SEED BORNE MYCOFLORA OF DIFFERENT VARIETIES OF COTTON (GOSSYPIUM HIRSUTUM L.) AND THEIR MANAGEMENT

Abstract

Cotton “The king of Fibers” is one of the most renowned, reliable fiber yielding cash crops around the world including Bangladesh. It is the most important cash crop next to jute in Bangladesh. The present research work was undertaken to detect, identify the seed borne mycoflora of 14 varieties (CB1-CB14) of upland cotton (Gossypium hirsutum) in Bangladesh and to screen out the efficacy of selected antagonistic fungi, plant parts extracts and fungicides against the fungal pathogens associated with cotton seeds. Seed samples were collected from Cotton Research, Training and Seed multiplication Farm, Sreepur under the district of Gazipur. Quality analysis showed that the percentage of pure seeds varied from 97.08-99.92%, the germination percentage of different varieties of cotton seeds were ranged from 80-93%, the mortality percentage were in the range of 16.05-50.30% and the moisture level was varied from 10.0-11.3%. The fungi associated with the different varieties of cotton seeds were isolated following Tissue planting method, Blotter method and Paper towel method. A total of twenty nine species of fungi namely Aspergillus aculeatus, A. flavus, A. fumigatus, A. niger, A. nidulans, A. subramanianii, A. tamarii, A. toxicarius, A. wentii, Curvularia lunata, Colletotrichum gloeosporioides, C. gossypii, Chaetomium globosum, Fusarium moniliforme, F. nivale, F. oxysporum, F. fujikuroi, F. solani, Lasiodiplodia theobromae, Meyerozyma guilliermondii, Mucor sp., Penicillium aculeatum, P. citrinum, Rhizoctonia solani, Rhizopus stolonifer, R. oryzae, Rhizomucor sp., Syncephalastrum racemosum and Trichoderma viride were found to be associated with the seeds of cotton. Isolated fungi were characterized and identified following standard literatures. Molecular identification of 19 fungi were conducted by using ITS sequence based analysis. Among the isolated fungi Aspergillus subramanianii, A. toxicarius, A. wentii, Penicillium aculeatum, P. citrinum, Rhizomucor sp. and Meyerozyma guilliermondii are the new records for Bangladesh. In Tissue planting method, the association of fungi varied with duration of storage periods. Aspergillus flavus, A. fumigatus, A. niger, Chaetomium globosum, Penicillium citrinum and Rhizopus stolonifer were the most predominant fungi in terms of prevalence and their frequency were also gradually increased with the increase of storage period. Chaetomium globosum was the most predominant fungi noticed in Blotter and Paper Towel method. Maximum number of fungi were found to be externally seed borne i.e. isolated from seed coat. Interrelationships among seed germination, purity percentage, seed moisture, fungi frequency and seedling mortality of cotton seeds were measured through correlation and regression analysis. Five positive correlations and 2 negative correlations were found among these 5 quality factors. Out of these 29 fungal species, nine were found to be pathogenic to cotton. They were Aspergillus flavus Link, A. niger Van Tiegh, A. tamarii Kita G., Colletotrichum gloeosporioides Penz & Sacc., Curvularia lunata (Wakker) Boedijn, Fusarium nivale (Fr.) Sorauer, F. moniliforme J. Shelden, Mucor sp. P. Micheli ex L. and Rhizoctonia solani Khun. These pathogenic fungi had remarkable effect on seed germination, vigor index, root-shoot length and mortality of cotton seedlings. All the pathogenic fungi showed transmission nature i.e. fungi transferred from seeds to seedlings in both earthen pot and water agar culture. In pot experiment, percentage of seed to seedling transmission of fungi varied from 17.85 (A. niger) to 46.56% (F. moniliforme) and in water agar test, Rhizoctonia solani showed highest percentage of seed to seedling transmission (35.27%). The antagonistic potentials of four soil fungi against pathogenic fungi were evaluated by "dual culture colony interaction”, volatile and non-volatile metabolites. In "dual culture colony interaction", out of four soil fungi, the highest growth inhibition (84.0%) was observed by A. fumigatus against C. gloeosporioides. Volatile substances from soil fungi inhibited radial growth of the test pathogens varied from 33.3-72.4%. The highest inhibition (72.4%) was found in A. fumigatus against R. solani. Non-volatile substances showed inhibition of mycelial growth of cotton pathogens range from 47.06 to 81.82% at 20% concentration. The highest inhibition was observed owing to A. niger against F. nivale. Ten fungicides with different active ingredients viz., Capvit 50 WP, Contaf 5 EC, Dithane M- 45, Knowin 50 WP, Nativo 75 WP, Ridomil MZ Gold, Score 250 EC, Secure, Silica 80 WG and Tilt 250 EC were selected to evaluate their in vitro efficacy at 100, 200, 300, 400 and 500 ppm concentrations against the nine pathogenic test fungi. Contaf and Tilt were found most efficient inhibitor which completely inhibited the radial growth of the test pathogens which was followed by Nativo, Knowin, Score, Dithane, Capvit, Secure, Ridomil and Silica. Antifungal properties of ethanol extracts of ten higher plants namely Adhatoda vasica L., Aegle mermelos L., Azadirachta indica A. Juss., Citrus lemon L., Datura metel L., Mangifera indica L., Moringa oleifera Lam., Ocimum sanctum L., Psidium guajava L. and Tagetes patula L. at 5, 10, 15 and 20% concentrations were evaluated against the test pathogens. As regards the plant extracts, the P. guajava and A. indica were found most efficient inhibitor of the test pathogens followed by C. lemon, A. vasica, D. metel, A. mermelos, T. patula, M. oleifera, O. sanctum and M. indica at 20% concentration. In field experiment out of 19 treatments, T1 (Tilt) and T11 (Tilt + A. indica + T. viride) showed highest seed germination, seedling vigor index against A. flavus, A. niger, C. lunata, F. nivale, Mucor sp. and A. tamarii, C. gloeosporioides, F. moniliforme and R. solani, respectively. On the other hand, T5 (T. viride), T10 (Tilt + P. guajava + T. viride) and T14 (Tilt + A. indica ) showed promising germination percentage and seedling vigor index against A. flavus, R. solani and A. tamarii, F. nivale and A. niger, C. gloeosporioides, C. lunata, F. moniliforme, Mucor sp., respectively.