Growth and Branching of Apple Seedlings as Influenced by Pressure-injected Plant Growth Regulators1

Pressure injection of certain plant growth regulators into pruned and unpruned apple ( Malus domestica Borkh.) seedlings reduced terminal growth and increased lateral development within 7 weeks of injection. One ml of daminozide (butanedioic acid mon-(2, 2-dimethylhydrazide), AVG (aminoethoxyvinly glycine), MBR 18337 (N-(4-(ethylthio)-2-(trifluoro-methyl) phenyl (-methanesulfornamide) or PP333 [l-(4-chlorophenyl)-4, 4-dimethyl-2-(l,2,4-triazol-l-yl) pentan-3-01] reduced terminal extension growth over controls. PP333, the most effective growth inhibitor tested at 0.5 mg/ml, reduced terminal extension growth by 80% over controls. Top and root fresh weight were reduced on pruned seedlings. Only PP333 reduced top weight among the chemicals tested; root weight was not affected by chemical injections. Budbreak was increased significantly by BA (6-benzylamino purine), mepiquat-chloride (N-N-dimethyl-piperidinium-chloride) and AVG, but these chemicals had little or no effect on terminal extension growth.