Yellow-fleshed Kiwifruit Research Articles

NbPTR1 confers resistance against Pseudomonas syringae pv. actinidiae in kiwifruit.

Pseudomonas syringae pv. actinidiae biovar 3 (Psa3) causes a devastating canker disease in yellow-fleshed kiwifruit (Actinidia chinensis). The effector HopZ5, which is present in all isolates of Psa3 causing global outbreaks of pandemic kiwifruit canker disease, triggers immunity in Nicotiana benthamiana and is not recognised in susceptible A. chinensis cultivars. In a search for N. benthamiana nonhost resistance genes against HopZ5, we found that the nucleotide-binding leucine-rich repeat receptor NbPTR1 recognised HopZ5. RPM1-interacting protein 4orthologues from N. benthamiana and A. chinensis formed a complex with NbPTR1 and HopZ5 activity was able to disrupt this interaction. No functional orthologues of NbPTR1 were found in A. chinensis. NbPTR1 transformed into Psa3-susceptible A. chinensis var. chinensis 'Hort16A' plants introduced HopZ5-specific resistance against Psa3. Altogether, this study suggested that expressing NbPTR1 in Psa3-susceptible kiwifruit is a viable approach to acquiring resistance to Psa3 and it provides valuable information for engineering resistance in otherwise susceptible kiwifruit genotypes.

Increased ascorbic acid synthesis by overexpression of AcGGP3 ameliorates copper toxicity in kiwifruit

The widespread application of copper (Cu) -based fertilizers and pesticides could increase the accumulation of Cu in kiwifruit. According to a global survey, red- and yellow-fleshed kiwifruit contained more elevated amounts of Cu than green-fleshed kiwifruit due to weaker disease resistance and higher use of Cu pesticides. Intriguingly, our research revealed that external and endogenous ascorbic acid (AsA) reduced the phenotypic and physiological injury of Cu toxicity in kiwifruit. Cu stress assays and transcriptional analysis have shown that Cu treatment for 12 h significantly increased the AsA content in kiwifruit leaves and up-regulated key genes involved in AsA biosynthesis, such as GDP-L-galactose phosphorylase3 (GGP3) and GDP-mannose-3′,5′-epimerase (GME). Overexpressing GGP3 in transgenic kiwifruit significantly increased the endogenous AsA content of kiwifruit, which was beneficial in mitigating Cu toxicity by decreasing levels of reactive oxygen species, malondialdehyde, and electrolyte leakage, as well as reducing damage to the chloroplast structure and photosystem II. This study presented a novel strategy to ameliorate plant Cu stress by increasing the endogenous antioxidant (AsA) content through transgenesis.

Maturity biomarkers predicting storage performance of early-harvested yellow-fleshed kiwifruit identified using integrated multi-omics analysis

Accurate determination of kiwifruit maturity in the first half of the harvest window is crucial in predicting storage risk, since early-harvested fruit are more susceptible to disorders and rots during extended cold storage. Maturity estimations are usually based on soluble solids content (SSC), but SSC alone is unreliable at early harvest times, necessitating the need for more precise markers. To address this, we performed multi-omics on harvested, yellow-fleshed kiwifruit at four chronological ages based on days after anthesis, namely early harvest (H1), early-mid (H2), late-mid (H3) and late harvest (H4), across two seasons from the same orchard. Analysis of phenotype, transcriptome, metabolome, proteome, hormone concentrations and enzyme activity profiles identified discriminating features within the datasets that separated harvest times, particularly in the first half of the harvest window. Strong seasonal variability was observed. The most reliable variates for maturity estimation were found in the transcriptome, and two transcripts with sharply decreasing abundance during early harvest (Aquaporin TIP4-1 and MYB10) and three transcripts with sharply increasing abundance during later harvest (β-Amylase 3.2, Pectinesterase inhibitor protein and α-Terpineol synthase) with relative seasonal stability were identified. In a different season we used these five potential biomarkers in combination with SSC as a predictive tool. This allowed precise assessment of the maturity stage of fruit in the first half of the harvest window from 12 orchards in four geographical regions, and accurate prediction of their storage outcome.

Integrative Analysis of Metabolome and Transcriptome Reveals the Mechanism of Color Formation in Yellow-Fleshed Kiwifruit.

During the development of yellow-fleshed kiwifruit (Actinidia chinensis), the flesh appeared light pink at the initial stage, the pink faded at the fastest growth stage, and gradually changed into green. At the maturity stage, it showed bright yellow. In order to analyze the mechanism of flesh color change at the metabolic and gene transcription level, the relationship between color and changes of metabolites and key enzyme genes was studied. In this study, five time points (20 d, 58 d, 97 d, 136 d, and 175 d) of yellow-fleshed kiwifruit were used for flavonoid metabolites detection and transcriptome, and four time points (20 d, 97 d, 136 d, and 175 d) were used for targeted detection of carotenoids. Through the analysis of the content changes of flavonoid metabolites, it was found that the accumulation of pelargonidin and cyanidin and their respective anthocyanin derivatives was related to the pink flesh of young fruit, but not to delphinidin and its derivative anthocyanins. A total of 140 flavonoid compounds were detected in the flesh, among which anthocyanin and 76% of the flavonoid compounds had the highest content at 20 d, and began to decrease significantly at 58 d until 175 d, resulting in the pale-pink fading of the flesh. At the mature stage of fruit development (175 d), the degradation of chlorophyll and the increase of carotenoids jointly led to the change of flesh color from green to yellow, in addition to chlorophyll degradation. In kiwifruit flesh, 10 carotenoids were detected, with none of them being linear carotenoids. During the whole development process of kiwifruit, the content of β-carotene was always higher than that of α-carotene. In addition, β-cryptoxanthin was the most-accumulated pigment in the kiwifruit at 175 d. Through transcriptome analysis of kiwifruit flesh, seven key transcription factors for flavonoid biosynthesis and ten key transcription factors for carotenoid synthesis were screened. This study was the first to analyze the effect of flavonoid accumulation on the pink color of yellow-fleshed kiwifruit. The high proportion of β-cryptoxanthin in yellow-fleshed kiwifruit was preliminarily found. This provides information on metabolite accumulation for further revealing the pink color of yellow-fleshed kiwifruit, and also provides a new direction for the study of carotenoid biosynthesis and regulation in yellow-fleshed kiwifruit.

Integration of transcriptomic and metabolomic data reveals new tetraploid kiwifruit hybrids with enhanced nutrients

Compared to traditional diploids, polyploid red-fleshed kiwifruit varieties usually present excellent characteristics such as larger fruit, storage resistance and strong stress resistance. In this study, the male seed progeny of the wild red-fleshed tetraploid germplasm, ‘FXJX-CK-04137' (04137), was crossed with the tetraploid yellow-fleshed kiwifruit ‘Jinshi 2' (J2). Two lines (Line O5D and Line 11E) were filtered out with excellent appearance quality from thirty F1 progenies. The phenotypes are stably inherited with big and red-fleshed fruit by progeny analysis for several years. The transcriptome and metabolome of fruit of both lines and their parental lines were integrated and analyzed to pursue nutritional qualities. The result shows that both F1 hybrids are rich in flavonoids, carotenoids and vitamin C, making them good candidates for new tetraploid varieties. Ultimately, our data indicate that using tetraploid kiwifruit varieties is an efficient way to breed new commercial varieties with enhanced nutrition.

The Effects of Bagging on Color Change and Chemical Composition in ‘Jinyan’ Kiwifruit (Actinidia chinensis)

To explore the effect of bagging on the nutritional quality and color of kiwifruit (Actinidia spp.), the fruits of yellow-fleshed kiwifruit cultivars were analyzed after bagging treatment. Bagging treatment promoted the degreening of mesocarp and increased brightness. Bagging significantly reduced the accumulation of dry matter, titratable acids, starch, sucrose, fructose, and glucose during kiwifruit development. Additionally, bagging significantly reduced the accumulation of chlorophyll and carotenoids during development, whereas after debagging, the chlorophyll and carotenoid contents were significantly increased. Gene expression analysis showed that during most of the fruit development periods, the chlorophyll biosynthesis genes AcRCBS, AcGLUTR, and AcCHLG, and degradation genes AcCBR, AcPAO, AcPPH, AcCLH, and AcSGR had significantly lower expression levels in bagged fruit. Bagging also inhibited the expression of carotenoid metabolism genes, especially AcSGR and AcLCYB, which may play a key role in the process of fruit development during bagging by decreasing the accumulation of chlorophyll and carotenoids in kiwifruit. Additionally, bagging significantly reduced the content of AsA. The expression of the AsA biosynthesis genes AcPMI2, AcGPP2, and AcGalDH in bagged fruit was significantly lower than in the control, indicating that these may be the key genes responsible for the difference in the accumulation of AsA after bagging.

Non-destructive follow-up of ‘Jintao’ kiwifruit ripening through VIS-NIR spectroscopy – individual vs. average calibration model’s predictions

Visible/near infrared spectroscopy (Vis-NIRS) was used to monitor the yellow-fleshed kiwifruit (Actinidia chinensis Planch ‘Jintao’) ripening on two selected orchards along 13 weeks, from pre-harvest to the late harvest. Calibration models for several Internal Quality Attibutes (IQA) were built from the spectral data of 375 individual kiwifruit. The analyzed IQA were L*, a* and b* from the CIELAB color space, hue angle, chroma, firmness, dry matter (DM), soluble solids content (SSC), juice pH and titratable acidity (TA). Different pre-processing methods were tested for the construction of PLS calibration models. SSC and Hue were the best performing models with a correlation coefficient of 0.81 and 0.88, and root mean square error of prediction (RMSEP) of 1.27% and 1.95∘, respectively. The interpretation of the models in terms of the known absorption bands and the impact of signal to noise ratio (SNR) in them is discussed. The calibration models were used to perform average predictions of the IQA on orchard subareas, for each day of the experiment. These average predictions were compared with the IQA’s average reference values on the same subareas and days. The model’s metrics improved significantly through the averaging procedure, with RMSEP = 0.26–0.36% and R2 = 0.99 for SSC; and RMSEP = 0.42∘ – 0.56∘ and R2 ≈ 1 for Hue. Since orchard management is done essentially through averages and not individual values, this result reinforces the applicability of the NIR technology for follow-up of fruit ripening in the tree.

Pollen Application Methods Affecting Fruit Quality and Seed Formation in Artificial Pollination of Yellow-Fleshed Kiwifruit

This study investigated pollen application methods for artificial pollination in tetraploid kiwifruit cultivars ‘Halla Gold’ and ‘Sweet Gold’ grown in a nonheated plastic-film house in Jeju, Korea. Pollen of the hexaploid cultivar ‘Bohwa’ (A. chinensis var. deliciosa) bred in Korea was used for artificial pollination. We examined the effect of repeated pollination, pretreatment of stigma with wetting materials, application of dry pollen or pollen in suspension on fruit quality, and seed formation. With repeated pollination, pollen tubes in the pistil reached and penetrated the ovule three days after artificial pollination, although the pattern varied depending on the number of dry pollen applications. In both cultivars, the number of pollen tubes was clearly higher following repeated pollination than following single pollination, and fruit weight, dry matter (DM), number of seeds, and 100-seed weight were also higher. When pistillate flowers were pollinated with dry pollen immediately after water sprinkle, both cultivars showed the lowest fruit weight, DM, firmness, number of seeds, and 100-seed weight, whereas there were no significant differences in fruit quality or seed formation for dry pollen application 1 h after water sprinkle, or immediately or 1 h after suspension medium sprinkle. For pollination using a pollen suspension, the fruit weight was lower in both cultivars. There were no significant differences in fruit quality and seed formation following application of dry pollen or a pollen suspension, except for fruit weight in ‘Sweet Gold’. It could be seen from the results of this study that raindrops or dewdrops on the stigma might reduce the efficiency of artificial pollination using dry pollen. Still, the application of repeated pollination enhanced the efficiency of artificial pollination.

Interactions of Linearly Polarized and Unpolarized Light on Kiwifruit Using Aquaphotomics.

Near infrared (NIR) spectroscopy is an important tool for predicting the internal qualities of fruits. Using aquaphotomics, spectral changes between linearly polarized and unpolarized light were assessed on 200 commercially grown yellow-fleshed kiwifruit (Actinidia chinensis var. chinensis ‘Zesy002’). Measurements were performed on different configurations of unpeeled (intact) and peeled (cut) kiwifruit using a commercial handheld NIR instrument. Absorbance after applying standard normal variate (SNV) and second derivative Savitzky–Golay filters produced different spectral features for all configurations. An aquagram depicting all configurations suggests that linearly polarized light activated more free water states and unpolarized light activated more bound water states. At depth (≥1 mm), after several scattering events, all radiation is expected to be fully depolarized and interactions for incident polarized or unpolarized light will be similar, so any observed differences are attributable to the surface layers of the fruit. Aquagrams generated in terms of the fruit soluble solids content (SSC) were similar for all configurations, suggesting the SSC in fruit is not a contributing factor here.

Characterization and functional validation of β-carotene hydroxylase AcBCH genes in Actinidia chinensis.

Carotenoids are the pigment substances of yellow-fleshed kiwifruit, and among them β-cryptoxanthin has only been detected in the brighter yellow-fleshed variety ‘Jinshi 1’. β-Carotene hydroxylase (BCH) catalyzes the formation of β-cryptoxanthin and zeaxanthin, but its molecular characteristics and functions have not been fully explained. Here we isolated two β-carotene hydroxylase genes, AcBCH1 and AcBCH2 from kiwifruit (Actinidia chinensis), and their relative expression levels exhibited a close correlation with the content of β-cryptoxanthin. AcBCH1 catalyzed the formation of β-cryptoxanthin when transformed into β-carotene-accumulating yeast cells. Moreover, silenced expression of AcBCH1 in kiwifruit caused decreases in the contents of zeaxanthin, lutein, and β-cryptoxanthin, and an increase in β-carotene content. The content of β-carotene decreased significantly after the AcBCH1/2 genes were overexpressed in tomato. The content of zeaxanthin increased and β-carotene decreased in transgenic kiwifruit seedlings. The results will enrich our knowledge of the molecular mechanisms of carotenoid biosynthesis in kiwifruit.

Performance evaluation of a portable near-infrared spectrometer for assessment of main quality parameters in yellow-fleshed kiwifruit

Performance evaluation of a portable near-infrared spectrometer for assessment of main quality parameters in yellow-fleshed kiwifruit

Dynamic of nutrient uptake and partitioning within yellow-fleshed kiwifruit (Actinidia chinensis var. chinensis) organs

Dynamic of nutrient uptake and partitioning within yellow-fleshed kiwifruit (<i>Actinidia chinensis</i> var. <i>chinensis</i>) organs

Water use of yellow-fleshed kiwifruit during an annual cycle

Water use of yellow-fleshed kiwifruit during an annual cycle

Biochemical and molecular factors governing flesh-color development in two yellow-fleshed kiwifruit cultivars

To identify the biochemical and molecular factors causing flesh-color variation between two yellow-flesh kiwifruit cultivars 'Jinshi 1′ and 'Jinyan', the composition of carotenoids and chlorophyll, and associated gene expression profile in their pulp were investigated during fruit development. At harvest, ‘Jinshi 1′ exhibited brighter yellow flesh than ‘Hort16A’ with a lower color hue angle, although they had a similar total carotenoid content. At the molecular level, ‘Jinshi 1′ exhibited higher expression level of chlorophyll catabolic genes (CBR, PPH, and PAO), leading to lower accumulation of chlorophyll in the flesh. Meanwhile, higher expression levels of NCED1 resulted in greater carotenoid degradation in ‘Hort16A’. In addition, ‘Hort16A’ had a higher content of lutein, zeaxanthin and β-carotene, whereas ‘Jinshi 1′ had specific β-cryptoxanthin on ripening, accordingly, the expression of CHYB1, which encodes the enzyme for the formation of zeaxanthin and β-cryptoxanthin, was higher during the last developmental stage in ‘Jinshi 1′ than in ‘Hort16A’. These results suggested that the higher carotenoid/chlorophyll ratio, as well as the higher β-cryptoxanthin proportion are the important reasons for the brighter yellow flesh color.

Transcriptome Analysis of ‘Haegeum’ Gold Kiwifruit Following Ethylene Treatment to Improve Postharvest Ripening Quality

Fruit ripening involves changes in physical, physiological and metabolic activities through the actions of enzymes and regulatory genes. This study was initiated to identify the genes related to the ripening of kiwifruit. Gold ‘Haegeum’ kiwifruit is a yellow-fleshed kiwifruit cultivar usually used for fresh marketing. The fruit is harvested at a physiologically mature but unripe stage for proper storage, marketing distribution and longer shelf life. To identify the differentially expressed genes (DEGs) during ripening, fruit treated with ethylene were compared with control fruit that ripened naturally without ethylene treatment. Firmness, respiration rate, ethylene production rate, total soluble solids (TSS), titratable acidity (TA), brix acid ratio (BAR) and overall acceptability were taken during the study as fruit ripening indicators. Total mRNAs were sequenced by Illumina high-throughput sequencing platform and the transcriptome gene set was constructed by de novo assembly. We identified 99,601 unigenes with an average length of 511.77 bp in transcriptome contigs. A total of 28,582 differentially expressed unigenes were identified in the ethylene treatment vs. control. Of these 28,582 unigenes, 13,361 and 15,221 genes were up- and downregulated, respectively, in the treated fruit. The results also showed that 1682 and 855 genes were up- and downregulated, respectively, more than 2-fold at p &lt; 0.05 in fruit treated with ethylene as compared with the control fruit. Moreover, we identified 75 genes showing significantly different expression; 42 were upregulated, and 33 were downregulated. A possible category of the identified ripening-related genes was also made. The findings of this study will add to the available information on the effect of ethylene treatment on ripening and the related changes of kiwifruit at the genomic level, and it could assist the further study of genes related to ripening for kiwifruit breeding and improvement.

Changes in the carotenoids profile of two yellow-fleshed kiwifruit cultivars during storage

Abstract Carotenoid level in fruit changes dynamically in response to storage condition, however, the underlying mechanism remains unclear. Here, we investigated the carotenoid profiles and associated gene expression to reveal its responses to different storage temperature (20 °C and 4 °C) in two kiwifruit cultivars, bright-yellow-fleshed Jinshi 1 and pale-yellow-fleshed Jinyan. At harvest, four main carotenoids were detected in cv. Jinshi 1, while only three in cv. Jinyan, excluding β-cryptoxanthin, which accounted for the majority of carotenoids in ‘Jinshi 1’. Storage at 20 °C increased content of the total carotenoid and β-carotene in both cultivars, and up-regulated the expression of biosynthesis gene PSY, but down-regulated the expression of carotenoid degradation genes CCD1 and NCED1. It also induced β-cryptoxanthin and α-carotene production in Jinyan at later stage. On the contrary, storage at 4 °C decreased total carotenoid content, but induced the expression of carotenoid biosynthetic gene PDS, LCYB, LCYE. These results suggested expression of PSY, CCD1 and NCED1 plays an important role in improvement of carotenoids level at 20 °C. Furthermore, high proportion of β-cryptoxanthin might contribute to yellower flesh in Jinshi 1.

Comparative analysis of volatile metabolites, quality and sensory attributes of Actinidia chinensis fruit

Volatile organic compounds, quality and sensory parameters of four yellow- (‘Dorì’, ‘G3’, ‘Jintao’ and ‘Soreli’) and two green-fleshed (‘Hayward’ and ‘Summer’) kiwifruit cultivars were assessed. Statistical analysis was performed on volatiles, quality and sensory data for the identification of biomarkers of different kiwifruit cultivars. Principal component analysis showed that for all six samples a very good discrimination based on the cultivar was achieved. In particular, 2-pentylfuran can be used to distinguish between the green- and yellow-fleshed kiwifruit cultivars, while seven volatiles, can be identified as biomarkers of ‘Dorì’. These findings are in agreement with the sensory analysis, which revealed that ‘Dorì’, the richest cultivar in esters, showed very high values of both ripe fruit smell and sweet sensory traits. Altogether, these results could offer recommendations for future breeding efforts for the production of kiwifruit cultivars with improved nutritional and aroma quality.

Melatonin Application Increases Accumulation of Phenol substances in Kiwifruit during Storage

To investigate the effect of melatonin on the fruit quality during storage, fruits of ‘Jingshi No 1’, a new yellow-fleshed kiwifruit variety, were used as materials by soaking in 0.1 mmol·L-1 melatonin (MT) solution. The results showed that MT treatment significantly delayed the decline of fruit hardness, reduced the loss of soluble protein, and significantly lowered the accumulation of malondialdehyde when compared with the control. Moreover, MT application improved content of antioxandants, such as total phenolic, total flavonoid and flavanol content, and the antioxidant capacity measured by ABTS and FRAP. These results indicate that MT application can delay fruit softening and improve antioxidant ability by enhancing the accumulation of phenolic substances during storage.

Establishment of in vitro culture systems for breeding new types of kiwifruit and forActinidiagenomics studies

During the past 20 years kiwifruit has expanded dramatically in planting area and location, in total production, and also in diversity with different types of fruit. For example, variations in flesh colour have resulted in the commercialisation of green-fleshed, yellow-fleshed and red-fleshed kiwifruit. This diversity is from two large-fruited Actinidia species, A. chinensis and A. deliciosa, now widely grown throughout many parts of the world. Other fruit types may become available through use of other Actinidia species. The New Zealand Institute for Plant & Food Research Limited (PFR) has an active kiwifruit breeding programme to produce new kiwifruit cultivars that meet market requirements. An efficient in vitro biotechnology platform had been established to preserve and create new genotypes for rapid kiwifruit breeding through in vitro culture and propagation of various Actinidia species. Petiole and nodal shoot segments are produced from cuttings collected from dormant canes of adult plants in our germplasm repositories and breeding programme. This paper reviews the establishment of in vitro culture systems to allow chromosome doubling, micro-propagation, the testing of tolerance to bacterial canker of kiwifruit, and the development of new kiwifruit cultivars.

New red- and yellow-fleshed kiwifruit cultivars

New red- and yellow-fleshed kiwifruit cultivars