Spatial Distribution, Cultural Diversity and Virulence of Colletotrichum spp. Causing Chilli Anthracnose in Kerala, India

Abstract

Chilli anthracnose (fruit rot), caused by Colletotrichum spp., is one of the most destructive diseases limiting chilli production, resulting in substantial pre- and post-harvest losses. This study assessed the distribution, symptom expression, cultural characteristics, mycelial growth and virulence of Colletotrichum isolates associated with chilli anthracnose in Kerala, India. A systematic roving survey was conducted from February to April 2023 at ten locations across three agro-ecological units in five districts. Disease incidence and per cent disease index (PDI) were determined, and ten isolates were characterised on potato dextrose agar and evaluated by artificial fruit inoculation. Anthracnose occurred at every surveyed location; incidence ranged from 28.12 to 49.02% and PDI from 9.33 to 27.51. Mannuthy recorded the highest incidence (49.02%) and PDI (27.51), whereas Parippally recorded the lowest values (28.12% and 9.33%, respectively). Symptoms included foliar brown spots and sunken brown-to-black fruit lesions with concentric zonation and acervuli; advanced infection caused fruit shrivelling and mummification. Although all isolates formed circular colonies, they differed in colour, texture, margin, zonation and pigmentation. Isolate C8 showed the greatest in vitro growth, reaching 9.00 cm at 7 days after inoculation and recording a growth rate of 1.33 cm day⁻¹, whereas C6 grew the slowest (0.56 cm day⁻¹). Virulence also varied markedly: C8 produced necrotic lesions within 3 days, followed by rapid lesion expansion and the highest assay PDI, while C5 and C7 produced delayed, smaller lesions. These findings demonstrate pronounced spatial, cultural and pathogenic variability and identify C8 as an aggressive isolate suitable for resistance screening. Location-specific surveillance and integrated disease management are therefore essential for effective anthracnose control in Kerala.