Genetic characterization of Plasmopara halstedii populations in Argentina using simple sequence repeats (SSR) and effectorbased markers

Abstract

Argentina is the fourth leading producing country of sunflower worldwide. Sunflower downy mildew, caused by the pathogenPlasmopara halstedii, is an economically important disease of sunflower. Since 2012, P. halstedii epiphytotics were identified inseveral production regions of Argentina. However, the genetic diversity of the pathogen in Argentina remains largely unknown. Fortytwofield isolates from Argentina were analyzed using eight loci SSR. The number of alleles per locus (APL), the expected (HE) andobserved heterozygosity (HO) were determined. SSR data were analyzed with regions (two), collection years (four) and races (six) asvariation sources (AMOVA), and the population structure was defined (Bayesian method). DNA sequences of two effector genes wereobtained from two isolates per race and the polymorphisms were analyzed (ClustalW). The mean APL was 2.6, varying from 1 to 4(total 21). The highest number of alleles and races were found in 2017. Average HO and HE were 0 and 0.369, respectively. Geneticvariation was observed among regions (7%) and years (32%), but not between races. Based on effectors, local races were similar to agroup of French races, without variation within the ARG races. Increased genetic variability observed in recent years seems to parallelwith the emergence of novel races reducing fungicides and/or R genes efficacy. The effector study suggests that the races evolutiondepends on country specific factors.