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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #409122

Research Project: Genetic Improvement of Lettuce, Spinach, Celery, Melon, and Related Species

Location: Crop Improvement and Protection Research

Title: Proanthocyanidins: Key for resistance to Globisporangium (formerly Pythium) seed rot of pea

item EWING, ELMER - Cornell University
item WEEDEN, NORMAN - Montana State University
item Simko, Ivan

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2023
Publication Date: 1/24/2024
Citation: Ewing, E.E., Weeden, N.F., Simko, I. 2024. Proanthocyanidins: Key for resistance to Globisporangium (formerly Pythium) seed rot of pea. Journal of the American Society for Horticultural Science. 149(1):37-49.

Interpretive Summary: Seed rot (also known as pre-emergence damping off) is a soil-borne disease common to many crops, including peas. High soil moisture content is typically the major environmental factor that increases disease severity, and in wet weather or on poorly drained soils the decay may result in crop failure. We examined the nature of seed rot resistance and determined that it was associated with seed coat phenotype, not embryo phenotype. Resistant genotypes contained a significantly higher content of proanthocyanidins than susceptible genotypes. Our results suggest more attention should be paid to proanthocyanidins and to accompanying cell structure, attributes less noticeable than coloration.

Technical Abstract: Peas (Pisum sativum) dominant for the fundamental color gene A showed a high level of resistance to Globisporangium ultimum (formerly Pythium ultimum) seed rot. Reciprocal crosses demonstrated in our materials such resistance was associated with testa (seed coat) phenotype, not embryo phenotype. Dominance of A over a was complete for this trait. Neither wrinkled seed form (r) nor green cotyledons (i) diminished resistance when A was dominant, though both recessive alleles did so when seeds were borne on white flowering (a) plants. The product of the A gene functions in the pathway leading to flavonoids, which include proanthocyanidins (PAs) and anthocyanidins. We found resistance to G. ultimum seed rot was closely associated not only with dominant A, but also with testa PAs and testa sclerenchyma. Even A testas that lacked anthocyanins but contained PAs and sclerenchyma showed a high level of seed rot resistance. Moreover, a mutation removing PAs and sclerenchyma in a narrow zone from the hilum to the radicle markedly increased susceptibility. The PAs in pea testas were predominantly prodelphinidins in seeds from purple-flowered plants (A B) and procyanidins from pink-flowered plants (A b). Compared to procyanidins, prodelphinidins reportedly have higher antioxidant activity but are more likely to sequester iron, a particular concern in dry peas. Although A B testas were more resistant than A b to seed rot, the difference seemed too slight to militate against growing pink-flowered peas. We stress the need for more histological comparisons of A B and A b testas, and we point out that genes and their phenotypic effects examined in the current study could be useful in modeling biosynthesis of PAs and related cell walls.