Pericarp strength of sunflower and its value for plant defense against the sunflower moth, Homoeosoma electellum

Authors: Prasifka, Jarrad; Hulke, Brent; Seiler, Gerald

Submitted to: Arthropod-Plant Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2014
Publication Date: 3/10/2014
Citation: Prasifka, J.R., Hulke, B.S., Seiler, G.J. 2014. Pericarp strength of sunflower and its value for plant defense against the sunflower moth, Homoeosoma electellum. Arthropod-Plant Interactions. 8:101-107.

Interpretive Summary: Sunflower hulls provide a physical barrier against seed-feeding by larvae of the sunflower moth, and broad variation in the strength of sunflower hulls exists. To facilitate the use of hull strength in sunflower breeding for insect resistance, the force required to puncture hulls was assessed for diverse sunflower germplasm, and feeding tests were used to evaluate if differences in hull strength prevent sunflower moth larvae from feeding on developing seeds. Using plants from field and greenhouse experiments, sunflower types previously identified as resistant to sunflower moths were found to have stronger hulls, while inbred lines that restore fertility in sunflower breeding generally had weaker hulls. In feeding tests with sunflower moth larvae, 7–9 d old sunflower moth larvae fed far more often on seed protected by a weaker hull, while 10 d old larvae were not affected by the levels of hull strength tested. The results contradict previous reports on this subject in several ways, but still support the generalization that physical resistance to the sunflower moth may be improved for sunflower hybrids. To breed with entries found to have exceptionally strong hulls, the inheritance of the trait and potential trade-offs with other desirable agronomic traits need to be understood.

Technical Abstract: Sunflower pericarps provide a barrier against seed-feeding by larvae of the sunflower moth, Homoeosoma electellum. Pericarp hardening is thought to be accelerated by a phytomelanin layer beneath the hypodermis, but among germplasm with phytomelanin, broad variation in sunflower pericarp strength exists. To facilitate the use of pericarp strength (not explained by phytomelanin) in sunflower breeding, resistance to mechanical puncture was assessed for diverse sunflower germplasm, and feeding tests were used to evaluate if differences in pericarp strength prevent H. electellum larvae from penetrating achenes. Test on field-grown sunflowers indicate that public restorer (RHA) lines have lower pericarp strengths compared to maintainer (HA) lines and commercial hybrids at 14 d after the start of anthesis. Interspecific crosses or Plant Introduction (PI) accessions believed to be resistant to H. electellum, including PI 170415, comprised a group with exceptionally high pericarp strength relative to other germplasm. In subsequent tests on greenhouse-grown sunflowers, overall results were similar, but using field-grown plants provided greater statistical power. In choice tests with achenes that differed in pericarp strength, 7–9 d old sunflower moth larvae fed more often on seed protected by a weaker pericarp, at a more than 5-to-1 ratio, while 10 d old larvae fed indiscriminately. Pericarp strength data contradict previous published results for individual entries and heterotic groups, but support the generalization that improved physical resistance to the sunflower moth is possible. To use pericarp strength in PI 170415 or similar sources, the inheritance of high pericarp strength and potential trade-offs between pericarp strength and other agronomic traits need to be understood.