Evaluation and Control of Ground Sucker Formation in Burley Tobacco Varieties

The use of hydroponically produced tobacco transplants, commonly referred to as "float plants", has been widely adopted by tobacco producers over the last several years. There are many advantages to using float plants, with reduction in labor, the ability to hold plants when soil conditions are too wet to transplant, uniform stand establishment, and rapid grow-off being the most important. However, one negative aspect of float plants is their increased propensity to form basal axillary buds or shoots, commonly referred to as "ground suckers". Growth of the axillary shoots is usually repressed after apical dominance is re-established in plants following transplanting; as a result, ground suckers often do not grow beyond 6-8 inches in length and therefore are of no consequence. However, if the re-establishment of apical dominance is delayed, or the apical meristem is injured from insect or hail damage, ground suckers may continue to grow, resulting in significant problems during harvest and potential reductions in yield. There is no clear understanding as to why ground suckers are so much more prevalent in hydroponically produced transplants. One possibility is that there is a difference in levels of specific levels of plant hormones between traditional versus hydroponically produced transplants. Of particular interest is the ratio of auxins, which are produced primarily in apical meristems, to cytokinins, which are primarily produced in the roots of plants. Before tobacco plants are topped, auxin from apical buds travels down the stalk to inhibit sucker growth. This promotes primary shoot growth, and restricts lateral branching. Cytokinin moves from the roots into the shoots, eventually signaling lateral bud growth. When the apical bud is removed from tobacco plants at topping, the auxin to cytokinin ratio is altered and sucker growth increases dramatically. The root to shoot ratio in hydroponically grown plants is much greater compared to plants grown in traditional plant beds. The hypothesis that the proposed research will investigate is that this difference in root to shoot ratio between traditional versus hydroponically produced transplants results in a significantly different auxin to cytokinin ratio, thereby initiating the development of ground suckers. The research will attempt to identify optimal levels of hormone concentrations that can be added to float water to minimize or eliminate ground sucker formation without adversely affecting plant growth or yield potential.