Dormancy regulation in conventional and oleic sunflower lines (Helianthus annuus L.)
Sunflower (Helianthus annuus L.), is currently the second most important source of vegetable oil in the world. Seed dormancy in sunflowers poses a risk for off-season seed production in South America. Seed companies must hold the seed lots from sale until they meet minimum germination specifications and will not pose a risk for the customer. This investigation was undertaken to examine the differences in dormancy between SF270, a traditional oil sunflower hybrid, and X8927 a mid oleic sunflower hybrid. Seed was grown in Texas in 1999 and 2000. Samples were divided between three storage temperatures, constant 100C, constant 140C, and ambient room temperature and tested two times per month. The standard warm germination test, alternating 20-300C warm germination test, and the ethrel warm germination test were used to evaluate germination and develop a dormancy profile for each genotype. A mathematical model was developed to calculate the average number of days to a specific germination value based on the laboratory germination data. The genotype SF270 broke dormancy soon after harvest, often before initial laboratory germination analysis could be completed. Genotype X8297 took longer to break dormancy than the traditional oil genotype. Both genotypes broke dormancy in a consistent pattern across the two production years. Storage of seed at constant 100C, and constant 140C prolonged the dormancy in both genotypes but, was more pronounced in the X8927 genotype. Storage at ambient room temperature had the most significant effect on breaking dormancy in the two genotypes. Of the three germination tests, the ethrel warm germination test was the best predictor of laboratory germination. Although these two genotypes cannot be considered representative of all genotypes, this study produced two very useful tools for seed producers. The model to calculate the average number of days after harvest to reach the target 85% germination goal, and the depth of dormancy or longevity of dormancy for a particular genotype. These tools can be used as a risk assessment tool to plan seed production placement, shipping, and anticipate product release.