SOYBEAN SEED COAT DISCOLORATION IN COOL-SEASON CLIMATES

Soybean [Glycine max (L.) Merr.] seed with yellow seed coat and hilum is preferred in North America for the export market. Seed coats may da rken or discolor when exposed to chilling temperatures during seed dev elopment. We examined the effects of chilling temperatures on seed coa t discoloration of yellow hilum, isogenic lines of 'Maple Presto' soyb ean (Maturity Group 000) differing in pubescence color (I, r, T, tawny ; I, r, t, gray). The isogenic lines were grown in the field for five seasons and once in the growth cabinet (25/20 degrees C day/night). We quantified seed coat discoloration using an image analyzer. When expo sed to cool temperatures during seed development, the seed coat darken ed. In the extreme case, the seed coat from the taw ny line looked gra y-brown. The tawny line discolored more than the gray line, both in th e field and the growth cabinet. Seed coat discoloration increased with the accumulation of daily minimum temperature less than or equal to 1 5 degrees C during seed development. In years with cool temperatures d uring seed development, seed coats may discolor, reducing the quality of the seed's appearance.