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Variation for Insect Resistance and Horticultural Traits in Tomato Inbred Backcross Populations Derived from Lycopersicon pennellii

East and Southern Africa Regional Center (IITA-ESARC), Kampala, Uganda
Dep. of Vegetable Crops, One Shield Ave., Univ. of California, Davis, CA 95616-8746 USA

^* Corresponding author (dastclair{at}ucdavis.edu).

Insect resistant accessions of wild Lycopersicon species were identified long ago, yet insect resistance has not been successfully introgressed into tomato cultivars. The effectiveness of the inbred backcross method for introgressing resistance to beet armyworm (Spodoptera exigua Hübner), tomato fruitworm (Helicoverpa zea Boddie), and potato aphid (Macrosiphum euphorbiae Thomas) from the resistant Lycopersicon pennellii (Corr) D'Arcy acc. ‘LA 716’ into Lycopersicon esculentum Mill. ‘Peto 95’ was examined. Inbred backcross populations at two backcross levels (BC₂ and BC₃) were developed and tested at two levels of selfing over 2 yr (i.e., $3 in 1994 and $4 in 1995) for resistance in no-choice egg-inoculated field assays to beet armyworm and tomato fruitworm and to natural populations of potato aphid. Variation among inbred backcross lines (IBL) in the amount of fruit damage from beet armyworm and tomato fruitworm and the proportion of potato aphid infested plants was observed. Significant line x year interactions suggest that genotype x environment effects may be important to beet armyworm and tomato fruitworm resistance. Differences between observed and predicted gain in beet armyworm and tomato fruitworm resistance of post hoc selected IBL were found, which might be attributed to underestimation of genotype x environment effects, or to non-additive genetic effects. Large genetic correlations (r²_g) between reduced fruit damage and later maturity, lower fruit yield, and smaller fruit mass were estimated. The inbred backcross method was used to successfully introgress insect resistance from L. esculentum to cultivated tomato, but the development of commercially acceptable cultivars will require further cycles of breeding.

Received for publication October 21, 1997.