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Ecology and Epidemiology

Insect Transmission of Pathogenic Xanthomonads to Bean and Cowpea in Puerto Rico. Walter J. Kaiser, Plant Pathologist, MayagŁez Institute of Tropical Agriculture, Agricultural Research Service, U.S. Department of Agriculture, MayagŁez, PR 00708, USA, Present address of senior author: East African Agriculture and Forestry Research Organization, P.O. Box 30148, Nairobi, Kenya; Nader G. Vakili, Plant Pathologist, MayagŁez Institute of Tropical Agriculture, Agricultural Research Service, U.S. Department of Agriculture, MayagŁez, PR 00708, USA. Phytopathology 68:1057-1063. Accepted for publication 29 November 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1057.

Bacterial blight lesions on beans (Phaseolus vulgaris) and cowpeas (Vigna unguiculata) frequently were associated with insect-feeding injuries. Three pathogenic xanthomonads, Xanthomonas phaseoli (Xp), X. phaseoli var. fuscans (Xpf), and X. phaseoli f. sp. vignicola (Xpv) (all members of the X. campestris group) were isolated from the washings of five leaf-feeding insect species, Cerotoma ruficornis, Chalcodermus ebeninus, Diaprepes abbreviata, Empoasca sp., and Nezara viridula collected from bacterial blight-infected bean plantings at Isabela, Puerto Rico. Pathogenicity tests with 51 pathogenic isolates from these insects indicated that 16 were either Xp or Xpf and 35 were Xpv. In controlled feeding trials, infection of caged bean and cowpea plants by pathogenic xanthomonads took place only at the feeding sites of naturally-infested C. ruficornis and D. abbreviata. Infection also resulted when four of the insect species (C. ebeninus was not tested) were artificially infested with different bacterial isolates. However, no infection occurred after 48 hr when C. ruficornis and D. abbreviata were infested and transferred at daily intervals to healthy test plants. Feeding injuries caused by Xpv-infested or noninfested D. abbreviata on noninoculated or inoculated bean leaves, respectively, greatly enhanced lesion development. Bean blight bacteria were isolated from fresh feces of C. ruficornis and D. abbreviata that had fed on infected bean leaves. Several xanthomonads survived for periods up to 19 days on the bodies of live and dead C. ruficornis and D. abbreviata.

Additional keywords: food legumes, tropics, vectors, strains.