Molecular Characterization of Magnaporthe oryzae in Punjab, Pakistan and its In Vitro Suppression by Fungicides and Botanicals

Abstract

Rice blast, caused by the fungus Magnaporthe oryzae (anamorph: Pyricularia oryzae), is a disease of major economic importance in rice-growing regions worldwide, but has received little attention in Pakistan. Surveys were conducted in five rice-cultivating districts of Punjab province, Pakistan during 2016 and 2017. Disease incidence was recorded in 25 surveyed fields. Pathogen identification was confirmed as M. oryzae based on the morphological characterization and pathogenicity assays. BLASTn comparison of sequences of four different gene regions (ITS, actin, beta tubulin, calmodulin) of 25 isolates resulted in ≥99% homology to type specimens of M. oryzae. In in vitro and greenhouse experiments, commercially available fungicides (difenoconazole, mancozeb, tetrachlorophthalide, tebuconazole + trifloxystrobin, carbendazim, propiconazole, thiophanate-methyl) were compared with applications of botanical extracts (black pepper, clove, aloe vera, neem, and ginger) for their ability to inhibit the growth of the pathogen. The maximum incidence of rice blast, 71.25%, was observed in Jalalpur Bhattian (Hafizabad). Morphological, pathogenicity and molecular studies confirmed the M. oryzae as the causal organism of the rice blast disease. Difenoconazole inhibited the in vitro mycelial growth of M. oryzae more than other compounds (83.55%), followed by black pepper (70.68%). In greenhouse trials, disease severity was lowest (28.50%) for difenoconazole, followed by black pepper (33.75%). Difenoconazole and black pepper showed the most promising fungicide and botanical for the management of rice blast in Punjab province, Pakistan.