Reaction of chilli (Capsicum annuum L.) genotypes against Colletotrichum truncatum under in-vitro conditions

Abstract

Fruit rot caused by Colletotrichum truncatum is recognized as one of the most destructive diseases of chilli (Capsicum annuum L.), leading to significant yield and quality losses worldwide. The development and deployment of resistant cultivars remain the most sustainable approach to manage this disease; however, resistance sources in cultivated germplasm are scarce. The present investigation aimed to evaluate the reaction of fifty red chilli genotypes against C. truncatum under controlled in vitro conditions. Screening was carried out using the standard detached fruit assay, wherein healthy, mature green fruits were surface sterilized, inoculated with a conidial suspension of a virulent isolate (1 × 10⁶ conidia/mL), and incubated under high humidity (≥90%) at 27 ± 1 °C for seven days. Disease severity was recorded from two replications, and Percent Disease Index (PDI) was calculated to categorize genotypes into five disease reaction classes: Immune (I), Resistant (R), Moderately Resistant (MR), Susceptible (S), and Highly Susceptible (HS). Results indicated significant variability among genotypes, with mean PDI values ranging from 16.50% (BKS-40) to 93.00% (BKS-27). None of the genotypes exhibited immune or resistant reactions. Five genotypes (BKS-04, BKS-09, BKS-16, BKS-25, BKS-40) were identified as moderately resistant (PDI ≤ 25%), twenty-one were classified as susceptible (26-50% PDI), and twenty-four were found highly susceptible (>50% PDI). The predominance of susceptible and highly susceptible genotypes highlights the narrow genetic base for fruit rot resistance in cultivated chilli. The moderately resistant genotypes identified in this study represent valuable genetic resources and may serve as donors in future breeding programs aimed at developing fruit rot tolerant cultivars.