Role of fruit surface mycoflora, wounding and storage conditions on post-harvest disease development on greenhouse tomatoes

Fungi causing post-harvest decay of greenhouse-grown tomato fruits in British Columbia were recovered from diseased samples collected during 2010 and 2011. The most frequently isolated fungi were Penicillium olsonii, Botrytis cinerea, Rhizopus stolonifer and Alternaria alternata, and to a lesser extent Galactomyces geotrichum. Pathogenicity tests showed that R. stolonifer caused the greatest fruit decay, followed by P. olsonii. The remaining fungi also caused some fruit rot, and lesion development by all fungi was enhanced by wounding of the fruits. A post-inoculation incubation temperature of 21 degrees C promoted much greater disease development compared with 13 degrees C. To assess the composition of the mycoflora on the surface of ripening tomato fruits, swab samples were collected weekly over a 6-18 week period from two commercial greenhouses during 2011 and 2012 and streaked onto potato dextrose agar. The most commonly recovered fungi from the fruit surfaces were species of Penicillium, Cladosporium, Aspergillus, Rhizopus and Alternaria. The composition of fungal populations fluctuated from one week to the next in both greenhouses and over both years. Samples of leaf litter consisting of discarded leaf prunings harboured all of these fungi that were present on the fruit surface. Harvested fruit samples were subsequently incubated at 21 degrees C to assess the level of disease development. The resulting fruit decay was caused primarily by species of Penicillium, Alternaria and Rhizopus, and a major source of inoculum originated from the stem and calyx tissues, which led to fruit infection near the stem end. Shipments of tomato fruits in refrigerated trucks were monitored over a 6-10 day period after harvest and showed variable temperature and humidity levels during transportation. Post-harvest decay of tomatoes is influenced by the composition of the fruit surface mycoflora, presence of fruit injury, storage temperatures and environmental conditions during shipping.