Experiments were developed to study the mechanism and genetic nature of the tobacco hornworm [ Manduca sexta (L.)] resistance factor in the wild tomato ( Lycopersicon hirsutum f. glabratum C. H. Mull. L hirsutum f. glabratum PI 134417 was crossed with the susceptible tomato ( L. esculentum Mill. cv. Walter) (cross A) and the susceptible L. hirsutum Humb. & Bonpl. PI 127826 (cross B). Excised leaflets from individual plants of the parental, F 1 , F 2 , and backcross populations of each cross were bioassayed for M. sexta resistance, assayed for 2-tridecanone concentration using gas chromatography, and evaluated for density of the type VI trichome. Additionally, plants in the cross A populations were scored for morphological traits of the type VI trichome. Results of genetic analyses suggest that M. sexta resistance is conditioned by at least three recessive genes; high 2-tridecanone concentration was found to be inherited in a similar manner. No associations were found between type VI trichome morphology and the variables 2-tridecanone, type VI trichrome density, and tobacco hornworm resistance. Polynomial regression analysis showed that there is a semilogarithmic relationship between 2-tridecanone concentration and resistance ratings. Multiple linear regression analysis indicated that 2-tridecanone is principally responsible for the high degree of M. sexta resistance exhibited by PI 134417. Type VI trichome density, however, did account for a significant, although small, amount of the total variation in resistance in several of the segregating populations. We conclude that the genetic system that conditions high 2-tridecanone concentration (i.e., at least three recessive genes) is the same genetic system responsible for the high level of M. sexta resistance exhibited by PI 134417.
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Fery et al. (1987) studied this question.
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