APS Homepage

Poster: Epidemiology: Population Biology Genetics


Genetic and phenotypic diversity of Puccinia kuehnii of sugarcane from Brazil
T. MISTURA (1), A. Urashima (1), L. Porto (1), C. Sakuno (2), R. Arias (3) (1) Federal University of Sao Carlos, Brazil; (2) Syngenta Crop Protection, Brazil; (3) USDA, ARS, South Atlantic Area Nat Peanut Res Lab, U.S.A.

Resistant genotypes are the most employed method to control orange rust of sugarcane (Puccinia kuehnii). This approach has been adopted in Brazil; however, recent outbreaks on previously unreported varieties show that the efficacy of this method is dependent and requires better knowledge of pathogen diversity. This can be achieved by applying genetic and phenotypic tools. Therefore, the present work aimed to examine the genetic distance and pathotype variability among isolates of P. kuehnii from São Paulo, the most important growing state of the Country. Thirty six rust isolates were genotyped by eight SSR markers and their genetic distances verified by the UPGMA clustering analysis using the software NTSYSpc v.2.2. Phenotypic data employed 22 isolates inoculated on five sugarcane varieties and evaluated at 21 days by examining percent diseased leaf area with Assess 2.0 and rating resistant/susceptible based on Santos et al. (2004). Moreover, an assay of disease progress over time was carried out with three isolates against five sugarcane cultivars examining disease score (Tai et al., 1981) at days 21, 28, 35 and 42. Our results showed two genetically distinct subpopulations of the pathogen with 79% of diversity, phenotypic data identified nine physiological races. In addition, disease progress over time showed that one cultivar considered resistant at day 21 became susceptible at day 42. Part of MSc dissertation by the second author at PPGPVBA, CAPES Scholarship