Effect of maternal environment on sunflower fruit dormancy (Helianthus annuus): photoperiod and incident radiation

PIZZORNO LUCIANA; DIEGO BATLLA; LOPEZ PEREYRA MONICA

MAR DEL PLATA

Conferencia; 18th International Sunflower Conference; 2012

ASAGIR

Sunflower fruit (Helianthus annuus) usually has a high level of dormancy at harvest time which determines problems in the processing and use of the fruit as seeds. Although this problem is relevant for the seed industry, there is little information in relation to maternal environmental effects (temperature, photoperiod, radiation, water, etc.) on the level of dormancy of sunflower fruit at harvest. Recent evidence strengthens temperature as the factor that modulates dormancy level of sunflower fruit. However, temperature does not explain all the variations that occur in contrasting environmental conditions (normal vs late planting dates), therefore other factors such as radiation and photoperiod may also be affecting fruit dormancy level. In this context, the objectives of this study were to evaluate: i) the effects of day length (Exp PHOTO) and incident radiation (Exp RAD) on sunflower fruit dormancy level and ii) the physiological basis of the observed responses. ? The Exp PHOTO and Exp RAD were conducted at the experimental field of the Facultad de Agronomía, Universidad de Buenos Aires (34º 35´ S., 58º 29´W.) during the 2010-2011 growing seasons. In Exp RAD the incident radiation was managed through the use of black shading cloth mounted on rectangular tubular structures at different times of fruit growth and development from: i) flower bud to first anthesis, ii) first anthesis to last anthesis and iii) last anthesis to 10 days after last anthesis. The Exp PHOTO was sown in January to achieve a difference of around 2.5 hours in day length during the grain filling period between control and treatment plots. The photoperiod extension in the treatment plots was achieved through the use of incandescent and low-intensity lights mounted on rectangular tubular structures. Weather conditions were recorded followed during both experiments. In both Exps, fruit was harvested with 11% humidity. Then, the fruit was dried at 40 ° C to reach 6% humidity and the grain was stored in chambers at 15 ° C. Dormancy level was determined from harvest and every 20-25 days until the proportion of fruit that germinated was equal to or greater than 90%. Germination experiments were performed at two temperatures (12 and 25°C) and included two treatments: fruit and embryo (fruit without pericarp and seed coat). ? A smaller amount of incident radiation during the period of growth and grain development diminished fruit dormancy level. Five months after harvest, when the fruits were incubated at 25 °C, the germination percentage was 75% in the radiation treatments while it was 30% in control. In contrast, when fruits were incubated at 12 °C, there were no differences between treatments. The embryos showed more than 80% germination after 30 days from harvest for control and radiation treatments, suggesting that dormancy is imposed by fruit covers. The day length during the filling period also affected fruit dormancy level. After 34 days from harvest, fruit germination percentage was 50 and 10% for treatments of 14 and 12 hrs day length during the grain filling period, respectively. However, in both treatments 90% of fruit germinated 74 days after harvest. ? Obtained results showed that incident radiation and photoperiod explored for sunflower fruit during development and maturation can affect the dormancy level of harvested fruit. In the case of incidence radiation, observed effects were mainly explained by difference in fruit covers imposed dormancy. On the other hand, the expression of the dormancy level imposed by fruit covers depended on incubation temperature (dormancy was expressed at higher incubation temperatures). Regarding the effect of photoperiod, obtained results showed that this factor can affect fruit dormancy level; however dormancy disappeared after a short period of storage, suggesting that photoperiod may be affecting embryo dormancy which has been proven to be less lasting than the dormancy imposed by fruit covers. ? The results presented in this abstract, are to the best of our knowledge, the first documented evidence that the incident radiation and photoperiod affect sunflower fruit dormancy. Therefore, the variation of these environmental factors, in addition with temperature, should be considered for designing management strategies (sowing dates, planting locations etc.) to obtain lower levels of dormancy of sunflower fruit at harvest.