Screening for Resistance to Tomato Fruitworm and Cabbage Looper among Tomato Accessions
Sinha, N. K. | McLaren, D. G.
Tomato fruitworm (Heliothis zea Boddie) and cabbage looper (Trichoplusia ni, Hübner) are two destructive insect pests of the cultivated tomato (Lycopersicon esculentum Mill.). The present investigation was conducted to screen wild (L. Hirsutum Hump and Bonpl., L. hirsutum f. glabratum Mull.) and cultivated tomato accessions for resistance to larvae of these insects, and to evaluate accession by environment (greenhouse vs. field grown plants), and by insect pest (polyphagous H. zea, vs. oligophagous T. ni) interactions for resistance. A petri dish bioassay technique was used, with larval survival on fresh foliage measured every 24 h over a 96-h period. Mean number of larvae surviving 96 h was taken as a measure of susceptibility of an accession. Number of accessions screened for resistance to H. zea and T. ni were 38 and 33, respectively. Mean larval survival on L. esculentum cultivars ranged from 32 to 52% for H. zea and from 25 to 76% for T. ni. In contrast, six field and three greenhouse grown wild accessions had less than 10% survival of H. zea larvae after 96 h. With few exceptions, all wild accessions were resistant to T. ni, with few or no larvae surviving 96 h. More than 50% of larval mortality occurred in the first 24 h, suggesting the toxic action of phytochemicals as a likely mechanism of insect resistance. Accession by plant growth environment and accession by insect species interactions were both significant. In conclusion, resistance of tomato foliage to insect pest larvae was shown, using a petri dish bioassay procedure, to differ significantly with plant genotype, insect species, and the plant growth environment.
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