Effect of irradiated chitosan treatment on storage life of fruits of two commercially grown papaya (Carica papaya L.) varieties

Potential use of gamma irradiated chitosan for control of the anthracnose disease causing organism, Colletotrichum gloeosporioides, and extension of storage life of papaya varieties Rathna and Red Lady were investigated. Chitin extracted from shrimp waste was converted into chitosan and used as an antifungal treatment against fungal strains isolated from both papaya varieties. Chitosan in powder form and as 1% solution were irradiated with different doses -5, 10, 25, 50, 75, 100 and 150 kGy of Co-60 gamma rays-in order to enhance antifungal activity. The effective irradiation dose for the inhibition of radial mycelial growth of respective fungal strains was selected via a series of in vitro experiments using potato dextrose agar (PDA). A complete inhibition of growth in both fungal strains was observed on PDA plates incorporated with 1% chitosan solution at all irradiated doses compared to the control (distilled water). The plates incorporated with non-irradiated chitosan (0 KGy) and inoculated with the fungus isolated from Red Lady papaya showed slight mycelial growth while Ratna isolate showed complete inhibition of growth with this treatment. However, irradiated chitosan powder was found to be less effective in inhibiting in vitro growth of both fungal strains, 1% chitosan solution (in 10% acetic acid) irradiated at the lowest dose (5 kGy) was selected for in vivo experiments on storage life extension of papaya fruits. Eighty percent marketable quality fruits were observed in Rathna papaya while 70% marketable quality fruits were observed in Red Lady subjected to irradiated chitosan treatment and stored at 13.5 degrees C, 95% RH for 14 days followed by 2 days at ambient temperatre (28 degrees C +/- 2).