Detection and variability of Plasmopara halstedii in Brazil and resistance of sunflower genotypes to downy mildew.
An experiment was conducted in Londrina, Parana, Brazil, during 1998, 2001 and 2002 to identify the physiological race of Plasmopara halstedii occurring in sunflower by evaluating the reaction of sunflower genotypes inoculated with downy mildew pathogen. Sunflower seedlings of the differentials set to identify races and of the cultivars were inoculated by immersion in zoosporangia suspension and were grown in autoclaved sand boxes. Seedlings were kept in growing chambers at 21°C for 11 days. After this period, the plants were intensively misted with distilled water, covered with plastic bag, and kept in the dark at 18°C. The next day, sporulation in cotyledons was observed. Plants with sporulation were considered susceptible and non-sporulated plants were resistant. The occurrence of race 330 (former American race 7) was observed. Sunflower genotypes Embrapa 122, BRS 191 and ornamental sunflower cultivars BRS Capri M, BRS Encanto M, BRS Oásis, BRS Paixão M, BRS Pesqueiro M, BRS Refúgio M, BRS Saudade M and BRS Saudade U and their respective parents were susceptible to P. halstedii race 330. The genotypes AGROBEL 910, AGROBEL 920, AGROBEL 960, AGROBEL 965, C11, EXP38, M734, M742 and RUMBOSOL 91 were resistant to race 330 and can be used by the growers in regions with high potential for disease occurrence.