Kiwifruit vines are easily damaged by strong wind such as typhoon because of a feature having long petiole and large leaf blade. Leaf defoliation and tearing is such a typical wind damage and directly affects the sufficiency of photosynthates to retain normal plant growth and development through temporary destruction and recon- struction of photosynthetic factory depending on damage severity. Severe leaf loss causes the imbalance of carbohydrate supply between source and sink while inducing the competition for the assimilates supply among the sinks. High priority sinks such as shoots can utilize more carbohydrate supply than the lower priority sinks such as fruits, roots, and return bloom. The competition for assimilates supply was much severe at the peak growth phase of sinks.

Generally, the lack of carbohydrate supply has been negatively affected on the fruit quality in the current year and the flowering in following years. Tombesi et al. (1993) reported the reduction in fruit weight and soluble solid concentration in the current year while the reduction of percentage of bud burst in the following years at high level of defoliation in ‘Hayward’ kiwifruit vines. Furthermore, the reduction of flowering in the following year much greater than the final fruit yields in the current year when the vines subjected to severe defoliation (Buwalda and Smith, 1990; Minchin et al., 2010; Tombesi et al, 1993). According to, our previous study, the regrowth was observed in the first week after defoliation and the amount of carbohydrate supply was not significantly different at 34 days after defoliation (Srisook et al., 2015). Although, the defoliated vines can recover within one month after the removal of leaves, the surpass of negative impact on flowering in the following year is incompetent. The flowering process in kiwifruit initiates with the floral evocation during summer of the current year and completes with the development of floral organs in following year (Hopping, 1990). Shortage of carbohydrate supply during the floral evocation affected to the number of flowers in the following year (Snelga and Clearwater, 2007).

The different responses of artificially defoliated plants had been reported with the severity of leaf loss, plant growth conditions, and type of cultivar in kiwifruit vine (Buwalda and Smith, 1990) as well as papaya (Zhou et al., 2000) and peach (Lloyd and Daryl, 1990). There are two economically important species in the genus Actinidia, i.e., A. deliciosa ‘Hayward’ is green-flesh kiwifruit and A. chinensis is yellow-flesh type. These two species are distinguished by different characteristics, ploidy levels, and vine growth (Cheng et al., 2004; Ferguson, 1990). Several studies have been reported the effects of defoliation on flowering of A. deliciosa ‘Hayward’, the green-flesh kiwifruit. Buwalda and Smith (1990) showed 29% reduction of flowering and complete cessation of flowering in following year by removing all shoots within fruiting zone and within the replacement cane zone, respectively. Moreover, Cruz-Castillo et al. (2010) observed the 25% and 53% reduction in return bloom as the number of flowers per winter bud in ‘Hayward’ kiwifruit vine at the 50% and 75% defoliations, respectively. However, few studies have been reported about flowering of the yellow-flesh kiwifruit, A. chinensis. Richardson et al. (2001) recorded the variation in flowering within vines of two Actinidia chinensis (Planch.) var. chinensis cultivars, ‘Hort16A’ and ‘37- 3-18A’ as flowering capacities of 39 terminal flowers/m² of canopy and 106 terminal flowers/m² of canopy, respectively. Furthermore, Kwack et al. (2013) also observed the reduction in flower number per floral shoot in ‘Goldrush’ kiwifruit vines when the vines were defoliated more than 50% and the reduction was higher in September than in July and August defoliated vines. Moreover, the responses of vines to defoliation might be different among the cultivars and imposed time and the effects of negative impacts might be persisted over more than two seasons.

The objective of the present study was to evaluate the effects of levels and times of defoliation on flowering and fruit quality in A. chinensis ‘Jecy Gold’ kiwifruit in the following two years.

MATERIALS AND METHODS

Plant Materials and Treatments

Defoliation trials were carried out from 2013 to 2015 at the National Institute of Subtropical Agriculture (NISA), RDA in Jeju, Republic of Korea. Six-year-old ‘Jecy Gold’ kiwifruit (Actinidia chinensis) vines trained to pergola system in a non-heated plastic house were used and subjected to the standard cultural practices. The treatments were comprised of different defoliation levels with 0, 50, 75, and 100% and different defoliation time. The leaves were removed at the petiole junction of shoots at the regular intervals with one after next and one after next two for 50 and 75% defoliation, respectively or totally for 100% on August 23, 2013 (100 days after anthesis, DAA). Three replications consisting of one vine per replication were randomly assigned. Also, the vines were completely defoliated on July 28, 2014 and August 29, 2014 for comparing the response to defoliation time. Two vines were randomly distributed into each replication.

Measurement of Return Bloom, Flowering, and Fruit Quality in Subsequent Years

In April 2014 and 2015, the number of flowers per shoot and number of flowers per florescences were determined on randomly selected ten shoots per vine. The fruits were harvested on November 24, 2014 and November 12, 2015, respectively. Every single vine was harvested individually and ten fruits were randomly selected from each vine. Fruit weight, length, firmness, total soluble solid (TSS), fresh weight, dry weight, and dry matter content (DM) were measured for fruit quality at harvest (Srisook et al., 2015).

Statistical Analysis

All data were evaluated by analysis of variance using ANOVA procedure of Statistix^® 8 (Analytical Software, 2003); the mean differences were determined by LSD test, at the 5% level of significance.

RESULTS AND DISCUSSION

Influence of Defoliation Levels on Return Bloom and Fruit Quality in the Following Two Years

‘Jecy Gold’ kiwifruit vines were defoliated at 0%, 50%, 75%, and 100% in August 23, 2013. The 100% defoliation treatment was significantly reduced the number of flowers per shoot in year 2014. The reduction of the number of flowers per shoot in defoliated vines compared to undefoliated vines was 15.38%, 19.23%, and 50.00% with 50%, 75%, and 100% defoliation, respectively. The number of flowers per inflorescence was significantly reduced in all defoliation treatments compared with control in year 2014. The reduction of the number of flowers per inflorescence was 16.66%, 37.5%, and 58.33% with 50%, 75%, and 100% defoliation, respectively (Table 1). The significant reduction of the number of flowers per inflorescence also was observed in year 2015 for 75, and 100% defoliations compared to control. The reduction was 17.85%, and 25.00% with 75%, and 100% defoliation, respectively. There was no significant difference in the number of flowers per shoot in year 2015 (Table 1).

In our previous study, the significant reduction of starch and sucrose contents in bark tissue of ‘Jecy Gold’ kiwifruit were reported at 3 and 7 days after the defoliation in August 23, 2014 and the recovery of defoliated vines was observed at 34 days after defoliation (Srisook et al., 2015). Therefore, the shortage of carbohydrate supply caused the competition for assimilate supply among the sinks. According to Buwalda and Smith (1990), competitive strengths of the assimilate sinks ranking in descending order as shoot, fruits, roots, and return bloom of flowering. Due to the negligible assimilation in the return bloom sink the large reduction of flowering resulted in the following year after defoliation. In addition, lack of assimilates in shoots and trunk bark at the time of floral evocation contributed to the significant reduction in return bloom in kiwifruit vines (Cruz-Castillo et al., 2010). Further, Snelga et al. (1992) also reported the considerable reduction in return bloom by means of percentage of flower bearing shoots and the number of flowers per shoot due to the competition in carbohydrate supply between fruit and vegetative growth during flower evocation. In our contemporary study, a significant reduction of the number of flowers per inflorescence was recorded with 75% and 100% defoliation in both years, 2014 and 2015 and the reduction in 2015 was accounted as 50% for both 75% and 100% defoliation compared to 2014 (Table 1). These results supported the study of Snelgar and Manson (1993) described that flower differentiation was very sensitive to a lack of carbohydrate supply. Although, the reduction of flowering occurs even at the lowest defoliation level (Tombesi et al., 1993).

Fruits from the all experimental vines were harvested on 4 November, 2014 and 12 November, 2015. The fruit yields in one year after defoliation (2014) and two consecutive years after defoliation (2015) were not affected by defoliation. Further, the fruit growth and quality parameters, i.e., fruit length, width, and weight, fruit firmness, TSS, acidity, and DM were not significantly different with the defoliation treatments, i.e., 50, 75, and 100%, compared to the control (Table 2).

According to the recent findings, the considerable effects on kiwifruit growth and quality in the following year or two consecutive years were not found based on different defoliation levels. The fruit qualities such as, TSS, acidity, and skin coloration of grapevines cv. ‘Pinot noir’ were not significantly different in the following two years after two different types of defoliations commenced by removing of lateral leaves and removing all main leaves (Candolfi-Vasconcelos and Koblet, 1990). Moreover, Yuan et al. (2005) implemented the different levels of defoliation on ‘Hamlin’ orange trees during the harvesting season and not founded any negative impacts on fruit yield and fruit quality. The fruit quality of ‘Hayward’ kiwifruit by means of TSS, flesh firmness, and DM in the following year after defoliation was not affected by defoliation (Tombesi et al., 1993). The balance of carbohydrate supply between source and sinks in plants which are not subjected to the 100% defoliation can be compensated by the remaining leaves and newly immerging leaves after defoliation. This phenomenon was supported by Srisook et al. (2015) and reported that the significant reduction of starch and sucrose contents in the first two weeks after defoliation and they were recovered in one month after the defoliation. The recovery of starch and sucrose contents and the balanced mobilization from sucrose to sink organs might be resulted from the newly immerged leaves and remained leaves after defoliation. The optimum fruit growth and quality can be obtained with the unlimited availability of carbohydrates (Tombesi et al., 1993). However, according to the present data, the fruit growth and quality in the following year and two consecutive years in kiwifruit vines defoliated in the previous growing season had no effects on fruit growth and quality in either the following year or two consecutive years.

Influence of Defoliation Time on Return Bloom and Fruit Quality in the Following Year

The 100% artificial defoliation in July 28 and August 29, 2014 affected to the return bloom. The number of flowers per inflorescence between the control and defoliated vines was significantly decreased by 29.15% and 37.28% in July 28 and August 29, respectively (Table 3). The number of flowers per shoot was not affected significantly by defoliation time, nevertheless, July 28 and August 29 defoliation tended to decrease the number of flowers per shoot compared to control vines (Table 3).

The 100% defoliation on July 28 and August 29 in ‘Jecy Gold’ kiwifruit vines caused reduction of the number of flowers per shoot and the number of flowers per inflorescence in the following year. Kwack et al. (2013) reported a similar tendency in young and non-bearing fruit of ‘Goldrush’ kiwifruit, and there was no flowering in the following season on 100% defoliation vines on August 15 while flowering in the following season was decreased compared to control on the defoliated vines on July 15, September 15, and October 14. Buwalda and Smith (1990) reported that the defoliation within the replacement zone in ‘Hayward’ kiwifruit vines reduced return bloom, especially in the early of growing season while defoliation within the fruiting zone reduced flowering in the following season by up to 29%. Furthermore, Candolfi-Vasconcelos and Koblet (1990) described that the defoliation commenced by removing the all main leaves of ‘Pinot noir’ grapevines in the early stage of berry development caused a large reduction of flowering in the following season. Therefore, the flowering in the following season of kiwifruit vines is accomplished as the consequence of the floral evocation in the current season. With the severe limitations of the carbohydrates at the time of floral evocation, the flowering in the following year has been reduced due to the competition among the strong sinks such as shoots and fruits (Tombesi et al., 1993; Cruz-Castiil et al., 2010). Moreover, Snelgar and Mansor (1992) also reported the reduction of the flowering percentage in the following year of kiwifruit vines which were defoliated at any time of the growing season compared to the non defoliated vines. However, the results of the current study showed the more intense competition for carbohydrate availability of the August 29 defoliation compared to the July 28 defoliation.

Defoliation on July 28 and August 29, 2014 had no effect on fruit growth and fruit quality in the first following year (2015) in ‘Jecy Gold’ kiwifruit. Fruit growth parameters such as, fruit length, width, and weight were not affected by July 28 and August 29 defoliation compared to the control (Table 4). Defoliation treatments did not affect on TSS, acidity, and DM in defoliated vines compared to non-defoliated vines (Table 4).

Fruit growth and fruit quality in subsequent years after treated with 100% defoliation were not affected by July 28 and August 29 defoliation treatments. Similarly, Howell et al. (1994) reported that the defoliation at the different stages of fruit growth had no significant effect on fruit yield and fruit quality in the following year in ‘Pinot noir’ grapevines. Tombesi et al. (1993) also did not report any effects on the fruit weight and fruit qualities, i.e., TSS, flesh firmness, and DM one year after the defoliation in ‘Hayward’ kiwifruit. Also, the interaction between source and sink is important to initiate the severity of negative impact on plant growth during the defoliation damage period (Mayer, 1998). Nevertheless, under the optimum carbohydrate supply fruits can reach to the maximum growth rate and it’s not affected by the defoliation treatments (Tombesi et al., 1993). Therefore, the fruit growth and quality were not affected by the previous season defoliation treatments since the abundance of carbohydrate supply from photosynthesis in the current season.

In conclusion, the defoliation levels and times caused the reduction of return bloom and flowering in the subsequent years in ‘Jecy Gold’ kiwifruit. Nevertheless, the fruit growth and quality in the following two years were not affected by either defoliation levels or times. However, the reduction in flowering might be decreased the fruit yield in the subsequent years.

적 요

본 연구는 태풍과 같은 강풍에 의해 낙엽된 참다래 나무에 서 이듬해 동안의 피해 지속 정도를 평가하기 위하여 수행하 였다. 비닐하우스에 재식된 5년생 ’제시골드’ 참다래에서 2013 년 8월 29일에 0, 50, 75 및100% 등 4개 수준의 적엽처리 를 실시하였으며, 2014년 7월 28일 및 8월 29일에 100% 적 엽처리를 실시하였다. 적엽처리된 나무들은 이듬해인 2014년 및 2015년 2년 동안, 개화와 과실 품질에 대해 조사하였다.