In the summer of 2001, a fruit rot of orange sweet peppers (Capsicum annum L. cv. Sympathy MZ) was observed in commercial greenhouses in British Columbia, Canada. According to the grower's estimate, approximately 40% of fruits in the commercial greenhouse were severely affected in the year 2001 and approximately 10% in 2002. The disease appeared on mature fruits at harvest time, and affected fruits are considered as culls. The disease appeared as discolored soft patches or necrotic spots predominantly at the calyx end and occasionally, anywhere on the mature fruit at harvest time. Seeds and the surrounding area inside the fruits were covered with fungal growth and orange-pink spore masses. Five fungal isolations were made from the lesions. Infected tissues from the edge of lesions were surface sterilized in 1% sodium hypochlorite for 2 min, blotted dry on sterile filter paper, and cultured on potato dextrose agar (PDA). Plates were incubated at 22°C for 7 days. Single spore fungal colonies isolated from the tissues yielded Fusarium sp. Only one fungal species was consistently isolated from affected pepper fruits. Morphology of the fungus was consistent with Fusarium subglutinans (Wollenweber & Reinking) Nelson et al. according to Keith Seifert of Eastern Cereal and Oilseed Research Centre, Ottawa, Canada. Molecular tests are being developed to confirm the identification of the fungus. To confirm pathogenicity, 10 flowers and developing fruits of sweet pepper cv. Sympathy MZ grown in a greenhouse were inoculated with the pathogen. For inoculation, 20 μl of spore suspension of the fungus (concentration 106 spores/ml) was drop-inoculated on the wounded and unwounded surfaces of fruits. To inoculate flowers, a spore suspension was drop-inoculated in the middle of flowers without any wounding. Controls were treated with 20 μl of sterile water. The experiment was repeated once. Approximately 80% of inoculated fruits and flowers developed symptoms on fruits similar to naturally infected fruits at maturity. Fruits from control plants did not develop any disease. On PDA, a Fusarium species identical to the original one was recovered from all inoculated infected fruits. A preliminary study showed that this pathogen does not infect other greenhouse crops such as tomato, cucumber, or lettuce. Sweet pepper stem and fruit rot caused by Fusarium solan has been reported previously (1) but there is no report of fruit rot caused by a Fusarium subglutinans-like species on greenhouse sweet peppers.
Reference: (1) J. G. Menzies and W. R. Jarvis. Fusarium stem and fruit rot. Pages 333--334 in: Diseases and Pests of Vegetable Crops in Canada. R. J. Howard et al. eds. The Canadian Phytopathological Society and Entomological Society of Canada, 1994.
