Interactions Between Meloidogyne incognita and Pratylenchus brachyurus on Soybean

Interactions among Meloidogyne incognita, Pratylenchus brachyurus, and soybean genotype on plant growth and nematode reproduction were studied in a greenhouse. Coker 317 (susceptible to both nematodes) and Gordon (resistant to M. incognita, susceptible to P. brachyurus) were inoculated with increasing initial population densities (Pi) of both nematodes individually and combined. M. incognita and P. brachyurus individually usually suppressed shoot growth of both cultivars, but only root growth on Coker 317 was influenced by a M. incognita × P. brachyurus interaction. Reproduction of both nematodes, although dependent on Pi, was mutually suppressed on Coker 317. P. brachyurus reproduced better on Gordon than on Coker 317 but did not affect resistance to M. incognita. Root systems of Coker 317 were split and inoculated with M. incognita or P. brachyurus or both to determine the nature of the interaction. M. incognita suppressed reproduction of P. brachyurus either when coinhabiting a half-root system or infecting opposing half-root systems; however, P. brachyurus affected M. incognita only if both nematodes infected the same half-root system.     

Fine Mapping and Characterization of Candidate Genes that Control Resistance to Cercospora sojina K. Hara in Two Soybean Germplasm Accessions

Frogeye leaf spot (FLS), caused by the fungus Cercospora sojina K. Hara, may cause a significant yield loss to soybean growers in regions with a warm and humid climate. Two soybean accessions, PI 594891 and PI 594774, were identified to carry a high level of resistance similar to that conditioned by the Rcs3 gene in ''Davis''. Previously, we reported that the resistance to FLS in these two plant introductions (PIs) was controlled by a novel gene (s) on chromosome 13 that is different from Rcs3. To fine-map the novel FLS resistance gene(s) in these two PIs, F_{2: 3} seeds from the crosses between PI 594891 and PI 594774, and the FLS susceptible genotype ''Blackhawk'' were genotyped with SNP markers that were designed based on the SoySNP50k iSelect BeadChip data to identify recombinant events and locate candidate genes. Analysis of lines possessing key recombination events helped narrow down the FLS-resistance genomic region in PI 594891 from 3.3 Mb to a 72.6 kb region with five annotated genes. The resistance gene in PI 594774 was fine-mapped into a 540 kb region that encompasses the 72.6 kb region found in PI 594891. Sequencing five candidate genes in PI 594891 identified three genes that have several mutations in the promoter, intron, 5'', and 3'' UTR regions. qPCR analysis showed a difference in expression levels of these genes in both lines compared to Blackhawk in the presence of C. sojina. Based on phenotype, genotype and haplotype analysis results, these two soybean accessions might carry different resistance alleles of the same gene or two different gene(s). The identified SNPs were used to develop Kompetitive Allele Specific PCR (KASP) assays to detect the resistance alleles on chromosome 13 from the two PIs for marker-assisted selection.     

Discovery and utilization of QTLs for insect resistance in soybean

Insect resistance in soybean has been an objective in numerous breeding programs, but efforts to develop high yielding cultivars with insect resistance have been unsuccessful. Three Japanese plant introductions, PIs 171451, 227687 and 229358, have been the primary sources of insect resistance alleles, but a combination of quantitative inheritance of resistance and poor agronomic performance has hindered progress. Linkage drag caused by co-introgression of undesirable agronomic trait alleles linked to the resistance quantitative trait loci (QTLs) is a persistent problem. Molecular marker studies have helped to elucidate the numbers, effects and interactions of insect resistance QTLs in the Japanese PIs, and markers are now being used in breeding programs to facilitate transfer of resistance alleles while minimizing linkage drag. Molecular markers also make it possible to evaluate QTLs independently and together in different genetic backgrounds, and in combination with transgenes from Bacillus thuringiensis.     

Combining cry1Ac with QTL alleles from PI 229358 to improve soybean resistance to lepidopteran pests

A QTL conditioning corn earworm resistance in soybean PI 229358 and asynthetic Bacillus thuringiensis cry1Ac transgene from therecurrent parent Jack-Bt were pyramided intoBC₂F₃ plants by marker-assisted selection. Segregatingindividuals were genotyped at SSR markers linked to an anitbiosis/antixenosisQTL on linkage group M, and were tested for the presence ofcry1Ac. Marker-assisted selection was used during andafter the two backcrosses to develop a series of BC₂F₃plants with or without the crylAc transgene and the QTLconditioning for resistance BC₂F₃ plants that werehomozygous for parental alleles at markers on LG M, and whicheither had or lacked cry1Ac, were assigned to one of fourpossible genotype classes. These plants were used in no-choice, detached leaffeeding bioassays with corn earworm and soybean looper larvae (Lepidoptera:Noctuidae) to evaluate the relative antibiosis in the different genotypeclasses. Resistance was measured as larval weight gain and degree of foliageconsumption. Few larvae of either species survived on leaves expressing theCry1Ac protein. Though not as great as the effect of Cry1Ac, the PI229358-derived LG M QTL also had a detrimental effect on larval weights of bothpest species, and on defoliation by corn earworm, but did not reduce defoliation bysoybean looper. Weights of soybean looper larvae fed foliage from transgenicplants with the PI-derived QTL were lower than those of larvae fed transgenictissue with the corresponding Jack chromosomal segment. This work demonstratesthe usefulness of SSRs for marker-assisted selection in soybean, and shows thatcombining transgene-and QTL-mediated resistance to lepidopteran pests may be aviable strategy for insect control.     

Physiological comparisons of two soybean cultivars differing in canopy photosynthesis. II. Variation in specific leaf weight,nitrogen, and protein components

Cultivar differences in canopy apparent photosynthesis (CAP) have been observed in soybean (Glycine max (L.) Merr.) but little is known about the physiological mechanisms which are responsible for such differences. This study was initiated to determine if variation in ribulose 1,5-bisphosphate carboxylase (RuBPCase) and soluble protein exists among cultivars which differ in CAP during reproductive growth. In addition, the relationship between specific leaf weight (SLW) and leaf protein was examined. Two Maturity Group VI cultivars, Tracy (high CAP) and Davis (low CAP), were grown in the field during 1979, 1980, and 1981 and in a greenhouse experiment. Leaves located at two canopy positions (topmost, fully expanded leaf and eighth node from the top) in 1979 and three canopy positions (those mentioned, plus the fourth node from the top) in 1980 and 1981 were sampled. Leaves at the two upper canopy positions exhibited greater SLW, RuBPCase m^–2, and soluble protein m^–2 than found at the eighth node down. Photosynthetic capacity of leaves at inner canopy regions was therefore affected by both light penetration into the canopy and leaf protein status. Over the three year period, the SLW was 23 percent and the soluble protein m^–2 leaf 21 percent greater in Tracy than in Davis. Although the trend in RuBPCase m^–2 leaf was not significant, it was consistently greater in Tracy in the field and greenhouse. No cultivar differences were observed when the proteins were expressed on a unit of leaf dry weight. The quantity of RuBPCase per unit leaf area was positively correlated with SLW with significant partial correlation coefficients of 0.62, 0.67, 0.35, and 0.82 for 1979, 1980, 1981, and the greenhouse study, respectively. Since these cultivars have similar leaf area indices during September, the greater SLW of Tracy is translated into more photosynthetic proteins per unit ground area and higher CAP rate.Abbreviations AP Leaf Apparent Photosynthesis - CAP Canopy Apparent Photosynthesis - DAP Days After Planting - DTT Dithothreitol - HEPES N-2-hydroethylpiperazine N-2 ethanesulfonic acid - LAI Leaf Area Index - LSD Least Significant Difference - PPFD Photosynthetic Photon Flux Density - PVP-40 Polyvinylpolypyrroledone (molecular weight, 4000) - RuBPCase Ribulose 1,5-bisphosphate Carboxylase - SLW Specific Leaf Weight     

Over de verdeeling van de agglutininen over de serumeiwitten

Ohne Zusammenfassung Voordracht voor de Vergadering van de Ned. Ver. v. Microbiologie, gehouden te Utrecht op 12 November 1938. Uitvoerige publicatie met literatuur volgt in den vorm van een dissertatie.     

SSR-marker analysis of the intracultivar phenotypic variation discovered within 3 soybean cultivars

Genetic variation within homogeneous gene pools in various crops is assumed to be very limited. One objective of this study was to use 144 simple sequence repeat (SSR) markers to determine if the single-plant lines selected at ultra-low plant density in honeycomb designs within the soybean cultivars Benning, Haskell, and Cook had unique SSR genetic fingerprints. Another objective was to investigate if the variation found was the result of residual genetic heterozygosity that could be detected in the original gene pool where selection initiated. Our results showed that the phenotypic variation for seed protein content and seed weight has a genotypic component identified by the SSR band variation. The 7 lines from Haskell had a total of 63 variant alleles, the 5 lines from Benning had 34 variant alleles, and the 7 lines from Cook had 34 variant alleles, therefore, possessing unique genetic fingerprints. Most of the intracultivar SSR band variation discovered was the result of residual heterozygosity in the initial plant selected to become the cultivar. More specifically, 82% of the SSR variant alleles were traced in the Benning Foundation seed source, 93% in the Haskell seed source, and 82% in the Cook seed source. The remaining variant bands (18% for Benning, 7% for Haskell, and 18% for Cook) could not be detected in the Foundation seed source and were likely the result of mutation or some other mechanism generating de novo variation. These results provide evidence that genetic variation among individual plants is present even in homogeneous gene pools and can be further utilized in breeding programs.     

RFLP loci associated with soybean seed protein and oil content across populations and locations

Molecular markers provide the opportunity to identify marker-quantitative trait locus (QTL) associations in different environments and populations. Two soybean [Glycine max (L.) Merr.] populations, Young x PI 416 937 and PI 97100 x Coker 237, were evaluated with restriction fragment length polymorphism (RFLP) markers to identify additional QTLs related to seed protein and oil. For the Young x PI 416937 population, 120 F₄-derived lines were secored for segregation at 155 RFLP loci. The F₄-derived lines and two parents were grown at Plains, G.a., and Windblow and Plymouth, N.C. in 1994, and evaluated for seed protein and oil. For the PI 97100 x Coker 237 population, 111 F₂-derived lines were evaluated for segregation at 153 RFLP loci. Phenotypic data for seed protein and oil were obtained in two different locations (Athens, G.a., and Blackville, S.C.) in 1994. Based on single-factor analysis of variance (ANOVA) for the Young x PI 416937 population, five of seven independent markers associated with seed protein, and all four independent markers associated with seed oil in the combined analysis over locations were detected at all three locations. For the PI 97 100 x Coker 237 population, both single-factor ANOVA and interval mapping were used to detect QTLs. Using single-factor ANOVA, three of four independent markers for seed protein and two of three independent markers for seed oil were detected at both locations. In both populations, singlefactor ANOVA, revealed the consistency of QTLs across locations, which might be due to the high heritability and the relatively few QTLs with large effects conditioning these traits. However, interval mapping of the PI 97100 x Coker 237 population indicated that QTLs identified at Athens for seed protein and oil were different from those at Blackville. This might result from the power of QTL mapping being dependent on the level of saturation of the genetic map. Increased seed protein was associated with decreased seed oil in the PI 97100 x Coker 237 population (r = –0.61). There were various common markers (P0.05) on linkage groups (LG) E, G,H,K, and UNK2 identified for both seed protein and oil. One QTL on LG E was associated with seed protein in both populations. The other QTLs for protein and oil were population specific.     

Genome Duplication in Soybean (Glycine Subgenus Soja)

Restriction fragment length polymorphism mapping data from nine populations (Glycine max X G. soja and G. max X G. max) of the Glycine subgenus soja genome led to the identification of many duplicated segments of the genome. Linkage groups contained up to 33 markers that were duplicated on other linkage groups. The size of homoeologous regions ranged from 1.5 to 106.4 cM, with an average size of 45.3 cM. We observed segments in the soybean genome that were present in as many as six copies with an average of 2.55 duplications per segment. The presence of nested duplications suggests that at least one of the original genomes may have undergone an additional round of tetraploidization. Tetraploidization, along with large internal duplications, accounts for the highly duplicated nature of the genome of the subgenus. Quantitative trait loci for seed protein and oil showed correspondence across homoeologous regions, suggesting that the genes or gene families contributing to seed composition have retained similar functions throughout the evolution of the chromosomes.