Fruit infection and postharvest decay of greenhouse tomatoes caused by Penicillium species in British Columbia

Abstract

A previously undescribed spotting of tomato fruit was observed in the packinghouse and storage facility of a commercial organic grower in the Fraser Valley of British Columbia during 2009–2011. Symptoms initially appeared as small black spots on the tomato fruit, barely visible after harvest. The black spots expanded to form larger grey-black lesions with evidence of mycelial growth in the centre after 5–10 days of storage at 12 °C or after tomatoes were shipped to retail outlets. Isolations from symptomatic skin and pericarp tissues from early and expanded lesions primarily yielded species of Penicillium. Healthy tomato fruit inoculated with conidia of Penicillium isolates developed black spots which progressed to form larger grey lesions, typical of symptoms observed in the commercial greenhouse. Several Penicillium species were identified using morphological characteristics and DNA sequencing of the ITS region and partial β-tubulin gene. Isolates identified as P. olsonii produced the characteristic spotting of fruit followed by expanding lesions, while other isolates identified as P. solitum and P. polonicum caused a rapid soft rot and decay. Ripe fruit inoculated with P. olsonii had a significantly higher disease severity index compared with those that were inoculated at the breaker or flush stages. Inoculations on the tomato shoulder resulted in significantly higher disease severity than inoculations at the middle or base of the fruit. Swabs of tomato fruit surfaces and calyx tissues taken while fruit were still on the vine followed by plating onto PDA revealed that high populations (>40 CFU) of resident P. olsonii were present on the fruit. Similar populations were detected when calyx tissues were plated directly onto PDA. The mode of entry of P. olsonii is likely through naturally occurring cracks or russeting of the fruit cuticle from resident populations. Wounding of the skin did not significantly enhance disease severity compared with unwounded treatments. Disease severity increased significantly when tomatoes were incubated at 12 °C compared with 22 °C following inoculation. This appears to be the first report of a fruit spotting and post-harvest decay of tomato fruit caused by P. olsonii.