IDENTIFICATION AND MANAGEMENT OF SEED BORNE FUNGI ASSOCIATED WITH SELECTED BRRI RICE VARIETIES

Abstract

A total of twenty BRRI rice varieties i.e., BRRI dhan 56 to BRRI dhan 75 were collected from Bangladesh Rice Research Institute (BRRI) for seed quality analysis, detection and identification of fungi associated with seeds of rice varieties. Dry inspection indicated that the percentage of pure seeds ranged from 92 to 99%, spotted 0.05-0.80%, discolored 0.20-1.50%, inert matter 0.10-1.00% and weed seeds 0.05-0.30%. The highest germination was recorded in BRRI dhan 74 (94%) and the lowest in BRRI dhan 63 (78%). The highest mortality was recorded in BRRI dhan 65 (25.40%) and the lowest in BRRI dhan 74 (9.80%). Root length was highest in BRRI dhan 72 (5.37cm) and lowest in BRRI dhan 58 (2.20cm). Shoot length was highest in BRRI dhan 74 (8.90cm) and lowest in BRRI dhan 65 (4cm). BRRI dhan 74 showed the highest vigor index (1289.6) and lowest in BRRI dhan 65 (598.60) variety. The lowest average seed moisture was recorded in BRRI dhan 67 (9.80%) and highest in BRRI dhan 63 (11.83%). 25 fungal species were isolated from the selected rice varieties following Tissue planting method and Blotter method. The fungi were Alternaria alternata, A. tenuissima, Aspergillus flavus, A. fumigatus, A. niger, A. ochraceus, A. terreus, Bipolaris multiformis, B. oryzae, B. sorokiniana, Chaetomium globosum, Curvularia lunata, Fusarium equiseti, F. fujikuroi, F. oxysporum, F. proliferatum, Microdochium fisheri, Nigrospora oryzae, Penicillium sp., Phanerochaete chrysosporium, Pestalotiopsis oxyanthi, Rhizopus stolonifer, Sarocladium oryzae, Syncephalastrum racemosum and Trichoderma viride. Morphologically identified twenty-five fungi were selected for molecular identification. Out of the 25 fungal isolates, 13 were confirmed up to species level through ITS sequence based molecular analysis. Among the isolated fungi Bipolaris multiformis, Microdochium fisheri and Pestalotiopsis oxyanthi are the new record for Bangladesh. In Tissue planting method B. oryzae, M. fisheri, A. flavus, A. fumigatus and Penicillium sp. were predominant in most of the rice varieties whereas B. multiformis, P. chrysosporium and A. tenuissima were recorded only in a few varieties of rice seeds. The highest fungal association was noticed in BRRI dhan 65 (75.46%) and lowest in BRRI dhan 73 (35.28%). In Blotter plate method C. globosum, B. oryzae and A. niger were predominant in most of the rice varieties whereas A. terreus, M. fisheri and A. flavus were recorded only in a few varieties of rice seeds. The maximum fungal infection was observed in BRRI dhan 56 (35%) while minimum in BRRI dhan 65 (2.75%). Correlation coefficient and regression analysis indicated that prevalence of fungi had significant effect on seed germination, pure seed, seedling mortality and moisture content. The present investigation suggested that out of 20 BRRI rice varieties, BRRI dhan 66, BRRI dhan 69 and BRRI dhan 74 showed better performances on the basis of percentage of pure seed, fungal association, seed germination and seedling mortality. Ten species of fungi were isolated from empty glume, flowering glume, embryo and endosperm. Six fungi viz., B. oryzae, C. lunata, F. equiseti, F. fujikuroi, M. fisheri and N. oryzae viz., showed positive results in pathogenicity test. These six fungi showed seed to seedling transmission nature in water agar test tube and earthen pot. Ten fungicides i.e., Bavistin 50WP, Capvit 50WP, Dithane M-45, Greengel 72WP, Knowin 50 WP, Nativo75 WG, Ridomil Gold 68 WG, Score 250 EC, Thiovit 80 WG and Tilt 250 EC at 100, 200, 300, 400 and 500 ppm concentrations were tested against the six test pathogens following “poisoned food technique”. Out of ten fungicides Bavistin showed the complete growth inhibition of B. oryzae, C. lunata, F. equiseti, M. fisheri and N. oryzae at all the tested concentrations. Tilt also completely inhibited the radial growth of B. oryzae, C. lunata, F. fujikuroi, M. fisheri and N. oryzae at all the concentrations. Knowin, Nativo, and Score were also found as most effective inhibitor of the test pathogens. Out of ten leaf extracts namely Adhatoda vasica L., Azadirachta indica A. Juss., Cassia alata L., Citrus limon L., Datura metel L, Heliotropium indicum L, Mangifera indica L., Moringa oleifera Lam, Psidium guajava L. and Vitex negundo L were evaluated for their efficacy at 5, 10, 15 and 20% concentrations against the above mentioned six test pathogens. Citrus lemon completely inhibited the radial growth of B. oryzae and M. fisheri at all the concentrations. Azadirachta indica and P. guajava showed the complete growth inhibition of C. lunata and M. fisheri. Azadirachta indica, C. alata and M. oleifera showed highest radial growth inhibition of F. equiseti, F. fujikuroi and N. oryzae at 20% concentration. Moreover, A. vasica, D. metel and V. negundo also showed desired growth inhibition of the test pathogens. Four antagonistic fungi were isolated from the rice field soil by serial dilution technique and were identified as Aspergillus flavus Link, A. fumigatus Fresenius, A. niger van Tieghem and Trichoderma viride Pers. ex Gray. The soil fungi were evaluated for their antagonistic potentiality against B. oryzae, C. lunata, F. equiseti, F. fujikuroi, M. fisheri and N. oryzae. In dual culture colony interaction, out of four antagonistic fungi, Trichoderma viride showed highest growth inhibition of B. oryzae (61.67%), C. lunata (63.64%), F. equiseti (70.58%), F. fujikuroi (87.15%), M. fisheri (65.35%) and N. oryzae (63.64%). Trichoderma viride showed the highest growth inhibition of B. oryzae (65.35%), C. lunata (54.37%), F. equiseti (63.90%), F. fujikuroi (57.12%), M. fisheri (62.40%) and N. oryzae (82.63%) owing to the effect of volatile metabolites. The maximum inhibition of radial growth of C. lunata (88.36%), F. fujikuroi (90.81%) and M. fisheri (68.40%) was observed owing to non-volatile metabolites of T. viride whereas A. niger showed the maximum inhibition of radial growth of B. oryzae (86.55%), F. equiseti (86.80%). Maximum inhibition of radial growth of N. oryzae (94.10%) was observed owing to non-volatile metabolites of A. fumigatus. Evaluation of combined effects of fungicides, plant extracts and biocontrol agents were also performed against the six test pathogens. Out of twelve treatments T10 (Tilt + A. indica + T. viride), T3 (Bavistin + Tilt) and T7 (T. viride) showed highest germination percentage and seedling vigor index against B. oryzae, C. lunata and F. fujikuroi. On the other hand T3 (Bavistin + Tilt), T7 (T. viride) and T1 (Bavistin) also showed promising germination percentage and seedling vigor index against F. equiseti, M. fisheri and N. oryzae. These three test pathogens were completely controlled by the treatments used in the experiment.