【News】 Gibberellin plant hormone improves fruit-to-flower ratio of Kiyo plums from 2.6 percent to over 15 percent: Kumamoto institute (April 3, 2015)


Kumamoto Prefectural Agricultural Research Center’s Fruit Tree Research Station has confirmed that a fruit-to-flower ratio of Kiyo plums improves greatly if a solution of gibberellic acid (GA), a hormone found in plants, is sprayed over the trees which underwent artificial pollination.

The center pruned the trees, trimming mainly short fruit-bearing branches, hand-pollinated them thoroughly and then sprinkled 100 to 200 ppm of GA solution twice, 20 days and 50 days after full bloom.

Kiyo is a large-size, good-tasting plum variety which is marketed at high prices. But since it is a triploid variety, it does not always bear fruit only by pollination.

Sprinkling GA solution on young fruits resulted in improved fruiting, and farmers were allowed to use the solution as an agricultural chemical starting in the 2014 crop year. According to the application table, producers should apply 100 to 200 ppm of the solution twice, 20 to 30 days and 50 to 60 days after full bloom.

The center conducted experiments of combining the use of GA solution with thorough hand pollination, because spraying the solution alone could not bring forth fruit big enough to be marketed. According to their experiments, fruit-to-flower ratio measured 50 days after full bloom was 2.6 percent for crops without the solution and over 15 percent for solution-sprayed crops. As for the concentration of the solution, 200 ppm proved to be more effective compared to 100 ppm.

Although fruit formed on long branches of solution-sprayed trees were slightly small, those formed on short branches weighed roughly 150 grams, about the same size as those produced on trees without the solution. Fruit formed on long branches had slightly low sugar content, while those formed on short branches had sugar content of 18 or 19 percent, roughly the same as those grown in unsprayed areas.

Since the experiment had less effect on long branches compared with short branches, the center recommends using short collateral branches. When using long fruit-bearing branches of young trees, the solution should be sprayed exactly 20 days after full bloom, because many fruits fall off before the first spraying.

The tips of short fruit-bearing branches become sharp and hard after solution spraying, so producers must be careful the branches do not cause damage to fruits.

“Because plums with an embryo grow larger than those without one, GA should be sprayed after pollination is complete,” said a center researcher Megumi Hiramoto. “Since the GA solution costs much, it is enough to hand spray the solution directly on the fruits alone.”

(April 3, 2015)

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