Kiwifruit Cultivation Research Articles

Copper Resistance in Pseudomonas syringae pv. actinidiae Strains from the Prefecture of Pella, Northern Greece, and a Comparison of the Effectiveness of Several Commercial Products to Control

This study highlights the growing concern over copper resistance in Pseudomonas syringae pv. actinidiae (Psa), a significant pathogen threatening kiwifruit cultivation globally. Copper-based treatments, widely used for their broad-spectrum bactericidal properties, have become less effective over time due to the emergence of copper-resistant strains. This study found that 22 strains of Psa, collected from Greek kiwifruit orchards, exhibited significant copper resistance. All strains were capable of growing in copper concentrations of at least 200 µg/mL (0.8 mM), and two strains (9.1%) survived even at higher concentrations of 400 µg/mL (1.6 mM). Additionally, resistant bacterial colonies were observed in four strains (18.2%), suggesting the presence of resistant subpopulations within the broader bacterial community. In addition to studying copper resistance, the research evaluated the effectiveness of several products in controlling Psa through field experiments. The copper products IONIC CONCENTRATED COPPER, MAGNA BLUE, and COPROFIX ULTRA were tested due to their historical effectiveness in managing bacterial diseases in plants. However, these copper products were unable to fully control Psa in this study, likely due to the observed resistance. In addition, the plant defense activator products MICONIC and NUTRI BIOCLEAN, NUTRI BIOCLEAN, BAR, and BION were evaluated and showed promising results in reducing the intensity of symptoms associated with Psa, suggesting that these formulations may enhance the plant’s natural defenses against the pathogen. While these products did not completely eliminate the disease, they significantly reduced symptom severity. The findings highlight the need for alternative strategies to combat Psa, particularly in areas where copper resistance has developed.

Pseudocercospora fengxinensis, a new species causing sooty spot of kiwifruit in China.

Pseudocercospora is a large cosmopolitan genus of plant pathogenic fungi that are commonly associated with leaf and fruit spots as well as blights on a wide range of plant hosts. P. actinidiae is a member of this genus, causing sooty spot on kiwifruit worldwide. With the expansion of kiwifruit cultivation, the incidence of sooty spot has become severe in Fengxin County, Jiangxi Province, China. Based on a survey conducted in 2022 across nine kiwifruit cultivars in six local orchards, the results showed that the disease incidence was higher in 'Donghong', 'Jinyan', 'Jinkui', 'Fenghuang No. 1' and 'Jinguo'. In contrast, it was lower in 'Gold3' and 'Hongshi No. 2'. No lesions were observed on 'Kuilv' and 'Miliang No. 1'. 31 fungal strains were isolated from infected leaves using single-spore isolation. Phylogenetic analysis of combined sequence data from the internal transcribed spacer region of ribosomal DNA (ITS), partial actin (actA), translation elongation factor 1-alpha (tef1), and the second largest subunit of RNA polymerase II (rpb2) sequence data, using maximum-likelihood (ML) and Bayesian inference (BI), revealed their taxonomic placement within Pseudocercospora. Both morphological and molecular phylogenetic analysis supported Pseudocercospora fengxinensis as a new taxon within Pseudocercospora. Pathogenicity tests confirmed P. fengxinensis as the causal agent of sooty spot on kiwifruit. This study is the first report of P. fengxinensis causing sooty spot of kiwifruit worldwide, enriching our understanding of Pseudocercospora diversity in China and providing a foundation for improved disease management strategies.

Actinidia strigosa Hook. f. & Thomson (Actinidiaceae): A Future Plant with Higher Economic Importance in Hilley-Barsey Sanctuary, Sikkim, India

The present study was conducted during the period August, 2021 to March, 2023 in Sikkim state of Northeast India. Actinidia strigosa Hook. f. & Thomson (Theki Phal/wild kiwifruit) is a temperate climbing shrubby plant species, collected from the Hilley-Barsey Sanctuary, West Sikkim, India. It has been observed that this plant is associated with the daily needs of the locals and used for various economic purposes, such as fresh fruit for table purposes, fodder, medicine, and for the preparation of fruit wine. During the field survey in 2021, the plant species A. strigosa was collected from Ribdi (2203 m) to Hilley (2679 m) within the Hilley-Barsey Sanctuary for further study. The distribution of Actinidia strigosa is confined to the Eastern Himalayas, specifically in Sikkim (West, South and East districts), West Bengal (Darjeeling hills), and eastern Nepal, at an altitudes of 2100-2600 m. It has the potential to be used in the kiwifruit breeding industry as gene source to enhance cold tolerance and expand kiwifruit cultivation to high altitudes in the Himalayan regions. Due to its economic importance and limited distribution, conservation is essential, as the plant is vulnerable to uprooting and injury, especially in areas like the Hilley-Barsey Sanctuary in West Sikkim. Being endemic to its area of occurrence with maximum diversity in its morphology at Hilley-Barsey Rhododendron Sanctuary, West Sikkim, the sanctuary must be recognised a biodiversity hotspot for A. strigosa.

Web-based Land Suitability Analysis for Horticulture Crop (Kiwi) in Champawat districts, Uttrakhand using MCDM and Geospatial Analysis

Identifying the suitability of a horticulture fruit with a defined area is an active research area, it has been attempted through different approaches, surveying and geographic information system are the two most popular techniques utilized extensively for this activity across the globe. GIS has its proven advantage over the field surveys based approach and modern GIS tools offers automation of the entire work flow for this activity. This study presents a web-based land suitability analysis for kiwi fruit cultivation in the Champawat District of Uttarakhand, using AHP, TOPSIS, and Ensemble modeling in conjunction with Multi-Criteria Decision Making (MCDM) and Geospatial Analysis. Land suitability was evaluated across various classes based on nine criteria viz. elevation, chilling hours, land use/land cover (LULC), soil texture, soil depth, temperature, rainfall, slope, and aspect. The AHP method identified 26.09 hectares as highly suitable, 14,606.19 hectares as suitable, 31,899.77 hectares as moderately suitable, 8,807.99 hectares as less suitable, and 192.23 hectares as not suitable. TOPSIS results showed 4,294.32 hectares as highly suitable, 14,193.54 hectares as suitable, 11,782.52 hectares as moderately suitable, and 2,399.21 hectares as less suitable. The ensemble method indicated 24.15 hectares as highly suitable, 8,763.51 hectares as suitable, 13,785.13 hectares as moderately suitable, 2,472.13 hectares as less suitable, and 191.94 hectares as not suitable. Integrating these findings revealed that the ensemble approach closely aligns with AHP in identifying highly suitable and less suitable areas, while TOPSIS emphasizes moderate suitability. This synthesis provides valuable insights for land use planning for kiwi cultivation. Additionally, an online spatial decision support system (SDSS) was developed using the Django framework, offering a modular and secure environment for informed decision-making.

Effect of the Localized Insecticides Spray Technique to Control Halyomorpha halys in Actinidia chinensis Orchards.

Kiwifruit (Actinidia chinensis) cultivation is expanding worldwide, with China, New Zealand, and Italy being the major producing countries. Halyomorpha halys, the brown marmorated stink bug, is raising serious concerns to kiwifruit cultivation both in China and Italy. This study aimed at improving the chemical control efficacy against this pest by comparing two insecticide spray techniques (a conventional ray atomizer and a trumpet-modified atomizer adapted for localized spray application) in kiwifruit. In fact, kiwifruit is often grown with a 'pergola' training system, which may reduce the effectiveness of insecticide penetration into the canopy. Experiments were performed in naturally infested orchards of both Actinidia chinensis var. chinensis 'Jintao' and A. chinensis var. deliciosa 'Hayward'. Furthermore, mesh cages containing H. halys adults were deployed within orchards to assess the insects' mortality at 1, 3, 7, and 10 days after an insecticide application with two spray techniques during two consecutive seasons. In the cultivar 'Jintao', the two systems performed similarly, while in the cultivar 'Hayward', an overall significantly higher insect mortality was recorded with the trumpet atomizer (94-100%) compared to the conventional atomizer (59-78%). Crop damage was also evaluated on both cultivars, simulating the grower insecticide applications with the two spray techniques. At harvest, no difference emerged between the spray techniques, which provided a significantly better protection compared to the untreated control (12-17% compared to 33-47% of injured fruits). Further investigations in this direction are needed also considering the restriction of insecticidal active substances ongoing in the European Union and the need to maximize the efficacy of the available tools.

Climate Change Impacts on and Response Strategies for Kiwifruit Production: A Comprehensive Review.

Climate change, a pressing global concern, poses significant challenges to agricultural systems worldwide. Among the myriad impacts of climate change, the cultivation of kiwifruit trees (Actinidia spp.) faces multifaceted challenges. In this review, we delve into the intricate effects of climate change on kiwifruit production, which span phenological shifts, distributional changes, physiological responses, and ecological interactions. Understanding these complexities is crucial for devising effective adaptation and mitigation strategies to safeguard kiwifruit production amidst climate variability. This review scrutinizes the influence of rising global temperatures, altered precipitation patterns, and a heightened frequency of extreme weather events on the regions where kiwifruits are cultivated. Additionally, it delves into the ramifications of changing climatic conditions on kiwifruit tree physiology, phenology, and susceptibility to pests and diseases. The economic and social repercussions of climate change on kiwifruit production, including yield losses, livelihood impacts, and market dynamics, are thoroughly examined. In response to these challenges, this review proposes tailored adaptation and mitigation strategies for kiwifruit cultivation. This includes breeding climate-resilient kiwifruit cultivars of the Actinidia species that could withstand drought and high temperatures. Additional measures would involve implementing sustainable farming practices like irrigation, mulching, rain shelters, and shade management, as well as conserving soil and water resources. Through an examination of the literature, this review showcases the existing innovative approaches for climate change adaptation in kiwifruit farming. It concludes with recommendations for future research directions aimed at promoting the sustainability and resilience of fruit production, particularly in the context of kiwifruit cultivation, amid a changing climate.

Kiwifruit in the Omics Age: Advances in Genomics, Breeding, and Beyond.

The kiwifruit, Actinidia genus, has emerged as a nutritionally rich and economically significant crop with a history rooted in China. This review paper examines the global journey of the kiwifruit, its genetic diversity, and the role of advanced breeding techniques in its cultivation and improvement. The expansion of kiwifruit cultivation from China to New Zealand, Italy, Chile and beyond, driven by the development of new cultivars and improved agricultural practices, is discussed, highlighting the fruit's high content of vitamins C, E, and K. The genetic resources within the Actinidia genus are reviewed, with emphasis on the potential of this diversity in breeding programs. The review provides extensive coverage to the application of modern omics technologies, including genomics, transcriptomics, proteomics, and metabolomics, which have revolutionized the understanding of the biology of kiwifruit and facilitated targeted breeding efforts. It examines both conventional breeding methods and modern approaches, like marker-assisted selection, genomic selection, mutation breeding, and the potential of CRISPR-Cas9 technology for precise trait enhancement. Special attention is paid to interspecific hybridization and cisgenesis as strategies for incorporating beneficial traits and developing superior kiwifruit varieties. This comprehensive synthesis not only sheds light on the current state of kiwifruit research and breeding, but also outlines the future directions and challenges in the field, underscoring the importance of integrating traditional and omics-based approaches to meet the demands of a changing global climate and market preferences.

Honeybee (Apis mellifera L.) pollination enhances the yield and flavor quality of kiwifruit.

Pollination is essential for achieving high yields and enhancing the quality of kiwifruit cultivation, both of which significantly influence growers' interests and consumers' preferences. However, compared to studies on yield, there are fewer studies exploring the impact of pollination methods on the flavor of kiwifruit Actinidia chinensis Planchon. This study examined the effects of bee (Apis mellifera L.) pollination and artificial pollination on the yield and flavor of kiwifruit in the main producing areas of China. Compared with those pollinated artificially, bee-pollinated kiwifruit exhibited a greater fruit set rate, heavier fruit weight, and greater number of seeds. Notably, the number of seeds was positively correlated with fruit weight in bee-pollinated kiwifruit, whereas no such correlation was detected in artificially pollinated fruit. Bee pollination not only enhanced the yield but also improved the flavor of kiwifruit. Specifically, bee-pollinated kiwifruit contained higher levels of sucrose and lower concentrations of glucose and fructose, while the acid content was less affected by pollination methods. Furthermore, significant differences were observed in the volatile organic compound (VOC) levels in kiwifruit subjected to different pollination treatments, with bee-pollinated fruit exhibiting a superior flavor. Our findings provide new insights into the beneficial role of bee pollination in enhancing kiwifruit yield and quality, underscoring the crucial importance of bees in kiwifruit pollination.

Socio-economic characterization of Portuguese kiwi growers: Facing current social and sustainability challenges

This paper reports a socio-economic characterization of the Portuguese kiwifruit sector. A survey was applied between 2019 and 2020 to a sample of 94 kiwifruit farmers (males 76%, females 24%). 72 percent of the participants declare that kiwi cultivation is a complementary occupation characterized by an intergenerational pattern (25.6%). Almost 70 percent of the orchards are under 5 ha, and 26.8 percent declare that their company does not have a positive turnover. The labour force is mainly seasonal. Regarding the challenges, 21.1 percent struggle with disease control in their orchards and 19.0 percent have difficulty in finding workers. The findings contribute to a nuanced understanding of the socio-economic dynamics underpinning kiwifruit cultivation in Portugal, offering insights for policy interventions and sectoral development strategies.

Advancement of kiwifruit cultivation in Nepal: Top working techniques

In recent years, there have been notable advancements in the cultivation techniques of kiwifruit, a fruit that is both popular and economically important. One particular practice that has gained recognition is top-working, which involves grafting new scions onto existing rootstocks. This horticultural technique has shown promise in improving yield, disease resistance, and overall productivity in orchards. This comprehensive review paper examines the different methods used in top working for kiwifruit cultivation, explores the factors that influence its success, and discusses the benefits and challenges associated with this practice. This review provides an overview of various techniques used for the top-working kiwifruit plants in Nepal. The success of top-working depends on factors such as timing, compatibility between scion and rootstock, grafting materials, and proper grafting techniques. This review paper also ranges over the importance of kiwifruit cultivation for Nepalese farmers, problems faced by them, persistent constraints in the country, and the future promise that kiwifruit cultivation holds for the economic advancement of the nation.

Melatonin and 14-hydroxyed brassinosteroid combined promote kiwifruit seedling growth by improving soil microbial distribution, enzyme activity and nutrients uptake.

Kiwifruit, a nutrient-dense fruit, has become increasingly popular with consumers in recent decades. However, kiwifruit trees are prone to stunted growth after a few years of planting, called early tree decline. In this study, melatonin (MT), pollen polysaccharide (SF), 14-hydroxyed brassinosteroid (14-HBR) were applied alone or in combination to investigate their influence on plant growth, nutrition absorption and rhizosphere bacterial abundance in kiwifruit seedlings. The results revealed that MT, SF and 14-HBR alone treatments significantly increased leaf chlorophyll content, photosynthetic capacity and activities of dismutase and catalase compared with the control. Among them, MT treatment significantly increased the dry root biomass by 35.7%, while MT+14-HBR treatment significant enhanced the dry shoot biomass by 36.9%. Furthermore, both MT and MT+14-HBR treatments markedly improved the activities of invertase, urease, protease and phosphatase in soil, as well as the abundance of Proteobacteria and Acidobacteria in rhizosphere microorganisms based on 16S rDNA sequencing. In addition, MT treatment improved the content of available K and organic matter in soil, and increased the uptake of P, K and Fe by seedlings. In summary, 14-HBR and MT combined had the best effect on promoting rhizosphere bacterial distribution, nutrient absorption and plant growth. These findings may provide valuable guidance for solving growth weakness problem in kiwifruit cultivation.

Beneficial Microorganisms in Kiwifruit Cultivation: Enhancing Growth and Disease Resistance

Beneficial Microorganisms in Kiwifruit Cultivation: Enhancing Growth and Disease Resistance

Effect of forchlorfenuron and thidiazuron on kiwifruits’ internal qualities, optical properties and their relationship during growth

Forchlorfenuron (1-(2-chloropyridin-4-yl)-3-phenylurea, CPPU) and thidiazuron (N-Phenyl-N′-1,2,3-thiadiazol-5-ylurea, TDZ) are two widely used plant growth regulators in kiwifruit cultivation. They can promote fruit size, but it is unclear whether they have same effect on internal qualities, optical properties and cell structure of kiwifruit, and whether the kiwifruits treated with CPPU and TDZ can be identified based on optical properties. To answer these questions, the kiwifruits treated with 20 mg/L CPPU and 2 mg/L TDZ solutions were used as samples, and the untreated kiwifruits were used as control to investigate the optical properties (absorption coefficient μa and reduced scattering coefficient μs′), internal qualities (soluble solids content (SSC), firmness and moisture content) and microstructure of pulp tissue during the growth. Moreover, the relationship between the optical properties and internal qualities were analyzed, and the potential for identifying the kiwifruits treated with CPPU and TDZ based on optical properties was evaluated. The results showed that CPPU and TDZ increased the SSC and reduced the firmness of kiwifruits, but had some different effects on the moisture content and cell size. CPPU and TDZ did not influence the change trend of μa and μs′ with wavelength, but affected their values and the relationship with internal qualities. In general, the mean μa of the kiwifruits treated with CPPU and with TDZ was the largest and the smallest at the absorption peaks (980 nm, 1190 nm and 1420 nm), respectively. The linear discriminant analysis modeling results showed that the spectra of μa with μs′ had greater potential in identifying the kiwifruits treated with CPPU/TDZ with accuracy of 75.76 %.

Deficit drip irrigation improves kiwifruit quality and water productivity under rain-shelter cultivation in the humid area of South China

Comprehending crop responses to water deficit at different growth stages is crucial for developing effective irrigation strategies. Different water deficit treatments (WDTs) were applied to the kiwifruit vines to investigate the effect of water deficit during different growth stages on the fruit quality, yield, and water productivity (WP); subsequently, the technique for order preference by similarity to an ideal solution method (TOPSIS) was employed to determine optimal treatments for kiwifruit cultivation. A total of 17 irrigation treatments were applied, including one control treatment (CTL, full irrigation) and four WDTs (denoted as D15%, D25%, D35%, and D45% respectively) during the bud burst to leafing (I), flowering to fruit set (II), fruit expansion (III), and fruit maturation (IV) stages. Results showed that WDTs during I, II, III, and IV decreased evapotranspiration (ET) over the whole growth period of kiwifruit vines by 1.2–3.8, 1.5–4.4, 4.7–14.3, and 6.9–21.3% compared with CTL, respectively. WDTs during stages I and II increased fruit volume (Vf) and fruit weight (FW), while exhibiting no significant impact on yield, WP, and chemical quality of kiwifruit. WDTs during stage III improved fruit firmness (Fn), total soluble solids (TSS), and titratable acidity (TA); however, it also caused severe reduction in Vf, FW, yield, and WP. Appropriate WDTs during stage IV significantly improved Fn, TSS, TA, vitamin C (Vc), and WP without compromising Vf, FW, and yield of kiwifruit. The IV-D25% treatment was determined to be the optimal treatment for improving fruit quality and WP of kiwifruit while maintaining yield, which increased TSS, TA, Vc, and WP by 9.1, 6.1, 19.2, 4.6%, respectively; the combination of D25%, D25%, full irrigation, and D25% treatments during stages I, II, III, and IV should be a viable irrigation strategy to simultaneously achieve high yield, quality, and WP of kiwifruit.

Development and evaluation of precision liquid pollinator for kiwifruit

Cultivation of kiwifruit heavily relies on assisted pollination, and sufficient pollination can enhance fruit quality. A precision liquid pollinator for kiwifruit robotic pollination was developed as part of the research, and it was optimized with the aim of improving pollination quality while saving pollen usage. The pollinator employs a grating ruler to measure the stroke of a pneumatic hydraulic cylinder to achieve precise control of pollen suspension dosage, and uses an internal mixing air-assisted nozzles to spray pollen suspension for pollination. Through experiments of optimizing pollen suspension volume control, constructing of pollination distance prediction model, and measuring droplet size distribution, a working range of air pressure and liquid pressure was established. Eight sets of air–liquid pressure parameters were selected to evaluate the planar pollen deposition of the pollination device, and the optimal parameters were applied to pollinate kiwifruit flowers. The results indicated that reducing droplet size enhanced the overall pollen deposition rate.. In a windless laboratory environment, the developed pollinator achieved a pollen deposition efficiency of 21.15% under an air pressure of 0.15 MPa and liquid pressure of 0.25 MPa. This precision liquid pollination device is advantageous for precise control under high pressure and low flow conditions, suitable for the end effector of autonomous pollination robots. The optimization and evaluation methods established within this study provide reference for the development of precision pollination devices.

Contribution of Sucrose Metabolism in Phloem to Kiwifruit Bacterial Canker Resistance.

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a catastrophic disease affecting kiwifruit worldwide. As no effective cure has been developed, planting Psa-resistant cultivars is the best way to avoid bacterial canker in kiwifruit cultivation. However, the differences in the mechanism of resistance between cultivars is poorly understood. In the present study, five local kiwifruit cultivars were used for Psa resistance evaluation and classified into different resistance categories, tolerant (T), susceptible (S), and highly susceptible (HS), based on their various symptoms of lesions on the cane. Susceptible and highly susceptible varieties had a higher sucrose concentration, and a greater decrease in sucrose content was observed after Psa inoculation in phloem than in tolerant varieties. Three invertase activities and their corresponding gene expressions were detected in the phloem with lesions and showed the same trends as the variations in sucrose concentration. Meanwhile, after Psa inoculation, enzyme activities involved in antioxidant defense responses, such as PAL, POD, and CAT, were also altered in the phloem of the lesion position. With no differences among cultivars, PAL and POD activities in phloem first increased and then decreased after Psa inoculation. However, great differences in CAT activities were observed between T and S/HS categories. Our results demonstrate that sucrose content was negatively correlated with the disease resistance of different cultivars and that the increase in immune response enzymes is likely caused by increased sucrose metabolism in the phloem.

Viromics Reveals the Viral Diversity in Cultivated and Wild Kiwifruit.

China, the center of origin of kiwifruit, has the largest kiwifruit cultivation and production area worldwide, and Shaanxi Province is the major kiwifruit-growing region in China. However, our knowledge of kiwifruit viruses is largely skewed toward their pathology in cultivated orchards, and little is known about viral diversity in wild kiwifruit. To determine the viral diversity in cultivated and wild kiwifruit, 32 cultivated kiwifruit samples from Shaanxi Province and 30 wild kiwifruit samples from the Qinling Mountains were collected and subjected to high-throughput sequencing in this study. Eleven known viruses were found among the 32 cultivated kiwifruit samples, and 8 known viruses and 2 new viruses were found among the 30 wild kiwifruit samples. One of the two new viruses, Actinidia yellowing virus 3 (AcYV3), a member of the genus Idaeovirus, may be associated with severe yellowing of kiwifruit leaves. In addition, more than 50 nearly full-length genome sequences of known viruses were obtained. The detection rates, recombination, and molecular variation of these viruses were further analyzed. The results obtained in this study provide valuable information for understanding the virome of cultivated and wild kiwifruit.

Potential geographical distribution of Actinidia spp. and its predominant indices under climate change

Kiwifruit (Actinidia ssp.) is an economically and nutritionally important fruit crop with a remarkably high vitamin C content. Shaanxi Province, China, has the world's largest production base for kiwifruit; hence, it is necessary to accurately assess the potential geographic distribution of kiwifruit in this area for planting planning and government management. To perform this analysis, we selected three categories of environmental indices (climate, soil, and topographical) for a total of 18 ecological suitability assessment indices. Based on fuzzy mathematic theory, we built 18 membership functions to show the quantitative relationship between kiwifruit yield and these 18 assessment indices. Furthermore, an assessment model of kiwifruit suitability for cultivation was constructed using a combination of the weighted average method and GIS spatial analysis of the present land-use map of Shaanxi. The results show that 5860.1 km2 (14.0%) of arable land and orchard can be demarcated as highly suitable for kiwifruit cultivation, 7868.9 km2 (18.7%) suitable for rapeseed cultivation; 11,392.1 km2 (27.1%) marginally suitable for rapeseed cultivation; and 16,892.5 km2 (40.2%) as unsuitable for kiwifruit cultivation in this province. We provide a useful assessment system for ecological zoning of kiwifruit suitability and identify the highly suitable planting area of kiwifruit in Shaanxi Province. south Shannan and south Guanzhong. These results provide a reference tool for distribution rationalization and resource optimization of kiwifruit-planting areas.

Alcohol acyl transferase genes at a high-flavor intensity locus contribute to ester biosynthesis in kiwifruit.

Volatile esters are key compounds contributing to flavor intensity in commonly consumed fruits including apple (Malus domestica), strawberry (Fragaria spp.), and banana (Musa sapientum). In kiwifruit (Actinidia spp.), ethyl butanoate and other esters have been proposed to contribute fruity, sweet notes to commercial cultivars. Here, we investigated the genetic basis for ester production in Actinidia in an A. chinensis mapping population (AcMPO). A major quantitative trait loci for the production of multiple esters was identified at the high-flavor intensity (HiFI) locus on chromosome 20. This locus co-located with eight tandemly arrayed alcohol acyl transferase genes in the Red5 genome that were expressed in a ripening-specific fashion that corresponded with ester production. Biochemical characterization suggested two genes at the HiFI locus, alcohol acyl transferase 16-b/c (AT16-MPb/c), probably contributed most to the production of ethyl butanoate. A third gene, AT16-MPa, probably contributed more to hexyl butanoate and butyl hexanoate production, two esters that segregated in AcMPO. Sensory analysis of AcMPO indicated that fruit from segregating lines with high ester concentrations were more commonly described as being "fruity" as opposed to "beany". The downregulation of AT16-MPa-c by RNAi reduced ester production in ripe "Hort16A" fruit by >90%. Gas chromatography-olfactometry indicated the loss of the major "fruity" notes contributed by ethyl butanoate. A comparison of unimproved Actinidia germplasm with those of commercial cultivars indicated that the selection of fruit with high concentrations of alkyl esters (but not green note aldehydes) was probably an important selection trait in kiwifruit cultivation. Understanding ester production at the HiFI locus is a critical step toward maintaining and improving flavor intensity in kiwifruit.

Potential of Different Actinidia Genotypes as Resistant Rootstocks for Preventing Kiwifruit Vine Decline Syndrome

Kiwifruit Vine Decline Syndrome (KVDS) is currently affecting Italian kiwifruit cultivation, causing dramatic yield and economic losses. The syndrome’s aetiology is due to soil-borne pathogens and waterlogging, leading to the decay of roots and then the canopy. Current knowledge about the disease is limited, and the techniques to control the syndrome are ineffective. The use of tolerant rootstocks is one of the most promising tools. Six genotypes of Actinidia were tested for two years at four infected experimental sites in Friuli Venezia Giulia (NE Italy). Plant evaluation and analysis were carried out on the root system and the vegetative parts. At all experimental sites, three genotypes, all belonging to the A. macrosperma group, grew normally. In contrast, plants of A. polygama died earlier and those of A. chinensis var. deliciosa ‘Hayward’ declined during the first year. A. arguta ‘Miss Green’ survived the first year but started to decline during the second year. After two years of study, we were able to identify three putative resistant genotypes: A. macrosperma accession numbers 176 and 183, and ‘Bounty71’, which will be a useful resource as rootstocks or as parents for breeding owing to their potential genetic resistance traits.