Seed germination ecology of the annual grass Leptochloa panicea ssp mucronata and a comparison with L-panicoides and L-fusca

Leptochloa panicea ssp. mucronata is an annual grass that grows in relative ly dry habitats. Requirements for dormancy loss and germination were determ ined for seeds of this species and compared to those of two species from we t habitats. Seeds of L. panicea were dormant at maturity in autumn, but whe n exposed to actual or simulated autumn temperatures (e.g. 20/10, 15/6 degr ees C), they entered conditional dormancy and thus germinated to high perce ntages in light at 35/20 degrees C. Seeds buried in non-hooded soil exposed to natural seasonal temperature changes in Kentucky (USA) were non-dormant by the following summer and germinated to 80-100 % in light at 25/15, 30/1 5 and 35/20 degrees C. Seeds buried in non-flooded soil exhibited an annual conditional dormancy/non-dormancy cycle, with seeds mostly germinating to 80-100 % in light at 30/15 and 35/20 degrees C throughout the year but to 8 0-100 % in light at 25/15 degrees C only in summer. Results for L. panicea were compared to published data for L. panicoides and L. fusca. Whereas see ds of L. panicea buried in hooded soil failed to come out of dormancy, thos e of L. panicoides, an annual of moist habitats such as mudflats, exhibited an annual conditional dormancy/non-dormancy cycle, and those of L. fusca, a semi-aquatic, required flooding for both dormancy loss and germination. D ifferences in dormancy breaking and germination responses of seeds of Lepto chloa species may help to explain why this genus occupies a wide range of h abitats with regard to soil moisture conditions. (C) 1999 Editions scientif iques et medicales Elsevier SAS.