Inheritance of potato aphid resistance in hybrids between Lycopersicon esculentum and L. pennellii

Abstract

The potato aphid, Macrosiphum euphorbiae Thomas, is an important pest of tomato, Lycopersicon esculentum Mill., because it transmits tomato viruses and directly reduces crop yields by its feeding. This study was conducted to determine whether the wild tomato species, Lycopersicon pennellii (Corr.) D'Arcy, would be useful as a source of potato aphid resistance for tomato. Type IV trichome density and aphid resistance were assessed in six generations (P1, P2, F1, F2, BC1P1, and BC1P2) from crosses between L. pennellii (LA 716) and two tomato cultivars, New Yorker and VF Vendor. Weighted leastsquares were used in joint scaling tests to estimate the relative importance of gene effects on type IV trichome density and potato aphid resistance of the hybrids. A simple additive-dominance model adequately explained the variation in type IV trichome density. Models which included digenic epistatic effects were required to explain the variation in aphid resistance. Standard unit heritability estimates of aphid resistance in the backcross to L. esculentum were obtained by regression of BC1F2 off-spring families on BC1F1 parents. Regression coefficients and heritability estimates varied between years with the level and uniformity of the aphid infestation. In the 1985-1986 growing seasons, when aphid infestations were uniform, aphid resistance exhibited a moderate level of heritability (29.8% ± 14.1% and 47.1% ± 11.5% in New Yorker and VF Vendor backcross populations, respectively). The non-uniform aphid infestation of 1984 resulted in lower heritability estimates in the 1984-1985 growing seasons (16.1% ± 15.7% and 21.9% ± 14.8% in the New Yorker and VF Vendor backcross populations, respectively). Selection for potato aphid resistance would probably be most efficient if it were delayed until gene combinations are fixed in later generations, because of the large epistatic effects and the low heritability of this trait in seasons with variable aphid infestations.

The nematode resistance geneMiof tomato confers resistance against the potato aphid

“…Studies of plant resistance against insects have centered mostly on chemical and morphological defenses (22)(23)(24)(25). General defenses that are induced by previous exposure to pests and are effective against broad categories of insects also have been well investigated (26,27).…”

An aphid-resistance locus is tightly linked to the nematode-resistance gene, Mi, in tomato.

“…Incorporation of the resistance into tomato has not yet been successful because of the complex inheritance of resistance (5). The resistance is attributed to the sugar esters present in the glandular exudates of type IV trichomes (6).…”

“…Plants homozygqus for each of the REX-1 alleles differed dramatically in number of aphids per leaflet (Fig. 1) (4,5,17). In contrast, the Mi-linked resistance that we describe is simply inherited, and we do not observe any obvious difference in trichomes between resistant and susceptible near-isogenic pairs (data not shown).…”

Host Plant Resistance for the Management of Bemisia tabaci: A Multi-crop Survey with Emphasis on Tomato

“…Similarly, leaf-trichome densities and presence of acyl sugars in the exudate of glandular trichomes as well as type of trichomes were reported to be important factors affecting whitefly-tomato relationships (Williams et al 1980;Kisha 1981;Berlinger 1986;Kishaba et al 1992;Simmons 1994;Freitas et al 2002;Baldin et al 2005;Srinivasan and Uthamasamy 2005;Simmons and Gurr 2005;Sanchez-Pena et al 2006). However, the actual effect of these, and other factors, on tomato resistance has been broadly questioned (Goffreda and Mutschler 1989;Steffens and Walters 1991;Liedl et al 1995;Toscano et al 2002a, b;Muigai et al 2003). Field resistance to B. tabaci was reported in different lines of the wild species L. peruvianum (L.) Mill (Hassan et al 1982;Channarayappa et al 1992), a close relative of commercial tomato, S. lycopersicum.…”