Germination responses of buried seeds of Capsella bursa‐pastoris exposed to seasonal temperature changes

Buried seeds of Capsella bursa‐pastoris exhibit an annual conditional dormancy/non‐dormancy cycle. Seeds after‐ripen during summer and remain non‐dormant during autumn and winter. Seeds enter conditional dormancy in early spring, first showing marked decreases in ability to germinate at high (35/20°C) and then at lower (30/15, 25/15°C) temperatures. Seeds do not lose the ability to germinate to high percentages at March (15/6°C) and April (20/10°C) temperatures in March and April. Thus, C. bursa‐pastoris is a facultative winter annual, germinating in both autumn and spring if seeds are exposed to light. However, because some seeds retain the ability to germinate at 30/15 and 25/15°C, they could do so throughout the growing season in regions with cool, moist summers. Conditional dormancy developed in all seeds given 12 weeks at 5°C and subsequently kept for 4 weeks each at March (15/6°C), April (20/10°C) and May (25/15°C) temperatures. Thus, seeds of C. bursa‐pastoris enter conditional dormancy as temperatures increase in spring.