A quantitative study of lateral branching in petunia

The monopodial shoot axis of petunia (Petunia hybrida Vilm) has two different patterns of branch development. Basal lateral branching develops acropetally and is limited to a discrete number of nodes that correlate with the late rosette phase of growth (Zone II). Two zones of suppressed buds immediately precede and follow this zone of branching. Apical branching occurs in response to flowering, develops in a basipetal direction, and is restricted to the distal-most nodes on the monopodial axis. When grown under a short-day regime, an extension to the basal branching zone occurs, and growth of the main shoot axis is retarded. The sym1 mutant has an overall decrease in basal lateral branching compared with wild type whereas the three dad mutants have increased basal branching. The dad1-1 and dad2-1 mutants have no initial zone of suppressed branching whereas the dad3 mutant has a similar Zone II to wild type, but with a greater potential to form branches within this zone. The dad1-1 mutant exhibits delayed flowering, but the dad1-1 sym1 double mutant flowers at a similar node number to wild-type and branching is similar to dad1-1 indicating that these two aspects of the mutant dad1-1 phenotype are independent.