Apical Dominance in the Tomato: Some Further Observations on Isogenic Lines Showing Varying Degrees of Side-shoot Development

A study has been made of the distribution of substances resembling indol-3-ylacetic acid (IAA), abscisic acid (ABA) and cytokinin-like substances in the stem tissue of Craigella tomato plants as compared with that found in two isogenic lines of this variety, Craigella Blind (blbl) and Craigella Lateral Suppressor (lsls), in both of which side shoot growth is suppressed to varying degrees. There was no evidence to suggest that the distribution of these hormones in the stem had any association with the different patterns of side shoot development of the three types, though some of the lateral suppressor plants which exhibited only partial bud inhibition did show a relation between high auxin and abscisic acid levels and lack of side shoot development from the central nodes of the shoot. Decapitation led to a stimulation of bud outgrowth from all nodes of the Craigella plants but the lateral suppressor plants remained inhibited. The blind plants were found to initiate bud primordia at the cotyledonary nodes only when the severed apex was replaced by exogenous IAA. The results are discussed in relation to our knowledge of the mechanisms controlling apical dominance in the tomato.