Incidence of Alternaria Fruit Rot as a Latent Postharvest Disease in Guava (Psidium guajava L.) in Kerala

A purposive random sampling survey was conducted to study the incidence of latent pathogens associated with postharvest losses in guava sourced from markets and homesteads of Ernakulam, Thrissur and Palakkad districts of Kerala during 2024. Fruits at mature green stage were collected, surface sterilized and incubated at room temperature for symptom development. After three to five days of incubation, few of the fruits collected from Thrissur district started development of dry brown lesions. The disease developed under high humidity and temperature between 30 and 35 °C. Four isolates of Alternaria sp. were isolated from the fruits. The highest disease incidence recorded was 75 % from Vettikkal while the highest severity of 20 % was recorded in fruits collected from Shakthan Market. The isolated pathogen appeared white to grey coloured, submerged to aerial mycelia which showed uniform and zonal growth at regular intervals. The isolates exhibited an average growth rate of 0.6-0.9 cm per day. The hyphae were brown-coloured, septate with straight or curved, geniculate, pale brown conidiophores bearing a branched chain of conidia. The conidia were brown, obclavate in shape with 3-4 transverse and 1-2 longitudinal septa having average size of 22.08 to 29.53 × 7.85 to 12.54 µm. Molecular characterization using ITS primers followed by sequence analysis in the NCBI database, identified the pathogen as Alternaria alternata.