PLANT-GROWTH REGULATOR AND GRAFT CONTROL OF AXILLARY BUD FORMATION AND DEVELOPMENT IN THE TO-2 MUTANT TOMATO

The torosa-2 tomato mutant is characterized by a strong inhibition of release of axillary shoots, that is not under the control of the main apex and IAA. Microscopic examination indicated that about 70% of leaf axils do not have axillary buds. Of the growth regulators tested, gibberellic acid and cytokinins were able to modify the to-2 phenotype: increasing bud number (GA3 treated) and developing shoots (both substances). Sequential application of growth regulators demonstrated that bud production was only affected by treatments given between sowing time and 32 days after germination. Grafting experiments indicated that endogenous root factors have no essential role in the lateral branching of the genotypes investigated. The control of axillary bud differentiation and the branching pattern in the to-2 appears to be dependent of a complex mechanism involving gibberellins and cytokinins.