EFFECT OF TEMPERATURE AND LIGHT ON SEED GERMINATION OF TWO ECOTYPES OF PORTULACA OLERACEA L.

SUMMARY The effect of various temperature and light conditions on the germination of freshly harvetesd and 1‐year‐old seeds of obovate leaf and narrowly obovate leaf ecotypes of Portulaca oleracea L. is reported. These plants are common weeds of moist cultivated fields in the Upper Gangetic Plain. Freshly harvested seeds showed insignificant germination in darkness at any temperature between 10–40° C, and required specific photoperiodic and thermoperiodic conditions for germination. In contrast 1‐year‐old seeds showed significant temperature‐dependent dark germination, and almost complete germination with a single light exposure given at high temperatures; they thereby exhibited the loss of photo‐thermoperiodic requirement. In general the seeds of the narrowly obovate leaf ecotype were more sensitive to light than those of the obovate leaf ecotype. The possible significance of the germination requirements in relation to the success of the plant in Nature and to its essentially tropical distribution is discussed.