THE INFLUENCE OF SEED SIZE AND SEED COAT CHARACTERISTICS ON SEED QUALITY OF SOYBEAN IN THE TROPICS - FIELD WEATHERING

Deterioration of soybean (Glycine max) seed quality has been associated with large seed size and permeable seed coat. Field trials were conducted during summer and autumn seasons of 1989 at the AVRDC in Taiwan, using soybean lines with different seed size and seed coat characteristics. Pods were harvested from the top 30% and bottom 70% of plants, at reproductive stages R7, R7.5, R8 and seven days after R8 (harvest maturity, HM). In the summer season, standard germination of seed from the top portion of large-seeded types was near 80% at R7 but declined to near 50% by R8. On the bottom portion, germination of two large-seeded types was near 55% at R7. Accelerated ageing germination (AAG) in the autumn season was 90% or more for all seed types and stages. The decline in germination observed in this study, was not consistently related to electrolyte leakage, Phomopsis infection or seed density. A black-seeded type with hard seed coat performed similar to a small yellow-seeded type with a rapid rate of imbibition. Three large-seeded types representing, hard seed coat, slow imbibition and rapid imbibition were susceptible to field weathering, with no major differences in germination between them at R8 and HM.