Disease Note.

First Report of Squash Leaf Curl Virus on Watermelon in Texas. T. Isakeit, Department of Plant Pathology and Microbiology, Texas A&M University, Weslaco 78596, and College Station 77843. N. L. Robertson, Department of Plant Pathology and Microbiology, Texas A&M University, Weslaco 78596, and College Station 77843. Plant Dis. 78:1010. Accepted for publication 14 July 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1010D.

In fall 1993, watermelon plants (Citrullus lanatus (Thunb.) Matsum. & Nakai) from all of 24 fields surveyed in eight south Texas counties exhibited curled, blistered, yellowed, mottled leaves and small, deformed fruit. Disease incidence ranged from 75 to 100%, and yield losses were 30-100%. The disease was associated with whitefly (B biotype of Bemisia tabaci (Gennadius), syn. B. argentifolii Bellows & Perring) infestation. Geminiviral nucleic acids were detected from symptomatic leaves in nine of 18 plants by squash blot hybridization analysis with a general DNA probe for whitefly-transmitted geminiviruses. No other viruses were detected in these plants by electron microscopy or PAGE analysis of viral minipurification extractions. Geminivirus DNA-A component fragments were amplified by PCR with degenerate primers and sequenced. A DNA fragment (450 bp) from a conserved region of the coat protein gene was 95 and 98% identical to fragments of two isolates of squash leaf curl virus (SLCV) from California (D) and Arizona (AZ), respectively. The common region sequence (determined from a 1.1 kbp DNA-A fragment) was 94% identical to that of a different California SLCV isolate (#490-4). Total nucleic acids isolated from diseased leaves were treated with RNase and inoculated into zucchini squash (Cucurbita pepo L. var. melopepo (L ) Alef.) and pumpkin (C. pepo var. pepo) plants using a particle delivery system. Typical SLCV symptoms developed in both hosts after 9 days. Adult whiteflies were allowed to feed on symptomatic plants for 24 hr followed by a 48-hr inoculation access period on pumpkin seedlings. Typical SLCV symptoms developed in these plants 9-10 days later. This is the first report of a whitefly-transmitted geminivirus infecting cucurbits in Texas.