Assessment of Genetic Variability in Onion against Purple Leaf Blotch Disease under Field Conditions and its Management

Purple blotch disease is exerting a severe threat on onion production.The current study was conducted for screening of accessions against purple blotch disease and determining the source of resistance against Purple blotch disease of onion caused by Alternaria porri.Potential of 50 onion accessions was evaluated against A. porri during 2017 and 2018 under field conditions.After that effect of some fungicides and plant extracts was determined for disease suppression on a susceptible variety of onion.During both years of study, eight accessions (Phulkara, Texas Early, Cylon, Sunset, Red Gystal, Rubi F1, Red Flame, ON-14133) exhibited resistant response with minimum percent disease index (PDI) which ranged between 5-10%, followed by Mirpurkhas, Nasarpuri, HON-1069, Pania, Rubi F2, GSL-132, Red Moon, PK-1032, F-1122, Red Imposta, Early Red, Desi Large and Vrio-4 which showed moderately resistant response to A.porri with PDI of 11-20%, whereas, the four accession including Golden Arab, Desired, Sultan F1 and Red Nasik expressed Moderately resistant response with PDI of 21-40%.Moreover, six accessions (Yellow Gystal, Vrio-9, Vrio-5, Vrio-4, Vrio-1, and Vrio-3) expressed susceptible response with high value of PDI 41-60% whereas; nine accessions (CBS-130, ON-14121, Pink Panther, Vrio-7, Vrio-3, F1 Zeus, SE-16, Vrio-8 and Marvi) showed maximum value (Above 60%) of PDI and expressed highly susceptible response to A.porri.Among fungicides and botanical extracts, Chlorostrobin and Azadirachta indica extract expressed significant reduction in disease severity.It was concluded that out of 50, only eight accessions were resistant which might be grown successfully for higher crop production.Moreover, use of Chlostrobin and extract of Azadirachta indica may be used for disease management.