Kiwifruit Yield Research Articles

Construction of a high-density genetic map and QTL mapping of growth traits in kiwifruit

The trunk diameter (TD) and annual branch diameter (ABD) are closely associated with the growth vigor, abiotic resistance and fruit yield of kiwifruit. These traits are quantitative traits that are controlled by more than one quantitative trait loci (QTLs). However, QTLs for TD and ABD in kiwifruit remain unelucidated. In this study, we generated a cross of the diploid species Actinidia chinensis ‘Hongyang’ (♀) × ‘Boshanbiyu’ (♂) and performed restriction-site associated DNA sequencing on the parents and 173 F1 progeny to identify single-nucleotide polymorphisms (SNPs) in the population. A high-density linkage map spanning 2,548.97 cM was developed using 6,506 bin markers. This bin map consisted of 29 linkage group (LG), with an average genetic distance of 0.39 cM. A total of 8 QTLs were identified: four for TD and four for ABD, with the variance explained by these QTLs ranging from 4.43 % to 16.11 %. A total of 358 TD genes and 181 ABD genes were extracted from the mapped QTLs, and analyzed by KEGG enrichment. In addition, we developed a TD marker from LG23 and an ABD marker from LG10 which were significantly correlated with growth traits. The TD marker is associated with Actinidia22292, a gene involved in protein polar localization, while the ABD marker is linked to Actinidia40478, an Ein3-binding F-box protein. The two SNP markers developed in this study were further validated in a biparental population, indicating their potential use in predicting seedling growth vigor. In summary, these genetic findings deepen our understanding of the genetic basis of growth traits in kiwifruit, and provide valuable information to facilitate kiwifruit breeding.

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.

Functional characterization of AcWRKY94 in response to Pseudomonas syringae pv. actinidiae in kiwifruit

WRKY transcription factors are essential for coping with various biotic stresses. Pseudomonas syringae pv. actinidiae (Psa)-induced kiwifruit canker is a major problem restricting kiwifruit yield. Nevertheless, it's unclear how the kiwifruit WRKY genes respond to Psa. Through genome-wide identification, 112 WRKY members were found in ‘Hongyang’ genome in this work. Promoter analysis revealed that there were many cis-acting elements associated with stress responses in the AcWRKY gene's promoter region. According to transcriptomic analysis, 90 of the AcWRKY genes were differently expressed following Psa, salicylic acid (SA), or methyl jasmonate (MeJA) treatments. Almost all group III WRKYs were responsive to at least one of these treatments, with tissue-specific expression patterns. Quantitative RT-PCR study provided more evidence that Psa and SA treatments significantly induced the expression of the group III WRKY gene AcWRKY94, whereas MeJA treatment repressed it. AcWRKY94 was a transcriptionally active protein localized in the nucleus. Transient overexpression of AcWRKY94 in the leaves of ‘Hongyang’ enhanced the resistance of kiwifruit to Psa. Overexpression of AcWRKY94 in kiwifruit callus remarkably promoted the expression of PR and JAZ genes associated with SA and JA signals, respectively. These data imply that AcWRKY94 controls the signaling pathway dependent on SA and JA, thereby enhancing resistance to Psa. Taken together, this study establishes the basis for functional research on WRKY genes and provides important information for elucidating the resistance mechanism of kiwifruit canker disease.

Impact of pollination schedules on the fruit characteristics of kiwifruit

Timings of pollination are crucial for adequate fruit set, development, quality and yield of kiwifruit. A study was undertaken for three years (2020-22) to find out the effective pollination period (EPP) of commercial kiwifruit cultivars in Sikkim conditions. Ten-year-old vines of the female cultivar Monty and the male cultivar Allison were taken for the study. It was found that 8 am is the most important time to perform pollination for obtaining bigger-sized fruits. Fruit set was found to be 100% when pollination was performed at 9 am, 10 am and 3 pm. The yield was found to be the highest at 9 am (35.20 kg/plant) pollination time; TSS recorded 1.38-fold variations with the maximum at 8 am (19.1°B). Total acidity was recorded as the minimum at 9 am (0.64%) pollination. Further, ascorbic acid was recorded at to be the maximum at 9 am (118.9 mg/100g) pollination. Primary and secondary nutrients were also found to be higher in pollinated flowers from 8.00 am to 12.00 pm. Thus, efforts for producing good quality and marketable size fruits in kiwifruit the vines should the flowers should be within the 8.00 am to 12.00 pm pollination timings.

Soil, rhizosphere, and root microbiome in kiwifruit vine decline, an emerging multifactorial disease.

Kiwifruit vine decline syndrome (KVDS) is characterized by severe root system impairment, which leads to irreversible wilting of the canopy. Plants usually collapse rapidly from the appearance of the first aboveground symptoms, without recovery even in the following seasons. The syndrome has been negatively impacting kiwifruit yield in different areas of Italy, the main producing European country, since its first outbreak in 2012. To date, a unique, common causal factor has yet to be found, and the syndrome is referred to as multifactorial. In this article, we investigated the whole biotic community (fungi, bacteria, and oomycetes) associated with the development of KVDS in three different belowground matrices/compartments (soil, rhizosphere, and root). Sampling was performed at both healthy and affected sites located in the main kiwifruit-producing area of Northwestern Italy. To address the multifactorial nature of the syndrome and to investigate the potential roles of abiotic factors in shaping these communities, a physicochemical analysis of soils was also performed. This study investigates the associations among taxonomic groups composing the microbiome and also between biotic and abiotic factors. Dysbiosis was considered as a driving event in shaping KVDS microbial communities. The results obtained from this study highlight the role of the oomycete genus Phytopythium, which resulted predominantly in the oomycete community composition of diseased matrices, though it was also present in healthy ones. Both bacterial and fungal communities resulted in a high richness of genera and were highly correlated to the sampling site and matrix, underlining the importance of multiple location sampling both geographically and spatially. The rhizosphere community associated with KVDS was driven by a dysbiotic process. In addition, analysis of the association network in the diseased rhizosphere revealed the presence of potential cross-kingdom competition for plant-derived carbon between saprobes, oomycetes, and bacteria.

Evaluation of the control efficacy of antagonistic bacteria from V-Ti magnetite mine tailings on kiwifruit brown spots in pot and field experiments.

Seemingly barren heavy-metal-polluted vanadium (V) and titanium (Ti) magnetite mine tailings contain various functional microbes, yet it is unclear whether this includes microbial resources relevant to the biological control of plant diseases. Kiwifruit brown leaf spot disease, caused by Corynespora cassiicola, can seriously reduce kiwifruit yield. To discover effective control measures for kiwifruit leaf spot, 18 bacteria strains among 136 tailing-isolated bacteria from V-Ti magnetite mine tailings were identified as inhibiting C. cassiicola by the confrontation plate method, indicating that antagonistic bacteria surviving in the V-Ti magnetite mine tailings were present at a low level. The 18 antagonistic strains could be divided into two BOX-A1R clusters. The 13 representative strains that were selected for phylogenetic tree construction based on their 16S rRNA sequences belonged to the Bacillus genus. Five predominant strains exhibited different toxin-production times and intensities, with four of them initiating toxin production at 32 h. Among them, Bacillus sp. KT-10 displayed the highest bacteriostatic rate (100%), with a 37.5% growth inhibition rate and an antagonistic band of 3.2 cm against C. cassiicola. Bacillus sp. KT10 also showed a significant inhibitory effect against the expansion speed of kiwifruit brown spots in the pot. The relative control effect was 78.48 and 83.89% at 7 days after the first and last spraying of KT-10 dilution, respectively, confirming a good effect of KT-10 on kiwifruit brown leaf spots in the field. This study demonstrated for the first time that there are some antagonistic bacteria to pathogenic C. cassiicola in V-Ti magnetite mine tailings, and Bacillus sp. KT10 was found to have a good control effect on kiwifruit brown leaf spots in pots and fields, which provided an effective biological control measurement for kiwifruit brown leaf spots.

Enhancing kiwifruit flower pollination detection through frequency domain feature fusion: a novel approach to agricultural monitoring.

The pollination process of kiwifruit flowers plays a crucial role in kiwifruit yield. Achieving accurate and rapid identification of the four stages of kiwifruit flowers is essential for enhancing pollination efficiency. In this study, to improve the efficiency of kiwifruit pollination, we propose a novel full-stage kiwifruit flower pollination detection algorithm named KIWI-YOLO, based on the fusion of frequency-domain features. Our algorithm leverages frequency-domain and spatial-domain information to improve recognition of contour-detailed features and integrates decision-making with contextual information. Additionally, we incorporate the Bi-Level Routing Attention (BRA) mechanism with C3 to enhance the algorithm's focus on critical areas, resulting in accurate, lightweight, and fast detection. The algorithm achieves a of 91.6% with only 1.8M parameters, the AP of the Female class and the Male class reaches 95% and 93.5%, which is an improvement of 3.8%, 1.2%, and 6.2% compared with the original algorithm. Furthermore, the Recall and F1-score of the algorithm are enhanced by 5.5% and 3.1%, respectively. Moreover, our model demonstrates significant advantages in detection speed, taking only 0.016s to process an image. The experimental results show that the algorithmic model proposed in this study can better assist the pollination of kiwifruit in the process of precision agriculture production and help the development of the kiwifruit industry.

Water-potassium coupling at different growth stages improved kiwifruit (Actinidia spp.) quality and water/potassium productivity without yield loss in the humid areas of South China

Precise water and nutrient regulation are the key to improving fruit quality and water productivity for kiwifruit orchards in Central Sichuan's hilly region where seasonal drought is becoming increasingly severe. Here, an experiment was set up to clarify how water-potassium coupling at different growth stages affects kiwifruit yield, water/potassium productivity and quality. A conventional fertigation was set as the control treatment (CK), and two water deficit treatments (60% and 80% CK, denoted as LW and HW, respectively) with three potassium (K) deficit levels (40%, 60% and 80% CK, denoted as LK, MK and HK, respectively) were applied at each growth stage of the cultivar “Jinyan” kiwifruit. The phenolic compounds and key enzyme activities were evaluated, in addition to the yield and traditional physical and nutritional properties. Results showed that the water and K deficit would reduce the yield of kiwifruit, however the yield of HWMK treatments at stages I and II showed no significant differences compared with CK (P > 0.05), HWMK treatment at stage III even increased the fruit yield. Water productivity (WP) and K partial factor productivity (KPFP) showed a trend of HW>LW, and reached the highest in HWMK treatment at all growth stages. The physical qualities were more affected by water, especially at stages I and II. HWMK treatments at stages I and II significantly increased fruit firmness by 30.20% and 21.56%, respectively (P < 0.05). Whereas, kiwifruit nutritional qualities were more affected by K, especially at stage III. Specifically, compared with CK, III-HWHK treatment significantly elevated vitamin C (Vc), total soluble solids (TSS), sugar/acid ratio, and total phenolic compounds by 22.45%, 30.58%, 24.91% and 54.87%, respectively (P < 0.05). Water-potassium coupling had significant effects on all five key quality-related enzyme activities (P < 0.05), except for the effect of water on ascorbate oxidase (AAO) activity (P > 0.05). The correlation analysis revealed a highly significant correlation between fruit nutritional qualities and key enzyme activities (P < 0.01), indicating that water-potassium coupling influenced nutritional quality by regulating the enzyme activity involved in metabolic processes. Principal component analysis (PCA) confirmed the results of correlation analysis, and found that HWMK treatment at stages I and II and HWHK treatment at stage III were most efficient in improving kiwifruit nutritional qualities. Overall, the stimulatory effect of fruit qualities to water-potassium coupling was growth stage dependent, water-potassium coupling affected fruit quality by regulating the enzyme activity. HWMK treatment at stages I and II and HWHK treatment at stage III were most efficient in improving fruit quality and water/potassium productivity without yield loss under water and fertilizer saving conditions, which could be suggested as the optimal strategy of fertigation in the humid areas of South China.

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.

Model Application for Estimation of Agri-Environmental Indicators of Kiwi Production: A Case Study in Northern Greece

Due to the sensitivity of kiwifruit to soil water and nutrient availability, kiwi production is often associated with over-watering and over-fertilization, especially with nitrogen (N), resulting in increased environmental risks. Crop models are powerful tools for simulating crop production and environmental impact of given management practices. In this study, the CropSyst model was applied to estimate soil N budget and environmental effects of kiwi production, with particular regard to N losses, in two grower-managed kiwi orchards in northern Greece, involving two seasons and different management practices. Management options included N fertilization and irrigation. Model estimates were compared with yield and soil mineral N content (0–90 cm depths) measured three times within the growing season. Agri-environmental indicators were calculated based on the N budget simulation results to assess the environmental consequences (focusing on N losses and water use efficiency) of the different management practices in kiwi production. According to model simulation results, kiwifruit yield and N uptake were similar in both orchards. N losses to the environment, however, were estimated on average to be 10.3% higher in the orchard with the higher inputs of irrigation water and N fertilizer. The orchard with the lower inputs showed better water and N use efficiency. N leaching losses were estimated to be higher than 70% of total available soil N in both study sites, indicating potential impact on groundwater quality. These findings demonstrate the necessity for improved irrigation and N fertilization management in kiwi production in the area.

Significant increases in Donghong kiwifruit yield by a novel umbrella-shaped trellis system and identification of associated molecular mechanisms.

China is the largest kiwifruit producer in the world, accounting for more than half of the total. However, in terms of yield per unit area, China is much lower than the global average and lags behind that of other countries. Yield improvement is of critical importance for the current kiwifruit industry in China. In this study, an improved overhead pergolas trellis (OPT) system, namely, the umbrella-shaped trellis (UST) system, was developed for Donghong kiwifruit, which is now the second most popular and widely cultivated red-fleshed kiwifruit in China. Surprisingly, the estimated yield on the UST system was more than two times higher than that with a traditional OPT, while the external fruit quality was maintained and the internal fruit quality was improved. One of the mechanisms contributing to the yield improvement was the significant promotion of the vegetative growth of canes at 6 ~ 10mm in diameter by the UST system. The upper canopy of the UST treatment served as a natural shading condition for the lower fruiting canopy and thus had positive effects on the accumulation of chlorophylls and total carotenoids in the fruiting canopy. The most productive zones on the fruiting canes (6 ~ 10mm in diameter) contained significantly higher (P < 0.05) levels of zeatin riboside (ZR) and auxin (IAA) and ratios of ZR/gibberellin (GA), ZR/abscisic acid (ABA), and ABA/GA. A relatively high carbon/nitrogen ratio may promote the flower bud differentiation process of Donghong kiwifruit. The outcomes of this study provide a scientific basis for manifold increase in production of kiwifruit and contribute to the sustainability of the kiwifruit industry.

Exogenous treatment with melatonin enhances waterlogging tolerance of kiwifruit plants.

Waterlogging stress has an enormous negative impact on the kiwifruit yield and quality. The protective role of exogenous melatonin on water stress has been widely studied, especially in drought stress. However, the research on melatonin-induced waterlogging tolerance is scarce. Here, we found that treatment with exogenous melatonin could effectively alleviate the damage on kiwifruit plants in response to waterlogging treatment. This was accompanied by higher antioxidant activity and lower ROS accumulation in kiwifruit roots during stress period. The detection of changes in amino acid levels of kiwifruit roots during waterlogging stress showed a possible interaction between melatonin and amino acid metabolism, which promoted the tolerance of kiwifruit plants to waterlogging. The higher levels of GABA and Pro in the roots of melatonin-treated kiwifruit plants partly contributed to their improved waterlogging tolerance. In addition, some plant hormones were also involved in the melatonin-mediated waterlogging tolerance, such as the enhancement of ACC accumulation. This study discussed the melatonin-mediated water stress tolerance of plants from the perspective of amino acid metabolism for the first time.

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.

Genome-Wide Analysis of Multiple Organellar RNA Editing Factor (MORF) Family in Kiwifruit (Actinidia chinensis) Reveals Its Roles in Chloroplast RNA Editing and Pathogens Stress.

Kiwifruit (Actinidia chinensis) is well known for its high vitamin C content and good taste. Various diseases, especially bacterial canker, are a serious threat to the yield of kiwifruit. Multiple organellar RNA editing factor (MORF) genes are pivotal factors in the RNA editosome that mediates Cytosine-to-Uracil RNA editing, and they are also indispensable for the regulation of chloroplast development, plant growth, and response to stresses. Although the kiwifruit genome has been released, little is known about MORF genes in kiwifruit at the genome-wide level, especially those involved in the response to pathogens stress. In this study, we identified ten MORF genes in the kiwifruit genome. The genomic structures and chromosomal locations analysis indicated that all the MORF genes consisted of three conserved motifs, and they were distributed widely across the seven linkage groups and one contig of the kiwifruit genome. Based on the structural features of MORF proteins and the topology of the phylogenetic tree, the kiwifruit MORF gene family members were classified into six groups (Groups A–F). A synteny analysis indicated that two pairs of MORF genes were tandemly duplicated and five pairs of MORF genes were segmentally duplicated. Moreover, based on analysis of RNA-seq data from five tissues of kiwifruit, we found that both expressions of MORF genes and chloroplast RNA editing exhibited tissue-specific patterns. MORF2 and MORF9 were highly expressed in leaf and shoot, and may be responsible for chloroplast RNA editing, especially the ndhB genes. We also observed different MORF expression and chloroplast RNA editing profiles between resistant and susceptible kiwifruits after pathogen infection, indicating the roles of MORF genes in stress response by modulating the editing extend of mRNA. These results provide a solid foundation for further analyses of the functions and molecular evolution of MORF genes, in particular, for clarifying the resistance mechanisms in kiwifruits and breeding new cultivars with high resistance.

Transcriptomics reveals the molecular mechanism underlying kiwifruit expansion following forchlorfenuron (CPPU) treatment

Kiwifruit is an economically and nutritionally valuable fruit. Forchlorfenuron (CPPU) is widely used to improve fruit set and yield of kiwifruit. However, the mechanism through which CPPU regulates fruit enlargement remains unclear. Physiological and RNA-seq data revealed that the greatest contribution of CPPU treatment to fruit growth occurred at 28 to 42 d after bloom (DAB). CPPU application accelerated sugar metabolism by increasing the content of sucrose through increasing the transcripts of genes such as <i>SUSY</i>, <i>HK</i>, and <i>FK</i> in sucrose metabolism. In the early stages of fruit development, up-regulation of the starch synthesis gene <i>AGPase</i> and the decomposition gene <i>β-AMY</i> indicated the occurrence of starch turnover. After CPPU treatment, genes related to the synthesis and signal transduction of auxin and gibberellins were down-regulated. During the early fruit developmental stage, the cytokinin content and the expression of signal transduction genes were increased. In addition, the expression of cyclin genes, related to cell division, was up-regulated within three weeks after CPPU treatment. This indicates that CPPU treatment promoted cell division during the fastest growth stage, which would lead to an increase in cell number and further increases in fruit size.

Transcriptome sequencing and endogenous phytohormone analysis reveal new insights in CPPU controlling fruit development in kiwifruit (Actinidia chinensis).

Kiwifruit (Actinidia chinensis) is a rich nutritious fruit crop owing to a markedly higher content of vitamin C and minerals. To promote fruit set and to increase the yield of kiwifruit, forchlorfenuron (CPPU) has been widely applied. However, the molecular details regarding CPPU controlling kiwifruit development, especially at the fastest fruit growth stage, remain unknown. In the present study, we measured the effect of CPPU on developmental regulation in red-fleshed kiwifruit (Actinidia chinensis ‘Hongyang’). Additionally, a cytological analysis was performed to clarify the precise changes in the cell structure of the CPPU-treated kiwifruits. Moreover, the concentration of endogenous phytohormones, including indoleacetic acid (IAA), zeatin (ZT), gibberellic acid 3 (GA3), and abscisic acid (ABA), were measured by Enzyme-linked Immunosorbent Assay (ELISA). Furthermore, RNA-Seq was performed to dissect the complicated molecular mechanisms, with a focus on biosynthesis, metabolism, and signaling compounds, such as endogenous hormones, sugars, and L-ascorbic acid. Our results demonstrated that CPPU treatment not only regulates the size and weight of a single fruit but also improves the quality in ‘Hongyang’ kiwifruit through the accumulation of both soluble sugar and vitamin C. It was also seen that CPPU regulates kiwifruit development by enhancing cell expansion of epidermal cells and parenchyma cells, while, promoting cell division of subepidermal cells. Additionally, CPPU significantly increased the gibberellin and cytokinin biosynthetic pathway and signaling, while repressing auxin and ABA biosynthetic pathway; thus, signaling plays an essential role in CPPU controlling kiwifruit development. Notably, transcriptomic analysis revealed that a total of 2244 genes, including 352 unannotated genes, were differentially expressed in kiwifruits because of CPPU treatment, including 127 transcription factors. These genes are mainly enriched in plant hormone signal transduction, photosynthesis, MAPK signaling pathway, starch and sucrose metabolism, and phenylpropanoid biosynthesis. Overall, our results highlight that CPPU regulation of kiwifruit development is mainly associated with an antagonistic and/or synergistic regulatory role of endogenous phytohormones, and enhancing the energy supply. This provides new insights into the molecular details of CPPU controlling kiwifruit development at the fastest fruit growth stage, which is of agricultural importance for kiwifruit breeding and crop improvement.

Evaluation of freezing tolerance in Actinidia germplasm based on relative electrolyte leakage

Cold stress in winter can have a disastrous effect on kiwifruit yield and affect geographical distribution. However, freezing tolerance in Actinidia genotypes remains largely unknown. Here, we report changes in metabolite content and enzyme activity in the shoots of Actinidia genotypes exposed to low-temperature stress (− 5 °C, − 10 °C, − 15 °C, − 20 °C, − 25 °C and − 30 °C). Moreover, the relative electrolyte leakage method was used to evaluate the freezing tolerance of kiwifruit germplasm; 51 genotypes from 16 species of Actinidia were evaluated in total. The data revealed that relative electrolyte leakage, proline (Pro), soluble protein, and catalase (CAT) activity changed with different low temperatures. Results showed that among 16 species, A. kolomikta, A. polygama, and A. arguta had lower LT50 than other species. A. arguta, originating from the northeast of China, exhibited stronger freezing resistance than the ones from other places. There was little difference in freezing tolerance between A. chinensis and A. deliciosa. These findings provide new insights into the freezing tolerance ability and mechanisms of kiwifruit and further contribute to our understanding of the relationship between freezing tolerance and geographic distribution.

Vision System for Automatic On-Tree Kiwifruit Counting and Yield Estimation

Yield estimation is an essential preharvest practice among most large-scale farming companies, since it enables the predetermination of essential logistics to be allocated (i.e., transportation means, supplies, labor force, among others). An overestimation may thus incur further costs, whereas an underestimation entails potential crop waste. More interestingly, an accurate yield estimation enables stakeholders to better place themselves in the market. Yet, computer-aided precision farming is set to play a pivotal role in this respect. Kiwifruit represents a major produce in several countries (e.g., Italy, China, New and Zealand). However, up to date, the relevant literature remains short of a complete as well as automatic system for kiwifruit yield estimation. In this paper, we present a fully automatic and noninvasive computer vision system for kiwifruit yield estimation across a given orchard. It consists mainly of an optical sensor mounted on a minitractor that surveys the orchard of interest at a low pace. Afterwards, the acquired images are fed to a pipeline that incorporates image preprocessing, stitching, and fruit counting stages and outputs an estimated fruit count and yield estimation. Experimental results conducted on two large kiwifruit orchards confirm a high plausibility (i.e., errors of 6% and 15%) of the proposed system. The proposed yield estimation solution has been in commercial use for about 2 years. With respect to the traditional manual yield estimation carried out by kiwifruit companies, it was demonstrated to save a significant amount of time and cut down on estimation errors, especially when speaking of large-scale farming.

Estimation of kiwifruit yield by leaf nutrients concentration and artificial neural network

AbstractThere is a fundamental concern regarding the prediction of kiwifruit yield based on the concentration of nutrients in the leaf (2–3 months before fruits harvesting). For this purpose, the current study was designed to employ an artificial neural network (ANN) to evaluate the kiwi yield of Hayward cultivar. In this regard, 31 kiwi orchards (6–7 years old) in different parts of Rudsar, Guilan Province, Iran, with 101 plots (three trees in every plot) were selected. The complete leaves of branches with fruits were harvested, and the concentration of nitrogen, potassium, calcium, and magnesium measured. After fruit harvesting in late November, the fruit yield of each plot was evaluated along with the fresh and dry weights of the fruit. The ANN analyses were carried out using a multi-layer perceptron with the Langburge-Marquardt training algorithm. Using calcium (Ca) as input data (Ca-model) was more accurate than using nitrogen (N-model). The maximum R2and the lowest root mean square error was obtained when all nutrients and related ratios were considered as input variables. Since the difference between the proposed model and the model fitted by the calcium variable (Ca-model) was only about 6%, the Ca-model is recommended.

Response of kiwifruit yield and fruit quality to chloride‐containing fertilizers

AbstractA 3‐yr field experiment was conducted to determine the effects of chloride‐containing fertilizer application on the yield and fruit quality of kiwifruit and the distribution of chloride ions (Cl–) in plants and soil. Five chlorine treatments were applied in a 10‐yr‐old kiwifruit (Actinidia deliciosa ‘Hayward’) orchard: (1) CO(NH2)2 + Ca(H2PO4)2 + K2SO4 (control, 0 kg Cl ha−1); (2) CO(NH2)2 + Ca(H2PO4)2 + 1/2KCl + 1/2K2SO4 (170 kg Cl ha−1); (3) CO(NH2)2 + Ca(H2PO4)2 + KCl (340 kg Cl ha−1); (4) 1/2CO(NH2)2 + 1/2NH4Cl + Ca(H2PO4)2 + KCl (910 kg Cl ha−1); and (5) NH4Cl + Ca(H2PO4)2 + KCl (1480 kg Cl ha−1). In terms of the 3‐yr average (2015–2017), a higher yield of kiwifruit was obtained under chlorine treatments at levels of 170 and 340 kg Cl ha−1, which increased by 18 and 12.5% compared with the control. Despite no significant differences in fruit soluble solids, titratable acid, and soluble sugar contents, all chlorine treatments, especially 910 and 1480 kg Cl ha−1, resulted in less vitamin C content after 3 yr of application compared with the control. Increasing chlorine application increased Cl– concentrations in both the plants and soil; however, maximum concentrations did not exceed the safe concentrations (&lt;20 g kg−1 and &lt; 400 mg kg−1, respectively). In conclusion, applying a restricted amount of chloride‐containing fertilizers (170–340 kg Cl ha−1) could increase kiwifruit yield under the experimental conditions, with no harm to plant leaves or soil.