Development of Tomato Hybrids (Lycopersicon Esculentum x Lycopersicon Hirsutum f. Glabratum) resistant to Robacco Spider Mite (Tetranychus Evansi)

Abstract

This study revealed that the mite resistance in L. hirsutum is heritable in L. esculentum and therefore can be utilized to improve tomato production by breeding mite resistant varieties. Glandular trichomes type IV may be responsible for high levels of resistance in accession LA 2204 to T. evansi. The study was to initiate inter-specific crosses between Lycopersicon hirsutum f glabratum C.H. Mull accession LA 2204 and the cultivated tomato Lycopersicon esculentum Mill. variety "Money Maker", and evaluate their resistance to tobacco spider mite Tetranychus evansi Baker and Pritchard. Screening studies carried out earlier revealed that accession LA2204 is resistant, while "Money Maker" is susceptible to mite damage. Trichome types that were identified on the abaxial and adaxial surfaces of both parent tomato plants and F1, F2, BC1 and BC2 generations included types I, III, IV, V, VI and VII. Type II trichomes were completely absent on parents and the F 1, F2, BC1 and BC2 generations. Type IV trichomes were absent on L.esculentum "Money Maker'', while type V were absent on L. hirsutum accession LA 2204. The F1, F2, BC1 and BC2 generations possessed both type IV and V trichomes.Development from egg to adult and survival were significantly higher on "Money Maker" compared to LA 2204, and the F1, F2, BC1 and BC2 generations. Fecundity and longevity were significantly higher on "Money Maker" with average 57.9 eggs/mite and 13.1 days respectively compared to LA 2204, and the F1, F2, BC1 and BC2 generations.Repellence studies revealed that leaves of accession LA 2204 and F1, F2, generations were more repellant to T. evansi than those of "Money Maker Shorter distances were covered on leaf surfaces in 20, 40 and 60 minutes respectively;and fewer mites attracted to accession LA 2204 and F1, F2, BC1 and BC2 generations compared to "Money Maker" in thumbtack and slide bioassays. Greenhouse whole leaf bioassays showed that population densities of eggs/cm2 and motiles/cm2 leaf area were significantly higher on "Money Maker" than on Fi, F 2, BC 1 and BC2 generations and accession LA 2204 eighteen days after infestation.