IRRIGATION DURING SEEDFILL AND GERMINABILITY OF SOYBEAN WITH IMPERMEABLE SEED COAT CHARACTER

The impermeable seed coat (ISC) trait in soybean [Glycine max (L.) Merr.] is valuable because impermeable seed retain viability longer than permeable seed under adverse conditions such as delayed harvest or lengthy storage. The objective of this study was to determine how drought stress during seedfilling affected the ISC trait. 'Forrest', a maturity group (MG) V determinate cultivar with normal seed coat, and D86-4565, an ISC MG V determinate line, were grown in the field In 1991 (hot, dry season) and 1992 (cool, wet season) at Stoneville, MS. No irrigation or furrow Irrigation between beginning seedfill (R5) and full seed (R6) growth stages were used to vary soil water content during seed development. Seed was harvested by hand and machine both years. In 1991, germination of machine-harvested, unscarified D86-4565 was increased by Irrigation, but the percentage of impermeable seed was not affected. In 1992, irrigation that was started at R5 and continued through R6 increased germination of machine-harvested, unscarified seed from both genotypes, and significantly decreased impermeability of unscarified seed of D86-4565. Unscarified seed from D86-4565 grown in 1992 had greater germination and higher permeability than seed from 1991. Unscarified seed from all treatments of D86-4565 germinated well below the standard of 80%. These results indicate that irrigation of soybean during the seedfilling period can influence the ISC trait and germination of unscarified seed with this trait, but the effect of diverse weather is much greater. Furthermore, adequate moisture during seedfill will not preclude preplant scarification to enhance germination of seed with the ISC trait.