Opposite effects of daylength and temperature on flowering and summer dormancy of Poa bulbosa

BACKGROUND AND AIMS: The timing of flowering and summer dormancy induction plays a central role in the adaptation of Mediterranean geophytes to changes in the length of the growth season along rainfall gradients. Our aim was to analyse the role of the variation in the responses of flowering and summer dormancy to vernalization, daylength and growth temperature for the adaptation of Poa bulbosa, a perennial geophytic grass, to increasing aridity. METHODS: Flowering and dormancy were studied under controlled daylengths 9 h short day (SD) vs. 16 h long day (LD)] and temperatures (16/10, 22/16 and 28/22 degrees C day/night) in four ecotypes originating in arid, semi-arid and mesic habitats (110, 276 and 810 mm rain year(-1), respectively) and differing in flowering capacity under natural conditions: arid-flowering, semi-arid-flowering, semi-arid-non-flowering and mesic-non-flowering. KEY RESULTS: Flowering and dormancy were affected in opposite ways by daylength and growth temperature. Flowering occurred almost exclusively under SD. In contrast, plants became dormant much earlier under LD than under SD. In both daylengths, high temperature and pre-chilling (6 weeks at 5 degrees C) enhanced dormancy imposition, but inhibited or postponed flowering, respectively. Induction of flowering and dormancy in the different ecotypes showed differential responsiveness to daylength and temperature. Arid and semi-arid ecotypes had a higher proportion of flowering plants and flowering tillers as well as more panicles per plant than mesic ecotypes. 'Flowering' ecotypes entered dormancy earlier than 'non-flowering' ecotypes, while the more arid the site of ecotype origin, the earlier the ecotype entered dormancy. CONCLUSIONS: Variation in the flowering capacity of ecotypes differing in drought tolerance was interpreted as the result of balanced opposite effects of daylength and temperature on the flowering and dormancy processes.