2019 ASHS Annual Conference

Helianthus verticillatus or whorled sunflower was recently designated an endangered species and grows only on a few prairie remnant sites in Tennessee, Georgia, and Alabama. This perennial species spreads locally by rhizomes and more distantly by seeds dispersed by foraging birds. Because few details about the reproductive biology of this species are known, our specific aims were to evaluate seed viability, assess temperatures conducive for seed germination, and develop methodologies for clonal, vegetative propagation. More than 98% of seeds collected in 2017 and stored dry at room temperature were viable after seven months. Only 77% of the seeds in the high-temperature treatment (33 C) germinated within 28 days, whereas, 96% of seeds in the other three regimes (22, 27, and 29 C) germinated. About half of the seed in the coldest treatment germinated within 7-8 days, whereas 50% germinated within 1-2 days in the three warmer treatments. Many of the leaf and node explants placed in culture became contaminated within two weeks. Axillary buds elongated on medium with or without cytokinins, but excised shoots failed to produce roots. Very few shoots were formed on excised leaves placed on medium containing various cytokinins. Almost all of the terminal cuttings harvested in late May formed robust root systems after four weeks, grew well and flowered normally in September. Only about 20% of the three node cuttings (without terminal buds) harvested in late June produced roots in response to either water of auxin treatments. We concluded from these experiments that whorled sunflower could be efficiently and effectively propagated from either seeds or terminal bud cuttings stuck in May.