Studies on Foliar Fungal Diseases of Sunflower (Helianthus annuus L) under Kashmir Conditions
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Date
2023
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SKUAST Kashmir
Abstract
Foliar fungal diseases of sunflower i.e. Alternaria leaf blight, Curvularia leaf spot and powdery mildew have been viewed as a possible biotic stress responsible for decreasing yield potential of this crop over the years. This necessitated basic investigations in the host-pathogen interactions vis-à-vis etiology, epidemiology and yield loss assessment. Alternaria helianthi, Curvularia lunata and Erysiphe cichoracearum, as supported by symptomatology, morphology and pathogenicity tests were identified as the causal pathogens of these disease of sunflower in Kashmir, respectively. Alternaria leaf blight disease symptoms on the lamina of the leaves comprised of small scattered brown spots which turn dark brown with yellow halo of 3-5mm in diameter. Mycelium was septate olivaceous green in colour smooth and branched shape. Conidia were septate with 3-8 transverse and 1-2 longitudinal septa light brown in colour. Curvularia leaf blight appeared as small reddish brown spots which became round brown with yellow halo. Mycelium was septate, olive brown in colour, branched and septate. Conidia were black to dark brown in colour with conidiophores septate black to dark brown in colour. The molecular identification using the ITS primers confirmed the identity of the Curvularia lunata showing a similarity of 98.00 per cent with reference sequences. To our knowledge, this is the first report of Curvularia blight on sunflower caused by Curvularia lunata in Jammu and Kashmir and in the country. The sequences of the Curvularia lunata was registered in NCBI Gen Bank under the accession numbers ON668436 & ON668437. The powdery mildew appeared as whitish powdery spots on upper surface of leaves. The severely infected leaves became yellow and dried up. Hyphae were septate and hyaline in colour. The conidia were single celled, hyaline in colour, cylindrical to ovoid in shape whereas conidiophores were straight, unbranched in shape, hyaline in color and septate. The correlation analysis revealed a positive and significant influence of relative humidity and rainfall on Alternaria leaf blight and Curvularia leaf spot whereas it was positive and non significant for powdery mildew . Studies on the requirements of leaf wetness and temperature levels for infection of Alternaria helianthi revealed a minimum leaf wetness of 4 hours and incubation period varying from 2-3 days at 25oC .This hints at the possibility of managing these diseases by altering sowing date such that most or some of the early growth stages enjoy rain free period The data on apparent infection rate(r) revealed that the early growth stage i.e.40 to 47 days after sowing were found to be highly vulnerable to Alternaria leaf blight. The disease progress curve had clearly indicated that the diseases developed very slowly at early crop growth stages and the rate of development increased with increase in age of the crop .This can help in deciding the sowing date and preparing a timely schedule for a fungicidal spray for their effective control of foliar diseases.. The assessment of yield loss in sunflower due to foliar diseases revealed that three sprays of mancozeb 63WP +carbendazim 12% @ 0.25% at 10 days interval starting from 30 days is optimum chemical control of foliar diseases of sunflower under Kashmir conditions and for realizing the maximum seed yield production. The yield losses can be much more under disease favouring weather, hence it should be considered a significant limiting factor in sunflower production. Suitable management strategies need to be evaluated for successful establishment of this potential oilseed crop in Kashmir.
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Keywords
sunflower, Alternaria helianthi, Curvularia lunata, Erysiphe cichoracearum, epidemiology, yield loss assessment, Plant Pathology.