The effect of maternal environment on sunflower (Helianthus annuus) achenes dormancy level at harvest: the thermal environment

PAULA BODRONE; DIEGO BATLLA; MARIA VERONICA RODRIGUEZ; SEBASTIAN ARISNABARRETA

MAR DEL PLATA

Conferencia; 18th International Sunflower Conference; 2012

ASAGIR

Thermal environment during seed development and maturation (thereafter just development) can affect the dormancy level of harvested seeds in several species. Field experiments were conducted with sunflower to investigate how the thermal environment during achene development affected their dormancy level at harvest, and evaluated if the observed response was related to changes in embryo and/or coat imposed dormancy. Three experiments were conducted in order to impose different thermal conditions during achene development, and to evaluate their effect on their dormancy level at harvest: i- different sowing dates ii- installation of polyethylene plastic tents covering whole plants that increased temperature artificially during the entire period of achene development, and iii- polyethylene plastic tents installed during each of three intervals within the period of achene development. Mature achenes were harvested for all experiments and dormancy level was assessed periodically for whole achenes and/or isolated embryos. ? Significantly higher levels of dormancy were observed in achenes from the earliest sowing dates (1st and 2nd), in which higher temperatures occurred during fruit development, as compared to achenes from the latest sowing date (3rd) in which lower temperatures occurred. Similarly, fruits from plots in which temperature was increased artificially with the use of plastic tents showed a higher dormancy level than seeds from control plots, although differences in dormancy level between treatments were somehow smaller than those observed between sowing dates. Experiments in which temperature was artificially increased at different intervals within grain development showed that dormancy was enhanced with respect to control plots only when temperature was increased during the last half of grain filling period, but not during the first half. The higher levels of dormancy in response to higher temperatures during development were mainly explained by an increase in coat imposed dormancy. Our results with sunflower indicate that higher temperatures during achene development can produce higher levels of dormancy at harvest due to an increase in coat imposed dormancy. On the other hand, results also suggest that this effect of temperature takes place at later stages of achene development. Finally, the fact that treatments in which temperature was increased artificially with plastic tents explained only partially the differences obtained between sowing dates suggests that other factors of the maternal environment (for example radiation and photoperiod) might also affect dormancy level of sunflower achenes.