Studies on pathogenicity in <i>Plasmopara halstedii</i> (sunflower downy mildew)

Abstract

Studies on morphological and genetic variabilities as well as alterations in pathogenicity were carried out in Plasmopara halstedii (sunflower downy mildew) isolates of several races. Aggressiveness was analyzed in one sunflower inbred line showing a high level of quantitative resistance. Viability analyses were performed on oval and spheric zoosporangia. Genetic relationships were detected between the pathogen isolates using 12 EST-derived markers. There were significant differences between pathogen isolates for aggressiveness criteria. Based on virulence and aggressiveness reaction for P. halstedii to D3 line of sunflower, there were two groups as more aggressive and less virulent isolates of 100 and 3xx races, and less aggressive and more virulent isolates of 7xx races. The oval zoosporangia for more aggressive isolates of races 100 and 3xx produced more zoospores than the oval ones for less aggressive isolates of races 7xx. The isolates of races 714, 704 and 314 had an intermediary genetic position between the two isolates of races 100 and 710. It is concluded that the relationship between aggressiveness and oval zoosporangia viability may be established in P. halstedii. No correlation was detected between pathogenicity traits and EST genotypes.Key words: aggressiveness; D3 line of sunflower; EST-derived markers; oval zoosporangia; spheric zoosporangia; virulenceDOI: 10.3126/ijls.v4i0.3481International Journal of Life Sciences Vol.4 2010 pp.48-59