Variation in tomato host response to Bemisia tabaci (Hemiptera : Aleyrodidae) in relation to acyl sugar content and presence of the nematode and potato aphid resistance gene Mi

Two commercial cultivars of tomato, Alta and Peto 95, the accession line nu mber LA716 of Lycopersicon pennellii and lines 94GH-006 and 94GH-033 (backc rosses between Peto 95 and LA716), with different leaf acyl sugar contents were screened for resistance to Bemisia argentifolii Bellows & Perring (cor responding to the Spanish B-biotype of Bemisia tabaci (Gennadius)), in gree nhouse- and field-no-choice experiments. There was no oviposition on LA716 (with the highest acyl sugar content) while the greatest fecundity and fert ility values were observed on the cultivar Alta (no acyl sugar content). Ho wever, no clear relationship was found between the low acyl sugar content i n the other tomato cultivars tested and whitefly reproduction. Thus, resist ance to B. tabaci did not appear to correlate with acyl sugar content below a threshold level of 37.8 mu g cm(-2) leaf. In a greenhouse choice-assay, B. tabaci exhibited reduced host preference and reproduction on the commerc ial tomato cultivars Motelle, VFN8 and Ronita all of which carry the Mi gen e resistance to Meloidogyne nematodes and the aphid Macrosiphum euphorbiae (Thomas), than on the Mi-lacking cultivars Moneymaker, Rio Fuego and Roma. When data of Mi-bearing plants were pooled, the mean values for daily infes tation and pupal production of B. tabaci were significantly lower than thos e of Mi-lacking plants. This reflected a level of antixenosis- and antibios is-based resistance in commercial tomato and indicated that Mi, or another closely linked gene, might be implicated in a partial resistance which was not associated either with the presence of glandular trichomes or their exu dates. These findings support the general hypothesis for the existence of s imilarities among the resistance mechanisms to whiteflies, aphids and nemat odes in commercial tomato plants.