Breaking tuber dormancy in Helianthus tuberosus L. and interspecific hybrids of Helianthus Annuus L. × Helianthus tuberosus
Tubers of Helianthus tuberosus L. are dormant after production in the late fall until the next spring. In the wild, tuber dormancy is broken after exposure to winter cold, resulting in sprouting and shoot development in the spring when conditions are favorable. The dormancy period typically limits H. tuberosus populations to one growth cycle per year. An efficient method for breaking tuber dormancy is needed to have an additional growth cycle per year in a breeding program, which could take place in winter inthenurseryorthegreenhouse allowingforincreased breedingefficiency.Theobjective of thisresearch was to compare chemicaland cold temperature treatments for artificially breaking tuber dormancy in 12 genotypes of H. tuberosus and interspecific hybrids of Helianthus annuus L. 3 H. tuberosus. Five cold exposures (2, 4, 6, 8, 10 weeks at 2 8C), three plant hormones (ethylene, cytokinin, and gibberellic acid), and one untreated control were examined. Gibberellic acid was the best chemical treatment, initiating plant growthwithin6.5to11.5daysinthemajorityofgenotypestested.Thebestcoldtreatment was exposure to 2 8C for 8 weeks, where plant growth began 63.6 to 67.5 days after treatment initiation. Although longer cold treatments shortened the time to emergence while in the greenhouse, the penalty of the long cold treatment per se was too long to be useful. The gibberellic acid treatment strategy described here may not need further optimization, because it is short enough to allow for two growth cycles of H. tuberosus per year.
Evaluating an interspecific Helianthus annuus × Helianthus tuberosus population for use in a perennial sunflower breeding program
Abstract Perennial crops show promise for sustainable agricultural production while providing ecosystem services (maintaining healthy soil, controlling erosion, improving water quality, and enhancing wildlife habitat). Perennial crops could also provide economically viable cropping option to farmers. Sunflower (Helianthus annuus L.) is an ideal crop for perennialization because of existing genetic resources and a wide variety of end-uses. The objective of this research was to evaluate interspecific hybrids between perennial Helianthus tuberosus L. (2n = 6x = 102) and annual H. annuus L. (2n = 2x = 34) for perenniality and agronomic traits; assessing their utility in developing a perennial seed crop. Field trials indicated that seed yield traits were positively correlated with head traits. Tuber traits, which are required for perenniality, and seed yield traits were not correlated, indicating that simultaneous selection may be able to target high yielding lines that also tuberize. The F1 individuals were intermated for one generation and the intermated F1 (IM1F1) showed increases in head size (up to 20%) compared to the best F1 individual. The lack of correlation between tuber and seed traits coupled with phenotypic improvement after one generation of intermating suggest that the best improvement strategy for perennial sunflower is a recurrent selection program focusing on yield.
THE EVOLUTION OF TRADE-OFFS: TESTING PREDICTIONS ON RESPONSE TO SELECTION AND ENVIRONMENTAL VARIATION
The concept of phenotypic trade-offs is a central element in evolutionary theory. In general, phenotypic models assume a fixed trade-off function, whereas quantitative genetic theory predicts that the trade-off function will change as a result of selection. For a linear trade-off function selection will readily change the intercept but will have to be relatively stronger to change the slope. We test these predictions by examining the trade-off between fecundity and flight capability, as measured by dorso-longitudinal muscle mass, in four different populations of the sand cricket, Gryllus firmus. Three populations were recently derived from the wild, and the fourth had been in the laboratory for 19 years. We hypothesized that the laboratory population had most likely undergone more and different selection from the three wild populations and therefore should differ from these in respect to both slope and intercept. Because of geographic variation in selection, we predicted a general difference in intercept among the four populations. We further tested the hypothesis that this intercept will be correlated with proportion macropterous and that this relationship will itself vary with environmental conditions experienced during both the nymphal and adult period. Observed variation in the phenotypic trade-off was consistent with the predictions of the quantitative genetic model. These results point to the importance of modeling trade-offs as dynamic rather than static relationships. We discuss how phenotypic models can incorporate such variation. The phenotypic trade-off between fecundity and dorso-longitudinal muscle mass is determined in part by variation in body size, illustrating the necessity of considering trade-offs to be multifactorial rather than simply bivariate relationships.