Epidemiological factors affecting purple blotch (Alternaria porri ) progression in garlic

Abstract

Purple blotch caused by Alternaria porri Ellis (Cif.), poses a serious threat to garlic cultivation. This study investigated key epidemiological factors influencing disease development, specifically inoculum concentration, age of host and pathogen culture, and its ability to infect other plant species on disease development. A spore concentration of 1×10⁵ conidia/ml resulted in highest disease severity (36.38%) within a shortest incubation period (6 days), establishing as optimal inoculum load. Among varying culture ages, 14-day-old culture exhibited peak virulence with disease severity (33.77%) and infection rate (0.04 r/day). Host susceptibility increased with plant age with maximum disease progression in 60-day-old plants. Host range assessments demonstrated that it could infect onion, tomato, and chilli with incubation period ranging from 7-12 days, while potato and cabbage remain unaffected, highlighting moderate host specificity. These findings enhance understanding of A. porri pathogenesis and provide framework for developing effective screening and disease management strategies in garlic.