Kiwifruit growth control by synthetic auxin 3,5,6-TPA

The effect of the synthetic auxin 3,5,6-trichloro-2-pyridyloxyacetic acid (3,5,6-TPA) on kiwifruit ( Actinidia deliciosa cv. Hayward) growth and quality was investigated in a 3-year study carried out in Bologna, Italy. Different concentrations of the chemical, commercially available as Maxim, were tested at different application times during the fruit growth period. The maximum effect was observed when the chemical was applied during cell extension. Treated fruits showed fresh weight values higher than control ones in all the trials and these data were confirmed also by the biometric parameters (diameter and length) measurements. A clear correlation between concentration and weight enhancement was observed. The chemical did not induced fruit abscission or phytotoxicity even at the highest concentration. The fruit quality traits were also affected: an increase in flesh firmness and a decrease in soluble solids content were recorded at harvest. No differences were observed in fruit quality traits after cold storage.