Variability in the Helminthosporium oryzae fungus

Abstract

Cultural and pathogenic variation in Helminthosporium oryzae was studied using 10 isolates under greenhouse conditions. In the absence of a known and standard differential set for H. oryzae, 10 cultivars of rice (Oryza sativa L.) Bluebelle, EEA 406, Caloro, BR-IRGA 410, Dawn, Brazos, Stirpe, IRGA 408, Lebonnet and IV-29-4, were used. Pathogenicity tests were conducted on 30-day old plants. The fungus isolates (H-1 to H-10), obtained from leaves, culms, and/or rice seeds collected from different localities were inoculated on the differential set. The cultures were maintained on Potato - Dextrose-Agar + Streptomicin (100 µg/l). Five single monosporic isolates obtained from each one of the three aggressive original isolates (H-1, H-5 and H-8) were tested on the differencial set. The results showed variation in cultural characters between the original isolates and within the more aggressive ones (monosporic). However, differencial interaction in pathogenicity was not observed among tho isolates and cultivars.