Plant Disease Research

Khasi mandarin, (Citrus reticulata Blanco.) is the most widely grown fruit crop in Arunachal Pradesh. Penicillium rot caused by Penicillium digitatum is one of the most economically important post harvest diseases of citrus causing up to 30–50% losses. Biocontrol organisms were isolated from the surface of healthy fruits identified and evaluated for their efficacy on controlling Penicllium digitatum at various concentrations. Biological control assays were performed at 25°C and 4°C and 90% R.H. ten khasi mandarin oranges were surface disinfected and wounded as described above. Each wound was treated with 30 µl of antagonists at 10⁷, 10⁸ or 10⁹ cfu.ml⁻¹. Controls were treated with the same volume of sterile distilled water. After 24 h, each wound was inoculated with 15 µl of Penicillium spore suspension at 10⁵ - 10⁶ conidia.ml⁻¹. Fruits were placed in carton boxes and stored at 4°C for 30 days followed by 7 days at room temperature (25^oC) and each experiment was repeated three times. After incubation period, wounds were examined and the percentage of incidence was determined. Among the biocontrol agents viz., Candida, Saccharomyces sp., Pseudomonas syringae, Bacillus subtilis and Pichia sp. the bacterial antagonist Pseudomonas syringae showed better performance in controlling post harvest rot. At 10⁹ cfu/ml, Pseudomonas showed only 87.5 per cent control over untreated.