IN VITRO EVALUATION OF FUNGICIDAL RESISTANCE OF RICE BLAST PATHOGEN (Magnaporthe oryzae L) STRAINS

Abstract

Rice blast disease caused by the fungus, Magnaporthe oryzae, is one of themajor fungal diseases affecting rice (Oryza sativa) cultivation. The resistance ofthis fungus to fungicides is imperative as the presence of fungicide resistantstrains (biotypes) has been associated with control failure, therefore managingresistance is critical to disease control. This study was carried out to evaluate thein vitro fungicidal resistance among the strains of M. oryzae found in rice fieldsin Niger State. The blast infested leaves, stems and panicles of rice plants werecollected in November, 2015 from five farmers’ field located in Gbako, Katchaand Lavun Local Government Areas in Niger state, Nigeria. Isolation of the pathogen was carried out on Potato Dextrose Agar (PDA) and the fungicidalsensitivity test of the isolates was conducted in PDA amended with Mancozeb and Benomyl fungicides. Ten M. oryzae strains designated as MOR001- 0010were isolated from all the samples collected and exposed to both fungicides(Mancozeb and Benomyl). Out of these, five strains (MOR001, MOR002,MOR004, MOR005 and MOR008) were resistant to mancozeb with varying percentage inhibitions (91.67, 45.45, 84.13, 86.67 and 83.88% respectively)while three isolates (MOR004, MOR005 and MOR010) were resistant to benomyl with varying percentage inhibition (85.25, 91.67 and 75.00%respectively). However, isolates MOR004 and MOR005 were resistant to both fungicides (84.13% and 86.67% in mancozeb while 85.25% and 91.67% in benomyl respectively). Molecular evaluation is recommended to actualise the relationship between the ten strains because species within the same fungal genus may respond differently to certain fungicides.