Estimation of hybrid seed production and efficient pollen flow using insect pollination of male sterile soybeans in caged plots

The aptitude of leafcutter bees to pollinate male sterile soybean plants (ms2 gene) in caged plots was evaluated in four experiments from both quantitative and qualitative points of view. The m.s. plant seed set was satisfactory: on average, it represented 60% of the male fertile isogenic seed set (with a range between 44 and 69%). The lower yield of m.s. plants was linked with a smaller number of fertile reproductive nodes. The efficient pollen flow was observed over the flowering period with both morphological and electrophoretic markers. Insect behaviour was not influenced by flower colour. Differences between flowering duration of pollen donors appear to be the major factor inducing unbalanced populations. The interest of this technique as a tool for dynamic management of the genetic variation in populations or for hybrid seed production is discussed.     

Pollen and coenocytic microspore germination in male-fertile and malesterilemsl soybean

Summary Light and fluorescence microscopy were used to study coenocytic microspore germination from male-sterile (ms1 ms1) soybean plants. Anther squashes from male-sterile plants revealed that a low frequency of natural coenocytic microspore germination occurred in male-sterile anthers of four independent lines; [ms1-North carolina (T260H),ms1-Urbana (T266H),ms1-Tonica (T267H), andms1-Ames (T268H)]. Abnormalities such as giant tubes, branched tubes, tubes with swollen areas, and multiple tubes were observed from coenocytic microspores from all four lines. The Urbana line, however, demonstrated a higher percentage of coenocytic microspore germination than did the other three lines. Flowers of the Urbana line from both malefertile and male-sterile plants, as well as gynoecia pollinated with coenocytic microspores from sterile plants, were used for in vivo studies. Pollen-tube growth appeared normal in male-fertile plants. In contrast, coenocytic microspore tubes rarely were observed in gynoecia from male-sterile plants or in gynoecia from malefertile plants that had been artificially cross-pollinated withms1 ms1 plants. Few tubes from coenocytic microspores were observed in the vicinity of the micropylar region. A low frequency of seed set was achieved in the greenhouse on Urbana male-sterile plants grown in the absence of male-fertile plants. Thus, we believe either that some gametes from coenocytic microspores are able to participate in fertilization at low frequency or that apomixis occurs inms1 ms1 plants.Joint contribution: Agricultural Research Service, U.S. Department of Agriculture, and Journal Paper No. J-12310 of the Iowa Agriculture and Home Economics Experiment Station, Ames IA, 50011 USA. Project 2471.     

A partially male-sterile mutant line of soybeans,Glycine max (L.) Merr.: inheritance

Summary A partial male sterility system in the soybean (Glycine max (L.) Merr.) germplasm population AP6(SI)CI was found to be controlled monogenically by a recessive allele, msp. Observations of msp msp plants in different environments suggested that environmental conditions significantly affect expressivity of the msp allele with respect to male sterility. We obtained no experimental evidence of cytoplasmic effects on msp expression. Background genotypes, however, seem to affect msp expressivity through their determination of flowering dates and resultant interactions with varying environmental conditions.Homogeneous populations of partially male-sterile plants can be generated by increasing families of msp msp plants in fertility-inducing environments, if measures are implemented to prevent the introduction and/or build-up of fertile genotypes that arise from natural cross-pollinations.Joint contribution: North Central Region, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Journal Paper No. J-9596 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011; Project 2107.     

A partially male-sterile mutant line of soybeans,Glycine max (L.) Merr.: Characterization of the msp phenotype variation

Summary Investigations of variable expression of msp partial male sterility in soybeans (Glycine max (L.) Merr.) showed that higher temperatures promote male fertility in msp homozygotes and showed that infectious agents are not intrinsic to the sterility system. Exchange grafts failed to modify fertility levels of msp msp rootstocks, Msp Msp scions, and their self-progeny. Tests for soybean mosaic virus and tobacco ringspot virus were negative in partially male-sterile plants, in control fertile plants, and in self-progeny of grafted plants. Growth-chamber experiments and field observations manifested that male fertility of msp msp plants is higher in hot environments than in cooler ones. The unexpected aberrant ratios of fertile to partially male-sterile plants observed in 1977 (Stelly & Palmer, 1980) are explainable on the basis of msp temperature sensitivity.Our observations suggest that homogeneous msp msp populations may be increased in hot environments.Research Geneticist, SEA-AR, USDA, Iowa State University, Ames, Iowa 50011, USA.     

Interrelationships among height,lodging and yield in determinate and indeterminate soybeans

Summary Seventy-three determinate and 93 indeterminate random F₉ lines from a cross between determinate and indeterminate soybean [Glycine max (L.) Merr.] parents were evaluated for seed yield, mature plant height, and lodging. Regression analyses indicated that among the determinate lines, seed yield increased by 350 kg/ha and lodging score increased by 0.008 for every 10 cm increase in plant height. Among indeterminate lines seed yield increased by 112 kg/ha and lodging score by 0.3 for every 10 cm increase in plant height. The highest yielding indeterminate lines were tall and very susceptible to lodging. The tall determinate lines had the best combination of high seed yield and excellent lodging resistance.Cooperative Investigations of the Science and Education Administration, U.S. Department of Agriculture and the Purdue University Agricultural Experiment Station.     

Inheritance of male fertility restoration of the cytoplasmic-nuclear male-sterile line NJCMS1A of soybean [Glycine max (L) Merr.]

At present, no report on inheritance of male fertility restoration has been released, yet more than 10 cytoplasmic-nuclear male-sterile soybean lines as well as their maintainers and restorers have been developed. Based on our previous work, 25 restorers for the male-sterile line NJCMS1A were identified and the inheritance of male fertility restoration for these restorers was studied. The results showed that F₁s between NJCMS1A and its restorers were completely male-fertile. The numbers of fertile and sterile plants in the F₂ population of Cross I (NJCMS1A × N23601) and Cross II (NJCMS1A × N23683) corresponded to a segregation ratio of 15:1, and the numbers of non-segregation lines, 3:1 segregation lines and 15:1 segregation lines in F_2:3 of the same two crosses fitted a 7:4:4 genotypic segregation ratio. The testcross BC₁F₁s between the F₁s of the above two crosses and NJCMS1A, NJCMS1B showed a 3:1 segregation ratio. Accordingly, it was inferred that two pairs of duplicate dominant genes controlled the male fertility restoration of NJCMS1A in both crosses. Meanwhile, F₂ of other 23 crosses between NJCMS1A and its 23 restorers showed a fertility segregation ratio of 3:1 or 15:1. The F₁s of the five testcrosses between NJCMS1A and the F₁s of five crosses selected from the above 23 crosses showed that fertility segregation was 3:1 in BC₁F₁s between NJCMS1A and F₁s of the crosses of which fertility segregation fitted 15:1 in F₂ population, while fertility segregation in BC₁F₁s was 1:1 for those fertility segregation fitted 3:1 in F₂ population. Allelism tests showed that restore genes of all restorers in the experiment were allelic to two pairs of dominant genes. All results showed that some restorers bore one pair of dominant restore gene and the others bore two pairs of duplicate dominant gene. The mechanism of F₁ male sterility of the cross N8855 × N2899 was discussed.     

Agronomic characteristics and genetics of a chromosome interchange in soybean

Summary A chromosome interchange in soybean (Glycine max (L.) Merr.) was studied agronomically and genetically, and comparisons of seed or abortion position within the pod were related to chromosome structure. Comparisons were among plants heterozygous for a chromosome interchange (N/T), plants homozygous for the interchange (T/T), and homozygous normal-chromosome plants (N/N). The latter two genotypes were male fertile and female fertile. Heterozygous interchange plants, which are about 50% pollen sterile and ovule sterile, are typical of a large number of plants that have equally frequent alternate and adjacent chromosome segregation. Yield, lodging, plant height, and seed oil and protein percentages among all three genotypes were similar even though significant differences existed for seed weight, seed number, and pod number per plant. Seed abortions were more frequent in the basal position of the pod than in either the middle or apical positions in N/N and T/T genotypes. Ovule abortions in N/T plants were equally frequent among all positions both in two- and three-ovule pods. The middle seed in a three-ovule pod was heavier than the basal or apical seed among all three genotypes.Joint contribution: USDA ARS, and Journal Paper No. J-11300 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011, USA, Project 2471.USDA ARS, Department of Agronomy and Genetics, Iowa State University, Ames, Iowa 50011, USA.Department of Agronomy, Iowa State University, Ames, Iowa 50001, USA.     

Implications of selecting improved strains of soybeans for dry-matter accumulation and grain yield

Summary Three maturity groups of soybeans (Glycine max L.) were used to investigate the relationship between dry-matter accumulation (DMA) and grain yield (GY), and the prospects for selection of high seed yielding strains among the existing soybean cultivars in a tropical environment. The positive and significant association between DMA and GY (r=0.888^***) indicated that selection for high DMA could give gains in GY. However, the higher harvest index (HI=37.5%) for the low seed yielding early maturing genotypes than the more vegetatively endowed and higher seed producing late maturity group, is an indication that excessive DMA could be disadvantageous. Total seed yield per land area for the three maturity groups of soybeans showed that the genotypes with high harvest index and low seed yield could be as good as those ones with high seed and dry-matter yields with low harvest index. The high coefficient of variation which ranged between 18.1 and 59.8% and the heritability estimations which also ranged from 34.4 to 82.2% are indicative of the presence of substantial genetic diversity and there are good prospects for the improvement of the crop through selection.     

Association of isozyme genotypes with agronomic and seed composition traits in soybean

Summary Two crosses between Glycine max (L.) Merr. and G. soja Sieb. & Zucc. parents were used to study the association between isozyme marker loci and agronomic and seed composition traits in soybean. The parents possessed different alleles at six isozyme loci for Cross 1 (A80-244036 × PI 326581) and at eight isozyme loci for Cross 2 (A81-157007 × PI 342618A). A total of 480 BC₂F_4:6 lines from the two crosses was evaluated for 13 traits in two environments. Lines were grouped in locus classes from 0 to 5 according to the number of loci homozygous for the G. soja alleles that they possessed. Within each locus class, each isozyme genotype was represented by five random lines.Selection for G. max alleles at the isozyme loci was not effective in recovering the recurrent parent phenotype in either cross. In cross 1, however, BC₂F₄-derived lines in the 0- or 1- locus class more closely resembled the G. max parent than lines in the 4- or 5- locus classes for most of the agronomic and seed composition traits evaluated. Significant associations were found between particular isozyme genotypes and every trait analyzed. The estimated effect of genes linked to the Pgm1 locus was a delay in maturity of 6.0±3.4 days. In cross 1, the Idh2 locus was associated with a significant effect on linolenic acid content. The percentage of variation accounted for by the models of estimation varied according to the heritability of the trait. The R² was high (up to 78%) for maturity, lodging, and vining, and low (up to 21%) for seed yield. Most of the variation was associated with the BC₂F₁ family from which the lines were derived. There was little evidence that digenic epistasis was an important source of variation.Journal Paper No. J-13505 of the Iowa Agric. Home Econ. Exp. Stn., Ames, IA, Project 2475.     

Effect of maturity on competitive ability in soybeans

Summary The effect of maturity on competitive ability in two cultivars of soybeans (Glycine max (L.) Merr.) was evaluated. Maturity dates within a genotype were simulated by removing half the plants from pure stands at end of flowering and twice later at approximately weekly intervals. Simulation of the early maturity of an equal competitor gave a significant competitive advantage to the late genotype only 2 out of 15 times. The average effect from simulation of earlier maturity within the genotype was statistically significant, but small, especially since the assumed difference in physiological maturity was 27 days. Most genotypic difference in competitive ability probably are due to characteristics other than maturity.Approved by the Director as a contribution from the Missouri Agricultural Experiment Station (Journal Series No. 7877).     

Interspecific hybridisation of soybeans and perennial Glycine species indigenous to Australia via embryo culture

Summary Five sterile hybrids (2n=59) between a synthetic amphiploid of Glycine tomentella (2n=38) and G. caneseens (2n=40) as female and soybean cultivars Lincoln and Hark as males have been produced by embryo or ovule culture using transplanted endosperm. The hybrid plants are twining perennials like the female parent but possess a number of morphological characters which reflect the presence of the soybean genome. Indophenol oxidase isozymes from leaf extracts also provide good evidence of the hybrid nature of the cultured plants. These hybrids open the way for the exploitation of the diverse germplasm resources of the perennial Glycine species in soybean breeding.     

Wide crosses in soybeans: Prospects and limitations

Summary It was attempted, though in vain, to cross soybean with Glycine species of the subgenus Glycine.     

Discovery of new male-sterile cytoplasm sources and development of a new cytoplasmic-nuclear male-sterile line NJCMS3A in soybean

Most of the cytoplasmic-nuclear male-sterile (CMS) lines of soybean were developed only from a limited cytoplasm sources and performed not as good as required in hybrid seed production, therefore, to explore new male-sterile cytoplasm sources should be one of the effective ways to improve the pollination and hybridization for a better pod-set in utilization of heterosis of soybeans. In the present study, total 80 crosses between 70 cultivated and annual wild soybean accessions and three maintainers (N2899, N21249, and N23998) of NJCMS1A were made for detecting potential new sources with male-sterile cytoplasm. The results showed that in addition to the crosses with N8855.1 (the cytoplasm donor parent of NJCMS1A) and its derived line NG99-893 as cytoplasm parent, there appeared three crosses, including N21566 × N21249 and N23168 × N21249, with male-sterile plants in their progenies. According to the male fertility performance of backcrosses and reciprocal crosses with the tester N21249, the landrace N21566 and annual wild soybean accession N23168 were further confirmed to have male-sterile cytoplasm. Accordingly, it was understood that the source with male-sterile cytoplasm in soybean gene pool might be not occasional. The results also showed that the genetic system of male sterility of the newly found cytoplasm source N21566 was different from the old cytoplasm source N8855.1, while N23168 was to be further studied. Based on the above results, the derived male-sterile plants from [(N21566 × N21249) F₁ × N21249] BC₁F₁ were back-crossed with the recurrent parent N21249 for five successive times, and a new CMS line and its maintainer line, designated as NJCMS3A and NJCMS3B, respectively, were obtained. NJCMS3A had normal female fertility and stable male sterility. Its microspore abortion was mainly at middle uninucleate stage, earlier than that of NJCMS1A and NJCMS2A. The male fertility of F₁s between NJCMS3A and 20 pollen parents showed that 7 accessions could restore its male fertility and other 13 could maintain its male sterility. The male sterility of NJCMS3A and its restoration were controlled by one pair of gametophyte male-sterile gene according to male fertility segregation of crosses between NJCMS3A and three restorers. The nuclear gene(s) of male sterility in NJCMS3A appeared different from the previously reported CMS lines, NJCMS1A and NJCMS2A. The development of NJCMS3A demonstrated the feasibility to discover new CMS system through choosing maintainers with suitable nuclear background.     

Genetic analysis of resistance to soybean cyst nematode in PI 438489B

Soybean (Glycine max L. Merr.) plant introduction PI 438489B is a unique source that has resistance to all known populations of soybean cyst nematode (Heterodera glycines Ichinohe, SCN). This PI line also has many desirable agronomic characteristics, which makes it an attractive source of SCN resistance for use in a soybean breeding program. However, characterization of SCN resistance genes in this PI line have not been fully researched. In this study, we investigated the inheritance of resistance to populations of SCN races 1, 2, 3, 5, and 14 in PI 438489B. PI 438489B was crossed to the susceptible cultivar ‘Hamilton’ to generate F₁ hybrids. The random F₂ plants and F₃ lines were evaluated in the greenhouse for reaction to these five populations of SCN races. Resistance to SCN races 1, 3, and 5 were mostly conditioned by three genes (Rhg Rhg rhg). Resistance to race 2 was controlled by four genes (Rhg rhg rgh rgh). Three recessive genes were most likely involved in giving resistance to race 14. We further concluded that resistance to different populations of SCN races may share some common genes or pleiotropic effects may be involved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variation in soybean (Glycine max (L.) Merril) for cookability and water absorption during cooking

Summary Improvement of cookability is an important objective in breeding of food legumes. The present study was undertaken to investigate variation in cookability in soybean. Genetic variation was observed among lines from two crosses. Absence of associations between cookability and protein content, oil content and grain yield indicate that selection for cookability can be achieved without adversely affecting the expression of these characters.     

Chemically induced sterility in wheat for hybrid seed production

Summary The gametocidal effects of RH-531, RH-532, and RH-2956 were studied with three rates and times of foliar application on two spring wheat (Triticum aestivum L.) varieties, Anza and Yecora 70. RH-531 and RH-532 applied at or before booting stage caused rather large reduction in plant height while RH-2956 had a small effect on height. Application of any of the three chemicals on Anza at meiotic stages reduced self-pollination (SP) fertility by 97–99%. If 90% SP fertility reduction is acceptable, the application time could vary from premeiosis to postmeiosis for Anza. Yecora 70 was less sensitive than Anza to gametocide treatments. The lowest SP fertility obtained in Yecora 70 with RH-531, RH-532, and RH-2956 was by treatment at booting (4 kg/ha), at premeiosis (2 kg/ha), and heading (8 kg/ha), and the corresponding SP fertility reductions were 74, 89, and 71%. Pollen stainability-determined by aceto-carmine, IKI, and Alexander's stains-was not affected by gametocide treatment and was not useful in evaluating sterility induced by these chemicals. For the RH-531-treated Anza and Yecora 70 and the RH-532-treated Anza, more than 94% of the seeds produced by open-pollination on treated plants were from self-or sib-pollination as determined by progeny testing. However, RH-532-treated Yecora 70 and RH-2956-treated Anza and Yecora 70 did result in more crossed seeds, with a maximum of 20% outcrossing. It was believed that spike compactness induced by the chemicals and the related poor flower opening were the major limitations for outcrossing. Artificial pollinations made to the test varieties showed that RH-531 induced both male and female sterility and was undesirable for practical use. RH-532, however, could be applied at the booting stage to avoid severe female sterility, and RH-2956 clearly was the best of the three chemicals, with the female fertility very close to those of the untreated checks of both Anza and Yecora 70. Of the three chemicals, RH-2956 gave the highest percentage of hybrid plants in the progeny of hand-or open-pollinated spikes. Its practical use for hybrid seed production, however, will depend largely on improvement of methods to increase cross pollination in wheat.     

Inheritance of resistance and genetic relationships among soybean plant introductions to races of soybean cyst nematode

Summary The objectives of this study were to determine if genes for resistance to soybean cyst nematode (SCN) in soybean PI 437654 were identical or different from the genes in Peking, and PI 90763. The F₂ plants and F₃ families were studied from crosses between PI 437654, Peking, and PI 90763. The cross PI 437654 × susceptible Essex was included to determine inheritance of resistance to SCN. For Race 3, PI 437654 was found to have genes in common with Peking and PI 90763. The segregation in PI 437654 × Essex indicated the presence of one dominant and two recessive genes. For Race 5, PI 437654 indicated the presence of similar genes as those in PI 90763 and Peking whereas, PI 437654 × Essex indicated the action of the segregation ratios of two dominant and two recessive genes. For Race 14, the data from the cross PI 437654 × PI 90763 indicated monogenic inheritance with resistance being dominant; whereas PI 437654 × Peking showed a recessive gene controlling resistance. The segregation in PI 437654(R) × Essex(S) suggested one dominant and two recessive genes for Race 14 reaction.     

Heterosis of interspecific soybean hybrids for traits related to N2 fixation

Summary Three greenhouse experiments were conducted to compare the performance of soybean (Glycine max (L.) Merr.), wild soybean (G. soja Sieb. et Zucc.), and soybean x wild soybean hybrids for traits relating to N₂ fixation including nodulation, acetylene reduction, nodule leghemoglobin concentration, and nitrogen (N) accumulation and dry matter (DM) accumulation. In all three experiments G. max generally exceeded G. soja in nodulation, acetylene reduction, and N and DM accumulation while the soybean possessed higher nodule leghemoglobin concentration. In Experiment I, the mean of the hybrids did not differ significantly from the G. max parent in nodule mass, acetylene reduction activity, nodule leghemoglobin concentration, or DM accumulation. The hybrids did exceed the soybean parent in N accumulation, thus demonstrating high parent heterosis. In Experiments IIA and IIB with a more carefully chosen set of G. soja parents, high parent heterosis of individual crosses was common. Across the three experiments average high parent heterosis was 34, 28, and 28%, respectively, for nodule mass, N accumulation, and DM accumulation. If one accepts the assumption that hybrid vigor results from the accumulation of dominant alleles, then these alleles could theoretically be accumulated via selection in a homozygous genotype. If this is true than the results of the experiments reported here suggest that interspecific soybean x wild soybean crosses could serve as sources of homozygous lines which would exceed currently available soybean cultivars in nodule mass, and N and DM accumulation.This work was supported in part by the USDA Competitive Grants Program, Grant 82-CRCR-1-1039 and Cooperative Agreement 58-32U4-2-370 between the U.S. Department of Agriculture and the Agronomy Department, University of Maryland, Scientific Article No. A-4648, Contribution No. 7644 of the Maryland Agricultural Experiment Station.     

Inheritance of resistance to pendimethalin herbicide induced stem damage in soybean

Selective herbicides are valuable weed control tools; however, selectivity is not always complete, resulting in crop damage. Stem breakage, lodging, and enlarged hypocotyls (brittle bean syndrome) limit yields of soybean [Glycine max (L.) Merr.] genotypes treated with pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine]. Developing genotypes with resistance to pendimethalin injury would eliminate or reduce this problem. Genetic studies were conducted to determine the inheritance of resistance to pendimethalin induced stem damage. The F_2:3 progeny of crosses involving resistant ('Asgrow A4715' and 'Flyer') and susceptible (`Essex' and K87-7-95) genotypes were screened in a greenhouse. Each genotype was treated with 1.68 kg ha^-1 pendimethalin preemergence and irrigated as needed. Plants were scored at V4 for stem breakage. Progeny distributions indicated that resistance to brittle bean syndrome damage behaved as a quantitative trait. Dominance for stem breakage was expressed in the population of A4715 × Essex. Flyer was more sensitive to herbicide damage than Asgrow A4715 because it has fewer genes for resistance or different alleles. The F_2:3 variance component heritability estimates ranged from 0.19 to 0.52. Gain from selection for resistance to pendimethalin injury is possible, and resistant progeny can be recovered from segregating populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

A cluster analysis of wild and domesticated soybean phenotypes

Summary Cluster analysis techniques were used to examine phenotypic variation within the USDA Soybean Germplasm Collection. This study included ten Plant Introductions each of the domesticated soybean, Glycine max (L). Merr., the wild soybean, G. soja Sieb. & Zucc., and a disputed species, G. gracilis Skvortz. G. max and G. soja were found to be morphologically distinct entities and G. gracilis was found to be conspecific with G. max. Because G. gracilis probably represents weedy races associated with the cultivated soybean and because gracilis phenotypes can be distinguished from G. max, the designation, G. max forma gracilis, is recommended.Joint contribution: North Central Region, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Journal Paper No. J-9389 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011; Project 2107.