Rice blast-mycoflora, symptomatology and pathogenicity

Abstract

Rice (Oryza sativa L.) is the second most important cereal crop of the world as well as of Pakistan. Rice blast caused by a Magnaporthe oryzae (syn: Pyricularia oryzae Cav.) is an infectious fungal disease which is distributed worldwide and prevailing in more than 85 countries of the world. Therefore, present studies were carried out to isolated different fungi associated with seeds and leaves of commercially grown rice varieties and to test the pathogenicity of predominantly isolated species. Seven fungi namely Magnaporthe oryzae, Curvularia lunata, Helminthosporium oryzae, Fusarium moniliforme, Alternaria alternata, Nigrospora oryzae and Aspergillus niger were isolated from seeds and affected leaves of five rice varieties viz., IRRI-6, IRRI-8, DR-82, KS-282 and Shua. N. oryzae was isolated only from IRRI-6 and IRRI-8 rice varieties. Among these fungi, M. oryzae was predominantly isolated both from seeds and leaves of the rice varieties studied. Rice variety IRRI-6 followed by KS-282 appeared as most susceptible rice cultivars to rice blast fungus. M. oryzae was detected with highest frequency from leaves and seeds of IRRI-6. All other fungi were isolated either occasionally or with low frequency. Pathogenicity test of M. oryzae conducted on apparently most susceptible variety IRRI-6 has confirmed the pathogenic nature of the fungus. Plant growth was significantly decreased in inoculated plants as compared to un-inoculated plants. Moreover, typical rice blast disease symptoms were also produced in inoculated plants.