Effects of 2,4-DP (2,4-dichlorophenoxypropionic acid) plant growth regulator on fruit size and yield of Valencia oranges (Citrus sinensis Osb.)

The Valencia orange is a high-quality fruit grown in Turkey; however, small fruit sizes and high fruit discard percentages are common in Valencia oranges. Small fruit size is the main factor limiting the marketing of Valencia oranges; thus, synthetic auxins are commonly used to enhance the size of citrus fruit. The objective of the present study was to observe the effects of 2,4-dichlorophenoxypropionic acid (2,4-DP) on the fruit size, yield and quality of Valencia oranges from 29-year-old trees budded on sour orange rootstock in Adana, Turkey during 2005-06. Three concentrations (50, 100 and 150 ppm) of 2,4-DP were applied during the June drop, when the mean fruit diameter was 13-15 mm. The results indicated that the application of 2,4-DP increased the fruit size of Valencia oranges without reducing yield. The application had a significant effect on fruit yield. Compared with the control trees, applications of 2,4-DP increased the number of large, commercially valuable Valencia oranges (75-80 mm). Moreover, an increase in the concentration of 2,4-DP increased the yield and weight of the fruits. As a result, fruit retention was highest in trees sprayed with 150 ppm 2,4-DP. Except for the titratable acid content (TA), which increased with an increase in the 2,4-DP concentration, the internal characteristics of the fruit were not affected by treatment with 2,4-DP. Thus, the results of the present study revealed that 2,4-DP can be used to improve the fruit size of Valencia fruitlets during the June drop.