Isolation and Characterisation of Microorganisms Associated with Rot Diseases of Fruit,Stem and Leaf of Carica papaya L.
Abstract:
Fruit, stem and leaf rot is a major constraint to Carica papaya production. Twenty-one papaya plant samples showing soft rot symptoms and comprising of fruits, stems and leaves were collected from the Covenant University Papaya Research Plantation for microbial investigation. The back, first layer after the back, inner layer and the seeds from four papaya fruits, as well as stems (4) and leaves (4), showing symptoms of sooty rot and white fluffy rot, were also analyzed. Following sample preparation and serial dilutions, three dilutions of each sample were plated out in duplicates on nutrient agar, potato dextrose agar and papaya fruit agar using the direct inoculation, streak, pour plate and spread plate methods. Pure cultures of each observed microorganism was purified using sub-culturing techniques, then cultural, microscopic and biochemical characteristics were used for identification of specific isolates. Koch’s postulates for the determination of the microbial etiology of diseases were used to determine the causal agent of the soft rot of papaya fruit. A total of ten microorganisms, Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus, Mucor spp, Penicillium spp, Alternaria spp, Colletotrichum gloeosporioides, Bacillus spp, Staphylococcus spp and Pseudomonas spp, belonging to five fungi and three bacteria genera were isolated. Papaya fruit agar supported the growth of A. niger, A. fumigatus, A. flavus, Mucor spp, Bacillus spp and Staphylococcus spp but not Pseudomonas spp. The most frequently isolated bacteria from the soft rot samples was Staphylococcus spp and was isolated from 85.7%, 42.9% and 71.4% of the fruits, stems and leaves respectively, while Pseudomonas spp was the least frequently isolated bacteria from all the plant parts. The most frequently isolated fungi from the soft rot fruits was Mucor spp while A. niger was the most frequently isolated from the stem (57.1 %) and leaf (42.9%). Colletotrichum gloeosporioides was isolated from the fruits, but not from the soft rot infected stems and leaves. The most frequently isolated bacteria from the sooty rot and white fluffy rot samples were Pseudomonas spp (75%) and Bacillus spp (62.5%) respectively, while Penicillium spp was the most frequently isolated fungus both from the sooty rot (56.3%) and white fluffy rot (43.8%) samples. Pathogenicity tests presumptively identified Mucor spp as the most important pathogen associated with soft rot of papaya fruit.ORDER COMPLETE MATERIAL (CHAPTER 1-5)
