Characteristics of the Fruits and Flesh Softening Delay Induced by GA3 and Thidiazuron (TDZ) Treatment in ‘Heukboseok’ Grape

Abstract

This research was conducted to investigate effect the plant growth regulators (PGRs) on the characteristics of fruit and flesh softening, using GA₃ and thidiazuron (TDZ) treatments in ‘Heukboseok’ grapes. The total yield obtained under PGR treatment was 88.3% lower than the target production when a single treatment with GA₃ of low concentrations was used, but the expected yield was recovered by combined treatment with TDZ and GA₃. When harvested on the basis of color, the harvest rate up to 100 days after full bloom (DAFB) was low with t he GA₃ single treatment, but was increased by the addition of TDZ, with the second TDZ mixed treatment being particularly effective. The soluble solids content in the PGR-treated samples demonstrated no significant changes after 90 DAFB, while the acidity content decreased rapidly starting from 90 DAFB. Measured on the basis of sugar and acidity content, maturity was reached much earlier in treated fruit than in the non-treated fruit. Firmness was maintained at a higher level until the final harvest time after PGR treatment compared to untreated grapes according to epidermis thickness and flesh density increase to activity cell division and expansion by GA₃ and TDZ. In particular, the fruit quality was improved based on the delay of softening in primary and secondary treatments of 25 ㎎·L -1 GA₃ + 2 .5 ㎎·L -1 TDZ. The production of seedless fruit was difficult, even with the inclusion of TDZ, reaching the highest seedless rate of only 65.5%. Fruit cracking was rare, occurring at a rate of about 0.0~0.9% in all treatments. Accordingly, ‘Heukboseok’ grapes should be harvested within 100 days after full bloom (DBFB) before a rapid decrease of firmness, conferred by primary and secondary treatments with 25 ㎎·L -1 GA₃ + 2.5 ㎎·L -1 TDZ.