Greenhouse Tests with Chemicals for Suppression of Lateral Branching of Decapitated Tobacco Plants.

Development of a simple and inexpensive method of suppressing axillary branching would be a matter of practical importance to tobacco growers. This has already been pointed out in a preliminary report of this work (10). Suckering or the removal of branches, is commonly practiced after topping, or decapitation of the tobacco plant at the bud or flower stage. More or less frequent suckering of the plants may be required for a period of from two to eight weeks, depending on the type of tobacco. Its purpose is primarily to improve quality of the leaf, but it is also alleged to increase yields under favorable conditions. The use of chemicals to suppress lateral branching might, if effective, possess the additional advantage of favorably modifying the quality of some types of tobacco (3, 6, 8). Obviously, it would be of the greatest importance to make certain that no harmful effects would follow such use of a chemical in commercial practice before recommending it for this purpose. The mechanism by which development of lateral buds is inhibited was a subject of study (9) even prior to the isolation of auxins a and b by KOGL (5), and of heteroauxin, or indoleacetic acid the growth hormones of green plants. That inhibition of axillary branching is due to formation of auxin in the terminal bud and its excessive accumulation in the lateral buds appeared probable from the results of experiments by THIJIANN and SKOOG (11). HITCHCOCK (4) found that indoleacetic acid, indolepropionic acid, ethylene, and propylene each inhibited axillary branching of decapitated tobacco plants. Since discovery of the hormonelike actions of many organic laboratory chemicals (13, 14) studies have been intensified. -Reviews of the extensive literature will be found in BOYSEN-JENSEN (2), WENT and THIMANN (12), and AVERY, JOHNSON, ADDOMS, and THOMSON (1). MITCHELL and MARTH (7) should also be consulted on the many potentialities of these compounds. The purpose of the experiments reported here was to obtain data on the comparative effectiveness of the available chemieal compounds as substitutes for manual suckering. That is to say, the degree to which development of the axillary buds can be suppressed in the absence of the terminal bud without injury to the planit. lt was realized that results of greenhouse tests might not hold quantitatively in the field. Moreover quality of cured leaf could not be studied with plants growil under greenhouse conditions, since such an environiiment is unsatisfactory for growing commercial