THE EFFECT OF THE THERMAL ENVIRONMENT DURING FRUIT DEVELOPMENT ON THE DORMANCY LEVEL OF SUNFLOWER (Helianthus annuus L.) ACHENES.

BODRONE, MA. PAULA; BATTLA, DIEGO; ARISNABARRETA, SEBASTIÁN; MA. VERÓNICA RODRÍGUEZ; BENECH-ARNOLD R.L.

Costa do Sauipe

Congreso; 10th Conference of the International Society for Seed Science; 2011

ISSS (International Seed Science Society)

THE EFFECT OF THE THERMAL ENVIRONMENT DURING FRUIT DEVELOPMENT ON THE DORMANCY LEVEL OF SUNFLOWER (Helianthus annuus L.) ACHENES.1Bodrone, P., 2Batlla, D., 1Arisnabarreta, S., 2Rodríguez, M.V., 2Benech-Arnold, R.L. Monsanto Argentina, Fontezuela Research Station, Pergamino-Buenos Aires, Argentina. paula.bodrone@monsanto.com, 2Faculty of Agronomy, University of Buenos Aires-IFEVA, CONICET, Ciudad de Buenos Aires-Buenos Aires, Argentina. The aim of the present work was to investigate the effect of the thermal environment experienced by sunflower achenes during development on the mother plant on their dormancy level at harvest. Also, it was evaluated if the response of achene dormancy level to the thermal conditions during development was associated to i-embryo and/or coat imposed dormancy (pericarp and seed coat), and ii- differences in achenes sensitivity to abscisic acid (ABA). Two experiments were conducted during 2008 and 2009 seasons in order to impose different thermal conditions during achene development: i-different planting dates (i.e. September 22nd, October 22nd and December 2nd), and ii- the disposition of polyethylene plastic cages installed on the mother plants to increase the temperature artificially during achene development. At commercial harvest (11% moisture), sunflower achenes, seeds (without pericarp) and naked embryos (without pericarp and seed coat) were germinated at 25 and 11ºC in distilled water. In addition, achenes were also germinated at 25ºC in mediums containing 100 uM fluridone (an inhibitor of ABA synthesis) and 100 uM fluridone + ABA 50uM. Obtained results showed higher levels of dormancy in achenes from the earliest planting dates, corresponding to higher temperatures during fruit development, and from plots where temperature was increased artificially through the implementation of plastic cages. These higher levels of dormancy were largely explained by an increase in coat imposed dormancy (mainly imposed by the seed coat), while in the opposite way, the embryos showed a slight decrease in their level of dormancy. In addition, it was observed that achenes exposed to higher temperatures during their development exhibited an increase in their sensitivity to exogenous ABA than those exposed to lower temperatures during the same period. The results obtained in this work indicate that higher temperatures during sunflower achene development would determine higher levels of achene dormancy at harvest due to an increase in coat imposed dormancy, and that this response might be mediated, at least in part, by an increased sensitivity to ABA. Keywords: achene development, dormancy, sunflower achene, temperature