*Indian Council of Agricultural Research.
Fruit Section Department of Agriculture, Patiala, Punjab.
Two growth regulating substances namely, 2,4-D and NAA were applied as aqueous sprays on Fajri mangoes on May 15 about 6 weeks after full bloom in con-centrat oris of 0, 10, 20, 30 and 40 ppm.
NAA at 30 and 40 ppm proved to be the best treatment for the control of fruit-drop registering only about 22% drop between May 15 and July 18 as compared with 52% in control. Its lower concentrations gave a fruit-drop of 35–37%. Such concentration effects were not visible in case of 2,4-D where even 10 ppm dose was as efective as any other giving a fruit-drop of about 28%. Averaged over all the concentrations employed, there was no difference in the effectiveness of 2,4-D and NAA in the control of fruit drop.
Maximum improvement in fruit size occurred at 10 ppm of 2,4-D and 20 ppm of NAA.
These auxins showed no prolongation effects on fruit growth nor was there any hastening of fruit maturity.
Increase in fruit-drop, early maturity and reduction in the fruit size of Amini mangoes with the application of 2,4,5-TP reported by Kennard and Winter (1956) was very likely due to the high range of concentrations employed by them.
In the present investigations, both NAA and 2,4-D were found to influence fruit quality by increasing total soluble solids, titrable acidity, and ascorbic acid content but the individual concentration effects were not well-defined.
A fair proportion of treated fruits was observed to exhibit a light red blush on yellow ground as against the normal green colouration of mature fruit in this variety.
It was also noticed that the flow of sap from the pedicel on the fruit surface which commonly blemished the untreated fruits, was greatly suppressed under auxin treatments. It was very likely due to the inhibition of the formation of abscission lays at this point near fruit maturity and non-rupturing of cortical tissues.
