable interactions between the gametes, zygote, embryo, endosperm, and/or maternal tissue. These interactions can eliminate recombinant genotypes with valuable information towards linkage analyses of the trait. Buffelgrass [Pennisetum ciliare (L.) Link syn. Cenchrus ciliaris L.], a polymorphic species with interfertile apomictic and sexual genotypes, offers an opportunity to genetically map apomixis by means of intraspecific hybrids with eupioid genomes. This study reports a linkage map of the apospory region in buffelgrass. Apospory, classified by progeny testing and cytologically observing megagametophytes, mapped to a single locus in the apomictic parent's genome. Two buffelgrass cDNAs (pPAP3A07 and pPAPSC08) and three previously reported apospory markers (UGT197, QH8, and OPC4) were tightly linked (1.4 centimorgans, cM) to the trait. As a tetraploid species (2n = 4x = 36), four copies of each chromosome are expected in buffelgrass. A single homolog and two homeologs were identified for the chromosome carrying apospory, indicating the formation of two bivalents during meiosis and the disomic inheritance of apospory in buffelgrass. Allelic bridges between the parents revealed suppressed recombination in the apospory linkage group. Segregation distortion between a marker on the sexual parent's homolog to the apospory linkage group and a marker on a separate maternal linkage group suggested specific allelic combinations in female gametes affect offspring survival in buffelgrass., APOMIXIS, asexual plant reproduction through seeds, results from the parthenogenetic development of an unreduced egg cell into a viable embryo (Bashaw and Hanna, 1990). Because apomixis permits the clonal propagation [...]

Fertilization of an unreduced egg (2n + n) increases ploidy level and creates a new hybrid. It occasionally occurs in apomictic species but at a frequency too low to be a reliable method for genetic improvement. This investigation was undertaken to determine if 2n + n fertilization could be increased by early pollination. Six buffelgrass, Pennisetum ciliare (L.) Link [syn. Cenchrus ciliaris L.], accessions, five apomicts and one sexual, were self-pollinated and cross-pollinated with birdwoodgrass, P. ciliare (L.) Link var. setigerum (Vahl.) Leek, at 3, 2,1, and 0 d before anthesis. The 2n + n progeny were identified by flow cytometry. DNA content (pg 2[C.sup.-1]) was determined for 1962 self-pollinated and 3072 cross-pollinated plants. Twenty-eight self-and 80 cross-pollinated plants had a higher DNA content and were products of 2n + n fertilization. The overall frequency of 2n + n fertilization when self- and cross-pollinated was 1.4 and 2.6%, respectively. For all protogynous intervals, the frequency ranged from 0 to 5.2% for self-pollinated plants and 0 to 8.2% for cross-pollinated plants. When self-pollinated, there was no correlation between time of pollination and recovery of 2n + n hybrids. When cross-pollinated, there was a linear relationship between time of pollination and number of 2n + n hybrids recovered. More 2n + n hybrids were recovered from crosses made 2 or 3 d before anthesis. Thus in apomictic buffelgrass, the frequency of 2n + n fertilization can be increased by pollinating early, and in apomictic species where sexual germplasm is not available, this approach has potential to produce new apomictic hybrids., FERTILIZATION of unreduced gametes has played a major role in the polyploidization and evolution of many plant species (Harlan and de Wet, 1975) and is recognized as the most common [...]

Designing a highly efficient backcross (BC) marker-assisted selection (MAS) experiment is not a straightforward exercise, efficiency being defined here as the ratio between the resources that need to be invested at each generation and the number of generations required to achieve the selection. This paper presents results of simulations conducted for different strategies, using the maize genome as a model, to compare allelic introgression with DNA markers through BCs. Simulation results indicate that the selection response in the B[C.sub.1] could be increased significantly when the selectable population size ([N.sub.sl]) is 100. Selectable population size is defined as the number of individuals with favorable alleles at the target loci from which selection with markers can be carried out on the rest of the genome at nontarget loci, simulations considered the allelic introgression at one to five target loci, with different population sizes, changes in the recombination frequency between target loci and flanking markers, and different numbers of genotypes selected at each generation. For an introgression at one target locus in a partial line conversion, and using MAS at nontarget loci only at one generation, a selection at B[C.sub.3] would be more efficient than a selection at B[C.sub.1] or B[C.sub.2], due to the increase over generations of the ratio of the standard deviation to the mean of the donor genome contribution. With selection only for the presence of a donor allele at one locus in B[C.sub.1] and B[C.sub.2], and MAS at B[C.sub.3], lines with, IN A BC SCHEME, the strategy is to transfer a specific elite allele at a target locus from a donor line to a recipient line. The use of DNA markers, [...]

Three quantitative trati loci (QTL) regions for the restoration of Owen CMS (cytoplasmic male sterility) in sugar beet (Beta vulgaris L.ssp. vulgaris) were identified through analysis of three populations segregating for genes restoring the fertility of cytoplasmic male sterile plants. Two large populations, A and B, were studied by means of 51 and 42 polymorphic and evenly distributed restriction fragment length polymorphism (RFLP) markers, respectively. A smaller population, C, was analyzed by use of six RFLP markers. Composite interval mapping in Population A detected a strong signal on linkage group IV that explained 79% of the phenotypic variation. More detailed analysis revealed the presence of two linked QTL on this chromosome. In Population B, a QTL that explained 72% of the phenotypic variation was detected at one end of linkage group III. Single-marker analysis of Population C resulted in significant signals for markers on linkage group IV, explaining 57% of the phenotypic variation. In each of the two large populations, what appeared to be minor alleles were also detected in the QTL regions., CYTOPLASMIC MALE STERILITY is a maternally inherited condition involving a plant's inability to produce functional pollen. It is commonly found in natural plant populations and is most frequently caused by [...]

Maintenance and use of germplasm collections of Vicia species is difficult because of limited information on their mating systems. Polymorphism of seven enzyme systems in 31 accessions of 12 Vicia species were measured by isoelectric focusing to infer their mating system. To compare variability within and among accessions and between species, polymorphism indices were calculated by means of isozyme bands. All enzymes studied had polymorphic banding patterns. Twenty-eight accessions were variable for at least one of the seven enzymes, whereas three other accessions were uniform for all seven enzymes. Within-accession variation was larger than that among accessions in V. villosa Roth and V. villosa ssp. varia (Host) Corbiere, whereas within-accession variation was smaller than that among accessions of V. articulata Hornem., V. benghalensis L., V. cracca L., V. ervilia (L.) Willd., V. lutea L., V. narbonensis L., V. pannonica Crantz, V. peregrina L., and V. sativa L.. The results agreed with field tests which demonstrated that V. villosa and V. villosa ssp. varia are predominantly cross-fertilizing species, whereas the other species are mainly self-fertilizing. The use of isozyme bands to determine mating system proved to be accurate. In addition, this method is convenient because it utilizes a small seed sample and is inexpensive and easy to perform., SEVERAL Vicia species are of considerable economic importance as grain, green manure, cover, and forage crops. Management and use of germplasm collections of this genus has become difficult because of [...]

Leaf N concentration (LRN), stomatal conductance (g,), and grain-assimilate demand each affect the leaf [CO.sub.2]-exchange rate (CER) of winter wheat (Triticum aestivum L.) during grain fill. Although leaf CER, g,, and LRN decrease during this time, little research has been conducted to examine whether these decreases occur simultaneously or to determine the effects of grain development on these declines. This field study was conducted (i) to monitor changes in CER, LRN, and g, during winter wheat reproductive development, (ii) to examine the relationships between the rate and duration of CER and the rate and duration of grain rill, and (iii) to determine the effects of crop N status on the decline in LRN and CER during grain fill. Two early (Andy and Gore) and two medium (Northrup King Coker 9803 and Northrup King Coker 9835) maturing cultivars were grown with irrigation and two rates of spring-applied N (56 and 112 kg N [ha.sup.-1]) in 1994 and 1995. Cultivar ranking was similar for the date of inflorescence emergence, the initiation and termination of grain development, and the complete loss of green leaf area and flag-leaf photosynthetic activity. For all cultivars, flag-leaf CER and g, began to decrease near the beginning of grain rill, whereas LRN and leaf area index (LAI) began to decrease prior to grain rill. Rapid reductions in LRN and CER were found only after significant grain growth occurred, with the rate of decrease being relative to the cultivar ranking found for inflorescence emergence date. Averaged over cultivars and years, increasing the rate of spring-applied N increased LAI and LRN near inflorescence emergence by 37 and 24%, respectively but only delayed the complete loss of green leaf area by 2 to 3 d and had little effect on the duration of grain fill. Stage of grain growth had little effect on the loss of LRN and CER until the latter portion of grain rill, 'hen rapid reductions in these variables occurred. Increasing the rate (if spring-applied N did not significantly delay these decreases or extend the duration of grain rill., Winter wheat grain N originates from both the remobilization of vegetative tissue N and from the active uptake and assimilation of N during grain fill. Remobilized N is usually the [...]

Eastern gamagrass [Tripsacum dactyloides (L.) L.], a native, warm-season species, is a nutritious and palatable forage for grazing livestock. The grass has potential for rangeland and pasture improvement. This field study was conducted over 10 yr and one location to determine the reproductive characteristics of the various cytotypes of Tripsacum and identify methods for breeding agronomically superior cultivars. Intra- and interspecific crosses were made and evaluated between several Tripsacum cytotypes. Cytological and polymerase chain reaction-random amplified polymorphic DNA (PCR-RAPD) techniques were used to identify methods of reproduction and types of individuals generated. Results of the study identified two methods for facilitating horizontal gene flow among sexual and apomictic cytotypes. Materials with triploid and hexaploid constitutions were essential in the movement of sexual germplasm into apomictic tetraploids and of tetraploid germplasm into sexual diploids, respectively. Triploids and hexaploids were useful materials to introgress and transfer desirable alleles across species, cytotypes, and reproductive barriers. In addition, the generation of triploid and hexaploid genotypes will continue to exert major influences on Tripsacum evolution and speciation. This study identified additional methods and systems for improving Tripsacum germplasm by utilizing its distant relative maize (Zea mays L.) in a breeding or genetic evaluation program., Eastern gamagrass is a native warm-season, perennial bunchgrass and is often referred to as 'the grandad of grasses' (Martin, 1963). Historical references and early land survey records of settlers who [...]

Paspalum is a large genus that contains several important forage and turf grasses. Little or no information is available concerning the cytology and reproductive behavior of many of these species. The objectives of this study were to determine the cytology, method of reproduction, and fertility of accessions of eight different Paspalum species. Paspalum modestum Mez., P. monostachyum Vasey, P. repens Bergius, and one P. alcalinum Mez. accession were sexual diploids with 2n = 2x = 20 chromosomes. Meiosis was regular with primarily bivalent pairing. Even though P. modestum was sexual, the female gametophyte deteriorated in 43% of the ovules. Two P. alcalinum, one P. falcatum Nees, two P. paucifolium Swallen, three P. polyphyllum Nees, and one P. unispicatum (Scribn. et Merr.) Nash accessions were tetraploids with 2n = 4x = 40 chromosomes. During meiosis their chromosomes associated primarily as bivalents, quadrivalents, and univalents. Regardless of the species, all tetraploids were facultative aposporous apomicts. One P. alcalinum accession was a pentaploid with 50 chromosomes. Meiosis was irregular with the chromosomes associating as univalents, bivalents, trivalents, and quadrivalents. This accession reproduced as an obligate aposporous apomict. Seed set in P. modestum and P. monostachyum was very low but was high enough in the other species that they could be propagated by seed. These findings demonstrate the cytological and reproductive diversity within this large complex genus., According to Chase (1929), the genus Paspalum consists of more than 400 species. Essentially all are native to the Americas with the majority occurring in tropical and sub-tropical Central and [...]

Isolation of a gene controlling apomixis would be useful to plant breeders for fixing hybrid vigor. A single gene encodes for aposporous apomixis in buffelgrass (Pennisetum ciliare L. Link), which is inherited in a autotetraploid fashion. Only two molecular markers linked to the gene are known: C04-600, a RAPD (random amplified polymorphic DNA) and UGT197-144, an STS (sequence-tagged site). The objective of this study was to identify new RAPD markers linked to the apospory locus in buffelgrass and to prepare a linkage map. Sexual clone B-2s was crossed to aposporous buffelgrass cultivar Higgins and to aposporous clone B-12-9. Progeny of each cross were screened for RAPD markers by bulked segregant analysis. Seven preparations of bulked genomic DNA (equal amounts DNA from each of 10 individuals) from sexual or aposporous progeny were examined for RAPD markers. Using 500 decanucleotide primers, we found five new markers potentially linked to the apospory gene. Analysis by MAPMAKER/EXP 3.0(1) indicated markers J16-800 and M02-680 were linked to the apospory gene, as was previously established marker UGT197-144, and the three were placed on the map. Marker A20-730 was loosely linked in both crosses, marker B14-550 was unlinked in the Higgins cross, and marker N15-370 was unlinked in both crosses, and they were not placed on the map. These data provide the first map for the buffelgrass chromosome bearing the apospory gene., The ability to interchange at will obligate asexual and sexual reproduction in crop breeding material would allow plant breeders to quickly develop superior varieties and to fix heterosis in a [...]

Callose, a Β-1,3-glucan, is synthesized and deposited in the walls of megaspore mother cells (MMCs) of angiosperms that produce either normal monosporic ([is greater than] 90% of all angiosperm species) or bisporic embryo sacs. Such deposits are absent in angiosperms that produce tetrasporic embryo sacs and were recently shown to be absent in diplosporous Elymus rectisetus (Nees in Lehm.) A. Love & Connor, Tripsacum L. spp., and Poa nemoralis L. We determined the extent of callose deposits in MMCs of diplosporous weeping lovegrass (Eragrostis curvula Schrad.), several additional diplosporous Tripsacum accessions and aposporous buffelgrass (Pennisetum ciliare (L.) Link), Kentucky bluegrass (Poa pratensis L.), and Pennisetum squamulatum Fresen. Callose deposition was studied in pistils cleared in an aqueous aniline blue clearing medium and observed by means of UV microscopy. Pistils cleared with conventional clearing media were studied by means of interference contrast microscopy. Some pistils were cleared and analyzed in one clearing medium and recleared and reanalyzed in the other. A callosic MMC was observed in only one of 376 appropriately staged pistils taken from diplosporous species. This pistil, one of 89 weeping lovegrass pistils studied, was probably facultatively sexual. An absence of callose during megasporogenesis may be characteristic of most types of diplospory. Though present, the distributions and quantities of callose observed in MMC walls of aposporous apomicts were erratically reduced, possibly as a result of early NMC abortion or early activation of nucellar initials. Callose deficiencies and vacuolization patterns support the following hypotheses: (i) apospory is caused by a moderately precocious gametophytization of nucellar cells, and (ii) bispory, tetraspory, and diplospory are caused by a moderately to extremely precocious gametophytization of the MMC that is nearly complete in the latter case and variably incomplete in the former two cases. Understanding how these precocious gametophytizations evolved and are regulated may be crucial to the eventual transfer of apomixis to major crop species and to its successful manipulation by breeders., Pure Callose is insoluble in water and is composed of glucans linked together by Β-1,3-glycosidic linkages. Normally, both Β-1,3- and Β-1,4- (cellulose) linkages occur in the same polysaccharide molecule. High [...]

Four [B.sub.III] hybrids (2n = 9x = 63, ABDStStYYWW) were obtained between wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD) and a diplosporic and 2n-pollen-producing Elymus rectisetus (2n = 6x = 42, StStYYWW) accession. We determined whether apomeiosis and 2n pollen formation, which occur in the male parent, also occur in the Bill hybrids. Pistils were cleared for UV microscopy of callose and recleared for cytological observations using interference contrast microscopy. Callose fluorescence from most megaspore mother cells (MMCs) was typical of sexual species. These were classified as sexual. Abnormally elongated MMCs with walls devoid of callose were observed in 4.7% of pistils collected at meiotic prophase. These traits are typical of many apomeiotic MMCs in E. rectisetus. Asynapsis followed by mitosis in pollen mother cells (PMCs) consistently preceded unreduced pollen formation in E. rectisetus. This was not observed in the [B.sub.III] hybrids, though the following meiotic anomalies were observed: (i) asynapsis, aggregation of chromosomes to several poles, and multiple divisions to form four to eight unbalanced microspores, and (ii) incomplete synapsis, formation of anaphase I laggards, and a second division resulting in four unbalanced microspores with micronuclei. The wheat haplome enforced PMC meiotic pairing (albeit abnormal) among homologous E. rectisetus chromosomes and generally inhibited apomeiosis, also by enforcing meiosis. Diplospory may be caused by the expression of embryo sac signals from one genome precociously expressed with megasporogenesis signals from another. If this is correct, the successful induction of apomixis in wheat may require the transfer of alien gene cassettes that confer appropriate degrees of reproductive asynchrony., The Australian wheatgrass Elymus rectisetus reproduces by facultative diplospory. During the early apomeiotic prophase, vacuoles accumulate in the chalazal region of the MMC, the nucleus moves to the center of [...]

The soybean [Glycine max (L.) Merrill] reproductive cycle represents more than 50% of the length of the total growth cycle. Immature embryo culture could be used to shorten this cycle. This study was conducted to develop an efficient technique to shorten the soybean reproductive cycle and to make it possible to develop recombinant lines from populations more rapidly. The importance of a pod pretreatment before embryo extraction, the effects of embryo age an germination rate, embryo position in the pod, and the composition of the germination medium (supplemented with sucrose or not) were analyzed to define an optimal technique. Plant recovery rate and genotype effects on germination were evaluated with 22 genotypes representing a broad genetic background. It was necessary to pretreat immature seed by exposing pods to 26 ° C for 4 d to induce germination. Best results (up to 100% germination) were obtained from embryos sampled at the end of lag phase of seed development (approximately 19 d after flowering). For three-seeded pods, the central embryos generally bad a higher germination rate than distal and proximal embryos (25 and 44 percentage points, respectively). Whatever the embryo position in the pod, adding sucrose significantly increased the germination of embryos sampled 14 to 18 d after flowering. Plantlets were obtained from 73% of the germinated embryos and the length of cycle win reduced from 130 to 140 d to 65 to 70 it. Average germination of the 22 genotypes was 80%; thus, this technique, paired with the single seed descent method, provides soybean breeders with a tool to develop lines quickly., The reproductive cycle represents more than 50% of the length of the total life cycle for soybean. In vitro culture of immature embryos has a number of basic and applied [...]

Apomixis involves the parthenogenetic development of apomeiotic eggs. It has the potential of cloning plants through seed, and thus furnishes a unique opportunity in alfalfa breeding for developing superior cultivars with permanently fixed heterosis. Megasporogenesis of a meiotic mutant of alfalfa Medicago sativa subsp. falcata (L.) Arcang. (2N=2x=16), named PG-F9, that produced 2n second division restitution (SDR) and apomeiotic eggs at high frequencies, was cytologically analyzed by both stain-clearing and sectioning techniques. The restitutional 2n egg formation was mainly due to the omission of the second meiotic division. The absence of cytokinesis was also documented after a normal second meiotic division. The concurrent examination of integument growth, cell appearance, and nucleolus size associated with either the absence of degenerating meiotic products or aposporic initials in the ovules allowed the production of apomeiotic 2n megaspores to be ascribed to a diplosporic pathway. The mutant PG-F9 was grown in the field and in a growth chamber and the frequencies of normal, restitutional, and diplosporic cells were recorded under both environments. Restitutional 2n megaspore formation (dyads and triads with 2n chalazal megaspores) and the suppression or modification of meiosis leading to apomeiotic 2n megaspore production were influenced by environmental conditions. The frequency of normal tetrads was three times higher in the field (23.08%) than in the growth chamber (7.91%). The same trend was found for functional reduced chalazal megaspores. The frequency of restitutional cells was largely preserved in the two environments (51.92% in the field versus 50.31% in the growth chamber). The omission of normal meiosis resulting in diplosporic cells increased from 16.35% in the field to 26.27% in the growth chamber. The fertility of seed set and seeds per pod values of PG-F9 in controlled matings carried out in the field and in the growth chamber using different diploid and tetraploid pollen sources furnished information on 2n egg viability and partially supported the cytological results. The discrepancy observed indicated that some 2n megaspores were unable to develop into a functional embryo sac., The formation of 2n gametes (i.e., gametes with the somatic chromosome number) has been investigated both for studies of evolution (Stanford et al., 1972; Harlan and de Wet, 1975) and [...]

Large losses in yield can occur in maize (Zea mays L.) growing in water-limited conditions (low [[Psi].sub.w]), particularly during flowering and early embryo growth where grain number is decreased. However, embryo growth is maintained where otherwise none would occur if the stems are infused with photosynthate (sucrose) and other nutrients (amino acids, salts, vitamins, and hormones) during exposure to low [[Psi].sub.w]. In the present investigation, we deleted or supplied various components of the complete infusion medium to identify the active solute. Infusions involved making a cavity in a stem internode, filling the cavity with water, sealing the cavity, and connecting the interior of the cavity to an external reservoir of the medium. A field experiment at high [[Psi].sub.w] showed that wounds and enhanced nutrient supplies from the infusions did not alter embryo growth or yield. In controlled environment chambers, low [[Psi].sub.w] was imposed by withholding water for 6 d beginning 5 d prior to pollinations. A new infusion was made each day for 5 d as the low [[Psi].sub.w] developed around pollination. The low [[Psi].sub.w] virtually eliminated grain development. Sucrose infusion reversed this loss and no other component of the medium showed activity under our conditions. In plants receiving no sucrose at low [[Psi].sub.w], ovary sucrose content was moderately lower and starch much lower than in controls. In plants receiving sucrose at low [[Psi].sub.w], ovary sucrose content was higher than in controls and starch recovered moderately. The difference in sucrose and starch responses indicates that carbohydrate metabolism was altered in the ovaries at low [[Psi].sub.w]. Embryo survival correlated more closely with the content of starch than sucrose. We conclude that there were two effects of low [[Psi].sub.w] that contributed to arrested embryo growth: a decreased sucrose flux and an altered carbohydrate metabolism in the ovaries.

Partitioning of energy reserves between sexual (flower and seed) and asexual (rhizome) reproduction in rhizoma peanut (Arachis glabrata Benth.), a perennial, tropical-forage legume, appears to be affected by environmental stress. If so, seed production may be enhanced by manipulating the growing environment. To investigate this possibility, the effect of defoliation frequency on the energy-allocation balance of sexual vs. asexual reproduction of rhizoma peanut was determined. Four defoliation frequencies (nondefoliated, weekly, every 4 wk, and every 8 wk) were imposed on 'Florigraze' rhizoma peanut. Aboveground and rhizome biomass were sampled prior to treatment initiation (6 June 1988 and 15 June 1989) and every 4 wk until frost (24 wk in 1988 and 16 wk in 1989). During the first 8 wk, aboveground biomass of the nondefoliated treatment nearly doubled. Concurrently, aboveground biomass of all defoliated treatments remained the same or declined. Rhizome biomass of all treatments declined during the same period but in most cases, recovered by the latter part of the growing season. Generally, aboveground biomass ranked (P < 0.05) 1 wk < 4 wk less than or equal to 8 wk < nondefoliated, and rhizome biomass ranked (P < 0.05) 1 wk = 4 wk = 8 wk < nondefoliated. Flowering was synchronous for all treatments, but sexual reproductive effort constituted

Drought stress affects yield of indeterminate species, but the effects on yield components, seed number, and individual seed weight at harvest are, in some cases, contradictory. The diversity of effects can result from the complex sequential development of these plants with respect to timing of drought. Two experiments were carried out in a glasshouse to study the effect of short-term drought (about 6 d) during different periods of reproductive development on the phenology of pea (Pisum sativum L.) cv Solara, and on seed abortion and seed growth rate at each nodal location on the stem. An additional experiment was carried out in the field. Short-term stresses did not change development except for the progression of flowering along the stem which was stopped prematurely. The duration of the lag-phase between flowering and initiation of seed filling, and the duration of seed filling, were not affected at any nodal position. Analysis of the distribution of seeds along the stem suggested that the final stage at which seed abortion occurred corresponded approximately to the initiation of linear seed filling. Seeds that reached this stage before the stress was imposed never aborted and their growth was maintained. Seed abortion in lag-phase was dependent on the intensity of drought. If the stress was imposed when all the seeds were filling, no abortion occurred and seed growth rates were maintained by mobilization of plant reserves. The results suggest that the plant responded to drought by reducing seed number when possible or mobilizing its reserves to maintain a constant seed growth rate.

The yield-enhancing effect of increased light interception (LI) in narrow row/late-planted soybean (Glycine max (L.) Merr.) culture could be better understood if LI effects on the reproductive period (first flower (R1) through physiological maturity (R7) were clarified. The primary objective was to determine yield and yield component responses to a LI gradient during R1 to R7. Field studies were conducted during 1989 and 1990 at a late planting with 'Centennial' determinate soybean using 50-cm row spacing. The test was conducted at Baton Rouge, LA, on a Mhoon silty clay soil (fine-silty, mixed, nonacid, thermic Typic Fluvaquent). Treatments were a control (no defoliation) and four partial defoliation treatments that consisted of keeping the area 12.5 cm to both sides of the interrow midline (i.e., 50% of the interrow area) free of leaf blade material until pod initiation (R3), pod elongation (R4), start of seed filling (R5), or mid-seed filling (R6.5). These treatments resulted in a LI gradient during R1 to R7, without affecting node production or leaf area index (LAI) and total dry matter (TDM) by R1. In response to reduced LI, pods per reproductive node and pod number (both formed during R3-R5) declined. Similar source/sink ratios (crop growth rate (CGR) at R5 divided by pod number) at seed initiation were maintained across all treatments. Thus seed per pod and seed size (formed during R5-R7) were unaffected. In conclusion, in cases such as narrow rows where LI is increased throughout the reproductive period, the determining effect on yield occurs during R1 through R5. Results also indicated that the relationship between seed number and LI (during R1-R7) occurs through adjustments in pod number.

Vernalization generally is required for adaptation of winter cereals to temperate climates and is basic to breeding and selection of new cultivars. The objective of this study was to assess the reproductive development of eight winter-sown wheat (Triticum aestivum L.) cultivars and a triticale (x Triticosecale Wittmack) as related to vernalization and heat accumulation using sequential sowing dates at four environments. The study was conducted at Gainesville, FL (29 degrees 38' N lat); Quincy, FL (30 degrees 36' N lat); and Griffin, GA (33 degrees 15' N lat), in 1987-1988 and was repeated at Gainesville in 1988-1989. Seed of cultivars were sown in field plots, beginning about 15 December and continued biweekly through 1 March. Cold and heat units were computed from Class AB weather-station air temperatures logged daily. Spring-type wheat cultivars Florida 301, Florida 303, and Owens and Beagle 82 triticale developed spike primordia after approximately equal to 2 mo and headed in 100 to 120 d, irrespective of vernalization. Intermediate winter cultivars Florida 302, Hunter, and Phoenix had not initiated spikes by approximately equal to 3 mo, and headed only if sown on or before 15 February. In contrast to this response in 1987-1988, Hunter headed irrespective of sowing dates at Gainesville in 1988-1989. Cultivars Coker 983 and Caldwell required vernalization, and headed only if sown by December in the warmer year (1988-1989) or if sown in December or January in the colder year (1987-1988). We conclude that spring-type wheat cultivars and triticale reproduce normally without vernalization, and are adapted to a broad range of latitudes and sowing dates in southern USA. Winter-type cultivars require vernalization and should be seeded in early winter at lower latitudes.

Seed-filling duration has generally shown a positive association with seed yield in soybean (Glycine max (L.) Merr.), but results have been inconsistent among studies. Four phenotypic recurrent selection programs were completed, increased flowering-period duration (FPD) vs. increased seed-filling duration (SFD) and long vs. short reproductive-period duration (RPD), with the objective of investigating the effects of these modifications on seed development and seed yield. Selection for average physiological maturity (R7) maintained R7 maturities among populations. Selection for increased RPD through FPD or SFD increased genetic correlations between reproductive stages. The major responses to selection occurred in the first cycle due in part to the 3-yr evaluation, but high correlations between stages also restricted progress. Manipulating RPD modified primarily FPD. The SFD seemed to have a minimum threshold, but responded to selection pressure. Divergent selection for RPD created a 10-d difference in RPD, but the selection had minimal effects on seed yield potential. The soybean has the capacity to achieve seed yield independent of changes in duration of reproductive stage. Increasing RPD through increased SFD within a broad-base population had an associated increase in seed set and in seed yield for a set of favorable environments, but this yield advantage was not expressed for a set of environments with drought stress during the reproductive period. Increased SFD was associated with increasing potential number of seed set and, as has been shown, decreasing assimilate uptake rate. Selection for increased SFD would be important for populations where SFD could be limiting. The effects of modifying seed-filling duration are not clear-cut, but manipulating facets that affect it can create unacceptable responses.

High night temperatures cause excessive floral abscission in cowpea (Vigna unguiculata (L.) Walp.), while similar or even higher temperatures during the day do not impair reproduction. The objectives of this study were to determine if high temperatures during the early part of the night have different effects on cowpea pod set than high temperatures during the late part of the night, and if distinct events of pollen development are associated with the diurnal sensitivity to heat. Two genotypes of cowpea were grown in controlled environments under a 12-h photoperiod and subjected to high temperatures (33 [degrees] C) during the day and either the first or second 6-h period of the night. Temperatures were optimal (24 [degrees] C) during the other 6 h of the night. All plants experienced the same heat units. Floral buds were sampled at different stages of development and the developing pollen were microscopically examined. For the two genotypes, high temperatures during the late-night period resulted in much lower pod set (7 and 20%) and pollen viability (2 and 35%) than high temperatures during the early-night period (51 and 76%, and 65 and 69%, respectively). No diurnal synchrony in pollen development was observed during the late-night period when developing pollen was the most sensitive to high night temperatures. No changes in floral morphology were observed that could impede pollen transfer from the anthers to the stigma and be responsible for the low pod set. We hypothesize that the results can be explained by the existence of a physiological process that is sensitive to heat and under circadian regulation., The reproductive responses of cowpea to high temperature changes during different parts of the night, as well as the possible synchronicity in pollen development associated with periodic variation in heat sensitivity were determined. The results showed that sensitivity of cowpea to heat, as reflected by pollen viability, is pronounced during the last six hours of the night. In addition, no diurnal synchrony in pollen development at this sensitive period was observed. Three possible hypotheses to explain this temporal sensitivity to heat stress are presented.

All known sources of lehmann lovegrass, Eragrostis lehmanniana Nees, reproduce by apomixis, which precludes hybridization and conventional genetic research. This study was conducted to locate sexual germplasm and describe the reproductive process in lehmann lovegrass. Purported diploid germplasm was grown in pots in a greenhouse. Chromosome number was determined and embryo sac development was studied and compared with another lehmann lovegrass accession. Self fertility, open-pollinated seed set, and mode of reproduction by progeny test were evaluated. Three accessions were diploid (2n = 2x = 3x = 30), and two were tetraploid (2n = 4r = 40). Triploid plants (2n = 3x = 30), discovered in the primarily diploid accessions, probably resulted either from the union of reduced and unreduced gametes or from fertilization of diploid plants by pollen from nearby tetraploid lehmann lovegrass. Diploid plants were sexual (i.e., megaspores were produced) and required cross pollination for seed set. Triploid and tetraploid plants were facultative diplosporous apomicts. Progeny tests were not conclusive. Although some diploid plants were clearly different from others, morphological differences were not sufficient to clearly and easily differentiate genetic from environmental variation. This is the first report of sexual reproduction in E. lehmanniana. This sexual germplasm will be essential to future genetic research with lehmann lovegrass., The mode of reproduction of lehmann lovegrass, Eragrostis lehmanniana Nees, was investigated, to locate possible sources of sexual germplasm. Somatic chromosome counts showed that three accessions were diploid, and two were tetraploid. Two triploid plants were probably the result of the union of a reduced and unreduced gametes or by fertilization of diploids by pollen from tetraploids. Further investigation revealed that the diploids reproduced sexually. Therefore, this sexual germplasm will be a valuable source of genes in the genetic study of lehmann lovegrass.

Breeders of self-pollinated crops often discard inferior lines at an early selfing generation so that more resources can be devoted to the further testing and selection of the more promising lines. Empirical studies have led to contradictory estimates of the correlation between the performance of lines at early and late selfing generations. Here I examine the theoretical effectiveness of early generation selection. When dominance is absent, the genetic correlation ([r.sub.G]) between the performance of an [F.sub.t]-derived [F.sub.g] line (i.e., [F.sub.t:g]) and a descendant homozygous line is equal to the square root of [1 + [F.sub.(t)]/2, where [F.sub.(t)] is the inbreeding coefficient at generation t. Dominance, when present, has little effect on [r.sub.G]. The minimum value of [r.sub.G] is high; that is, 0.707 for an [F.sub.2]--derived line. From a genetic standpoint, early generation selection is expected to be effective, but in practice it becomes ineffective if nongenetic effects are large., EARLY GENERATION SELECTION in self-pollinated crops typically involves the evaluation of [F.sub.2]- or [F.sub.3]-derived lines from the cross between two inbreds. Inferior [F.sub.2]- or [F.sub.3]-derived lines are then discarded to [...]

Kura clover (Trifolium ambiguum M. Bieb.) is a rhizomatous perennial forage legume that has outstanding persistence once established. Low seedling vigor presents a challenge to kura clover establishment. Kura clover seedlings partition a significant portion of their dry matter to below ground growth. Therefore, seedling vigor could be improved by increasing dry matter allocation to the shoot. Our objective was to study the potential of recurrent phenotypic selection in the greenhouse for reduced root/shoot ratio to increase seedling vigor. Three cycles of divergent selection for root/shoot ratio and a control selection for large plant biomass (LP) were performed from a parent population consisting of `Rhizo', ARS-2678, KZ1, and Erect Spreader populations. Selections for low root/shoot ratio (LoRS) and high root/shoot ratio (HiRS) were performed by independent culling after first selecting for large total biomass. Parent and selected populations were evaluated in the greenhouse and field. Three cycles of selection for LoRS and LP increased shoot yield in the field 42 d after planting (DAP) by 35 and 34%, respectively. Three cycles of selection for LoRS reduced root/shoot ratio in the field by 16%. Selection for HiRS did not affect seedling size in the field. Population mean shoot and total plant weights were correlated between greenhouse and field environments (average r = 0.89). Population mean seed weight was correlated with shoot weight in the field (r = 0.68, P [is less than] 0.05). The results indicate that phenotypic greenhouse selection for seedling size is an effective means of increasing seedling vigor in kura clover., KURA CLOVER (Trifolium ambiguum M. Bieb.) is a rhizomatous perennial forage legume that has demonstrated outstanding persistence (Sheaffer and Marten, 1991). It has potential to enhance the productivity and profitability [...]

Assortative mating can increase additive variance ([V.sub.A]) and, consequently, selection response. Marker-based assortative mating (MAM)--the mating of individuals that have similar marker genotypes--has not been studied. My objectives in this simulation study were to (i) compare the selection response associated with MAM, phenotypic assortative mating (PAM), and random mating (RM) of selected individuals and (ii) determine when MAM will be most useful in breeding programs. I simulated 25 generations of selection among 200 individuals, followed by MAM, PAM, or RM, in a cross between two inbreds. A total of 100 codominant marker loci and 100 quantitative trait loci (QTL) were randomly distributed across 10 chromosomes, each 100 centimorgans (cM) long. The effects of QTL were additive and followed an exponential distribution. Cumulative selection response was determined for different initial levels of heritability ([h.sup.2] = 0.20, 0.50, and 0.80) and different numbers of individuals selected (N = 4, 8, 16, and 32) in each generation. Compared with RM, MAM resulted in slight increases of 3 to 8% in selection response during the first several generations, particularly when [h.sup.2] = 0.20 and N = 32. The PAM procedure led to slight increases of 2 to 4% when [h.sup.2] = 0.80 and N = 32. Any advantage of assortative mating over RM dissipated by Generation 8 for MAM and Generation 15 for PAM. The loss of QTL heterozygosity was much greater with MAM than with PAM or RM. For long-term improvement, selected individuals should be intermated by RM. The MAM procedure will be most useful for short-term improvement in a biparental cross, particularly when [h.sup.2] and selection pressure are low., Genetic gain is achieved by (i) selecting superior individuals in a population and (ii) intermating the selected individuals to form the next generation. The use of molecular markers to enhance [...]

In plant breeding trials and other experiments with many treatments, there may be spatial effects due to large-scale trends and small-scale autocorrelation. Geostatistical analysis may be used to investigate the extent of spatially structured variation. When spatial structure is present, neighbor analysis can be superior to classical analysis of variance (ANOVA). The objectives of this study were to assess the validity and efficiency of neighbor analysis and to investigate the extent of spatially structured variation in cereal breeding trials. Three neighbor analysis methods (the Papadakis procedure, the iterated Papadakis method, and the first differences with errors in variables [FD-EV]) were applied to data from uniformity trials and to data from a set of 361 cereal breeding trials. The iterated Papadakis method consistently underestimated the variance, producing tests with highly inflated Type I error rates. Thus, its relative efficiency could not be estimated correctly. Geostatistical analysis indicated that spatially structured variation was frequently present in the cereal breeding trials, and that first differencing was effective in removing it. The FDEV analysis consistently improved the accuracy and precision of the estimation of entry effects compared with classical analysis of variance and Papadakis analysis. Efficiency relative to classical analysis of variance averaged 152% for FD-EV and 116% for the Papadakis procedure. Considering both validity and efficiency, FD-EV was the best method. In the presence of spatially structured variation, FDEV can improve the interpretation of data from field trials. In the absence of spatial structure, FD-EV causes no loss of efficiency., Agricultural field experiments, including plant breeding trials, often use the randomized complete block (RCB) design. Within each block of an RCB experiment, plots should have similar character response potential. This [...]

Maize breeders reduce inbreeding either by increasing the number of selected units or by intermating unrelated selection units. To determine optimal sample size for selection, one needs explicit functions to estimate the expected inbreeding in recurrent selection. The objectives of this study were to develop functions for mass (MS) and modified ear-to-row selection (METRS) in maize (Zea mays L.). By considering the number of half-sib families and the number of plants per family, the initial inbreeding of the base population, and the intra- and inter-family coancestries, I obtained a basic equation to calculate inbreeding. Knowledge of the basic population origin permitted me to extend inbreeding and coancestries of this population to any randomly mated advanced cycle of selection. Then the actual number of plants in the selection plot was transformed into the variance effective number for MS and METRS, proposed for sampling half-sib families from an open-pollinated population. The actual number of plants was also transformed into inbreeding effective number proposed for absence of selfing in both MS and METRS, and proposed for different numbers of males and females in METRS. Since the variance effective population size is a function of selection pressure, it was possible to obtain a general equation that included the numbers of sampled families, plants per family, and selected plants for any cycle of selection. For commonly used numbers of families, and plants per family, and selection pressures, inbreeding due to fixation by the variance effective number was very low;, less than 7% for both selection methods even with 100 cycles of selection., Recurrent selection programs in maize include selection and recombination of individuals to form an improved population. Inbreeding occurs in each selection cycle because a finite number of plants are selected [...]