Crop Genotype and Plant Population Density Impact Flowering Phenology and Synchrony between Cropped and Volunteer Spring Wheat

Wheat (Triticum aestivum L.) is one of many crops into which novel traits have been incorporated using recombinant DNA technology, and thus may require segregation from nontransgenic wheat. Volunteer wheat populations, which cannot be selectively removed from wheat crops, pose a challenge to segregation because they may serve to facilitate trait movement. However, diverse flowering phenologies among wheat genotypes planted at various densities may result in flowering asynchrony, thus minimizing pollen-mediated gene flow (PMGF). We tested this theory with a comparative analysis that examined the influence of crop plant population density, genotype, and height on flowering phenology and synchrony between volunteer and cropped wheat populations. We found that time from crop sowing to first flower, peak flowering, and flowering cessation varied significantly among genotypes. Increasing crop plant population density resulted in accelerated crop flowering for all genotypes, but had little effect on flowering synchrony. Although not always significant, the time interval from sowing to 5, 50, and 95% flowering, as well as the flowering duration of the volunteer population, were also greater at low crop plant population densities. Synchronicity of flowering varied among genotypes, with tall genotypes consistently exhibiting more flowering synchrony with volunteer wheat than short genotypes. However, the response of flowering synchrony to height may have been a product of the genotypes tested and further study to confirm these results is needed. The results of this study suggest that, despite a short flowering period, there is considerable potential for flowering synchrony between cropped and volunteer wheat populations. Nevertheless, opportunity exists to reduce flowering synchrony between cropped and volunteer wheat populations by utilizing genotypic variation for flowering phenology to minimize flowering overlap, provided that an adequate crop plant population density is attained.