Introduction

The cultivation of kiwifruit (Actinidia Lindl.) in Korea is limited to the southern coastal region due to the potential for freezing injury in other regions during winter (Kwack et al. 2012, 2014). Kiwifruit has a simple cultivar composition in the market compared to other fruit crops. Currently, the predominant kiwifruit cultivar worldwide, including Korea, is green-fleshed ‘Hayward’ (Ferguson 1999). However, following the changes in commercial kiwifruit cultivars that occurred in 2000 with the advent of the yellow-fleshed kiwifruit, ‘Hort16A’, variability has been introduced into kiwifruit breeding programs.

Yellow - fleshed kiwifruit cultivars taste sweeter than the traditional, widely grown green cultivar. Therefore, the demand for yellow kiwifruit is increasing. However, farmers are subject to rules aimedat cultivar protection by the Plant Variety Protection Act. For example, in Korea, ‘Hort16A’ is produced on Jeju Island with permission from Zespri International. Farmers who do not have permission from Zespri cannot grow ‘Hort16A’ commercially.

Our kiwifruit breeding team, in coordination with the Rural Development Administration (RDA), has focused on releasing new yellow - fleshed kiwifruit cultivars for use by domestic farmers unable to grow ‘Hort16A’. Based on our efforts, which began in 2000, we have released nine yellow - fleshed cultivars to date. Some of the cultivars developed in the early 2000s have poor fruit quality and many lateral flowers, which must be thinned, requiring more labor compared to cultivars from New Zealand. The cultivar ‘Goldone’ was developed to compensate for these weaknesses. Here, we describe the characteristics of ‘Goldone’ kiwifruit.

Origin

In 2003, a conventional field cross was conducted at the RDA kiwifruit - breeding orchard (latitude: 34° 48’N; longitude: 127° 55’E) in Namhae, a region on the southern coast of South Korea. The parents of ‘Goldone’ originated from germplasm collections of A. chinensis var. chinensis that were introduced to Korea from China. The maternal vine, ‘Red Princess’, has red - colored flesh, and the paternal germplasm is named NHK0013 or IT233175 (Fig. 1). The first selection was made in 2006 and designated ‘2003 - 1 - 251’. After a 3 - year examination period to evaluate the vine and fruit characteristics of this cross, the resulting ‘Goldone’ cultivar was released in 2011. All observations and evaluations of fruit and vine features were performed according to the test guidelines of the Korea Seed & Variety Service (KSVS) for kiwifruit (2007) and the International Union for the Protection of New Varieties of Plants (UPOV) guidelines forA ctinidia (2001).

Description

‘Goldone’ is a tetraploid plant that produces oblong - shaped fruit (Figure 2). In general, this cultivar produced a few lateral flowers per cyme during the three season trials conducted in 2009, 2010 and 2011. Like other A. chinensis var. chinensis cultivars, this cultivar has no bud cover (Table 1), and it weakly expresses a calyx ring when the fruits are mature. The phenotypes of the fruit include sparse downy hairs on the exterior and a yellowish outer pericarp when ripe.

Table 1. Qualitative characteristics of ‘Goldone’ kiwifruit compared to other commercial cultivars grown under open field cultivation from 2009 – 2011 in Namhae, South Korea.

zPloidy level was determined via flow cytometry with a Partec ploidy analyzer, Partec CyFlow SL (Partec GmbH, Münster, Germany).

‘Goldone’ usually blooms in mid - May (Table 2). In our experimental field, ‘Hort16A’ bloomed approximately 6 to 10 days earlier than ‘Goldone’ during the three consecutive seasonal trials. Conversely, ‘Goldone’ was harvested approximately 6 to 19 days earlier than ‘Hort16A’ in late October (165 - 170 days after anthesis).

Table 2. Bud break, blooming, and harvest time for ‘Goldone’ kiwifruit compared to other commercial cultivars grown under open field cultivation from 2009 – 2011 in Namhae, South Korea.

zBeginning of bloom, when ‚ 10% of flowers on the vines had bloomed yFull bloom, when 70 ‚ 80% of flowers on the vines had bloomed xPick time, when soluble solids content reached 7.5 ‚ 8.5 °Brix.

The average fruit weight for ‘Goldone’ was 129 g, which is heavier than the control cultivars that were grown in parallel: ‘Hayward’, ‘Goldrush’ and ‘Hort16A’ (Table 3). By contrast, the length - to - diameter (LD) ratio and the flat ratio (max - to - minequatorial diameter) for ‘Goldone’ were smaller than those of the three other cultivars (Table 3). ‘Goldone’ also had a slightly lower soluble solids content (SSC) than the other cultivars. The acidity of ‘Goldone’ is similar to that of the other cultivars, except ‘Goldrush’ (Table 3).

Table 3. Quantitative characteristics of ‘Goldone’ kiwifruit compared to other commercial cultivars grown under open field cultivation from 2009 – 2011 in Namhae, South Korea.

zLD ratio, ratio of fruit length to fruit diameter yFlat ratio, ratio of maximum fruit diameter to minimum fruit daimeter xSoluble solids content was measured with an refractometer (PR -32 α, Atago, Bellevue, WA, USA) wTitratable acidity, citric acid content titrated with an automated titrimeter (TitroLine Easy, Schott, Mainz, Germany) vFlesh hardness was measured after cutting into the fruit skin .c 2 mm with a handy hardness meter (12 mm probe diamete, rFujiwara Scientific Co., Japan). umean separation in columns by the Duncan’s multiple range test at p = 0.05.

Performance

Like many other kiwifruit cultivars in this genus, ‘Goldone’ is not self - fertile (Ferguson 1990). Therefore, ‘Goldone’ requires artificial pollination or bee pollination to obtain commercial fruit set. However, there are currently no commercially available male vines that bloom at the same time or earlier than ‘Goldone’. Consequently, growers of ‘Goldone’ must keep pollen grains in a deep freezer at least one year prior to artificial pollination during the season of interest. ‘Goldone’ has 7 - 8 flowers per fruiting shoot, while the number of lateral flowers in a fruiting shoot is minimal (data not shown). Thus, ‘Goldone’ must also undergo flower thinning prior to blooming in order to reduce the amount of poleln grains required for pollination.

Compared with ‘Hayward’, ‘Goldrush’, and ‘Hort16A’, ‘Goldone’ produces the largest fruits (Table 3). Moreover, with proper fruit thinning to achieve fewer than two fruits per fruiting shoot, the resulting fruit weight can range from 150 to 180 g (data not shown). Thus, plant growth regulators are not required to increase fruit weight in this cultivar. Furthermore, in a practical orchard growing test, the SSC ranged from 13- 18 °Brix (data not shown).

Availability

‘Goldone’ was officially registered as a new cultivar in 2014 according to the Plant Variety Protection Act by the Commissioner of the KSVS under plant variety rights grant number 4835T. his cultivar was released for commercial growth in the Republic of Korea in 2015. All rights, including the propagation and selling of vines, were granted to Great Korea Kiwifruit Orchardist as specified in a 7- year contract approved by the RDA.

Disclosure Statement

The authors have no potential conflicts of interest to report.