Browsing by Subject "Sudden death syndrome"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Genome wide association mapping and genomic selection for agronomic and disease traits in soybean
    (2014-09) Bao, Yong
    Genome-wide association mapping and genomic selection are two emerging genomic approaches for investigating genetic architecture and improving breeding efficiency for complex traits in crop species. The objectives of our study were to: 1) dissect the genetic basis of resistance to soybean cyst nematode (SCN) and sudden death syndrome (SDS) through association mapping (AM) and 2) evaluate genomic selection (GS) as an improved marker-based selection tool for predicting agronomic and disease traits in a public soybean breeding program. For AM, we genotyped 282 common breeding parents from the University of Minnesota soybean breeding program using a genome-wide panel of 1,536 single nucleotide polymorphism (SNP) markers and evaluated plant responses to SCN and SDS in the greenhouse. AM rediscovered reported resistance genes (rhg1 and FGAM1 for SCN resistance; cqSDS001, cqRfs4, and SDS11-2 for SDS resistance) and also identified novel loci. For GS, average prediction accuracy through cross-validation studies was 0.67 for SCN resistance and 0.64 for root lesion severity associated with SDS resistance. We also empirically assessed the prediction accuracy and responses to GS for agronomic traits. Soybean lines in the AM panel were used as a training set and a validation set consisting of 273 breeding lines were selected from the ongoing breeding program. Existing historical trial data were used to train the GS model. GS was then conducted to select the top 20% individuals from the validation set based on a comprehensive consideration including genomic estimated breeding values. Our GS model predicted yield with a significant positive accuracy in only two MN x MN crosses, while the prediction accuracy was near to zero or negative for protein and oil, and for the rest of crosses. Moreover, one generation of GS didn't significantly change the population mean of yield, seed protein and oil content. Overall, our study suggested AM holds promise to be used as an alternative approach for mapping QTL in soybean breeding germplasm, and GS deserves further investigation prior to implementation in genetic improvement in existing soybean breeding programs.
  • Thumbnail Image
    Item
    Substrates from Soybean and Corn Influence Pathogenesis and Growth of Fusarium virguliforme
    (2014-04) Freed, Gretchen Marie
    Symptoms of sudden death syndrome of soybean (SDS), caused by Fusarium virguliforme, include root rot and leaf scorch symptoms The goal of this study was to understand the roles of inoculum rate, crop residues, and seed exudates on growth of F. virguliforme and the development of SDS. The first study was a greenhouse experiment to investigate the influence of inoculum rate and crop substrate on disease development using moderately resistant and susceptible soybean cultivars to SDS. Soybean seeds were planted in soil mix containing an inoculum at four rates (0, 101, 102, or 103 conidia/cc) and with one of seven crop residue substrate treatments (none, soybean seed, corn seed, sorghum seed, corn stalk, corn root, or soybean stem) incorporated into the soil mix. Root rot severity was assessed 15 and 50 days after inoculation (dai) and foliar disease severity and fresh biomass were assessed 50 dai. Root rot and foliar symptom severity were positively associated with the increase of inoculum rate, especially in cultivar MN1410 Plants grown with no added substrate exhibited very low to no disease severity. Disease severity was greater in the treatments with the soybean, corn, and sorghum seed substrates compared to the other treatments examined. Early root rot severity (15 dai) corresponded with the foliar disease severity for all treatments examined. In the second study, the influence of seed exudates on the growth of F. virguliforme was investigated. Seed exudates from four soybean cultivars, two moderately resistant and two susceptible to SDS, and one corn hybrid, which is an asymptomatic host, were collected at different time points during seed germination. These seed exudates were transferred to the wells of a 96-well plate along with macroconidia of one of four F. virguliforme isolates or one Fusarium solani isolate. Optical density values, used as an indication of fungal growth, were recorded after five days of incubation. Soybean seed exudates of the SDS moderately resistant cultivar MN1606, collected just prior to radicle emergence, triggered significantly (p<0.001) more fungal growth compared to all other exudates studied. Exudates from soybean cultivars susceptible to SDS did not promote greater growth of F. virguliforme than the moderately resistant cultivars tested. The effect of corn exudates on fungal growth was similar to the moderately resistant and susceptible soybean cultivars tested. Overall, these findings indicate that organic substrates from soybean and corn promote the growth of F. virguliforme, seedling root infection and the development of SDS in soybean.