Epidemiology and management of Stemphylium blight of onion
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Date
2022-04-29
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palampur
Abstract
The present investigation entitled “Epidemiology and management of Stemphylium blight of onion” was conducted in the Department of Plant Pathology, CSK HPKV, Palampur during 2018-2021with aim to identify disease & pathogen, variability studies, factors affecting pathogen & disease development and evaluation of IDM components viz., chemicals, cultural practices (spacing and date of sowing), plant extracts, biocontrol agents and organic inputs under in vitro, in vivo and field conditions for the management of the Stemphylium blight of onion. During the survey it was observed that disease was prevalent in all the onion growing districts of Himachal Pradesh. The maximum disease severity was observed in district Una (45.4%) followed by Bilaspur (42.5%), Mandi (37.5%) and Kangra (36.9%) whereas, minimum disease severity (35.2%) was observed in district Hamirpur. The disease was identified as Stemphylium blight based on symptoms and pathogen was identified as Stemphylium vesicarium on the basis of morpho-cultural characteristics and molecular characterization. The pathogen variability was studied on the basis of virulence, morphological characters, physiological and molecular characterization, which grouped 32 isolates of S. vesicarium into 6, 14, 12, 12, 9 and 5 groups, respectively. Among different media tested Potato dextrose agar was observed as best media with maximum radial growth whereas, sporulation of S. vesicarium was observed on V8 agar, Oatmeal agar and PDA media. Temperature 250C was found best for the mycelial growth, whereas maximum sporulation occurred at 15-200C. The pathogen perpetuated on debris for quite longer time (8 months) as compared to perpetuation in soil and seeds. The incubation period and latent period of S. vesicarium was observed as 3 & 5 days on detached leaves at 250C and 5 & 7 days on potted plants, respectively. The inoculum level i.e., 3x104 conidia/ml, was found optimum for disease development. Temperature was observed as the most important factor in the disease development having a significant positive correlation with disease severity. Among the eight fungicides viz., trifloxystrobin 25% + tebuconazole 50%WG, azoxystrobin 25EC, difenoconazole 25 EC, carbendazim 50 WP, propiconazole 25 EC, zineb 75 WP, mancozeb 75 WP & copper oxychloride 50 WP evaluated in vitro, propiconazole 25 EC (250 ppm), difenoconazole 25 EC (500 ppm) and trifloxystrobin 25% + tebuconazole 50% WG (1500 ppm) were found most effective which gave complete mycelial inhibition at 250, 500 and 1500 ppm, respectively. Cultural practices revealed that late sown crop at wider spacing resulted into less disease severity with higher bulb yield. In vitro evaluation of plant extracts (aqueous & alcoholic) of Melia azedarach, Lantana camera, Eupatorium adenophorum and Eucalyptus camaldulensis showed that aqueous extract of Eucalyptus gave maximum mycelial inhibition of 53.30 per cent (@ 50%) whereas, alcoholic extracts of all botanicals at 50 per cent concentration except Lantana provided complete mycelial inhibition. In vitro evaluation of bio agents i.e., Trichoderma viride, T. harzianum (JMA-4 and SMA-5), T. koningii (DMA-8 and JMA-11)) and Pseudomonas fluoroscens gave mycelial inhibition ranging from 10.40 to 35.65 per cent. The organic inputs viz; Tamarlassi, Bijamrit, Biosol, Vermiwash, Jeevamrit and Eucalyptus ark evaluated under in vitro, revealed that Eupatorium ark was most effective with complete mycelium inhibition at 10 per cent concentration being followed by Jeevamrit with 88.78 per cent mycelial inhibition at 25 per cent concentration. Under in vivo conditions propiconazole gave maximum disease control (79.85%) however, among non-chemical components T. koningii (DMA-8), Eupatorium ark and plant extracts of Eucalyptus provided 53.99, 68.15 and 59.98 per cent disease control, respectively over check. Under field conditions (KVK Berthin & RSS Akrot), individually among chemicals three sprays of propiconazole 25EC and among non-chemical three sprays of Eupatorium ark were found most effective with 63.96 and 28.03 per cent disease control, respectively. However, integrated treatments of chemical with non-chemical, two sprays of propiconazole 25EC + one spray of Eupatorium ark resulted best with 54.10 per cent disease control whereas, single spray each of propiconazole 25EC, Eucalyptus extract and Eupatorium ark at 10 days intervals also gave good management of disease i.e., 44.37 per cent disease control over check.