Helianthus annuus is the most common species of sunflower in North America and is commonly found growing and flowering year-round in South Texas. In previous studies, we found no differences in growth and photosynthetic characteristics between progeny from summer-active and winter-active plants from South Texas during each season. We also found no differences in growth and photosynthetic characteristics during a winter experiment in which we grew progeny from both winter-active South Texas plants and progeny from summer-active plants from Central Texas. Currently, H. annuus does not grow during the winter in Central Texas. Our results suggest that in a future warmer climate when winters in Central Texas are more similar to current winters in South Texas, plants already in the Central Texas area would be able to grow and reproduce during that season. However, in response to current conditions Central Texas plants may have seed dormancy that would prevent germination and subsequent growth during future warmer winters in Central Texas. Our germination experiment, conducted in the field in South Texas, was designed to determine if seeds from Central Texas plants produced during the summer could germinate the following fall/winter season under warmer winter season conditions.
Results/Conclusions
For the period of 12 November 2015 to 21 January 2016, germination percentage of seeds produced by South Texas plants was 76%, 73%, 87% and 84% in four replicate 128 cell trays. Germination percentages for seeds produced by Central Texas plants were 49%, 46%, 76% and 45%. In general, South Texas plants produced seeds that germinated earlier than did Central Texas plants, with the first South Texas seed germinating 8 days into the experiment and the first Central Texas seed germinating on day 16 of the experiment. Clearly, at least some Central Texas seeds are not dormant and can germinate under what may be similar to future winter conditions in Central Texas. Roughly half of the Central Texas seeds germinated in a time frame that allowed for growth and reproduction during the South Texas winter season. These results, along with our previous results, indicate that H. annuus could extend its growing season in regions farther north of South Texas if winters become warmer in these areas.