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

'흑보석' 포도의 GA₃와 Thidiazuron(TDZ) 처리에 따른 과육 연화 지연 및 과실특성

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 $GA_3$ of low concentrations was used, but the expected yield was recovered by combined treatment with TDZ and $GA_3$. When harvested on the basis of color, the harvest rate up to 100 days after full bloom (DAFB) was low with the $GA_3$ 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 $GA_3$ and TDZ. In particular, the fruit quality was improved based on the delay of softening in primary and secondary treatments of $25mg{\cdot}L^{-1}\;GA_3+2.5mg{\cdot}L^{-1}$ 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 $25mg{\cdot}L^{-1}\;GA_3+2.5mg{\cdot}L^{-1}$ TDZ.

본 연구는 $GA_3$와 TDZ 처리에 따른 '흑보석' 포도의 품질 특성변화와 과실 연화 지연을 위한 생장조절제의 효과를 구명하기 위하여 실시하였다. 최종생산량은 저농도 $GA_3$ 단용처리에서 목표생산량 대비 88.3%로 낮았으나 TDZ를 2차에 혼용함으로써 최종생산량은 회복되었다. 착색을 기준으로 수확하였을 때 만개 후 100일까지의 수확률은 $GA_3$ 단용처리시 낮은 수확률을 보였으며 TDZ를 혼용할 경우 상쇄되었고 특히 2차에 혼용할 경우 효과적이었다. 반면에 생장조절제 처리시 가용성 고형물 함량은 만개 후 90일 이후에는 큰 변화가 없었으며 산 함량은 만개 후 90일부터 급격히 감소되어 당도와 산도를 기준으로 할 경우 오히려 무처리구에 비해 일찍 성숙기에 도달하였다. 경도는 $GA_3$와 TDZ 처리에 의해 활발한 세포비대와 세포분열로 과피가 두꺼워지고 밀도가 증가함에 따라 무처리구에 비해 만개 후 최종 수확시까지 높게 유지되었으며 특히 1, 2차 $GA_3$ $2.5mg{\cdot}L^{-1}$ + TDZ $2.5mg{\cdot}L^{-1}$ 처리구에서 연화가 지연되어 과실의 품질을 개선할 수 있을 것으로 생각되었다. 무핵과실은 TDZ를 혼용시에도 가장 높은 무핵률이 65.5%에 불과하여 무핵유기가 어려웠으며 열과발생은 모든 처리구에서 0.0-0.9%로 거의 발생하지 않았다. 따라서 '흑보석' 포도는 1, 2차 $GA_3$ $2.5mg{\cdot}L^{-1}$ + TDZ $2.5mg{\cdot}L^{-1}$로 처리하여 경도가 급격히 낮아지기 전인 만개 후 100일 이전에 수확하는 것이 적절할 것으로 생각되었다.