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M. Marutani, L. Yudin, D. Nafus, F. Cruz, and V. Santos

The outbreak of a new whitefly was first reported in Summer 1993 at two sites in the southern part of Guam. Vegetable crops heavily damaged by this pest included cucumber, yardlong beans, and tomato. At present, the whitefly is found infesting tomato, eggplants, cucumbers, watermelon, and other vegetable crops throughout the island. The whitefly was identified as Bemisia argentifolii with the characteristics of a wide host range and the presence of silvering leaves on cucurbits. A larval parasitoid was recovered from eggplant and tomato leaves. The efficacy of pesticides against the pest is being investigated.

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V. Cruz, J. Cuartero, M.C. Bolarin, and M. Romero

Plant height; stem thickness; fresh and dry weights of leaves and stems; numbers of leaves, trusses, flowers, and fruits; and leaf concentrations of Cl, Na, N-NO3, K, Ca, and Mg were measured in mature plants from 39 tomato accessions representing five species of Lycopersicon [L. esculentum Mill., L. peruvianum (L.) Mill., L. pimpinellifoliurn (Jusl.) Mill., L. hirsutum H. & B., L. pennellii (Corr.) D'Arcy] in response to various NaCl concentrations. Plants were irrigated with a nutrient solution, plus one of four levels of NaCl with electrical conductivities of 0.28, 0.63, 1.39, and 2.15 S·m-1. Characters were evaluated for each genotype taking into consideration: 1) the significant differences between NaCl concentrations, 2) the experimental errors in the analyses of variance, and 3) the uniformity of response to the salt concentrations. The characters that fulfilled these criteria for all 39 genotypes were: plant height, dry weights of leaves, fresh and dry weights of stems, and leaf concentrations of Cl and Na. However, other characters, although not generally applicable to the entire data set, were good indicators of response differences within a particular species. Leaf concentrations of N-NO3 and Mg were useful indicators in L. pimpinellifolium and L. esculentum and number of leaves and leaf concentration of Mg were useful indicators in L. hirsutum for responses of mature plants to salt stress.

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M.C. Bolarín, F.G. Fernández, V. Cruz, and J. Cuartero

The salinity tolerances of 21 accessions belonging to four wild tomato species [Lycopersicon pimpinellifolium (Jusl.) Mill., L. peruvianum (Corr.) D'Arcy, L. hirsutum (L.) Mill., and L. pennellii Humb. Bonpl.) were evaluated using their vegetative yield-salinity response curves at the adult stage, determined by a piecewise-linear response model. The slope (yield decrease per unit salinity increase), salinity response threshold, maximum electrical conductivity without yield reduction (ECo), and salinity level for which yield would be zero (ECo) were determined by a nonlinear least-squares inversion method from curves based on the response of leaf and stem dry weights to substrate EC. The genotype PE-2 (L. pimpinellifolium) had the highest salt tolerance, followed by PE-45 (L. pennellii), PE-34, PE-43 (L. hirsutum), and PE-16 (L. peruvianum). The model also was tested replacing substrate salinity levels with leaf Cl- or Na+ concentrations. Concentrations of both ions for which vegetative yields were zero (Clo and Nao) were determined from the response curves. In general, the most tolerant genotypes were those with the highest Clo and Nao values, suggesting that the dominant salt-tolerance mechanism is ion accumulation, but there were cases in which salt tolerance was not related to Clo and Nao.