EFFECT OF NAA, 2,4-D, AND THEIR SODIUM SALTS ON TANKAN (Citrus reticulata, var. tankan) FRUIT ABSCJSSION

(l) Most typhoons strike the island during the summer months, therefore, an earlier auxin spray before the season begins would be more effective in reducing the loss due to the storms. (2) Stewart and Hield of California (1950) reported an early spray of 2,4-D, or 2,4,5-T could increase the fruit size considerably in sweet orange, lemon, and grape-fruit. (An increase in lemon fruit size up to 31.9% was reported.) (3) Hield and Ruchel (1956) reported that the isopropyl and butyl esters of 2,4-D are the most effective derivatives of 2,4-D in preventing fruits from abscissed. However they are more difficult to obtain and expensive from local market. The sodium salts are water soluble and be easily prepared in a labratory with limited equipments. (4) Previous records showed that auxins, particularly NAA, of higher concentrations (70-200 ppms) resulted in a decrease in yield by increasing premature fruit abscission. (5) Collins said the maturity of the pineapple fruits could be delayed by NAA, sprayed at the early stage of the fruit development. The same effect was also observed by the author in Touliu Experimental Station, Taiwan Pineapple Corporation. (6) Reece and Horanic (1952) reported a December spray of 2,4,5-TP (concentration: 25-50 ppms) reduced up to 35% pre-harvest drop in Temple and Pineapple oranges. California (1949) reported that 2,4-D (4-8 ppms, ester form) with oil spray in September reduced pre-harvest drop in Washington Navel orange, and keep the fruits in good shape on trees till next March.