THE REDUCTION OF NARINGIN CONTENT OF GRAPEFRUIT BY APPLICATIONS OF GIBBERELLIC-ACID

Four different plant growth regulators, gibberellic acid (GA3), naphthaleneacetic acid (NAA), benzyladenine (BA) and abscisic acid (ABA), were individually mixed in a lanolin paste and applied to immature fruit on grapefruit trees beginning soon after fruit set. The treated fruit was allowed to mature on the tree. Application of 1000 ppm GA3 in this manner generally increased fruit size, decreased the concentration of the total acid in the juice and decreased the concentration of naringin in the juice sacs compared to that of the controls. GA3 increased the total soluble solids (brix) in the juice in some experiments. Treatment of fruit with 1000 ppm ABA and BA significantly decreased the size of the fruit and increased the naringin concentration, but had variable effects on the soluble solids content and the acid content. Treatment with 1000 ppm NAA did not produce any significant changes in size, acid content, brix or naringin concentration.