Disease severity and sporulation potential of Pyricularia oryzae in some native rice cultivars in Iran

Rice is one of the most important crops in Iran and the rice blast caused by Pyricularia oryzae causes significant losses in rice fields during outbreak season. At the beginning of the disease cycle, the primary inoculum imposes severe damage to plants as it leads to plant weakness. The damage will shortly become significant as the second wave of inoculum spreads. This study aimed to determine the occurrence and severity of blast disease on some native Iranian cultivars and estimate the number of conidia produced on second leaves. Pyricularia oryzae Cavara isolates were collected from rice leaves from the north of Iran. One out of 123 isolates was inoculated on seven Iranian native cultivars named Hashemi, Tarom Mahali, Sang Tarom, Binam, Champa, Alikazemi, and Domsiyah at the four-leaf stage. Lesions on leaves were scored and the percentage of the spotted area was calculated by software Image J1.52a. Various lesion types and a range of diseased areas varying from 30% recorded in Hashemi to 55% in Tarom Mahali were observed. Under optimum conditions, the sporulation potential was calculated. Isolate produced different amounts of spores on different cultivars; Hashemi showed the highest and Tarom Mahali showed the lowest sporulation with 63 and 11 spores per mm2 of spotted area. The result indicated that the resistance threshold of the native cultivars could be different but not sufficient. Additionally, to estimate the damage on each cultivar on farms, we need to investigate the sporulation potential of the pathogen through time in each cultivar