Seed Composition and Physiological Changes in Thai Peanut cv. Kaset 1 and Tainan 9 during Maturation

Abstract

Physiological changes and chemical compositions in peanut seed during maturation were investigated in two Thai cultivars: large-seeded Kaset 1 and medium-seeded Tainan 9. Nine maturity stages (5-13) of both cultivars designated by the Physiological Maturity Index (PMI) method were
studied to determine its appropriateness for maturity classification. Physiological maturity (PM) of Kaset 1 was evident at stage 10 with a seed moisture content of 36.37% while in Tainan 9 PM was attained at stage 11 with a seed moisture content of 35.48%. Peanut seed size, seed weight and the seed/hull dry-weight ratio increased as the seed matured and reached a maximum at PM, while seed moisture content declined and was stable from PM onwards. In Kaset 1, seed dormancy was found at stage 5 and was maximized (90%) at stage 9, while in Tainan 9, seed dormancy was found marginally at stage 12 (4.0%) and 13 (1.3%). During seed maturation of both cultivars, oil accumulation increased rapidly while carbohydrate content declined. Protein content did not change notceably during seed development. The oleic acid and the O/L (oleic/linoleic acid) ratio also increased while palmitic, linoleic, ecosenoic and behenic acid contents decreased. At maturity (stage 13), oil, carbohydrate and protein contents in Kaset 1 seed were 55.9, 21.7 and 20.1%, respectively and in Tainan 9 seed were 54.8, 21.5 and 21.2%, respectively. Regardless of the difference in seed size, the oil content of Kaset 1 and Tainan 9 peanut seeds was marginally different, while the O/L ratio of Kaset 1 seed was higher than that of Tainan 9 seed. It can be concluded that the PMI method was appropriate for classifying the maturation of peanut fruit and predicting the harvest date for Thai peanut cultivars.