Seed coat development and effects of relative humidity on development of hardseededness in mungbean (Vigna radiata (L.) Wilczek)
1995
Suwimol Thanomsub
Experiments were carried out in the late rainy season, 1992 and the dry season, 1993 at Chainat Field Crops Research Centre. Two mungbean cultivars, TC 1966 and PSU-1 were used. In each growing season, fresh and dried seeds from pods collected at different stages of development (8, 10, 12, 14, 16, 18, 20, 22, 24 and 26 days after anthesis, DAA) were subjected to examine seed moisture content (SMC), germination, hardseededness and structures and chemical substances of seed coats. Pods at seed physiological maturity were harvested and placed under different regimes of relative humidity (RH) i.e. low (25 percent), medium (55 percent), high (85 percent) and ambient conditions for four weeks. Each week, samples were taken to determined hard seed, seed moisture content and seed germination. Hard seed development of fresh seeds was apparent at 16 DAA (SMC 17 - 19 percent) for TC 1966 and 20 DAA (SMC 14 percent) for PSU-1. For dried seeds (SMC 8 - 10 percent), hard seed was detected in the pods collected at 8 DAA. Determination of seed coat structures indicated that palisade layer of TC 1966 was thicker than that of PSU-1. In examining chemical substances, cellulose of palisade cell, cutin and suberin in seed coat surface, lignin in tracheid bar of hilum and pectic substance in palisade layer and counter palisade cell of hilum of hard seed and normal seed were not different. In studying the effect of RH on hard seed development of mungbean, the result showed that SMC and hardseededness was affected by RH. For TC 1966, hard seed occurred when SMC was lower than 19 percent, whereas for PSU-1 hard seed was observed when SMC reached 14 percent. This result was similar to the result observed in the field condition, indicating that RH is a major factor responsible for hard seed development.
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