INFLUENCE OF TEMPERATURE AND WATER-UPTAKE ON THE EXPRESSION OF COTYLEDON NECROSIS IN SOYBEAN (GLYCINE-MAX (L) MERRILL)

Cotyledon necrosis on germinating seedlings has been related to loss o f seed vigour in soybean. This experiment evaluated the effect of wate r uptake, matrix priming, and temperature on germination and the expre ssion of cotyledon necrosis. Seeds of 'Winchester', 'Beck 352', and 'E ssex' were conditioned to SO to 400 g kg(-1) moisture prior to germina tion at 10, lj, 20, 30 and 20/30 degrees C. Cotyledon necrosis was fir st visible when seeds imbibed water prior to radicle emergence. The ex pression of necrosis following radicle emergence was greatly accelerat ed when water uptake occurred at higher temperatures (30, 20/30 degree s C) compared to lower temperatures (10, 20 degrees C). Water uptake a t 10 degrees C for 3 to 7 days prior to germination at 20/30 degrees C reduced the occurrence of cotyledon necrosis of seedlings during germ ination. Reducing soybean seed moisture to 80 g kg(-1) Drier to imbibi tion caused slightly lower germination due to imbibitional injury, but had no effect on cotyledon necrosis: Controlling the rare of water up take by increasing initial seed moisture to > 300 g kg(-1) or through matrix priming improved germination, but had no effect on the level or occurrence of cotyledon necrosis compared to nonimbibed seeds. Thus, imbibitional injury was not the cause of cotyledon injury. Cotyledon n ecrosis was most directly influenced by temperature during imbibition and germination and appears to be associated with physiological aging. Although cotyledon necrosis was related to a decline in seed vigor, t he actual mechanism(s) that causes necrosis is (are) still unknown.