Abstract
Gray mold and soft rot are the most important postharvest diseases of tomato worldwide. A survey of fresh-market tomato fruit was conducted in Oahu to determine which fungal and bacterial pathogens were most commonly associated with postharvest disease. Alternaria, Botrytis, Colletotrichum, Fusarium, Geotrichum, Mucor, Stemphyllium, Rhizopus and Penicillium were the most frequently isolated fungi and Acetobacter, Gluconobacter, Klebsiella, Leuconostoc and Pectobacterium were the prevalent bacteria. Fifty-one percent of the diseased tomatoes had been imported from California and Mexico and 49% had been grown locally at three sites in Oahu. Pathogenicity tests revealed that 33 of 99 fungal isolates and 10 of 17 bacterial isolates were pathogenic on tomato types known as common market, cherry and grape tomato. Based on fruit assays, Botrytis cinerea (B03) and Pectobacterium carotovorum (BA17) were the most virulent isolates. Tested leaf extracts of Capsicum annuum cv. Stocky Red, C. annuum cv. Criolla de cocina, Capsicum chinense cv. NuMexsuave, Tagetes tenuifolia, Aloe vera, Origanum vulgare and Azadirachta indica were ineffective as biopesticides and did not reduce spore germination or mycelial growth of B. cinerea (B03) nor P. carotovorum (BA17). In contrast, a proprietary product (PF) reduced mycelial growth of B. cinerea (B03) and was further evaluated at doubling concentrations ranging from 0.0625 to 1 ml/L. Mycelial growth of B. cinerea and other fungi was completely inhibited by exposure to PF at 1 ml/L. On the other hand, PF was not an effective biopesticides against P. carotovorum. PF shows promise for reducing gray mold and will be evaluated as a preharvest spray on tomato plants in the greenhouse. Key words: Survey, postharvest diseases, tomato, natural product, Botrytis cinerea, Pectobacterium carotovorum.
Highlights
Public concern about fungicide residues on raw fruits and vegetables has stimulated research efforts using natural products to reduce incidence of postharvest diseases
A survey of fresh-market tomato fruit was conducted in Oahu to determine which fungal and bacterial pathogens were most commonly associated with postharvest disease
NuMexsuave, Tagetes tenuifolia, Aloe vera, Origanum vulgare and Azadirachta indica were ineffective as biopesticides and did not reduce spore germination or mycelial growth of B. cinerea (B03) nor P. carotovorum (BA17)
Summary
Public concern about fungicide residues on raw fruits and vegetables has stimulated research efforts using natural products to reduce incidence of postharvest diseases. 25 and 38% of harvested fruits and vegetables, respectively, are lost to postharvest spoilage in the U.S and global markets (Kantor et al, 1997). The first objective of this work was to determine the most serious postharvest diseases of tomato in Oahu and to identify the most virulent pathogens associated with each disease. The second objective was to evaluate natural products for biopesticidal activity against pathogenic fungi and bacteria associated with tomato postharvest diseases
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