Evaluation of ashwagandha (Withania somnifera L.) Dunal accessions and breeding lines against leaf spot disease caused by Alternaria alternata under subtropical condition of India

Abstract

Withania somnifera L. Dunal, is one of the important medicinal crops and extensively used in the traditional medicine systems of India. Leaf spot disease caused by Alternaria alternata is a major concern and adversely affect the commercial cultivation as well as production of crop. The disease symptoms appear around 50 days after sowing (DAS) on naturally infected plants while on artificially inoculated plants symptoms developed within 2 weeks. The associated pathogen was characterized for precise identification based on the sequencing of partial internal transcribed spacer (ITS) and actin gene considering the microscopic observations. The disease is prevailing more severe at flowering stage, 90 DAS under high temperature and low relative humidity. In the present study 328 breeding lines and 140 accessions of W. somnifera were procured under breeding program and screened against leaf spot disease under natural field conditions for three consecutive years. The results of our study revealed that only 12.85% of accession lines viz., RAS – 36, MWS-207, MWS-211, MWS-303, MWS-304, RAS -10, RAS – 49, RAS – 50, MWS-336, RAS – 130, IC – 283942, RAS – 60, RAS – 61, RAS – 143, RAS – 133, RAS – 137, MWS-139 and RAS – 41 and 7.32% of breeding lines viz., DWS-108, DSW-130, DWS-74, DWS-118, DWS-152, DWS-279, DWS-96, DWS-37, DWS-107, DWS-133, DWS-234, DWS-311,DWS-34, DWS-41, DWS-42, DWS-69, DWS-86, DWS-127, DWS-170, DWS-223, DWS-293, DWS-270, DWS-296 and DWS-309 were falling under the highly resistant class. The pathogenesis as well as disease progress mechanisms influenced by environmental factors and growth stages of crop. Maximum temperature 35 + 5 °C when coincide with low relative humidity (66 + 5% RH1) supported the aggressiveness of the pathogen.