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Submitted to: Plant Genetic Resources
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/3/2014 Publication Date: 3/2/2015 Citation: Prasifka, J.R. 2015. Variation in the number of capitate glandular trichomes in wild and cultivated sunflower germplasm and potential for use in host plant resistance. Plant Genetic Resources. 13:68-74. Interpretive Summary: Glandular trichomes (= hairs) of wild sunflowers species are considered an effective defense against the larvae of the sunflower moth, but cultivated sunflowers reportedly have few glandular trichomes. To investigate whether glandular trichomes help protect cultivated sunflowers from insect pests, the number of glandular trichomes on wild and cultivated sunflowers were counted. Extracts from glandular trichomes of cultivated sunflowers were also tested for toxic effects against sunflower moth larvae, and survival of sunflower moth larvae was tested on cultivated sunflower lines with relatively low or high numbers of glandular trichomes. Glandular trichomes were often abundant in cultivated sunflower; relative to wild sunflowers, many inbred lines have as many glandular trichomes per floret, while, on average, commercial hybrids have just 20% fewer. Glandular trichome extracts increased death of sunflower moth larvae (exposed from hatch to 9 days). For larvae that survived to 9 days, extracts still reduced mass and head size. When plants were infested with sunflower moth eggs, survival of sunflower moth larvae was lower on a high glandular trichome line in one of two tests. Though glandular trichomes cannot completely protect plants from sunflower moth larvae, feeding deterrent or toxic effects of sunflower glandular trichome extracts suggests there is value for resistance to other sunflower pests. Additional research is needed to understand the inheritance and value of glandular trichomes in commercial sunflower inbreds and hybrids. Technical Abstract: Capitate glandular trichomes of wild sunflower (Helianthus spp.) are considered an effective defense against the sunflower moth, Homoeosoma electellum (Hulst), but cultivated sunflowers are reportedly deficient in glandular trichomes. To investigate whether glandular trichomes have a role in protecting cultivated sunflowers from insect pests, wild and cultivated Helianthus annuus L. were used to quantify glandular trichome density and assess potential antibiosis of terpenoids in cultivated sunflower. Evaluation revealed capitate glandular trichomes are often abundant in cultivated sunflower; relative to wild H. annuus, inbred maintainer (HA) lines have similar numbers of glandular trichomes per floret, while commercial hybrids show only ˜ 20% fewer. A laboratory assay using artificial diet treated with glandular trichome extracts increased mortality of H. electellum exposed from neonate to 9 d. For surviving H. electellum, extracts significantly reduced larval mass and head capsule width at 9 d, though a low dose of HA 89 (a low glandular trichome line) was similar to the untreated and solvent-only controls. When sunflowers were infested with H. electellum eggs, the mean number of larvae per head was significantly less in a high glandular trichome line in one of two trials. Though there are potential limitations to the value of glandular trichomes for host plant resistance, including removal by pollinators, the feeding deterrent or toxic effects of sesquiterpene lactones and diterpenes in sunflower glandular trichomes are not limited to H. electellum, suggesting possible value for resistance to other sunflower insect pests. Additional research is needed to understand the inheritance and value of glandular trichomes in commercial sunflower inbreds and hybrids. |
