Evaluation of Guava (Psidium guajava L.) Genotypes for Resistance to Phomopsis psidii Causing Stylar End Rot

Stylar end rot can affect guava fruit quality, and disease development may differ among genotypes and fruit developmental stages. The present study aimed to identify the fungus associated with stylar end rot, evaluate its pathogenicity and temperature requirements, and assess the response of seven guava genotypes at different fruit developmental stages. Diseased fruits were collected from Sabour, Bhagalpur, Bihar, and the associated fungus was isolated on potato dextrose agar (PDA). Cultural and morphological characteristics were examined, and pathogenicity was assessed on healthy guava fruits following Koch’s postulates. The effect of six temperatures (10, 15, 20, 25, 30 and 35 °C) on mycelial growth and colony characteristics was evaluated. Seven genotypes, namely Allahabad Safeda, Arka Kiran, Arka Mridula, CISH-1, GS-35, L-49 and VNR, were screened using 80- and 100-day-old fruits under laboratory conditions. Lesion development, incubation period and area under the lesion progress curve (AULPC) were assessed, and total soluble solids (TSS) and ascorbic acid content were evaluated to characterise fruit quality. The isolate produced characteristic disease symptoms following artificial inoculation and was successfully re-isolated from symptomatic fruits. Maximum mycelial growth was recorded at 25 and 30 °C, with a growth rate of 11.6 mm day⁻¹, whereas the minimum growth rate (1.0 mm day⁻¹) occurred at 35 °C. Genotype screening revealed differences in disease development between the two fruit ages. In 100-day-old fruits, Arka Kiran recorded the highest AULPC, while L-49, CISH-1 and GS-35 showed comparatively lower values. In 80-day-old fruits, VNR recorded the highest AULPC, whereas GS-35, CISH-1 and L-49 showed lower values. L-49 exhibited the longest incubation period (72 h) at both fruit ages, while VNR showed the shortest incubation period (24 h in 100-day-old fruits and 48 h in 80-day-old fruits). Overall, the findings demonstrated variation in temperature response and genotype susceptibility according to fruit developmental stage. GS-35, L-49 and CISH-1 were identified as promising candidates for further evaluation of reduced susceptibility to guava stylar end rot. Molecular confirmation of the pathogen and further field evaluation are required to validate these findings.