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First Report of Blight of Field Peppers Caused by Phytophthora capsici in Ontario

In August 1994, a disease of sweet peppers (Capsicum annuum L.) and butternut squash (Cucurbita pepo L.) was observed in a 2-ha field near Harrow, Essex County, ON, Canada. In 1995, a similar disease was noted on peppers at two locations 30 km apart in Essex County. In 1997, the disease occurred on peppers in a 20-ha field in the vicinity of the 1994 outbreak. Yield loss was estimated at 40 to 60% in pepper fields and 20% in the affected squash field. Brown, necrotic lesions were more prevalent on pepper fruits and upper stems and lateral branches than basal stems. Affected plants occurred in lower areas of fields that had been flooded by rain or irrigation. Gray, floccose masses of sporangia were evident on fruits and stems under humid conditions and on the internal surfaces of infected fruits. Symptoms were similar to those described for Phytophthora blight of pepper (1). Squash infections occurred where fruits contacted soil. Isolations were made from sections of fruit, stems, and leaves of pepper and squash plants with symptoms of disease on lima beans (Difco Laboratories, Detroit) or 20% V8 agar medium and incubated at 22°C. Phytophthora capsici was readily isolated from all plants with disease symptoms. Observations of colony morphology and growth were made on cultures on 20% V8 agar at 25°C under continuous fluorescent light. Sporangia were papillate and averaged 45 ± 5.9 × 27 ± 3.5 μm in size (range 28 to 58 × 21 × 39 μm). Oospores were spherical and 23 ± 2.9 μm in diameter (range 16 to 28 μm) and, when the external wall was included, were 28 ±2.7 μm in diameter (range 23 to 37 μm). Pedicels varied in length, averaging 63 ± 30.9 μm (range 9 to 129 μm). These observations are similar to those described for P. capsici (2). Mating type was determined by coculture with isolates obtained from A. F. Schmitthenner (OARDC, Wooster, OH) designated A1 and A2. Oospore development was determined after 10 days growth at 25°C on 20% V8 agar. Mating types A1 and A2 occurred among Ontario isolates from pepper and squash. In 1995, 13 of 15 isolates tested were A1, and in 1997, 1 of 5 was A1. Both mating types were found in the same field. Pathogenicity of pepper and squash isolates was tested by inoculating greenhouse-grown pepper cvs. Merlin and North Star at the 5-leaf stage by adding 5 ml of a spore suspension (1,000 sporangia per ml) to the crown and adjacent soil or sprayed on the foliage until run off. Plants were covered in plastic bags for 24 h. Wilting and plant death occurred at 4 and 10 days, respectively, with both cultivars. Crown-inoculated plants wilted prior to development of brown lesions on lower stems at the soil line. Symptoms on foliar-inoculated plants were first observed on young tissue at growing points and stem nodes. P. capsici was reisolated from affected tissue. This is the first report of Phytophthora blight of sweet pepper in Ontario.

References: (1) L. H. Leonian. Phytopathology 12:401, 1922. (2) P. H. Tsao and A. Alizadeh. 1988. Proceedings of the 10th International Cocoa Research Conference. Santo Domingo, Dominican Republic, pp. 441--445.