Gibberellic Acid Produces Seedless Rambutan Fruits
Isn’t it more enjoyable to eat rambutan fruits when these are seedless? Yes, just like grapes, rambutan fruits can also be produced sans the seeds, a technology which is now being pioneered by the Aklan State University (ASU) in Banga, Aklan.
Dr. Marilyn Romaquin, dean of ASU College of Agriculture, Forestry and Environmental Sciences, accidentally came up with “seedless” rambutan that is sweet and has thicker aril or flesh by spraying them with gibberellic acid (GA3), a plant growth regulator or hormone.
“My discovery occurred in September 2003 while evaluating the effect of gibberellic acid on the yield and quality of rambutan (Nephelium lappaceum Linn.) fruits at harvest for my dissertation,” says Romaquin. That time, she was about to finish a doctorate degree in crop science, major in horticulture, from Central Luzon State University (CLSU) in the Science City of Muñoz, Nueva Ecija.
Romaquin said that GA3 induces parthenocarpy or seedlessness in fruits like grapes and is widely used for commercial crop production.
“I conducted my research using nine eight-year-old asexually propagated “Maharlika” rambutan trees near the ASU ranch,” Romaquin said. The trees were of uniform vigor, height and canopy.
The trees were divided into three groups, with each group representing the time of application with different concentrations (0 parts per million or ppm, 50 ppm, 100 ppm and 200 ppm) of GA3. These were before bud break, before full bloom and at fruit setting.
Upon sampling, however, Romaquin was surprised to see the fruits without seeds. A bit worried as she was wondering how to gather data, she called up her adviser, Dr. Danilo T. Eligio of CLSU. “It’s a breakthrough,” was all he said after telling him what she got. Suddenly, she realized that she had actually come up with a seedless rambutan.
Thus, Romaquin focused her study in the establishment of the proper concentration and time of application of GA3 that could induce seedlessness and to determine its influence on the physical attributes and quality of the fruits.
It has been noted that although rambutan fruits are produced in large bunches, each fruit has thin aril and big seed which make eating uncomfortable as one has to remove the seed, which in some varieties, sticks to the aril. Another drawback, is that the seeds add extra weight which also add to the cost. That is why a technology that may reduce the seed size or inhibit seed development through the use of growth regulators can help the rambutan industry, according to Romaquin.
In her study, Romaquin’s GA3-treated rambutan branches produced higher yields of 18 to 28 percent compared to untreated branches. The fruits have reduced length but not in diameter and weight which remained comparable with seeded fruits. The reason for this is that seeds are a source of growth hormones necessary for cell division and cell elongation. Thus, the absence of seeds may affect the growth of the fruit.
Romaquin also found that although GA3-treated trees produced smaller fruits, the weight of the aril was not affected and was sweeter over the seeded fruit.
What about the percentage of seedless fruits obtained?
Romaquin explained that the production of seedless fruits occurs naturally in rambutan but rare, with an average of 4.46 percent. But with the application of GA3 at 100 to 200 ppm, seedlessness is induced up to 100 percent.
Romaquin said, however, that the proper time of application is very crucial to the production of seedless rambutan fruits. And this she has yet to determine in the ongoing verification and validation studies that she is conducting with funding from the University.
Now on its third year, Romaquin said that the verification and validation trials did not yield data for the last two years due to typhoon Frank two years ago that devastated the province of Aklan. Added to this is the effect brought about by climate change that somehow hampered the regular fruit bearing pattern of some fruit trees, including rambutan. This year, she is hopeful that the trials will yield favorable results as these would determine the technology’s viability when adopted at the farmers’ level, especially during the off-season.
Romaquin is optimistic that the success of her research would mean a big help to rambutan growers in Aklan, particularly in Banga, which is the number one producer of this fruit in the province.
She said that seedless rambutan could open new opportunities for the rambutan industry. These include higher profit for the farmers as seedless rambutan can fetch a higher price, and the potential for processing such as canning, making into prunes or as an ingredient for specialty pies.
Researchers in the University have been finding the most suitable and marketable method of processing rambutan to address the oversupply of this fruit during peak season.
By Melpha M. Abello