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Soybean [Glycine max (L.) Merr.] reproduction is sensitive to temperatures > 35[degrees]C. Two studies were conducted to determine temperature effects on soybean pollen germination (PG) and to detect genotypic differences. Pollen collected from 44 genotypes (Maturity Groups III to VI) grown outdoors was subjected to in vitro temperatures from 15 to 50[degrees]C at 5[degrees]C intervals. Genotypes differed significantly for in vitro PG percentage (mean of 81%) and tube length (mean of 437 [micro]m). Mean cardinal temperatures ([T.sub.min], [T.sub.opt], and [T.sub.max]) were 13.2, 30.2, and 47.2[degrees]C for PG and 12.1, 36.1, and 47.0[degrees]C for pollen tube growth. Genotypes differed for leaf cell membrane thermostability (CMTS), but CMTS did not correlate with pollen parameters. Cumulative temperature response index, CTRI (unitless), of each genotype calculated as the sum of eight individual stress responses (ISRs) derived from maximum PG, maximum pollen tube length (PTL), and the maximum ([T.sub.max]), minimum ([T.sub.min]), and optimum ([T.sub.opt]) temperatures for PG and for PTLs was used to group genotypes for temperature tolerance. Heat-tolerant genotype (DG 5630RR) was less sensitive to high temperature (38/30[degrees]C) compared with heat-intermediate (PI 471938) and heat-sensitive (Stalwart III) genotypes that had deformed pollen, with reduced apertures and collumellae heads. Hence, pollen can be used as a screening tool for heat tolerance. Most sensitive to temperature was D88-5320 with a CTRI of 6.8, while AG 4403RR was most tolerant with a CTRI of 7.5. Elevated [C[O.sub.2]] did not modify reproductive parameters or CTRI. The study also revealed that heat tolerance of vegetative tissue had little or no relationship with the heat tolerance of reproductive tissue. Maturity groups lacked a specific trend for tolerance to high temperature. The identified high temperature-tulerant genotypes and temperature-dependent pollen response functions might be useful in soybean breeding and modeling programs, respectively.

Ergot (caused predominantly by Claviceps africana Freder., Mantle & De Milliano) is a disease of sorghum (Sorghum bicolor L. Moench), with pollen trails reported to be associated with resistance. This study investigated the genetic architecture and the role of pollen quantity (PQ) and pollen viability (PV) in ergot resistance in an F5 recombinant inbred line (RIL) sorghum population developed from the cross between an elite germplasm line, 31945-2-2 from Australia, and a recently reported putatively resistance source line, IS8525. Percentage ergot infection (PCERGOT) in IS8525 was very low, while in contrast, 31945-2-2 was heavily infected at all inoculation dates of the two field trials conducted under artificial epiphytotic conditions during 2001 and 2002. The distribution of the predicted means for PCERGOT, PQ, and PV was normal, suggesting that the traits are polygenic in nature. Genetic correlations between the two pollen traits and PCERGOT were moderately negative, indicating that there might be some common genetic factors controlling these traits. However, low [R.sup.2] values of PQ (11%) and PV (9%) suggest that only a small part of the total variability in ergot resistance in this population was due In the variability in PQ and PV. Correlations between ergot scores for different sampling dates (SDATEs) and years were moderate to high, indicating relatively low levels of genotype x environment interaction. Genetic variance and broad sense heritability were also high, indicating that ergot resistance is likely to respond well to conventional selection.

The ability to evaluate maize (Zea mays L.) hybrids and inbreds for grain quality traits is important. Twelve maize hybrids were grown in research plots under open-pollinated (OP) and self-pollinated (SP) conditions to determine pollen source effects on kernel oil, protein, and starch concentrations. Self-pollinated kernels were higher in protein concentration than OP kernels but hybrid rank did not change within pollination treatments. Evaluation of reciprocal crosses indicated a strong maternal effect for protein concentration and no pollen effect. Field evaluations of hybrids for protein concentration are feasible under OP small plot conditions. Oil concentration was significantly higher in OP kernels than in SP kernels. Significant differences among hybrids for oil concentration indicated a maternal effect, and data from reciprocal crosses indicated a pollen effect. Although the range in oil concentration for the hybrids was relatively narrow (41-55 g [kg.sup.-1]), rankings of the three highest and three lowest hybrids for oil concentration did not change within pollination treatments. Field evaluations with OP will separate genotypes with extreme oil concentrations, but accurate determinations of oil concentration should be conducted under SP or sib-pollinated conditions. Open-pollinated kernels were higher in starch concentration than SP kernels, Reciprocal crosses indicated a maternal effect for starch concentration and no pollen effect. Field evaluations for starch concentration are feasible under OP research plot conditions. Significant differences existed for kernel weight, kernel size, and kernel density among the maize hybrids within pollination treatments., Maize is one of the most important cereal crops in the USA for livestock feeding, commercial products, and human consumption. Increasing kernel protein, oil, and starch concentrations, as well as [...]

Pollen is an important vector of gene flow in maize (Zea mays L.). Experiments were conducted to investigate the duration of pollen viability and the effectiveness of isolation distance for controlling gene flow. Pollen longevity was tested by collecting pollen at dehiscence and exposing it in a thin layer in the open air and sunshine for prescribed time periods before assessing pollen viability by measuring seed set after pollination and scoring visual appearance. Isolation distance efficacy was evaluated by growing 12.8-[m.sup.2] plot of maize at various distances from a 4000-[m.sup.2] pollen source. The pollinator contained either a genetic leaf or seed marker that allowed pollen flow to be measured. Pollen maintained viability for 1 to 2 h after dehiscence depending on atmospheric water potential. The theoretical, maximum distance viable pollen could move was 32 km, assuming pollen was transported linearly at the maximum average afternoon windspeeds for our location, viability was maintained for 2 h, and pollen settling rate was ignored. Cross pollinations occurred at a maximum distance of 200 m from the source planting, and only a limited number of cross pollinations occurred at the shortest distance (100 m). No cross pollinations occurred at 300 m from the source planting. The results are consistent with conclusions that maize pollen is desiccation intolerant and has a high settling rate. The results indicate isolation distance can be a useful tool for controlling gene flow via pollination in research scale plantings., CONSIDERABLE RESEARCH has been conducted on the effects of gene flow from improved cultivars of maize into the landraces and teosinte that grows in the ancient farming areas of Mexico [...]

Maize (Zea mays L.) pollen can be stored up to several hours in inert medium such as paraffin oil. However, biological activity and genetic manipulation are almost precluded. In aqueous media, maize pollen loses viability within a few minutes when in conditions different from those promoting germination. We have evidence that viability of maize pollen can be preserved in a hypertonic aqueous solution at 0 degree C. Detrimental if individually applied, low temperature and high sucrose concentrations, together, allow storage of maize pollen up to 10 to 12 hr in an aqueous medium. Such stored pollen can then germinate on agar medium. The lack of in vivo fertilization by liquid pollination, at first interpreted by an osmotic hypothesis, led us to the development of a new, rapid procedure for in vitro germination. Short-term storage of maize pollen in aqueous medium is now possible and should support new techniques of genetic manipulation.

Pollen containment may be necessary to prevent the dissemination of novel genes from transgenic crops into sexually compatible land races or wild relatives in locations where these are grown or occur naturally in the same vicinity. Routine maize (Zea mays L.) breeding activities employ controlled pollinations and are sometimes done in areas where !and races or wild relatives are known to occur. The ability of researchers to control pollen movement and to thereby control the potential flow of novel genes from transgenic maize to land races or wild relatives was investigated. Using white- and yellow-seeded inbreds, pollen control was measured in two mating designs. The ability to control pollen was assessed by observing seed color in pollinations on adjacent plantings intended to trap uncontrolled pollen. In one experiment, the yellow-seeded maize contained a transgene. In this experiment contaminant seeds observed in the white maize were analyzed for the presence of recombinant DNA and the gene expression product. The results from these experiments indicated that routine plant breeding activities can be conducted with completely effective pollen containment if the transgenic line is detasseled and serves as the female for pollination with a nontransgenic mule inbred. However, precautions in addition to those used in these experiments are necessary to provide complete control of pollen dissemination if a transgenic male is used to make crosses and [approximately equals] 0.1% outcrossing to adjacent rows is deemed unacceptable., Plant breeding research has undergone great changes in the last decade. Plant breeders have implemented numerous advances in crop improvement technology to increase the speed of genetic improvement and to [...]