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Chlorotic Streak of Bell Pepper: A New Toxicogenic Disorder Induced by Feeding of the Silverleaf Whitefly, Bemisia argentifolii . C. G. Summers, Department of Entomology, University of California, Davis 95616. D. Estrada, Department of Entomology, University of California, Davis 95616. Plant Dis. 80:822. Accepted for publication 6 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0822A.

Feeding by the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, causes toxicogenic disorders such as irregular ripening of tomato, stem blanching of Brassica spp., and silverleaf of squash, Cucur-bita spp. (2,3,4). These disorders are thought to be induced by a translo-catable toxicogenic product or a plant material (2,4). During the summer of 1994, we observed chlorotic streaking on fruit harvested from bell pepper, Capsicum annuum L., plants heavily infested with B. argentifolii nymphs, but not from uninfested plants. To determine whether B. argentifolii feeding induced the chlorotic streaking, we exposed 40 12-week-old bell pepper plants, cv. Jupiter, grown in 15-cm-diameter pots in the greenhouse, to silverleaf whiteflies reared on zucchini squash plants, C. pepo L., and known to cause silverleaf symptoms. Aldicarb (0.625 g a.i./pot) was added to 20 pots (treated) and watered in 1 week before exposure to the whiteflies. No aldicarb was added to (he other 20 pots (controls). Whitefly densities were recorded as the number of nymphs present on 3.6 cm2 disks cut with a #14 cork borer from 1 fully expanded leaf from each plant. Sampling began 1 week after initial exposure and continued weekly for 6 weeks. Whitefly densities over (he 6 weeks averaged 0.3 and 17.7 nymphs/cm2 of leaf surface in the treated and control plants, respectively. Counts of adults were not made because feeding by adults did not induce toxicogenic disorders in other vegetables (1,2). Fruit from all 20 whitefly-infested plants developed longitudinal chlorotic streaks approximately 2 to 3 mm wide alternating with darker green streaks of similar size. Fruit from infested plants had a lighter overall green color than did fruit from the uninfested plants. No chlorotic streaking was observed on fruit from the uninfested plants and the fruit was uniformly dark green All fruit, flowers, and buds were removed from the 20 originally infested control plants, and 0.625 g a.i./pot of aldicarb was added to each pot and incorporated by watering. Leaf disk samples were taken 1 week later as described above, and all whitefly nymphs originally present on the leaves of these plants had been killed. Whitefly densities over the next 6 weeks (sampled as described above) averaged 0.2 nymphs/cm2 of leaf surface. Fruit harvested from these plants showed no symptoms of chlorotic streaking and were uniformly dark green. The production of nonsymptomatic fruit following the removal of whitefly nymphs is characteristic of a toxicogenic disorder rather than a pathogenic relationship (2,4). The number of silverleaf whitefly nymphs per unit area (cm2 or leaf) or the length of feeding time necessary to incite this disorder is not currently known

References: (1) H. S. Costa et al. Phytopathology 83:763, 1993. (2) H. S. Costa el al. Plant Dis. 77:969, 1993. (3) D. J. Schuster et al. HortScience 25:1618. 1990. (4) R. K. Yokomi et al. Phytopathology 80:895, 1990.