BackgroundRed colour in kiwifruit results from the presence of anthocyanin pigments. Their expression, however, is complex, and varies among genotypes, species, tissues and environments. An understanding of the biosynthesis, physiology and genetics of the anthocyanins involved, and the control of their expression in different tissues, is required. A complex, the MBW complex, consisting of R2R3-MYB and bHLH transcription factors together with a WD-repeat protein, activates anthocyanin 3-O-galactosyltransferase (F3GT1) to produce anthocyanins. We examined the expression and genetic control of anthocyanins in flowers of Actinidia hybrid families segregating for red and white petal colour.ResultsFour inter-related backcross families between Actinidia chinensis Planch. var. chinensis and Actinidia eriantha Benth. were identified that segregated 1:1 for red or white petal colour. Flower pigments consisted of five known anthocyanins (two delphinidin-based and three cyanidin-based) and three unknowns. Intensity and hue differed in red petals from pale pink to deep magenta, and while intensity of colour increased with total concentration of anthocyanin, no association was found between any particular anthocyanin data and hue. Real time qPCR demonstrated that an R2R3 MYB, MYB110a, was expressed at significant levels in red-petalled progeny, but not in individuals with white petals.A microsatellite marker was developed that identified alleles that segregated with red petal colour, but not with ovary, stamen filament, or fruit flesh colour in these families. The marker mapped to chromosome 10 in Actinidia.The white petal phenotype was complemented by syringing Agrobacterium tumefaciens carrying Actinidia 35S::MYB110a into the petal tissue. Red pigments developed in white petals both with, and without, co-transformation with Actinidia bHLH partners. MYB110a was shown to directly activate Actinidia F3GT1 in transient assays.ConclusionsThe transcription factor, MYB110a, regulates anthocyanin production in petals in this hybrid population, but not in other flower tissues or mature fruit. The identification of delphinidin-based anthocyanins in these flowers provides candidates for colour enhancement in novel fruits.

No abstract

The current study illustrates that fruit breeding should not only target elite fruit that are significantly more liked than existing cultivars, but also target special unique fruit that create major new flavour niches. Breeding targets can be identified in terms of consumer preferences for new and defined flavours. A trained panel was used to assess the flavours of a wide range of kiwifruit, and these characteristics were systematically arranged into flavour and odour wheels. These wheels describe some of the diversity found within the kiwifruit germplasm. Next, consumers from Japan and New Zealand rated their overall liking of fruit from each of 10 genotypes. Consumer preference mapping was used to explore the relationships between consumer liking and flavour. Cluster analysis was used to explore the diverse responses consumers may have to the same fruit. Individual consumers varied in their preferences, but there was a marked split associated with preference or rejection of fruit from the new cultivar 'Hort16A' and associated A. chinensis genotypes. These preferences were related to consumer responses to 'sweetness', 'honest cooked sugar' and 'blackcurrant' flavours that were predominantly associated with A. chinensis genotypes, and absent in previous commercial kiwifruit cultivars. The first significant export of 'Hort16A' fruit occurred in 1998. Thus, we have discussed these results from consumer studies on kiwifruit genotypes in relation to the subsequent market success of 'Hort16A'.

Flowers of diploid Actinidia chinensis (kiwifruit) were hand-pollinated with pollen from either hexaploid A. deliciosa or diploid A. chinensis males and the subsequent fruit were evaluated. Following pollination with A. deliciosa pollen, fruit set, fresh weight, dry matter content, and seed weight and number were reduced. However, the most striking effect was on fruit flesh colour: the proportion of seedlings expressing red pigmentation, the intensity of pigmentation and the anthocyanin concentration were greatly reduced. The effects on maternal fruit tissues were probably indirect consequences of a reduction in the number of fertilized ovules due to partial pollen incompatibility. Effects on seed development could be explained largely by the ploidy difference between the seed and pollen parents. Growers should be cautious about using A. deliciosa pollen to pollinate diploid A. chinensis females, especially red-fleshed cultivars.

Chromosome numbers are reported for the first time for seven taxa ofActinidia: A. arguta var. purpurea, 2n = 8x = c. 232; A. deliciosa var. chlorocarpa, 2n = 6x = 174; A. deliciosa var. coloris, 2n = 6x = 174; A. glaucophylla, 2n = 2x = 58; A. guilinensis, 2n = 2x = 58; A. indochinensis, 2n = 2x = 58 and A. setosa 2n = 2x = 58. Ploidy variation has also been observed in A. melanandra and confinned in A. chinensis var. chinensis: 2n = 2x = 58 and 2n = 4x = 116. Chromosome numbers for another 11 Actinidia taxa were found to be in agreement with those previously reported. Chromosome numbers were the same for male and female plants of the same taxon. Detailed studies of chromosome morphology was not possible under the light micro- B96060Received 30 September 1996; accepted 10 March 1997 scope because of the small size of Actinidia chromosomes.

Kiwifruit are still a relatively minor crop making up perhaps 0.2% of total world annual production of fruit. The kiwifruit of commerce are large-fruited selections of two closely related species Actinidia chinensis and A. deliciosa. Most current kiwifruit cultivars are selections from the wild or from seedling populations and only a few result from planned hybridizations. The main emphasis in the breeding programs underway is on fruit novelty, flavor, size, time of harvest, flesh color, length of storage life, environmental adaptation and vine productivity. Until recently, nearly all the kiwifruit grown commercially outside China were of one green-fruited cultivar of A. deliciosa; now yellow-fleshed, sweeter flavored kiwifruit are becoming important in international trade. To take advantage of the considerable diversity within the genus requires good germplasm resources and a better knowledge of the reproductive biology of kiwifruit. The main constraints to breeding include dioecy, the long generation time and the complexity of some key traits as well as the need for support structures, the exuberant vegetative growth and the need to control growth to ensure fruiting. Many of the traits associated with fruit quality are quantitatively inherited. Use of molecular biological and biotechnological techniques should facilitate improvement programs.

BackgroundUnlike in abscission or dehiscence, fruit of kiwifruit Actinidia eriantha develop the ability for peel detachment when they are ripe and soft in the absence of a morphologically identifiable abscission zone. Two closely-related genotypes with contrasting detachment behaviour have been identified. The ‘good-peeling’ genotype has detachment with clean debonding of cells, and a peel tissue that does not tear. The ‘poor-peeling’ genotype has poor detachability, with cells that rupture upon debonding, and peel tissue that fragments easily.ResultsStructural studies indicated that peel detachability in both genotypes occurred in the outer pericarp beneath the hypodermis. Immunolabelling showed differences in methylesterification of pectin, where the interface of labelling coincided with the location of detachment in the good-peeling genotype, whereas in the poor-peeling genotype, no such interface existed. This zone of difference in methylesterification was enhanced by differential cell wall changes between the peel and outer pericarp tissue. Although both genotypes expressed two polygalacturonase genes, no enzyme activity was detected in the good-peeling genotype, suggesting limited pectin breakdown, keeping cell walls strong without tearing or fragmentation of the peel and flesh upon detachment. Differences in location and amounts of wall-stiffening galactan in the peel of the good-peeling genotype possibly contributed to this phenotype. Hemicellulose-acting transglycosylases were more active in the good-peeling genotype, suggesting an influence on peel flexibility by remodelling their substrates during development of detachability. High xyloglucanase activity in the peel of the good-peeling genotype may contribute by having a strengthening effect on the cellulose-xyloglucan network.ConclusionsIn fruit of A. eriantha, peel detachability is due to the establishment of a zone of discontinuity created by differential cell wall changes in peel and outer pericarp tissues that lead to changes in mechanical properties of the peel. During ripening, the peel becomes flexible and the cells continue to adhere strongly to each other, preventing breakage, whereas the underlying outer pericarp loses cell wall strength as softening proceeds. Together these results reveal a novel and interesting mechanism for enabling cell separation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-017-1034-2) contains supplementary material, which is available to authorized users.

Actinidia (kiwifruit) vary in peeling behavior from “difficult to peel” to “easy to peel.” Thus, the breeding of new cultivars of commercially acceptable kiwifruit with peelable skins is possible. Identification of skin properties conferring peelability and development of a simple, repeatable method for measuring peelability will be critical to the success of breeding programs. We assessed mechanical and biological characteristics of kiwifruit skins with respect to the ease with which fruit could be peeled. Values for skin–flesh adhesion, skin compliance in tension, and skin tearing were obtained, and a simple method for quantifying peelability developed based on knowledge of tearing of sheet materials. Using this test, we established that peelability varies among kiwifruit selections, but is only evident once fruit has ripened. We demonstrated that efficiency of peeling was dependent on the radius of curvature from which the skin is drawn away from the flesh. PRACTICAL APPLICATIONS The development of a peelable kiwifruit will enhance the diversity of products in the kiwifruit category and provide consumers with a more convenient option for eating this type of fruit. The information presented in this study contributes to the knowledge of the biological, structural and mechanical properties that influence skin‐to‐flesh adhesion and skin tearing behavior. The simple protocol for assessing peelability may be adapted for use in screening seedling populations for this trait.