Resistance of two accessions of Lycopersicon hirsutum f. glabratum C. H. Mull to apterous forms of the pink potato aphid, Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae)
Abstract
Potato aphid, Macrosiphum euphorbiae (Thomas), populations under field and greenhouse conditions were significantly lower on plants of Lycopersicon hirsutum f. glabratum C. H. Mull, accessions PI 126449 and PI 134417, than on L. esculentum. Density and type of glandular trichomes varied among plant lines and between abaxial and adaxial leaf surfaces within a line, particularly for the L. hirsutum f. glabratum plants. Removal of trichome glands and exudates by wiping the leaf surface with a moistened cotton swab resulted in significant decrease in mortality of aphids confined in clip cages. Aphid behavior on L. hirsutum f. glabratum plants was characterized by abandonment, delay in time for first probe, reduction of number and duration of probes and decrease in the total proportion of time probing, when compared to L. esculentum. Removal of the trichomes reduced the percentage of abandonment and increased the total proportion of time probing. Volatiles in leaf extracts of L. hirsutum f. glabratum and dichloromethane extract fractions from a silica gel column disrupted aphid settling, inducing restlessness. The major components in the active fractions were 2-tridecanone and 2-undecanone. Volatiles of synthetic 2-tridecanone produced similar behavioral responses. EC$\sb{50}$ for 2-tridecanone at 60 min was 227 $\mu$g/cage, while 2-undecanone concentrations up to 680 $\mu$g/cage did not elicit visible effects on aphids. Topical LD$\sb{50}$ for 2-tridecanone was 1.0 $\mu$g/aphid. Trichome exudates and 2-tridecanone applied to artificial membranes elicited feeding inhibition and toxicity. Type VI trichomes of PI 126449 and PI 134417 were confirmed as a major source of 2-tridecanone, with 9.9 and 14.6 ng/trichome head, respectively. No detectable levels of 2-tridecanone were found in L. esculentum Ohio.
Degree
Ph.D.
Advisors
Neal, Purdue University.
Subject Area
Entomology|Agronomy|Botany
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