Contributions to management of diseases of peanut (Arachis hypogaea) through Bolivian-derived host resistance, integrated disease management and knowledge of pathogen variability
Gremillion, Sara Katherine
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Applied and basic research experiments were conducted to improve current management of the fungal pathogens Cercospora arachidicola, cause of early leaf spot, Cercosporidium personatum, cause of late leaf spot, Puccinia arachidis, cause of peanut rust, and Tomato spotted wilt (TSW), caused by Tomato spotted wilt virus. A series of breeding lines and the Bolivian cultivar, Bayo Grande (BG), were evaluated for resistance to these diseases compared to Georgia Green (GG), a cultivar with high susceptibility to early and late leaf spot and moderate resistance to TSW. When grown in the U.S., BG and the breeding lines showed improved leaf spot resistance compared to GG. When grown in Bolivia, no improved leaf spot resistance was observed among any genotypes tested. No improved rust resistance was observed among genotypes in any experiment. When evaluated as part of an integrated disease management (IDM) system, the improved resistance of BG and the breeding lines coupled with zero to four reduced fungicide sprays reduced leaf spot to levels comparable to those seen under a full season, six to eight spray fungicide regimes. The addition of the cultural practice of strip tillage negated the need for fungicides in most genotypes in one year, when compared to those genotypes grown under conventional tillage. However, in the following year, strip tillage did not contribute to spray reduction. To predict the potential for development of resistance in populations of C. arachidicola, genetic diversity was measured in populations from the U.S. and Bolivia by comparing sequences of the B-tubulin and calmodulin genes and by comparing spore length. Genetic and phenotypic results indicate that populations of C. arachidicola have low diversity.