RESISTANCE OF WHITE-FLOWERED GOURD TO SWEET-POTATO WHITEFLY

Confined-leaf tests in a greenhouse showed Lagenaria siceraria (Molina) Standley plant introduction (PI) 442369 was as susceptible to sweetpotato whitefly, Bemisia tabaci Gennadius, oviposition as Cucumis melo L., Cucurbita ecuadorensis Cutler and Whitaker, and Cucurbita lundelliana Bailey, whereas L. siceraria accessions PI 419090, PI 419215, PI 432341, and PI 432342 were resistant. Resistance rankings of L. siceraria accessions based on adult counts in greenhouse and field tests were similar. Adult entrapment among trichomes was highest on adaxial leaf surfaces of L. siceraria PI 419090. Abaxial leaf trichome density was 48.7/mm2 on sweetpotato whitefly-resistant L. siceraria PI 432342, 42.1/mm2 on Cucurbita lundelliana PI 540895, and ranged from 51.0 to 85.5/mm2 on Cucurbita ecuadorensis PI 540896. Leaf trichome densities of selected plants of four L. siceraria accessions ranged from 33.0 to 52/mm2 on the abaxial and from 6.3 to 20.8/mm2 on the adaxial surface. Scanning electron micrographs of the abaxial leaf surface, the preferred surface for oviposition, suggest that trichome configuration (density and arrangement of different lengths) could be a factor in reduction of whitefly oviposition on L. siceraria.