Disease Note.

Phytophthora Blight of Squash Caused by Phytophthora capsici in Arkansas. L. A. Wasilwa, Departments of Plant Pathology and Horticulture, University of Arkansas, Fayetteville 72701.. J. C. Correll, and T. E. Morelock, Departments of Plant Pathology and Horticulture, University of Arkansas, Fayetteville 72701. Plant Dis. 79:1188. Accepted for publication 21 August 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1188A.

Phytophthora blight was observed on the squash (Cucurbita maxima L.) cultivar Northrup King 530, in Crawford County, Ark., in 1994. The disease appeared after rainfall in excess of 25 cm during the month of July and resulted in the total loss of a 16-ha commercial squash field. Field symptoms included water-soaked lesions covered with white, cottony mycelium on the fruit, blight of leaves resulting in complete defoliation, and collapse of stems. Symptomatic tissue samples were collected on 28 July. The majority of (he plant samples yielded a Phytophthora sp. upon isolation. A representative isolate was examined in detail. The Phytophthora isolate produced papillate sporangia (some with multiple papilla), formed chlamydospores and hyphal swellings, and did not produce oospores. The isolate was identified as Phytophthora capsici Leonian. Inoculations were performed on fruit and squash seedlings of Northrup King 530 and 580. Squash fruit were inoculated by inserting an 8-mm plug of P. capsid growing on V8 agar into a wound. The fruit were incubated in a plastic bag and kept at 100% relative humidity. Plants with two true leaves also were sprayed to runoff with a zoospore suspension (1 x 106 zoospores per ml). After inoculation, the plants were incubated for 24 h in a dew chamber at 24°C, at 100% relative humidity. Less than 24 h after inoculation, leaf and petiole blight was observed. Lesions also were observed on the stems, resulting in a complete collapse of plants. Water-soaked lesions and white, cottony mycelium were observed on fruit 3 days after inoculation. Phytophthora capsid was reisolated from leaves, stems, and fruit. Similar disease symptoms have been reported on summer squash in North Carolina (1).