Phenotypic relationships among oil, protein, fatty acid composition and seed size traits in Cucurbita pepo

Pumpkin seed (Cucurbita pepo L.) is high in oil, protein and total unsaturated fatty acids (TUFA), and provides an important source of nutrition and income globally. Use of pumpkin seed in the snacking and vegetable oil industry in the U.S. is expected to rise as the market for healthy foods increases. Currently, most of the pumpkin seed consumed in the U.S. is imported, and there is need to breed high-yielding and nutritious cultivars that are locally adapted to various agro-ecological growing zones in the country. In the current study, phenotypic variation of key seed nutrition traits among 35C. pepo accessions of different seed phenotypes (hulled, semi-hulled, thin layer and 'naked') was determined with the primary goal of identifying the best parental material for breeding as well as elucidating phenotypic relationships among the traits. Seed oil percentage ranged from 29.33% to 48.41% and was significantly (P < 0.05) negatively correlated (−0.51) with seed protein percentage, which ranged from 19.48% to 31.35%. Linoleic acid (x̅ = 51.19%) was the major fatty acid in the seed, followed by oleic (x̅ = 30.77%), palmitic (x̅ = 9.84%), and stearic (x̅ = 5.63%) acid. Significant negative correlations were found between linoleic and oleic acid (−0.96), linoleic and stearic acid (−0.37), and seed size and seed protein percentage (−0.39). Conversely, significant positive correlations were found between seed size and oil content (0.56-0.70), seed size and palmitic acid (0.49-0.65), seed size and stearic acid (0.38-0.46), palmitic acid and seed oil percentage (0.50), and stearic acid and seed oil percentage (0.31). Hulled seed accessions were significantly lower in seed oil percentage, palmitic acid and seed size than 'naked' seed accessions. On the other hand, 'naked' seed accessions had significantly lower seed protein percentage than semi-hulled seed accessions. Collectively, this data suggests a wide variation in seed nutrition within C. pepo and provides insight into the phenotypic relationships among important seed traits. Several accessions high in oil, protein and TUFA were identified and will be useful in breeding for enhanced pumpkin seed nutrition.