Characterizing peanut rust resistance
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Peanut rust, caused by Puccinia arachidis Speg., is an important foliar disease of peanut (Arachis hypogaea L.) in tropical countries. Host resistance is the best option for disease management in these countries. Field, green house and growth chamber experiments were conducted to evaluate the response of peanut breeding lines with Bolivian genetic background, parents of mapping populations and peanut cultivars used in Georgia, U.S. to peanut rust. In field studies conducted over 2010-2013, several breeding lines developed in the UF150 project of the Peanut Collaborative Research and Support Program (Peanut CRSP) as part of the United States Agency for International Development (USAID) demonstrated varying levels of rust resistance, and a select few were resistant to late leaf spot, caused by Cercosporidium personatum, as well. The greenhouse and growth chamber assays revealed that infection frequency and percent diseased area can be used as indicators for field resistance, as genotypes with longer latent periods typically had low infection frequency at 7 days after inoculation and smaller percent diseased areas. Newly developed CRSP breeding lines, plant introductions and commonly grown cultivars, were molecularly characterized using polymorphic SSR markers. These markers used detected polymorphisms but were not able to distinguish resistant from susceptible peanut genotypes. None of the 22 private bands generated for the resistant population were absolute and no marker alleles could be exclusively linked to all resistant or all susceptible genotypes. This could be because the resistance observed in the genotypes may be explained by other partial resistance genes than previously identified. Highly resistant and highly susceptible genotypes did cluster; which may indicate that some of the resistant genotypes evaluated in this study may be identified with existing markers on molecular level. Three loci of P. arachidis isolates collected from different regions in the U.S. and countries in Asia, South and Central America were sequenced to determine the genetic variation of P. arachidis. The loci 5.8S-ITS2-28S region, translongation elongation factor 1α, and cytochrome b, do not indicate high genetic variability among the populations: there was no clustering of isolates according to location or time collected.
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