ANTIBIOSIS TO BEET ARMYWORM (SPODOPTERA-EXIGUA) IN LYCOPERSICON ACCESSIONS

Four accessions of Lycopersicon hirsutum f. glabratum Mull. and eight accessions of L. hirsutum f. typicum Humb. & Bonpl. were evaluated for their resistance to the beet armyworm [Spodoptera exigua (Hubner)]. Survival of S. exigua neonate larvae for up to 96 hours on foliage of all these accessions differed significantly from their survival on a susceptible tomato cultivar. Spodoptera exigua survival did not differ significantly between the two forms of L. hirsutum. Antibiosis to S. exigua in L. hirsutum f. glabratum appears similar to the levels found to other Lepidoptera. Accessions of L. hirsutum f. typicum included the very susceptible PI 199381 and the two most resistant accessions, LA 2329 and LA 1777. Insect resistance had not been reported previously in four of the L. hirsutum f. typicum accessions. Spodoptera exigua survival was significantly negatively correlated with the density of type IV glandular trichomes on the leaf surfaces, calculated across all 12 accessions. This relationship did not occur within L. hirsutum f. glabratum or L. hirsutum f. typicum accessions, nor was it significant if PI 199381 was excluded from the analysis. Leaf-surface exudates of L. hirsutum f. glabratum accessions were dominated by the methylketones 2-undecanone and 2-tridecanone. Leaf-surface exudates of L. hirsutum f. typicum were dominated by three sesquiterpenes-zingiberene, delta-elemene, and gamma-elemene. Resistance was not correlated with the amounts of these specific compounds within or across botanical form. Spodoptera exigua survival in L. hirsutum f. typicum (excluding PI 199381) correlated negatively with the total estimated amount of leaf-surface volatiles extracted. PI 199381 may be useful as a susceptible parent for intraspecific crosses to examine S. exigua resistance in L. hirsutum.