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The plant root system is earmarked as key to the next Green Revolution. Field experiments were conducted in 2010–2011 and 2011–2012 to determine the impact of N management system on root growth in cultivar Pavon 76 (Pavon), bread wheat (Triticum aestivumL.), and wheat–rye (Secale cerealeL.) translocations Pavon‐1RS.1AL (1RS.1AL), and Pavon‐1RS.1BL (1RS.1BL). The three genotypes were examined under organic N (manure) and synthetic N fertilizer regimes each at a high and low rate, and an unfertilized control. The translocated genotype 1RS.1BL had 23 and 9% higher total root biomass than Pavon in the 2010–2011 and 2011–2012 growing seasons, respectively. Compared to Pavon, root mass of genotypes 1RS.1AL and 1RS.1BL was 23.3 to 55.9 g m−3higher in the top 40 cm of the soil profile and 15.1 to 31 g m−3higher in soil profiles below 40 cm. The 1RS translocations also had higher root dry mass than Pavon under synthetic N, low organic N and the unfertilized control. Mean genotype grain yields for both growing seasons ranged from 3.8 to 4.1 Mg ha−1and there were no differences between 1RS lines and Pavon. These studies show that the root system was enhanced without a subsequent loss of yield in a high yield potential environment; similar research is needed for low wheat yield potential environments.

Wild diploid goatgrass, Aegilops tauschiiCoss., is the D-genome donor to hexaploid bread wheat. Goatgrass has been crossed with tetraploid durum wheat (Triticum turgidumvar. durumL.) and hexaploid bread wheat (T. aestivumL. ssp. aestivum) to broaden the genetic base of bread wheat. We examined the contribution of main stem water-soluble carbohydrates (WSC) and current assimilates to grain yield in one goatgrass relative to those in one durum and four cultivars of bread wheat under well-watered and droughted field conditions across two years. Drought reduced grain yield and its components. Number of tillers per plant was higher in goatgrass, but 55% of tillers produced were sterile. Number of grains per spike was lower in goatgrass. Grain weight was the component severely limiting potential yield in goatgrass. Main stem WSC and concentration was lowest in goatgrass. Linear rate of grain growth in goatgrass was 20 and 17 mg spike-1day-1under well-watered and droughted conditions, whereas those in durum and bread wheats ranged from 55 to 73 and from 37 to 60 mg spike-1day-1, respectively. Current assimilates were the major source of carbon to fill the grains under both irrigation regimes. A large number of goatgrass accessions and adapted durum cultivars should be examined for grain yield and its components to identify promising accessions to be used in producing synthetics.

Grain filling in wheat crops grown in semiarid regions may depend more on stored water‐soluble carbohydrates (WSC) than on current photosynthesis. We evaluated the hypothesis that internode WSC content, specific content (WSC content/internode length), and concentration (WSC content/internode weight) of genotypes affect accumulation and mobilization of stem WSC. Genotypic variation for internode WSC‐related traits was measured on the main stem at 10‐d intervals in 11 diverse wheats grown under well‐watered and droughted field conditions across 2 yr. Relationships among internode WSC‐related traits were determined. Date of harvest was the most important factor affecting internode WSC‐related traits followed by genotype, irrigation, and year. Genotype × date of harvest was the most important interaction. Drought reduced WSC content, specific content, and concentration in different internodes, except WSC concentration in peduncles. Mobilized WSC from peduncle, penultimate, and lower internodes ranged from 70 to 244 mg, from 95 to 227 mg, and from 175 to 450 mg, respectively. The lower internodes provided 51% of the stem mobilized WSC. Mobilized WSC was higher in well‐watered than in droughted conditions for penultimate (164 vs. 135 mg) and lower internodes (274 vs. 244 mg). Drought improved mobilization efficiency in the peduncle, penultimate, and lower internodes by 33, 17, and 11%, respectively. Postanthesis maximum WSC content was highly correlated (r= 0.89 to 0.99) with the amount of WSC mobilized in different internodes, and could be used as a selection criterion to stabilize grain yield under stressful environments.

Wheat crops grown in dryland areas may depend more on stem reserves for grain filling than on current photosynthesis. We evaluated the hypothesis that internode length, weight, and specific weight of genotypes affect accumulation and mobilization of stem reserves. This knowledge might complement selection in stressful environments. Genotypic variation for internode characteristics and their effects on dry matter accumulation and mobilization were measured at 10‐d intervals in 11 diverse wheat cultivars grown under well‐watered and droughted field conditions across 2 yr. Relationships among internode characteristics and accumulation and mobilization of stem reserves were determined. The main effect of year, irrigation, genotype, and harvest date and genotype × harvest date interaction were significant. Internode length, weight, and specific weight were reduced under drought. Mobilized dry matter from peduncle, penultimate, and the lower internodes ranged from 43 to 171, 81 to 272, and from 198 to 474 mg, respectively. Mobilized dry matter was less in well‐watered than in droughted conditions for peduncle (93 vs. 110 mg) but not for penultimate (173 vs. 143 mg) and the lower internodes (331 vs. 304 mg). Drought increased mobilization efficiency, expressed as percentage of maximum dry mater mobilized, in the peduncle, penultimate, and the lower internodes by 65, 11, and 5%, respectively. Stem maximum specific weight was correlated (r= 0.64) with stem mobilized dry matter. Balanced partitioning of stem length into upper and lower internodes and internode maximum specific weight are important in genotypic accumulation and mobilization of stem reserves in wheat.

Introgression between cultivars and wild relatives is common in several angiosperm taxa including the grass family Poaceae. Bread wheat (Triticum aestivumL.) is a domesticated allohexaploid species (genome formula BBAADD) without any known wild hexaploid relative in the genus TriticumBread wheat is also related to the genus AegilopsL., which has probably contributed two of the three genomes of bread wheat. A few tetraploid Aegilopsspecies, including Ae. cylindricaHost. and Ae. triuncialisL., occur as weeds both in the Mediterranean basin and in West Asia. Introduced populations of these weeds are also known to occur in North America. These species have been known to introgress occasionally with bread wheat when grown near wheat fields. Similarly, rye (Secale cerealeL.), a species from a distant genus, has a potential to introgress with bread wheat. A few natural introgressive hybrids between herbicide resistant wheat and Ae. cylindricaand between wheat and rye have been created or recovered in North America. Natural hybrids between wheat and Ae. triuncialishave not been observed in North America. The available data do not suggest the prevalence of large‐scale introgression between bread wheat and its wild relatives in North America. Nevertheless, with modern bread wheat cultivars being developed with novel traits, such as herbicide and disease resistance, an in‐depth evaluation of the extent and nature of introgression between weedy Aegilopsor Secalespecies and bread wheat is useful both for assessing potential ecological risks that may be associated with trait presence in hybrids and for formulating strategies to manage gene transfer to hybrids. In this review, we discuss the existing literature on reproductive ecology of bread wheat and on introgression between bread wheat and its wild relatives in the genera Aegilopsand Secalethat occur in North America. We also discuss the implications of introgression in consideration of the current and possible future development of transgenic wheat.

Gene flow is transfer of genetic information between populations of the same or different species. Gene flow in bread wheat (Triticum aestivumL.) occurs via pollen or seed dispersal. Under normal conditions, gene flow between wheat cultivars is negligible due to selfing of flowers. Factors such as reproductive biology and environmental conditions at vegetative and reproductive stages bring variation in the extent of gene flow. Cultivars with open florets during pollination may have increased gene flow. High or low humidity or temperature during anthesis may decrease gene flow. Although pollen movement has been observed 1000 m from the source, substantial outcrossing beyond 30 m was not observed. Rigorous and systematic gene flow studies in wheat are absent from the scientific literature. Gene flow data could establish an appropriate isolation distance between cultivars and genetically modified (GM) plants or hybrids.

Positive performance is reported for centric translocations of chromosome 1 of rye (Secale cerealeL.) in bread wheat (Triticum aestivumL.). Objectives were to determine the effects of short arm translocations of rye chromosome 1 (1RS) derived from ‘Kavkaz’ winter wheat, in ‘Pavon’ spring wheat background, on root biomass, water‐use efficiency, and agronomic performance. Pavon and its translocations were evaluated in glasshouse pot experiments in 1997 and 1998 and in field experiments in 1999 and 2000 under well‐watered and droughted treatments. The 1RS translocations in Pavon delayed maturity, reduced plant height in some cases, and increased root biomass. Association between root biomass and grain yield was significant under droughted and under well‐watered conditions. The 1RS translocations increased grain yield and grain weight, especially under well‐watered field conditions. The overall mean grain yield was 4.066 Mg ha−1for Pavon, 4.895 Mg ha−1for 1RS.1AL, 4.503 Mg ha−1for 1RS.1BL, and 4.632 Mg ha−1for 1RS.1DL. The 1RS translocations, in general, were more tolerant to field environmental stresses than Pavon. These results encourage the development and use of the 1RS.1AL and 1RS.1DL translocations in wheat breeding programs.

The wild and weedy relatives of bread wheat, Triticum aestivumL., are suggested as potential sources of useful alleles for bread wheat improvement. For example, the genus AegilopsL. has contributed two of the three bread wheat genomes. In this study we measured the nature and extent of allozyme variation for 10 isozymes in three diploid and eight polyploid Aegilops, one Amblyopyrum(Jaub. & Spach), and one feral SecaleL. species collected from 15 populations in their centers of origin in Syria, Lebanon, Turkey, and California. The predominantly autogamous Aegilopsspecies were, to a large extent, homozygous and homogeneous. The presence of heterozygous genotypes in Aegilops tauschiiCoss. (H0= 0.0033 ± 0.01) and Ae. crassaBoiss (H0= 0.0048 ± 0.08) indicated the possibility of limited facultative outcrossing in these Aegilopsspecies. The obligate outcrossers, Amblyopyrum muticum(Boiss.) Eig (He= 0.09 ± 0.16) and Secale cerealeL. (He= 0.09 − 0.13), showed less than expected genetic variation. The extent and nature of genetic variation were identical between the introduced Californian Ae. cylindricaHost and that which occurs in the Fertile Crescent (He= 0.00); however, in Ae. triuncialisL., the introduced Californian population had a higher genetic diversity estimate (He= 0.06 ± 0.12) than the population from the Fertile Crescent (He= 0.00). The average genetic distance between the polyploid Aegilopsspecies was greater (D = 0.64 ± 0.28) than that observed between the diploid Aegilopsspecies (D = 0.18 ± 0.10), or between the diploid Aegilopsand weedy S. cereale(D = 0.52 ± 0.06). We discuss the implication of these findings for germplasm collection and wheat breeding.

Genetic variation and its distribution within and among 23 populations of Triticum urartucollected from Syria, Lebanon, Turkey, Armenia, and Iran was estimated using isozyme markers at eight polymorphic loci. The number of alleles per locus (A= 1.21), percentage polymorphic loci (P= 20.1%), and mean gene diversity (He= 0.024) were relatively low. In a population from Lebanon, a high number of alleles per locus (A= 2.13) and percentage polymorphic loci (P= 87.5%) was found. On average, genetic variation among populations (GST= 0.407) was smaller than within-population variation (0.593). However, different patterns of genetic structure were found among various geographic regions. Interpopulation variation was highest for the Iranian populations (0.89) followed by the Turkish populations (0.66). A reverse pattern was observed for the Syrian (0.11) and for the Lebanese (0.13) populations. The Armenian populations exhibited similar interpopulation and within-population variation. Principal component and cluster analyses resulted in distinct grouping of the geographically proximal populations, with the exception of the two Iranian populations. The Turkish populations were different from the neighboring Armenian populations compared to other countries. The populations from southern Syria and those from Lebanon also exhibited a high degree of genetic diversity. The two most heterozygous loci, Mdh-2and Pgi-2, separated the populations along the first and second principal components, respectively. Most of the rare alleles were scattered sporadically throughout the geographic regions. Rare alleles with high frequencies were found in the Turkish and Armenian populations. These results indicated that different geographic regions require specific sampling procedures in order to capture the range of genetic variation observed in T. urartupopulations.

Insect tripping might enhance seed production in common bean (Phaseolus vulgarisL.). The effect of flower visits by insects on seed production was studied during 3 yr, 1992 to 1994, in Riverside, CA, using four cultivars with different growth habits: Linden, Pindak, PI 164778, and Ferry Morse 53 (FM 53). Each year, a factorial experiment in a randomized complete block design with four replicates was used. Each cultivar was grown under three treatments: (i) exposed to open visitation by all insects, (ii) in insect‐proof cages, and (iii) in cages with bumblebees. All pods produced by bean plants were collected and counted, and seed yield was determined. Year‐to‐year variation had signiticant impact on cultivar performance and treatment effects. The bean lines were significantly different for seed yield. The treatment effects were not consistent across years. The old cultivar FM 53 and line PI 164778 had no clear trend for seed yield response to insect visits across years, whereas Linden and Pindak showed a more defined and positive response to visits. Seed yield of Linden was similar in the open visitation and caged‐with‐bumblebees treatments but was significantly higher than that of caged plants, by 13% in 1992 and by 35% in 1994. Pindak showed a 9% increase in seed yield when plants were visited by insects in the open or in caged treatments compared with caged plants in 1992. The results indicate that cultivars such as Linden and Pindak, which behave as determinate plants, may respond to bumblebee tripping by increasing seed yield.

Ninety‐three accessions of primitive domesticated diploid wheat (Triticum monococcumL.), five each of two wild tetraploid wheats (T. turgidumL. var. dicoccoidesKörn and T. timopheeviiZhuk. var. araraticumJakubz.), one cultivated durum wheat (T. turgidumL. var. durumDesf. ‘Modoc’) and one cultivated bread wheat (T. aestivumL. var. aestivum‘Anza’) were compared for plant height, seed weight, flour protein content, flour lysine content, lysine content in protein, spike weight, days to head, and days to flower under irrigated and dryland conditions in 1977. Superior lines were retested in 1979. Variation among lines for each trait in different species was significant except plant height in dicoccoides and araraticum. Over all species, plant height and seed weight were significantly higher, and protein and lysine contents were significantly lower in irrigated than in dryland conditions, although differences within dicoccoidesfor seed weight and protein and lysine contents were nonsignificant. Two accessions of monococcumwere short and headed and flowered as early as Modoc and Anza. Primitive and wild wheats were higher in protein content and lysine content but lower in spike weight and seed weight than the two modern cultivars. Wild tetraploids were higher in flour protein content and in flour lysine content but lower in lysine content in protein than monococcum. Accessions of dicoccoidesand araraticumhaving 30.9 and 30.5% protein, respectively, were identified. Correlations between traits were influenced by species and by moisture conditions. Best lines of monococcum, dicoccoides, and araraticumwere identified as sources of genes for different traits.

Resistance to root‐knot nematode, Meloidogyne incognita(Kofoid and white) Chitwood, has been identified and incorporated into commercial cultivars of common bean, Phaseolus vulgarisL. However, the effective use of host resistance as a management tactic against root‐knot nematodes attacking common bean requires identification and incorporation of resistance to other economically important root‐knot nematodes, namely M.javanica(Treub) Chitwood, M. arenariaand M. hapla. Fifty‐four common bean and 64 tepary bean, P. acutifoliusA. Gray, lines were screened for resistance to root‐knot nematodes under greenhouse and growth chamber conditions. In the greenhouse, the plants were grown in pots filled with loamy sand and, in the growth chamber, the plants were grown in growth pouches. Bean plants in the greehouse were inoculated with 5000 nematode eggs and evaluated for nematode reproduction (eggs) 6 wk after inoculation. In the growth chamber, plants were inoculated with 1000 second‐stage juveniles and evaluated for egg numbers 4 wk after inoculation. Common bean lines PI 165426 and Alabama no. 1 were found to be resistant to M. incognitaRace 2, 3 and 4 but were susceptible to M. incognitaRace 1 and to M. arenaria. Breeding lines A252, A315, A328, A443 and A445 were resistant to M. javanicaand M. incognitaRace 1. Resistance in the A lines was found to be derived from two common bean landraces, G1805 and G2618. The resistance was also effective against M. arenaria. The tepary bean accession PI 310606 was found to have good resistance to all nematode isolates tested. We postulate that resistance derived from G1805 and G2618 may be under different genetic control than that in PI 165426 and Alabama no. 1.

Genetic variation exists for season‐long water‐use efficiency (WUE) among bread wheat (Triticum aestivumL.) cultivars. To facilitate the study of such variation, we define WUE and its components so that the contribution of each component trait to variation in WUE can be evaluated. Seven diverse bread wheat cultivars were grown in replicated glasshouse pot experiments under well‐watered conditions. Significant genotypic variation was observed for WUE (ratio of grain yield to water used), evapotranspiration efficiency (ETE, ratio of total dry matter to water used), and harvest index (HI, ratio of grain yield to total dry matter). Old tall cultivars, on average, had relatively higher ETE (3.95 vs. 2.67 g kg−1), but much lower HI (0.35 vs. 0.53) than modern semidwarf and dwarf cultivars. Cultivars with similar WUE showed different patterns of component traits. Evapotranspiration efficiency, and HI accounted for 59%, and 41%, respectively, of the genotypic variation in WUE. A path coefficient analysis revealed that ETE had a higher direct effect on WUE than did HI. However, their positive direct effects were counterbalanced by negative indirect effects via each other, because ETE and HI were negatively correlated. Carbon isotope discrimination showed a negative correlation with WUE (−0.62) and ETE (−0.84), but a positive correlation with HI (0.43). Days from planting to maturity, plant height, root dry matter, and shoot dry matter each had a positive correlation coefficient with ETE, but a negative correlation with HI.

The tepary bean (Phaseolus acutifoliusA. Gray) is reputed to be heat and drought tolerant, but the literature contains little information on yield performance of tepary in different conditions. To fill this void, replicated field studies were conducted to measure and compare yield, seed protein concentration, and seed weight of 16 domesticated and eight wild tepary lines at the hot, dry location of Riverside, CA. Well‐watered and drought‐stressed conditions were set up in the summer of 1978. The experiment was repeated with six of the domesticated lines in the spring and summer of 1979. Significant differences were found among the wild lines and among the domesticated lines for the three traits measured. Mean yield and seed weight of wild teparies were 40 and 75% lower than those of domesticates, but mean protein concentration of the two groups was the same (27.6%). Moderate drought‐stress reduced the mean yield of teparies by 55%, but did not reduce protein concentration or seed weight. Seed yield showed a positive correlation with seed weight (r= 0.78), but a negative correlation with seed protein concentration (r= −0.75) in domesticated teparies.

Since a significant portion of applied soil N is lost by leaching and denitrification, it is desirable to breed crop cultivars with improved N use efficiency. This study was undertaken to determine the influence of soil N supply on genotypic variation for preanthesis and postanthesis shoot N accumulation, the effect of preanthesis N and grain N yield on postanthesis N accumulation, and N use efficiency. A set of 12 bread (Triticum aestivumL.) and two durum (T. turgidumL. var durumDesf.) wheat genotypes was studied over three planting dates in 2 yr with three N levels within each planting date on a Ramona type A sandy loam (coarse fine‐loamy, mixed thermic Typic Haploxeralf). Differences among genotypes for shoot N accumulation before and after anthesis became obvious at the highest soil N level. At this level, some genotypes either stopped accumulating or showed a net loss of shoot N between anthesis and maturity, which appeared to be associated with superior preanthesis N accumulation capacity and reduced grain N yield of such genotypes. Uptake efficiency (total shoot N/soil N supply) became slightly more important than utilization efficiency (grain yield/total shoot N) in determining N use efficiency (grain yield/soil N supply) with increasing soil N supply. Nitrogen harvest index (grain N yield/total shoot N) fully explained the reduced contribution of utilization efficiency at higher soil N levels. We suggest that bread wheat genotypes G4843 and ‘Anza’ should be crossed in an attempt to recombine the superior N accumulation capacity of the former with the superior grain yield of the latter to develop a cultivar with improved N use efficiency.

The two most commonly used dwarfing genes of bread wheat (Triticure aestivumL.) are Rhtland Rht2. The Rht3gene is also a potent dwarfing gene. Information in the literature is limited as to the comparative effects of these genes on transpiration efficiency (TE) and wateruse efficiency (WUE). Carbon isotope discrimination (Δ) has proposed as a criterion to select for improved TE. Four near‐isogenic lines, rhtrht, RhtlRhtl, Rht2Rht2, and Rht3Rht3, in ‘Maringa’ bread wheat background and four of their near‐isogenic F1hybrids derived from crossing the original lines were used to determine the effects of dwarfing genes on plant height, root dry matter, shoot dry matter including grains, grain yield, total dry matter (TDM), TE (TDM/water transpired), WUE (grain yield/water used), and Δ in well‐watered droughted pot experiments in the glasshouse. The near‐isogenlc lines and their six F1hybrids were also grown in well‐watered and droughted field conditions. Plant height ranged from 60 to 124 cm and from 53 to 121 em in well‐watered and droughted pot experiments, and it varied from 50 to 94 cm and from 49 to 90 cm in well‐watered and droughted field experiments, respectively. Total dry matter, grain yield, TE, and WUE declined with plant height in well‐watered glasshouse conditions. No significant relationships were found between plant height and these traits in droughted glasshouse conditions. Carbon isotope discrimination was negatively correlated with TE, but significantly so only in the well‐watered pot experiment. Plant height was negatively associated with Δ in both well‐watered and droughted pot and field experiments. Grain yield and shoot dry matter also declined with plant height in field conditions. Negative correlations were observed between Δ and grain yield and Δ and shoot dry matter in well‐watered field conditions. In most cases, the dwarfing genes reduced shoot dry matter more than grain yield and, therefore, harvest index of the semidwarf and dwarf lines was higher than that of the tall standard fine. The dwarfism caused by RhH, Rht2, and Rht3genes had, in general, depressing effects on TE, WUE, TDM, and grain yield.

Temperature affects crop development and yield. In this study the effect of temperature on emergence, vegetative development, and yield of common bean (Phaseolus vulgarisL.) and tepary bean (P. acutifoliusA. Gray) was compared. In the growth chamber nine common bean accessions were evaluated for emergence response over planting depths of 25, 50 and 75 mm, and at constant temperatures of 15,20,25,30, and 35 °C. The three depths had no significant effect on emergence between 20 and 30 °C, but at 15 and 35°C the increased depth significantly delayed emergence. The most rapid germination and emergence occurred at 30 °C under these controlled conditions. In the field emergence of the same common bean accessions was compared to tepary bean; tepary bean emerged about 1.5 d earlier than common bean at soil temperatures of 18 to 28 °C. The effect of temperature on vegetative development was evaluated by a linear heat unit system that measured base temperature (Tbase) and heat units to flowering. Under field conditions common bean had an average base temperature (Tbase) lower than tepary bean, and required more heat units to flower. Genotypic differences for base temperatures and heat unit requirements existed among accessions within both species. Temperature strongly affected the yields of both species when grown at Riverside, CA, on an Arlington fine sandy loam (coarse‐loamy, mixed, thermic Haplic Durixeralf). Tepary bean produced higher yields than common bean under hot summer conditions, but lower yields under early spring conditions.

Diallel crosses among Triticum boeoticum (4 lines from different geographical areas), T.urartu, Aegilops squarrosa and Ae. speltoides exhibited reciprocal differences in hybrid seed morphology, endosperm development, and embryo viability. T. urartu and Ae. squarrosa as females with T. boeotiaum and Ae. speltoides lead to shrivelled inviable seed. T.boeoticum accessions as female with Ae.speltoides also lead to shrivelled seeds. The reciprocal crosses produced plump seeds which either resembled the maternal parent or showed size differences. By altering the endospermic genome ratios, hybrid seeds with 1 (PF)/1 (PM) showed extreme shrivelling whereas those with 4 (PF)/1 (PM) were medium shrivelled to plump. Genetic experiments involving hybrids of T. boeoticum, T. urartu and T. monococcum showed that a factor is present in pollen or male gametes, which shows dosage effect and which, by interacting with the maternal genome, leads to endosperm abortion.

Drought and heat stress are major environmental factors reducing grain production of rainfed wheat (Triticum aestivumL.) in semiarid regions. The objective of this research was to identify bread wheats with improved adaptation to hot, dry environments. Field studies were conducted to measure effects of terminal drought and heat stress on duration of developmental phases, grain yield, and yield related traits of day‐length insensitive spring wheats. Fifteen genotypes, including lines from landraces of southwestern Iran and improved cultivars from Iran and California, were grown in a nonstress and three artificially imposed stress environments at Moreno Valley, CA, in 1986. Genotype ✕ environment interactions were significant for grain yield and its components. Stress susceptibility of each genotype was estimated using a calculated index based on grain yield. Landrace genotypes and improved cultivars that were evaluated exhibited a wide range in stress susceptibility and adaptation to stress environments. Landrace genotypes and cultivars did not vary for mean stress‐susceptibility index values. Landrace genotypes generally had lower yield potential than the cultivars. The stress‐susceptibility index identified some genotypes that did not have outstanding yield performance per se in stress environments due to low yield potential and others that had high average yield in stress conditions. Stress susceptibility and yield potential were not associated, indicating that they may be independent components which both contribute to adaptation to stress environments. The stress‐susceptibility index was negatively correlated with number of grains per head, grain weight, grain yield, and harvest index under stress conditions, indicating selection for these characters in stress environments might result in decreased susceptibility to stress.

Genetic variability for seedling root number within the genus Triticumwas characterized to determine if this trait could be used in wheat breeding. Average seedling root numbers were determined in the laboratory for 143 accessions of wheat including the diploid species Triticum boeoticumBoiss., T. monococcumL., and T. urartuTum.; the tetraploid species T. araraticumJakubz., T. dicoccoidesKörn., T. turgidumL. var. dicocconSchrank and var. durumDesf., and T. timopheeviZhuk.; the hexaploid species T. aestivumL. var. aestivum, vat. compactum, var. macha, var. spelta, var. sphaerococcum. and var. vavilovii, and T. zhukovskyiMen. & Er. Significantly differently mean root numbers were found within each ploidy level and, in most cases, within each species or variety. The highest mean root number, 6.45, was found in an accession of T. turgidumvar. durum, the lowest, 2.50, in accession of T. araraticum. Seed weight was positively correlated with mean root number (r = 0.71) but within each ploidy level accessions having similar seed weights and significantly different mean root numbers were found. Progeny tests of 15 diploid and seven tetraploid accessions showed that seedling root number was stable from one generation to the next. A test of 33 of these accessions and progeny in a greenhouse experiment showed this trait was stable (r = 0.91) across the two environments tested. Embryos sectioned by hand showed that all accessions tested had about five seminal root primordia present. In general, greater seedling root number may be selected for by selecting for higher seed weight, but exceptions to this rule were observed.

Meiotic analyses and pollen viability tests were performed on F, hybrids between diploid guayule (Parthenium argentatumGray 2n= 36), P. rollinsianumRzedowski (2n= 36), P. alpinumvar. tetraneurisBarneby (2n= 36), and P. alpinumvar. alpinumNutt. (2n= 36). Partheniumchromosomes are small and karyomorphologically similar, and meiotic analysis is difficult because of chromosome clumping. However, cytogenetic studies at metaphase I indicated univalents can be seen in a lateral view of the metaphase plate. Chromosome pairing and the number of univalents varied within and between the interspecific hybrids, with an average univalent number of 1.54 for the P. rollinsianumhybrids, 2.36 for the P. alpinumvar. tetraneurishybrids, and 2.46 for the P. alpinumvar. alpinumhybrids. Pollen viability tests for the parental species and the hybrids were conducted by germination of pollen grains on stigmas. The percent of viable pollen recorded for the diploid guayule hybrids with P. rollinsianum, P. alpinumvar. tetraneuris,and P. alpinumvar. alpinumare 21.94, 13.47, and 11.17, respectively. The degree of chromosome pairing and pollen viability is striking because there are many morphological differences between the parents. The chromosome homology of these species based on their pairing behavior allows for the design of a backcross breeding program that would permit the transfer of the desirable characteristics from these species into diploid guayule.

Interspecific hybrids between woody Parthenium argentatumGray (guayule), native to Mexico and Southwest Texas, and herbaceous perennial P. hispidumvar. auriculatum(Britton) Rollins, native to the United States, were obtained successfully. The F1hybrids were intermediate for most morphological characters with the exception of the short woody stem, yellow pollen color, and the trichome morphology. Chromosome counts revealed the presence of 2n= 36 A‐chromosomes in P. argentatum.The same number of A‐chromosomes and four B‐chromosomes were found in P. hispidumvar. auriculatum.Observations of pollen mother cells showed regular meiosis in both parental species. At diakinesis, chiasmata averaged 1.12 and 1.24 per bivalent for P. argentatumand P. hispidumvar. auriculatum, respectively. Meiotic behavior of the F1hybrids was irregular. F1hybrids averaged 4.43 univalents at metaphase I, 1.95 laggards at anaphase I, and 1.62 micronuclei at the tetrad stage. The low pollen stainability (5.1%) in the F1hybrids and the limited number of viable BC1seeds (4.07%) may be reflections of the irregular meiosis. Although these primary hybrids are partially fertile, they can be used to introduce desirable characteristics of P. hispidumvar. auriculatum, such as herbaceous perennial habit, regrowth ability, and cold tolerance into guayule.

To distribute the high cost of stand establishment across several years of production, guayule (Parthenium argentatumA. Gray) is harvested after a minimum of 4 yr by digging entire plants. An alternative is multiple harvest of the shrub, cut at ground level, at an optimal interval as long as an economic yield is obtainable. for this, guayule cultivars with nearly 100% survival after each harvest are required. The objectives of this study were to compare guayule cultivars and selections in the filed for their regrowth ability after harvest, and to determine the relative contributions of under‐ and aboveground parts to the overall rubber yield of the plant. In a completely randomized design with three replications, 84‐week‐old dormant, 96‐week‐old actively growing, and 132‐week‐old dormant plants of 11 cultivars and selections were cut at ground level in February and May 1985, and February 1986. Harvest date was found to be a critical factor: an average of 49% of the plants harvested in February regrew, while only 1.4% of those harvested in May regrew. Marked differences between lines were observed in the February harvests. Approximately 97% of selection C2501 plants produced vigorous regrowth, but only 5.5% of C2551 plants regrew. Regrowth of the other entries lay within these extremes. Five of the entries were compared for the contributions of the under‐ and aboveground parts to the overall yield. The underground part produced 6.0 to 13.5% of the total rubber yield. If plants were harvested at 5 and 10 cm above the soil surface, 3.4 to 8.9% and 9.4 to 22.5%, respectively, of the aboveground yield was not recovered. This study identified selections that meet the demands of multiple harvest.

An objective procedure was developed to find and eliminate repeated genotypes from a set of crop cultivars or accessions which may be used as parents for future plant breeding programs. Nonhierarchical, nonexclusive, exhaustive cluster analysis was used to group 93 diploid wheat accessions using LSD multiple comparisons of accession means based on data measured on seven characters. Beginning with the rarest accessions, i.e. those represented in the fewest clusters resulting from the clusters analysis, a minimum number of the accessions were chosen to represent the phenotypes of all 93 of the accessions. Two analyses were performed, one using data from an irrigated trial, the other from a dryland trial. The dryland trial data was more discriminating in that it required 71 accessions to represent all of the clusters generated from the original 93 accessions while the irrigated trial data required only 60 of the 93 accessions. In addition to the 71 accessions chosen from the dryland trial analysis, the irrigated trial analysis suggested an additional 12 accessions were phenotypically and, therefore, genotypically unique. The total of 83 unique accessions left 10 phenotypically duplicate accessions to be eliminated from the set of potential parents. Four of the 10 duplicated accessions were ‘rare’ in that they were represented in very few clusters in either the irrigated trial analysis or in the dryland trial analysis. Because their phenotypes were not unique in spite of being rare, we believe such accessions were duplicated genotypically as well as phenotypically. The other six duplicates were ‘common’ in that they were represented in a large number of clusters. Such accessions may not prove to be duplicates if grown in additional environments (trials), or if measured on additional characters.

Carbon isotope discrimination (?) has been suggested as a selection criterion to improve transpiration efficiency (W) in bread wheat (Triticum aestivum L.). Cultivars ‘Chinese Spring’ with low A (high W) and ‘Yecora Rojo’ with high ? (low W) were crossed to develop F1, F2, BC1, and BC2 populations for genetic analysis of ? and other agronomic characters under well-watered (wet) and water-stressed (dry) field conditions. Significant variation was observed among the generations for ? only under the wet environment. Generation x irrigation interactions were not significant for ?. Generation means analysis indicated that additive gene action is of primary importance in the expression of ? under nonstress conditions. Dominance gene action was also detected for ?, and the direction of dominance was toward higher values of ?. The broad-sense and the narrow-sense heritabilities for ? were 61 % and 57% under the wet conditions, but were 48% and 12% under the draughted conditions, respectively. The narrow-sense heritabilities for grain yield, above-ground dry matter, and harvest index were 36%, 39%, and 60% under the wet conditions and 21%, 44%, and 20% under dry conditions, respectively. The significant additive genetic variation and moderate estimate of the narrow-sense heritability observed for ? indicated that selection under wet environments should be effective in changing ? in spring bread wheat.

The methods used to study cytoplasmic effects in quantitative traits often do not measure quantitative genetic parameters, while those that do are either complicated or do not take into account situations where the expression of cytoplasmic effects does not persist, but decreases in advanced generations. We present two simple models that take cytoplasmic effects and the quantitative genetic parameters into account. One of the models (A) is for cases where cytoplasmic effects remain constant through successive generations, and the second model (B) is for traits where cytoplasm-genotype interactions are present. This model also takes into account the decreasing persistence of cytoplasmic effects with advancing generations, which is often reported in the literature.

Variation in high molecular weight (HMW) glutenin subunit composition among 167 accessions of dicoccum wheat (Triticum turgidum L. var. dicoccum Schrank) of diverse origins was investigated using one-dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). A total of 20 alleles were identified, and 9 of them were found to be different from those previously detected by Payne and Lawrence (1983 b) in hexaploid wheat (Triticum aestivum L.). The newly discovered alleles enhance the genetic variability available to improve the industrial quality of wheats and some of them may facilitate basic research on the relationship of industrial quality with HMW glutenin subunit number. The novel variants include a GLU-A1 encoded subunit which has higher molecular mass than any other so far described in tetraploid and hexaploid wheats, and a ‘null’ GLU-B1 allele. Dicoccums containing neither GLU-A1- nor GLU-B1-encoded subunits were also identified. A comparison of the mean number of HMW glutenin subunits contained in various primitive and modern domesticated wheats of different ploidy levels and the identification of wheats containing no HMW glutenin subunits suggest that the occurrence of ‘null’ GLU-1 alleles in these species depends on chance rather on an inherent tendency on the part of modern polyploid wheats to suppress the activity of redundant GLU-1 genes.

Soil temperature strongly influences the germination and emergence of common beans (Phaseolus vulgarisL.) and tepary beans (Phaseolus acutifoliusA. Gray). The purpose of this investigation was to identify accessions of both species that could potentially germinate and emerge under cool soil conditions, and to determine an optimum germination temperature for tepary beans. Germination of 129 common and 18 tepary bean accessions was initially evaluated at 10°C. The 10 earliest common and the five earliest tepary beans to germinate were entered into an emergence test at three temperatures (12, 14, and 16°C). The common beans emerged 1 day earlier than the teparies at 12 and 14°C, while the teparies emerged 1 day earlier at 16°C. The most cold‐tolerant common bean at emergence was PI 165‐426, while accessions G40034 and PI 319‐443 displayed the highest cold tolerance among the tepary beans. Subsequently, tepary beans were compared to common beans for germination response over six temperatures from 10 to 35°C. In general, tepary and common beans took approximately the same time to germinate except at 35°C where teparies germinated faster. A scarification experiment was undertaken with the same six temperatures as above to determine any effects of the seedcoat on tepary bean germination. Scarification generally resulted in an earlier germination response, but the effect was small. Both germination experiments indicate that the optimum temperature range for teparies is 25 to 35°C, whereas it is lower, 20 to 30°C, for common beans.

Nine pure lines of bread wheat collected from landraces of southwestern Iran and one local Iranian cultivar from the same area were used to estimate genetic variation and heritability for 12 developmental and yield component characters. Path-analysis was used to partition the genetic correlations between some of the characters into direct and indirect effects. Mean values for these lines were also compared with those of five improved cultivars from Iran and California. The goal of the experiment is to breed improved landraces and/or modern cultivars for areas of low input agriculture in southern California, southwestern Iran, and regions with similar environmental and agronomic conditions.

Drought stress is one of the most limiting factors to crop production in semiarid regions. Improved water‐use efficiency (WUE) could provide breeding programs with a means to improve adaptation to drought‐prone environments. Carbon isotope discrimination (Δ) has been proposed as a criterion to select for improved WUE. This study evaluates differences in total dry matter (TDM), WUE (TDM/transpiration), and Δ of flag leaves of landrace and modern wheat (Triticum aestivumL.) genotypes grown in pots in a well‐watered (wet) and in a drought‐stressed (dry) experiment for 2 yr. The wheat genotypes were also grown in wet and dry field conditions. In the pot experiments, average WUE of the genotypes varied from 2.85 to 4.41 g dry matter kg−1water in the wet experiment and from 3.08 to 4.53 in the dry experiment. The mean values of Δ were 21.7 ✕ 1O−10for the wet pot experiment and 21.6 ✕ 10−3for the dry pot experiment. The tall landrace genotypes had greater TDM and WUE, but were later in maturity than the modern dwarf and semi‐dwarf genotypes. Values of Δ associated with different genotypes were negatively correlated with WUE. Broad‐sense heritabilities for WUE and Δ were 93 and 90%, respectively, in the pot experiments. In the dry field experiments, Δ was positively associated with above‐ground dry matter and grain yield in both years. In the wet field experiments, there was a positive correlation between Δ and grain yield only in 1988. Broad‐sense heritabilities for Δ were 72% for wet field conditions and 74% for dry field conditions. These observations indicate that selection for C isotope discrimination, under either wet or dry conditions, can improve water use efficiency in wheat.

Standard unit heritabilities for grain yield of common bean (Phaseolus vulgarisL.) were determined for F2‐derived F4and F5progenies and for F2individual plants and their F3progenies of three common bean crosses. Standard unit heritabilities were determined by correlating F2‐derived F4line grain yields with F2‐derived F5line grain yields. Heritabilities were determined for direct selection (F4and F5lines in the same cropping system) and indirect selection (F4and F5lines in different cropping systems). Selection gains were also estimated for direct selection, indirect selection, and for selection based on the means of both systems. Parent‐offspring genotypic correlations were determined for the F2‐derived F4and F5progenies. Standardized correlated responses to selection for grain yield based on selection for harvest index were estimated for F2individual plants. Standard unit heritabilities were larger in intercrop than in sole crop. The difference in heritability between cropping systems was larger for F2plants than for the F2‐derived F4progenies. Direct selection in intercrop and sole crop was always superior to indirect selection in the alternate cropping system. Indirect selection in intercrop for sole crop gave the lowest gains. Direct selection in intercrop or in sole crop gave the highest genetic gains in each respective cropping system. Selection on the mean of both systems gave gains in each system almost as high as those of direct selection. Selection in sole crop for improvement in the mean of both systems resulted in lower gains than selection on the mean of both systems, but was better than selection in intercrop. Standardized correlated responses in grain yield by selection for harvest index were larger in intercrop than in sole crop. Single plant selection for yield may be effective for beans which are intercropped.

ABSTRACT Caespitose and cold‐tolerant plants of Parthenium ligulatum(Jones) Barneby (Asteraceae) from a native population in the Uinta Basin, Utah, were uprooted, potted, and transferred to a greenhouse in California. Approximately two years after transfer, the plants flowered and subsequently were crossed to diploid guayule (Parthenium argentatumGray), the rubber‐bearing species, native to the state of Durango, Mexico. Only female guayule × male P. ligulatumcrosses produced F1hybrids. Only crosses involving guayule as female parent and F1plants as male parents produced backcross (BC,) plants. Hybrid plants were variable with respect to their growth habit, inflorescence, and leaf shape. Both parents and F1hybrids had 2n= 36 chromosomes. Unlike the parents, however, meiosis was irregular in the hybrids which showed a range of 0–5 and an average of 2.1 univalents at metaphase I. Hybrids averaged 0.87 laggards at anaphase I and 0.83 micronuclei at the tetrad stage. The crossability of guayule and P. ligulatum, the high degree of chromosome pairing of the F1hybrids, and the production of BC1plants indicate that the two species are related in spite of their distinct morphological and ecological differences. This study suggests that the cold‐tolerance trait of P. ligulatummay be transferred to guayule through interspecific hybridization followed by backcrossing. The development of cold‐tolerant guayule cultivars is expected to expand the areas of guayule production beyond that of the Chihuahuan desert and similar climates.

In order to determine the pattern of genetic diversity within and among the species of Cicer and to estimate interspecific genetic relationships, allelic variation was assayed for 23 isozyme loci in 63 accessions of 11 species of Cicer using starch gel electrophoresis. The total allozymic variation observed in the genus (Ht)was equal to 0.60. When partitioned (Gst), 96% of this allelic diversity was found among rather than within species. The allelic diversity among species (Dst)and allelic diversity within species (Hs)were equal to 0.58 and 0.02, respectively. Cicer reticulatum and C. pinnatifidum had the highest proportion of polymorphic loci (17.39%) and the highest mean number of alleles per locus (1.22 and 1.17, respectively). UPGMA cluster analysis of Nei's unbiased genetic distance revealed four genetic groups. One includes C. reticulatum, C. arietinum and C. echino spermum where the first 2 species represent a putative derivative-progenitor pair. A second cluster contains C. bijugum, C. pinnatifidum and C. judaicum. Cicer yamashitae, C. chorassanicum, C. anatolicum and C. songoricum form a third group. Finally, C. cuneatum, which has a very distinct isozyme profile and peculiar morphological features, is the only member of a fourth species group. This species grouping agrees partially with those obtained from crossability and cytogenetic studies. The results suggest that the annual habit arose from perennial progenitors at least twice in the genus Cicer.

The genetic diversity of two wild diploid wheat species, Triticum monococcum var. boeoticum and T. urartu, was assessed using starch gel electrophoresis. Genetic diversity is uniformly low in both species. Number of alleles per locus was very low with a mean of 1.22 for T. monococcum var. boeoticum and 1.19 in T. urartu. Percentage of polymorphic loci was also low, with a mean of 19.71 for T. monococcum var. boeoticum and a mean of 18.35 for T. urartu. Mean gene diversity was low with a mean of 0.052 in populations of T. monococcum var. boeoticum and a mean of 0.040 in populations of T. urartu. Genetic affinities of the species and of populations were computed using Nei's identity index (NI). Overall genetic affinities of the two species are NI=0.697. The genetic affinities of different populations of a species are uniformly high with NIs ranging from 0.894 to 1.000 in T. monococcum var. boeoticum and from 0.898 to 1.000 in T. urartu.

The high molecular weight (HMW) subunit composition of glutenin was analysed by sodium dodecyl sulphate, polyacrylamide gel electrophoresis (SDS-PAGE) in the A genome of 497 diploid wheats and in 851 landraces of bread wheat. The material comprised 209 accessions of wild Triticum monococcum ssp. boeoticum from Greece, Turkey, Lebanon, Armenia, Iraq, and Iran; 132 accessions of the primitive domesticate T. monococcum ssp. monococcum from many different germplasm collections; one accession of free-threshing T. monococcum ssp. sinskajae; 155 accessions of wild T. urartu from Lebanon, Turkey, Armenia, Iraq, and Iran; and landraces of T. aestivum, mainly from the Mediterranean area and countries bordering on the Himalayan Mountains. Four novel HMW glutenin sub-units were discovered in the landraces of bread wheat, and the alleles that control them were designated Glu-Ald through Glu-Alg, respectively. The HMW subunits of T. monococcum ssp. boeoticum have a major, “x” subunit of slow mobility and several, less prominent, “y” subunits of greater mobility, all of which fall within the mobility range of HMW subunits reported for bread wheat. In T. monococcum ssp. monococcum the range of the banding patterns for HMW subunits was similar to that of ssp. boeoticum. However, two accessions, while containing “y” subunits were null for “x” subunits. The single accession of Triticum monococcum ssp. sinskajae had a banding pattern similar to that of most ssp. boeoticum and ssp. monococcum accessions. The HMW subunit banding patterns of T. urartu accessions were distinct from those of T. monococcum. All of them contained one major “x” and most contained one major “y” subunit. In the other accessions a “y” subunit was not expressed. The active genes for “y” subunits, if transferred to bread wheat, may be useful in improving bread-making quality.

To assess genetic and environmental variation for outcrossing in common bean (Phaseolus vulgarisL.), a bulk of nine purplehypocotyled (dominant), black‐seeded, common bean lines (pollen parents) and six green‐hypocotyled (recessive), white‐seeded, common bean lines (seed parents) representing Mexican germplasm were used to estimate outcrossing rate. The experiment was conducted at Irvine and Riverside, CA, in mid‐May and mid‐July of 1989 and 1991. Outcrossing estimates were based on the proportion of purplehypocotyled progeny from green‐hypocotyled parents. Approximately 1400 single‐plant families were progeny tested in which 120 278 seedlings were scored for the presence of anthocyanin in the hypocotyl. Of these, 113 246 were classified as selfed progeny and 7031 as hybrid progeny, giving rise to a weighted mean outcrossing rate of 6.9%. Entire progenies from each maternal line were grown and scored, and the minimum and maximum rates of outcrossing observed ranged between 0.0 and 78.0%. Mean outcrossing rate for the six white‐seeded lines ranged from 4.41 to 10.16%. However, differences in outcrossing rate among these lines were not significant, nor were differences between dates of planting, locations, or years. The combined analysis of variance showed significant location × planting date × line interaction and year × location × line interaction, indicating that environmental factors had a strong effect on rate of outcrossing in the lines examined.

Focuses on the adaptation of lilacs to coastal southern California. Construction of homes and gardens in the coastal strip; Selection of lilac cultivars; Leafing and blooming of lilacs.

Comments on lilac cultivars that bloom out of normal season in southern California. Experimental plant developed by Louis Erickson, called E2 (LE); Blooming of Grace Mackenzie in early February; Flowering of the Lilac Sunday and the Clarke hyacinthiflora in spring.

Protein contents and 1,000 grain weights of wild and domesticated tepary beans (Phaseolus acutifoliusA. Gray) were compared with values for domesticated common beans (P. vulgarisL.). The wild teparies tested had significantly higher mean protein values, but significantly lower grain weights than the domesticated teparies. Domesticated teparies had a larger range of protein values than the wild teparies. Wild and domesticated teparies had significantly lower mean protein contents and much lower mean grain weights than the cultivars of P. vulgaris tested. Only in cultivars of common bean were protein content and grain weight significantly negatively correlated. Teparies may have potential for breeding and for interspecific hybridization to transfer drought tolerance, heat resistance, ozone‐smog tolerance, narrow leaves, and disease resistance from teparies to common beans.

Values for nitrogen concentrations in yellow‐berry kernels of bread wheat (Triticum aestivumL. em Thell.) varied from 91.6 to 72.9% of those for normal kernels of the same cultivar. Values for total amino acid concentrations in whole‐wheat flour of yellow‐berry kernels were less than those of whole‐wheat flour of normal kernels. When the values were expressed as concentrations of amino acid per gram protein, those for lysine and threonine were higher in yellow‐berry kernels than in normal kernels, and the differences were significant and highly significant, respectively: that for glutamic acid was significantly lower in yellow‐berry kernels than in normal kernels. Isoelectric focusing patterns of albumins and gliadins from the two kinds of kernels showed no differences. Additional index

Lath house experiments were conducted to study the relationship between the timing of N deprivation, subsequent N metabolism and yellowberry expression of two spring bread wheat (Triticum aestivumL. ‘Chinese Spring’ and ‘Anza’) cultivars. Wheat plants were grown in pots containing sand and were supplied with 350 ml Hoagland's solution containing 15.0 mM nitrate every 4 days. Plants were initially deprived of N (nitrate) at the jointing, boot, and flowering growth stages. Nitrogen deprivation at each growth stage increased percent yellowberry and decreased percent grain N. Percent yellowberry was inversely and curvillnearly related to percent grain N. The N metabolism traits which controlled percent yellowberry and percent grain N were percent above‐ground plant N, percentage of N in reduced form, and harvest index for dry weight and for N.

Pollen stainability appears to be a reliable indication of the ultimate seed set in diploid interspecific hybrid and backcross populations in TriticumL. The correlation between percent pollen stained and number of seeds set is positive and highly significant (r =0.92). Estimates of male and female fertility in the hybrids and backcrosses are interpreted to indicate that the domesticated diploid Triticum monococcumL. and wild diploid T. boeoticumBoiss. em. Schiem, are one and the same species, and that T. urartuTum. is not a variety of monococcumor boeoticum, but rather a separate species. The F1hybrids and backcrosses between monococcumand boeoticumare normally male and female fertile. The F1hybrids between monococcumand urartuare completely sterile and complete to partial sterility exists in backcrosses.

The outcrossing rate of a species is an important parameter to consider when making a decision on the method to improve the species. Outcrossing rates were estimated for six white‐seeded common bean (Phaseolus vulgarisL.) lines sown in May and July 1985, at Irvine, CA. Estimates were based upon the proportion of black‐seeded (dominant) progeny from white‐seeded parents. Genetic variation for outcrossing rates among the six lines studied was suggested by the large difference between the mean estimate for ‘FM 53’ (66.8%) and the combined mean estimate for the other five lines (19.3%). Outcrosses occurred less frequently at the early planting date (18.8%) than at the late‐planting date (47.0%). Further studies on the outcrossing in the common bean and its application to recurrent selection are warranted in light of the reported results.

The inheritance, genetics, and linkage of 12 variable isozymes from eight enzyme systems in Phaseolus acutifollus A. Gray (tepary bean) were determined using F2 progenies. The allozymes were encoded by codominant alleles of nine simply inherited loci, and four pairs of linked loci were detected. Moderate linkage was detected between loci Fdh-1 and 6pgd-2, Gpi-c1 and 6pgd-2, and Aco-2 and Idh-x. Adh-1 and Gpi-c2 were tightly linked; no recombinants were detected between these loci. Pgm-2 and Skdh-1 segregated independently of the others. The proposed quaternary structures of the various enzymes, with the exception of 6PGD-2, conformed to previous reports. ADH-1, FDH-1, IDH-4, GPI-1, and GPI-3 behave as dimers, and ACO-2 and PGM-2 behave as monomers. The formation of an active hybrid isozyme from the polypeptides of Gpi-c1 and Gpi-c2 and the independent segregation of these two loci provide evidence of a Gpi duplication in tepary bean.