Studies on biological control of Venturia inaequalis (Cke.) Wint., incitant of apple scab in Kashmir valley

Epiphytic mycoflora were isolated from buds, twigs, leaves, flowers, fruits and leaf debris in soil of four apple cultivars Maharaji, Red Delicious, Benoni and Shireen at different intervals during the years 1998 and 1999. Maximum mycoflora population of 967.50 cfu/cm dia disc was observed on leaves at post harvest leaf fall stage and minimum of 67.50 cfu/flower from flowers at bud stage. Maximum mycoflora population was isolated from cv. Maharaji from all above ground parts and cv. Red Delicious from leaf debris in soil. Mycoflora population was maximum at bud swell stage and gradually declined reaching to a minimum at 0.5 inch green stage. On leaves the population gradually increased from open bud leaf stage to post harvest leaf fall stage whereas on fruits it increased gradually from fruit-let stage to pre-harvest stage. On twigs, flowers and leaf debris in soil maximum mycoflora population was recorded at growing, open flower and late dormant stages, respectively. From above ground parts of the plant, Maharaji cultivar harboured maximum colony forming units of different mycoflora. A diverse fungal flora of 33 species was obtained from leaves at post-harvest leaf fall stage whereas minimum 8 species were obtained from flower buds. Fifteen common fungal species were isolated from all the above ground parts as well as from leaf debris in soil. The prominent fungi included species of Alternaria, Aspergillus, Penicillium, Rhizopus, Curvularia, Trichoderma and Nigrospora. Of the isolated fungal species, propagule and cell free extract of 6 fungal species viz. Cladosporium herbarum, Trichoderma hamatum, Trichothecium roseum, Trichoderma viride, T. harzianum and Chaetomium globosum significantly reduced germination of conidia of V. inaequalis, in vitro with C. globosum showing maximum reduction of 73.91 and 84.56 per cent, respectively. The propagule and cell free extract sprays of these antagonists significantly reduced leaf scab severity with C. globosum exhibiting maximum control of 44.21 and 89.78 per cent respectively under growth chamber conditions. Under field conditions, again antagonistic propagules and cell free extract of six fungal species reduced significantly leaf scab incidence and intensity with C. globosum treated leaves showing a maximum control of 23.16 and 33.15 per cent in incidence and 26.31 and 34.11 per cent in intensity when propagules and cell free extracts were sprayed respectively. The antagonistic mycoflora successfully colonized the unsprayed, diseased and senescent apple leaf discs with C. globosum recording maximum colonization of 88.25 per cent. The decomposition rate of the fallen leaves sprayed with the antagonistic propagule suspension in autumn was also significantly enhanced during winter. Significant reduction was also observed in pseudothecial density, number of asci per pseudothecium, ascospore production and pseudothecial and ascal maturity with C. globosum showing maximum reduction of 81.21, 81.73, 83.96 and 81.29 per cent respectively and C. globosum proved to be an outstanding antagonis