PATHOGENIC MYCOFLORA OF RICE GRAINS AND ITS MANAGEMENT

Abstract

The present investigation is based on diseased rice grains of four commercially cultivated rice varieties namely BRRI 28, 29, Kalijira and Pajam collected from 14 districts of 7 divisions and 40 rice samples viz. Hybrid 2, 3, 4, BR 7, 11, 12, 14 ,16, 22, 23, 25, 26 and BRRI 28 to BRRI 55 were collected from Bangladesh Rice Research Institute at Joydebpur. Quality analysis showed that the percentage of pure seed varies from 94-99%. The germination and mortality percentage of rice seeds of different varieties were in the range of 62-100% and 10-30%, respectively. Twenty five species of fungi belonging to 15 genera were associated with these rice varieties. The isolated fungi were Alternaria alternata, Aspergillus clavatus, A. flavus, A. fumigatus, A. niger, A. ochraceous A. oryzae, A. terreus, Chaetomium globosum, Cladosporium cladosporioides, Colletotrichum gloeosporioides, Curvularia lunata, C. lunata var. aeria, Drechslera oryzae, Fusarium moniliforme, F. oxysporum, F. solani, Microdochium oryzae, Nigrospora oryzae, Penicillium spp, Pestalotiopsis guepinii, Rhizopus stolonifer, Sarocladium oryzae and Trichoderma viride. Their pathogenic potentiality was tested by seed inoculation technique. Amongst twenty five species nine viz., Alternaria alternata (Fr.) Keissler, Aspergillus flavus Link Curvularia lunata (Wakker) Boedijn, Drechslera oryzae Breda de Haan (Subramanian and Jain), Fusarium moniliforme Sheldon, F. solani (Mart.) Sacc., Microdochium oryzae (Hashloka and Yokogi) Sam. and Hal., Pestalotiopsis guepinii (Desm.) Stay. and Sarocladium oryzae (Sawada) W. Gams and D. Hawks were found to be pathogenic. These nine pathogenic fungi were transmitted from seed to seedlings and produced different types of symptoms. Ten fungicides i.e. Bavistin 50 WP, Capvit 50 WP, Dithane M-45, Greengel, Hayvit 80 WP, Indofil M-45, Ridomil MZ Gold, Salcox 50 WP, MC Sulphur 80 and Tall 25 EC at 100, 200, 300, 400 and 500 ppm were evaluated against the above mentioned nine pathogenic fungi. Tall 25 EC completely inhibited the radial growth of the test pathogens at all the concentrations except F. moniliforme and Microdochium oryzae. Antifungal properties of Allium sativum L., Artocarpus heterophyllus Lamk., Asparagus racemosus Willd., Azadirachta indica A. Juss., Citrus medica L., Datura metel L., Mangifera indica L., Nerium indicum Mill., Senna alata (L.) Roxb. and Tagetes erecta L. at 5, 10 and 20% concentrations were evaluated against the nine test pathogens. All the plant extracts completely inhibited the radial growth of the test pathogens at 20% concentration except Asparagus racemosus and Nerium indicum. Antagonistic potential of the selected six soil fungi against pathogenic fungi were evaluated. Amongst 48 interactions grade 3 was found in 22 interactions. Volatile substances from soil fungi inhibited radial growth of the test pathogens varied from 8.33-57.36%.The highest inhibition (57.36%) was found due to T. harzianum against P. guepinii. Non-volatile substances showed inhibition of mycelial growth ranged from 29.05 to 64.5%. The highest inhibition was observed owing to the T. harzianum against C. lunata. In colony interaction, the highest growth inhibition (88%) was observed by T. harzianum against A. alternata. In the field experiment out of 13 treatments, T6 (Bavistin+Azadirachta indica+Trichoderma harzianum) and T10 (Bavistin+Tall+Azadirachta indica+Citrus medica) treated seeds showed highest per cent of germination and seedling vigor index against all the test pathogens.