Epidemiology and management of Alternaria leaf spot of Bael incited by Alternaria alternata (Fr.) Keissler
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Date
2023-05
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CCSHAU, Hisar
Abstract
The present investigation entitled “Epidemiology and management of Alternaria leaf spot of Bael incited by Alternaria alternata (Fr.) Keissler” was conducted in the laboratory in department of plant pathology, COA, Hisar and research farm of Regional Research Station, Bawal, CCS HAU during 2022-23. Characteristic symptoms were observed on leaves as concentric circles in the centre of the leaf spots surrounded by a chlorotic yellow halo. The presence of brown to black necrotic lesions on older leaves that produce a bulll’s eye pattern. The pathogen, A. alternata was isolated as pure culture on PDA medium. The colony appeared as black or olivaceous black and sometimes of grey color. The fungus produces conidia that are light brown, having muriform shape with both cross and longitudinal septa and having conical or cylindrical beak of 2 to 5 µm thickness. The average size of the conidia was 25-60 x 10-16 µm and the conidiophores were dark bearing a chain of conidia. Epidemiology of disease was studies under field condition revealed that significant but negative correlation was observed between per cent disease severity and temperature (minimum and maximum), average evening relative humidity (RHe), wind speed and rainfall. The average morning relative humidity (RHm) and Sun shine hours showed non-significant positive correlation with disease severity. Tmax. 28°C and relative humidity 79% were found most favourable conditions for the progression of the disease. Among four bioagents evaluated in dual culture under in vitro conditions against A. alternata, Trichoderma viride showed highest mycelial growth inhibition of 72.62 per cent followed by Trichoderma harzianum (68.43 per cent ) and Pseudomonas fluorescens (61.56 per cent) while least effective was Bacillus subtilis (54.37 per cent). Out of six fungicides/non-conventional chemicals evaluated against A. alternata, metiram 55% + pyraclostrobin 5% WG and tebuconazole 50 + trifloxystrobin 25% (75 WG) with 78.92 and 71.25 percnet mycelial growth inhibition, respectively were found most effective and significantly superior among the treatments under in vitro conditions. Under field conditions, metiram 55% + pyraclostrobin 5 % WG was found superior over other treatments with highest per cent disease reduction over control (82.43 per cent) followed by tebuconazole 50 + trifloxystrobin 25 % (75 WG) (76.83 per cent). The maximum yield was recorded in plants treated with metriam 55% pyraclostrobin 5% WG @ 0.25 per cent (63.27 kg/tree) followed by tebuconazole 50+ trifloxystrobin 25% (75 WG) @ 0.10 per cent (60.24 kg/tree). An increasing consciousness about environmental pollution due to fungicides and development of fungicide resistance in pathogen population has challenged the plant pathologist to search for eco-friendly tools for A. alternata management. The use of integrated approaches to disease management is, therefore, a high-priority research area.