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Fruit of colchicine-induced tetraploids of Actinidia chinensis were 50% to 60% larger than those of their diploid progenitors. In addition to fruit size, fruit quality is a key issue in any commercialization of these autotetraploids. We have made the first detailed study of the effects of chromosome doubling on fruit quality parameters other than size: these attributes include flesh firmness, color, soluble solid content (SSC), dry matter content (DM), vitamin C content, fruit skin thickness, and red pigmentation distribution in red-fleshed kiwifruit. Four selections from colchicine-induced tetraploids from the yellow-fleshed kiwifruit cultivar Hort16A were trialed for the stability of their fruit quality. Analysis of fruit at harvest over 3 years showed that fruit of the induced autotetraploids were significantly softer (lower flesh firmness), had lower DM, and had a less intense golden flesh color than fruit of their diploid progenitor. During development, SSC of fruit of the autotetraploid plants started to increase earlier than in the diploid ‘Hort16A’. This has been confirmed by replicated trials. No difference was found in vitamin C content between fruit of autotetraploids and diploids. Autotetraploids had significantly thicker skins than diploid ‘Hort16A’. Induced autotetraploids from three female genotypes of red-fleshed A. chinensis showed similar trends to autotetraploids of ‘Hort16A’ in fruit flesh firmness and outer pericarp flesh color, DM, SSC, and vitamin C. All the traits analyzed indicated that fruit of the autotetraploid plants matured earlier than those of their diploid progenitors. Furthermore, red pigmentation, one of the most important traits for red-fleshed kiwifruit breeding, showed a reduction in both intensity and distribution in the autotetraploids compared with their diploid progenitors. There was considerable variation among fruit of autotetraploid plants regenerated from each diploid progenitor. Therefore, selection among the regenerants may be required to achieve the best outcome after ploidy manipulation in kiwifruit breeding. Chromosome doubling has been widely explored as a bridge to help gene introgression between different ploidy levels both between and within species for crop improvement (Hayward et al., 1993; Meru, 2012; Wu et al., 2011). Both fruit and seed are often larger after chromosome doubling (Campos et al., 2009; Wu et al., 2012; Ye et al., 2010). However, very little information has been available on the effects of increasing ploidy level on other attributes of fruit quality considered important in crop improvement. Actinidia Lindl. (kiwifruit) species have only relatively recently been introduced into cultivation and grown as commercial crops. Most kiwifruit produced are consumed fresh (Ferguson, 2009), so returns to producers depend on the prices obtained for the fresh fruit. Factors influencing fruit price include total supply, season of supply, cultivar and, most important, fruit quality. Fruit quality in kiwifruit has many components such as fruit size, shape, flesh texture, color, flavor, firmness, DM, SSC, vitamin C content, core size, and skin color and thickness. Further expansion of the kiwifruit industry will require the development of new cultivars with enhanced sweetness, flavor, and storage life and a variety of flesh colors (Ferguson and Seal, 2008) as well as optimum fruit quality with easy handling during field management and harvesting, packing, storage, and marketing. In this article, we compare some aspects of fruit quality in some diploid selections of Actinidia chinensis with those of fruit from autotetraploids produced by colchicineinduced chromosome doubling. Our aim was to determine the effects of increasing the number of genomes on fruit quality and development using a number of easily measured attributes. During fruit development, SSC at harvest is an indicator of fruit maturity, and DM content reflects the potential SSC at eating ripeness once starch reserves have been converted to sugar (Burdon et al., 2004; Feng et al., 2011). Flesh firmness can also be used to assess fruit maturity and storage ability. One of the selections studied was ‘Hort16A’ and autotetraploids derived from it. As fruit of ‘Hort16A’ mature, the flesh color changes from green to yellow, and flesh hue angle (h) is one of the key parameters used to determine the quality and maturity of its fruit because the color appeals greatly to consumers. The three other selections studied came from a program to develop kiwifruit with red flesh: the extent and intensity of red pigmentation are important parameters for assessing quality in these selections. These various quality attributes were used to assess the possible commercial potential of the different selections and the autotetraploid plants derived from them. Materials and Methods Plants. The plants used comprised 11 clonally propagated vines of the diploid A. chinensis cultivar Hort16A and 77 independently derived colchicine-induced tetraploid regenerants of this cultivar. There were 11 clonally propagated plants of three genotypes of A. chinensis with red flesh, ‘Hort22D’, Selection 1 and Selection 2 (Wu et al., 2012), and 88 independently derived colchicine-induced autotetraploid plants produced from these three genotypes. Autotetraploids of ‘Hort16A’ were grouped into Type A (55 regenerants with large fruit of the same general shape as those of their diploid progenitor, ‘Hort16A’) and Type B (22 regenerants with smaller ‘‘fasciated’’ fruit); no such variation was observed in the autotetraploid plants regenerated from the three diploid red-fleshed genotypes of A. chinensis (Wu et al., 2012). All the regenerated autotetraploids were grown from in vitro culture and were on their own roots. The plants of ‘Hort16A’ and the 77 tetraploid regenerants were planted in the Plant & Food Research Orchard at Kerikeri. Two different genotypes of tetraploid A. chinensis Received for publication 23 Jan. 2013. Accepted for publication 11 Apr. 2013. We thank Nihal de Silva for statistical advice and Ian Hallett for guidance on measurements of skin thickness; Robert Campin, Paul Datson, Meng Meng, Eric Wu, and Hao Wu for assistance with fruit analysis and collection of some data; Tony Corbett for figure design; Jem Burdon, Jinquan Feng, and Anne Gunson for critical comments on the manuscript; and Mike Currie, Pauline Mooney. and Alan Seal for useful discussions. To whom reprint requests should be addressed; e-mail jinhu.wu@plantandfood.co.nz. HORTSCIENCE VOL. 48(6) JUNE 2013 701 males from the Plant & Food Research germplasm collection and a diploid A. chinensis male cultivar (Meteor) (1:2) were planted at a ratio of one male:eight female plants. The three ‘‘red-fleshed’’ genotypes and their autotetraploids were planted in the Plant & Food Research Orchard at Te Puke. The diploid male (‘Meteor’) was planted at a ratio of one male:six females along the same row. The tetraploid plants with their clonally propagated progenitor plants as controls, and males as pollenizers, were planted randomly in the rows of the two orchards as described by Wu et al. (2012). All vines were managed following standard orchard practices and grown on a modified T-bar structure. Fruit quality attributes. Fruit quality was evaluated on a sample of 10 fruit/year (2006– 08) that had been used to measure individual fruit weights and dimensions as described previously by Wu et al. (2012). Measurements began in the third year after planting in the orchard. Fruit were harvested on 23 May in 2006, 5 Apr. in 2007, and 11 May in 2008. The method of sampling was described previously (Wu et al., 2012). Fruit quality was evaluated over three seasons (2006–08) for diploid ‘Hort16A’ and its autotetraploid regenerants and two or three seasons (2007, 2008, and 2009) for the three diploid redfleshed genotypes and their autotetraploid regenerants. Fruit attributes other than fruit weight and dimensions were evaluated as follows: Flesh firmness was measured, using a handheld penetrometer (EFFEGI, Alphonsine, Italy; 8-mm probe), at opposite sides at the equator of the fruit after removal of a 1-mm layer of skin and outer pericarp. The two readings were averaged (Feng et al., 2003). Flesh color in the outer pericarp was measured at opposite sides at the equator of each fruit using a Minolta CR-300 Chroma meter (Osaka, Japan) after removal of a 2-mm layer of skin and outer pericarp. The two readings were averaged and color was expressed as hue angle (h), chroma (C*), and lightness (L*) (Feng et al., 2003). Soluble solids content was measured using a handheld refractometer (Atago , Tokyo, Japan) with one drop of juice from each end of the fruit combined. Dry matter content was measured by weighing a 4-mm thick equatorial slice of fruit cross-section (including skin, flesh, seeds. and core tissue) before and after drying at 60 C for 24 h. Vitamin C (ascorbic acid) was measured by the method described by Ferguson and MacRae (1992) using three batches of 15 fruit from each plant. A composite sample from each batch of 300 g was prepared by taking a sector, approximately onesixth, from each fruit. The reduced ascorbic acid of the samples was measured by titration against 2,6-dichlorophenolindophenol (Deutsch, 1996). Skin thickness was measured by taking a section of the skin using a Vibratome sectioning system (Series 1000, USA), photographing with a digital camera attached to an Olympus microscope (VanoxAHBT3), and determining skin thickness using an ImageJ system (image process and analysis in Java). Pigmentation in red-fleshed A. chinensis. The intensity of red pigmentation was scored on a 0 to 5 scale with no red scored as 0 and scores 1 to 5 (right to left, Fig. 1) representing a slight tinge of red, pale pink or red color, distinct red, dark red, and intense red, respectively, in equatorial cross-sections (Cheng et al., 2007). Pigment distribution was scored separately in fruit cr

Fruit Quality in Induced Polyploids of Actinidia chinensis