To study the susceptibility of Ashwagandha (Withania somnifera L. Dunal) at different growth stages of leaf spot caused by Alternaria alternate (Fr.) Keissler

Abstract

The present investigation was carried out at the Department of Plant Pathology, Rajasthan College of Agriculture, MPUAT, Udaipur, Rajasthan during Rabi 2024-2025 “To study the susceptibility of Ashwagandha (Withania somnifera L. Dunal) at different stages of leaf spot caused by Alternaria alternata (Fr.) Keissler. The pathogen was isolated from diseased leaves and identified based on morphological characteristics, further confirmed by the Indian Type Culture Collection (ITCC), New Delhi. Pathogenicity tests on susceptible cultivar ‘RAV-100’ reproduced typical symptoms, fulfilling Koch’s postulates. A pot experiment involving five plant age groups (10, 20, 30, 40, and 50 days) revealed that disease severity, expressed as Percent Disease Index (PDI), increased with plant age.
Minimum disease was recorded in 10-day-old plants (PDI 6.2%, resistant), while the highest was observed in 50-day-old plants (PDI 97.8%, highly susceptible). The critical infection stage was identified from 30 days onwards, indicating the need for timely application of control measures before this stage to reduce disease impact and protect crop yield and quality.