Browsing by Author "Dr. David S. Marshall, Committee Member"

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    Genetics of Resistance to Powdery Mildew in Several Wheat Germplasm Lines
    (2003-10-30) Srnic, Goran; Dr. J. Paul Murphy, Committee Chair; Dr. Thomas G. Isleib, Committee Member; Dr. David S. Marshall, Committee Member; Dr. Steven Leath, Committee Member
    Powdery mildew (Blumeria graminis f. sp. tritici) of wheat (Triticum aestivum L.) is especially devastating in temperate, cool and moist regions. It increasingly affects wheat in drier and warmer areas as a consequence of changing crop practices such as irrigation, increased nitrogen fertilization, and the use of semi-dwarf cultivars. The highest impact on wheat yields have been observed in Europe, southwestern Asia, and in the eastern and western parts of the North America, including large areas of the southeastern USA. Resistant wheat cultivars remain the most cost efficient and effective means for powdery mildew control. Monogenic resistance is generally very efficient but tends to be a short time solution if variability in the pathogen population is great. A clearer understanding of the genetics of host resistance to wheat powdery mildew would be helpful in employing new resistance genes, especially for pyramidal complexes containing several resistance genes. The objectives of this study were to investigate the inheritance and efficiency of resistance to naturally occurring powdery mildew in the four wheat germplasm lines NC96BGTD1 (NCD1), NC96BGTA4 (NCA4), NC98BGTAB10 (NCAB10) and NC99BGTAG11 (NCAG11), and to identify AFLP markers linked to the resistance genes in NCD1 and NCAG11. Each germplasm was crossed to the susceptible parent Saluda, which was utilized as the recurrent parent in the development of each germplasm line and to each other. F2:3 progenies of each of the four Saluda by germplasm line crosses and six germplasm by germplasm crosses were tested in greenhouse and field studies. Resistance factors in all four germplasms segregated in a monogenic fashion. Five germplasm by germplasm populations (NCD1 x NCAG11, NCAG11 x NCAB10, NCA4 x NCAB10, NCD1 x NCAB10, and NCD1 x NCA4) segregated in a digenic fashion indicating independent segregation of their resistance loci. Resistance genes in NCA4 and NCAG11 co-segregated as if linked in repulsion phase. The recombination between these two genes was estimated to be 2%. The resistance genes in the four germplasms appear to be novel genes that were not previously used in commercial cultivars or breeding lines. A total of four AFLP markers were linked to resistance in NCAG11 (M-act/cct-196bp at 0.8 cM and M-acc/cga-126bp at 2.2 cM) and NCD1 (M-aca/cgt-182bp at 20.7 cM and Maag/cga-148bp at 36.9 cM). All four markers were also confirmed after two additional generations of self-pollination of resistant F2 individuals from Saluda x NCD1 and Saluda x AG11 crosses. Pyramided markers from each parent were identified in F2:4 wheat lines homogeneous for powdery mildew resistance from the cross between NCD1 and NCAG11. Testcrosses have been made to identify lines segregating for both resistance genes.