Author : Surachai Muchjajib

Summary : To induce early flowering, four-year-old rambutan trees ("Roengrean") were sprayed twice during their vegetative stage with a commercial grade of ethephon at 1.0, 1.5, and 2.0 mM; paclobutrazol at 1.5, 3.0, and 4.5 mM and SADH at 15.0, 30.0, and 45.0 mM on 5 and 19 September 1987. Paclobutrazol sprayed at 1.5 or 3.0 mM appeared to be optimal for inducing earlier flower bud initiation. Flower buds were initiated 12 days earlier than control. A higher dosage (4.5 mM) of paclobutrazol retarded growth extensively and resulted to compact panicle. However, there were no adverse effect on flowering, fruit setting, and subsequent fruit development. SADH sprayed at all those concentrations and ethephon at 1.0 and 1.5 mM significantly induced earlier flower bud initiation by about five days. Foliar application of ethephon at 1.0 mM and paclobutrazol at 1.5 mM foliar significantly increased the percentage of flowering by 88.7 percent and 88.2 percent, respectively. The control trees had 75.0 percent flowering. Paclobutrazol sprayed at 1.5 mM was the optimum concentration to produce the highest yield (9.7 ton/ha), followed by SADH sprayed at 45.0 and 15.0 mM, and paclobutrazol at 4.5 mM. The control had 6.9 ton/ha and ethephon at 2.0 mM had the least (5.6 ton/ha). Yield increases of trees sprayed with paclobutrazol and SADH were due mainly to increase in the number of flowers/panicle, number of fruits/panicle, and enhanced percent flowering. The chemicals sprayed did not affect the fruit weight, size, aril thickness, and quality parameters of fruit at harvest. The greatest economic benefit derived from the various treatments was the accelerated fruit maturation, specially of those obtained by applied paclobutrazol sprayed at 3.0 and 1.5 mM. These concentrations may be commercially used to advance flowering of rambutan trees. "Roengrean" rambutan trees were sampled for anatomical study at a two-week interval. Flower bud ontogeny was similar in plants of rambutan grown under normal conditions and under treatment