POSTHARVEST SEED DORMANCY EFFECTS ON KLEINGRASS GERMINATION FOLLOWINGSIMULATED DIGESTION BY CATTLE

Grass seed germinability declines linearly with increased exposure to in vivo and in vitro digestion, but the factors that regulate loss of seed germinability are unknown. One potential mechanism of seed surviv al during digestion is seed dormancy. A recently developed in vitro pr ocedure to simulate grass seed passage through the digestive system of cattle (Bos spp.) has permitted the evaluation of mechanisms controll ing seed germinability following digestion. Ou hypothesis was that 'Se lection 75' kleingrass (Panicum coloratum L.) seed with a high level o f post-harvest dormancy would withstand the negative effects of digest ion better than TEM-LD1 kleingrass seed with a low level of post-harve st dormancy. Seed harvested in 1991 and 1992 was frozen to maintain do rmancy status and subjected to 24, 48, and 72 h of in vitro digestion each year. Germinability was tested in half of the seed immediately fo llowing digestion, and half was stored at 24 degrees C to allow for na tural loss of dormancy. When germinated immediately following digestio n. Selection 74 seed maintained most of its dormancy and germinated po orer than TEM-LD1 kleingrass seed. However, after 6 to 8 mo of storage , digested seed of both genotypes exhibited similar linear declines in germination with increased digestion time. Seed of TEM-LD1 digested f or 48 or 72 h and then stored for 6 to 8 mo, germinated 15 to 25 perce ntage units poorer than similarly digested seed without storage. We co ncluded that post-harvest seed dormancy of kleingrass is not an effect ive mechanism for maintaining viability of seeds when passed through t he digestive system of cattle; however, such dormancy probably is a fa ctor in maintaining seed viability after it is excreted.