Genetic Analysis of the Resistance of Soybean Genotypes to Sclerotinia Sclerotiorum

82 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2001.The objectives of this research were to: (i) evaluate soybean germplasm to identify new genetic sources of sclerotinia stem rot resistance; (ii) determine the inheritance of field resistance to sclerotinia stem rot in a cross between the partially resistant cultivars Asgrow 'A2506' (A2506) and Novartis 'S19--90' (S19--90); (iii) determine the inheritance of field resistance to sclerotinia stem rot in crosses between S19--90 and plant introductions (PIs) 358.318A, 391.589B, and 561.353; and (iv) identify molecular markers associated with field resistance in a cross between S19--90 and Williams 82. Sixty-eight PIs had sclerotinia stem rot resistance levels equal to or better than current partially resistant cultivars. Maturity group I--III PIs 153.282, 189.931, 196.157, 398.637, 417.201, 423.818, and 561.331 have high levels of resistance and were agronomically similar to the resistant standards. These Pls could be valuable for incorporating new sources of sclerotinia stem rot resistance into elite germplasm. The broad-sense heritability estimate was 0.37 for disease severity across environments in the A2506 by S19--90 population. Although lower disease severity was associated with short plant height and reduced canopy closure at flowering, which may be escape mechanisms, lines from this population may be a good source of sclerotinia stem rot resistance for breeders to use in cultivar development programs. There was significant genetic variation in the PI 358.318A and 391.589B populations. This indicates these PIs, may be useful sources of sclerotinia stem rot resistance. In the S19--90 by Williams 82 population, the simple sequence repeat markers Satt 129 and Satt 163 were associated with disease resistance and seed yield, which suggests these markers may be linked to genes that improve physiological resistance. Additional research is needed to confirm these markers are contributing resistance alleles for sclerotinia stem rot resistance in other populations. Researchers should be able to utilize the soybean cultivars, lines, and germplasm identified in this study as new sources of sclerotinia stem rot resistance, and the molecular markers identified may be useful in breeding programs where sclerotinia stem rot is difficult to evaluate in the field.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD