Regrowth of Buds and Flower Bud Formation in Kiwifruit as Affected by Early Defoliation

BACKGROUND: Kiwifruit, which was introduced to Korea in late 1970s, is a warm-temperate fruit tree, whose leaves are easily damaged by wind because of their large size. To produce high quality fruits, efficient windbreak is necessary to protect leaves until harvest. In Korea, typhoons from July onwards usually influence the production of kiwifruit. Damages from typhoons include low fruit quality in the current year and low flowering ratio the following year. This study was conducted to investigate the effect of early defoliation of kiwifruit vines from July to October on the regrowth of shoot axillary buds the current year and bud break and flowering the following year. METHODS AND RESULTS: Scions of kiwifruit cultivar 'Goldrush' were veneer grafted onto five-year-old Actinidia deliciosa rootstocks, planted in Wagner pots (13L) and grown in a rain shelter. Kiwifruit leaves in the proximity of leaf stalk were cut by lopping shears to simulate mechanical damage from typhoon since only leaf stalks were left when kiwifruit vines were damaged by typhoons. Kiwifruit vines were defoliated from July 15 to October 14 with one monthintervals and degrees of defoliation were 0, 25, 50, 75 and 100%. All experiments were conducted in the rain shelter and replicated at least five times. Defoliation in July 15 resulted in a high regrowth ratio of 20-40% regardless of degree of defoliation but that in August 16 showed only 5.8% of regrowth ratio in the no defoliation treatment; however, more than 25% of defoliation in August 16 showed 17-23% of regrowth ratio. In September 15, regrowth ratio decreased further to less than 10% in all treatments and no regrowth was observed in October 14. Percent bud break of all defoliation treatments were not significant in comparison to 64.7% in no defoliation except for 42.1% and 42.9% in 100% defoliation in July 15 and August 16, respectively. Floral shoot in the no defoliation treatment was 70.2% and defoliation of 50% or less resulted in the same or increased floral shoot ratio in July 15, August 16, and September 15; however, defoliation in October 14 showed no difference in all treatments. In flower number per floral shoot, 2-3 flowers appeared in no defoliation and only 1 flower was observed when the vines were defoliated more than 50% in July 15 and September 15. In October 14, contrary to the floral shoot ratio, flower number decreased with increased defoliation. CONCLUSION(S): Therefore, it is suggested that dormancy of 'Goldrush' axillary buds, was started in August and completed in October. The effect of defoliation on bud break of axillary buds the following year was insignificant, except for 100% defoliation in July 15 and August 16. From July 15 to September 15, floral bud ratio was significantly reduced when more than 50% of leaves were defoliated compared to no defoliation. Also, the number of flowers per flower-bearing shoot the following year decreased by less than 50% when compared to no defoliation, and this decrease was more prominent in September 15 than July 15 and August 16.

조기낙엽에 따른 참다래(골드러쉬) 무착과 유목 액아의 발아와 착화

본 연구는 태풍에 의한 참다래 (골드러쉬) 조기 낙엽이 무착과 유목의 액아 발아와 착화에 미치는 영향을 분석하기 위해서 7, 8, 9, 및 10월에 인위적인 적엽처리를 하였다. 먼저 당해연도 액아의 재발아는 7월 적엽처리에서는 무처리의 23.2%와 마찬가지로 높은 재발아율을 나타냈다. 또한 8월의 경우 무처리의 재발아율은 5.8%로 낮았지만 적엽처리구는 17.23%의 높은 재발아율을 나타냈다. 하지만, 9월 적엽처리는 무처리의4.2%와 비슷한 낮은 재발아율을 나타냈으며, 10월 적엽처리에서는 재발아가 전혀 되지 않아 액아가 완전히 휴면에 진입한 것으로 판단되었다. 적엽처리에 의한 익년 착화율은 적엽시기와 적엽률에 따라 큰 영향을 받았다. 적엽 시기 중 7, 8, 9월에 75% 및 100% 적엽처리구는 무처리에 비해 유의성 있는 착화율 감소를 보인 반면, 10월 적엽처리는 적엽률에 관계없이 착화율에는 영향을 미치지 않는 것으로 나타났다. 그리고 착화 신초 한 개에 맺히는 꽃봉오리 수의 경우 75% 이상 적엽이 될 경우 무처리에 비해 절반 이하로 감소 되었다. 이와 같은 결과는 7월과 8월의 경우 적엽에 의해 꽃눈의 원기형성이 진행되어야할 액아의 재발아율이 높아 원기 형성이 감소했기 때문이며, 9월과 10월은 액아의 꽃눈 원기 형성은 어느 정도 이루어졌으나 광합성 산물 생산을 위한 잎의 부족 또는 부재로 저장양분 축적이 부족하여 이듬해 봄 꽃눈의 형태적 분화가 감소되었기 때문인 것으로 판단된다.