MARILYN E. ROMAQUIN, PhD DANILO T. ELIGIO, PhD Effect of Gibberellic Acid (GA3) on Seedlessness of Rambutan (Nephelium lappaceum, Linn.) MARILYN E. ROMAQUIN, PhD DANILO T. ELIGIO, PhD Aklan State University Banga, Aklan, Philippines

Rationale Rambutan (Nephelium lappaceum, Linn.), under the family Sapindaceae is native to Malaysia and Indonesia. It is presently grown and cultivated in Thailand, Burma, Vietnam, India, Sri Lanka, Australia and Puerto Rico. Rambutan is consumed fresh, canned, or preserved. The colorful fruits are frequently used in displays with flower arrangements. One major drawback for rambutan is its thin edible flesh and big seeds which makes it relatively expensive for consumers.

Rationale Rambutan flower buds could be induced to produce functional stamen using a plant growth regulator. The problem regarding the quality of rambutan cultivars could be resolved with the proper timing in the applications of plant growth regulators and fertilizers. Gibberellic acid (GA3) is one of the plant growth regulators that has gained popularity and demand among commercial fruit growers. The effect of GA3 in rambutan production was not yet tested. In this study, the influence of GA3 at different concentrations applied at different times on the quality of rambutan was evaluated.

Objectives The study was conducted to evaluate the effect of GA3 at different times of application and concentration on the yield and quality of rambutan fruits at harvest. Specifically it is aimed to: determine the effect of different concentrations of GA3 applied at different times; evaluate the effect of time of GA3 application on the quality of rambutan fruits; and find out the interaction effect of GA3 and time of application on the over-all yield and quality of rambutan fruits.

Experimental Site This study was conducted at the Rambutan Project of the Aklan State University, Banga, Aklan. The site is characterized by a sloping terrain with a ground elevation between 10 to 20 meters above sea level. The location falls under type 3 climate which has no pronounced season, dry period in February through April and wet period during the rest of the year. The wettest mouth is November; the driest month is April (Source: PAGASA – Roxas City).

Experimental Trees Nine 8-year old asexually propagated and bearing rambutan trees with almost uniform vigor, height and canopy was used.

Cultural Practices The following cultural practices were observed during the duration of the research: Weeding Fertilization Pruning

Experimental Design A Split-plot in Randomized Complete Block Design (RCBD) with three replications was used in this study. Main Treatment (A) - Time of application of GA3 A1 - Before Bud Break (BBB) A2 - Before Full Bloom (BFB) A3 - Fruit Setting Stage (FSS) Sub-treatment (B) - Varying concentration of GA3 B1 - 0 ppm (distilled water) B2 - 50 ppm B3 - 100 ppm B4 - 200 ppm

Data Gathered Total No. of Fruits per Cluster Length of the fruit Fruit Diameter Weight Per Fruit Percent Seedless Fruit Total Soluble Solids pH of the Fruit at Harvest Yield Per Branch Aril Weight

Statistical Tools F-test Analysis of Variance (ANOVA) Randomized Complete Block Design (RCBD) Duncan’s Multiple Range Test (DMRT)

Results and Discussion Results presented herein were reduced to the application of GA3 before bud break which showed positive response to the induction of seedlessness. Application at other times did not significantly promote seedlessness. The results are presented in the succeeding graphs.

Figure 1. Effect of GA3 on the Number of Rambutan Fruits per Cluster. ab Figure 1. Effect of GA3 on the Number of Rambutan Fruits per Cluster.

Figure 2. Effect of GA3 on the Length of Rambutan Fruits (mm).

Figure 3. Effect of GA3 on the Percentage of Seedless Fruits. b ab a Figure 3. Effect of GA3 on the Percentage of Seedless Fruits.

Figure 4. Effect of GA3 on TSS (°Brix).

Results and Discussion Production of seedless fruits occurs naturally in rambutan but rare with an average of 4.45 percent. Upon application of 50 ppm GA3, seedlessness significantly increased to 86.67 percent, attaining 100% with 200 ppm. This was noted when GA3 was applied before bud break. The consequence of seedlessness is the significant reduction in the length of fruits but not in diameter and weight of individual fruits which remained comparable to the seeded fruits.

Results and Discussion Decrease in the length of fruit was attributed to GA3 and not on the number of fruits, which also significant by increased with the application of GA3. Correlation analysis between length and the number of fruits was not significant (r=-0.155) while highly significant correlation was noted between seedlessness and length (r=-0.673**). Weight of aril, the edible portion, was not significantly affected by seedlessness, but seedless fruits was found to be significantly sweeter over the seeded ones. This was disclosed by the positive highly significant correlation between seedlessness and total soluble solid (r= 0.83**).

Results and Discussion Yield was the same for all treatments. By and large, it could be inferred that GA3 could induce seedlessness in rambutan. However, it should be applied at the proper stage and concentration. Based on the results of the study, 50 to 200 ppm GA3 applied before floral bud break could induced seedlessness.

Findings Results showed that the number of fruits significantly increased with the application of 50 to 200 ppm before bud break. Length and diameter of fruit, however, were significantly reduced by GA3, as a consequence, the weight of fruit likewise decreased. Proportion of seedless fruit significantly increased with the application of GA3 before bud break, which decreased at the later stages. Aril weight of the fruit remained comparable among treatments.

Findings Fruits harvested from branches applied with GA3 before bud break were found sweeter than fruits harvested from branches applied before full bloom and at fruit setting stage, as shown by the result of total soluble solids. Significantly higher yield was produced from GA3 treated branch before full bloom and at fruit setting stage due to higher number of harvested fruits.

Findings Application of GA3 can increase yield and induce higher proportion seedlessness in rambutan provided, GA3 is applied at the proper concentration and time. GA3 at 100-200 ppm sprayed before bud break produced high proportion of seedless fruits, which could solve problem of big seeds in rambutan without sacrificing aril weight and quality.

Conclusion Based on the results of the study, GA3 should be used from 100 to 200 ppm before bud break if the intention is to induce seedlessness.

Maraming salamat po!