Japanese Plum Research Articles

Efficacy of Edible Coatings in Alleviating Shrivel and Maintaining Quality of Japanese Plum (Prunus salicina Lindl.) during Export and Shelf Life Conditions

The effect of six edible coatings were investigated on the ability to alleviate shrivel and extend shelf life of plums. Fruit were subjected to a simulated shipping period (−0.5 ± 2 °C and 90 ± 5% relative humidity (RH)) for five weeks and a subsequent shelf life period (20 ± 2 °C and 80 ± 5% RH) for 20 d. Overall, the study showed that it is possible to alleviate shrivel and also extend shelf life of plum (‘African Delight™’) at export and shelf life conditions. Amongst the edible coatings investigated, the findings in fruit coated with gum arabic and the commercial products were comparable and promising for postharvest preservation of the investigated plum cultivar. The coatings showed a moderate delay of fruit ripening, significantly reduced weight loss and shrivel development, allowing for the export of fruit over a long distance (five weeks) and up to 20 d of shelf life.

Effect of rootstocks and grafting time on graft success and growth of peach cv. Shan-i-Punjab in sub tropics of India

The present investigation was carried with the aim to study the effect of time of grafting and rootstock on graft success and growth in low chill peach cv. Shan- e-Punjab under sub tropics of Haryana (India). Study comprising of three different rootstocks viz., Peach cv. Sharbati seedling and Japanese Plum cv. Kala Amritsari and European plum cv. Green Gage rooted cuttings grafted on 9th and 25th January with three replications. Results reveal that advanced grafting (9th January) had significantly higher graft success (64.75%) and sprouting (69.02%) over 25th January, whereas, all growth parameters viz., plant height, percent increase in scion diameter, fresh and dry weight of shoot and root, relative water content, leaf nitrogen and total chlorophyll contents were significantly superior when wedge grafting was done on 25th January. On the other hand, among different rootstock, Sharbati seedling as rootstock performed better as compared to Kala Amritsari and Green Gage cutting for all the above recorded parameters. This investigation additionally gives the chances for further research to explore whether this pattern proceeds in the productive year of the peach plant.

A Plum Marbling Conundrum: Identification of a New Viroid Associated with Marbling and Corky Flesh in Japanese Plums.

Over the past 2 decades, fruit symptoms resembling a marbling pattern on the fruit skin or corking of the fruit flesh were observed on Japanese plums in South Africa, resulting in unmarketable fruit. The ability of high-throughput sequencing (HTS) to detect known and unknown pathogens was exploited by assaying affected and unaffected fruit tree accessions to identify the potential aetiological agent of marbling and/or corky flesh disease. In this study, it is shown that the disease is associated with a previously undescribed small RNA with typical viroid structural features. The potential viroid was the only pathological agent consistently detected in all symptomatic trees by HTS, and the association with the symptoms was confirmed in field surveys over two seasons. To date, this RNA was not detectable by RT-PCR in seedlings raised from seeds collected from infected trees. Although the autonomous replication of this viroid-like RNA was not proven, it was shown to be transmissible by grafting and associated with a range of symptoms that include marbling on the fruit skin, corky flesh, reduced fruit size, irregular shape, and uneven fruit surface depending on the cultivar. Moreover, the circular RNA genome, consisting of 317 nucleotides, strongly supports that this viroid-like RNA is most likely a viroid for which the name plum viroid I (PVd-I) is proposed. The primary structure of this viroid showed a less than 90% nucleotide sequence identity to viroids of the genus Apscaviroid, with which it has close phylogenetic relationships and shares conserved structural motifs.

Influence of Prunus rootstocks and spacing on performance of Japanese plum grown under sub–tropical conditions

In India as well as in other significant regions of the world, plum production is focussed on a very small pool of varieties that inhibits its expansion and limits the availability of fruits all year round. This situation emphasizes on the urgent requirement of evolving alternative cultivars of rootstock and scion, with better performance under local situation and contrasting spacing. Japanese plum cultivar ‘Satluj Purple’ (Fla 1–2) is known for its hardy nature, precocity, high productivity and regularity in bearing appropriate for both the juice manufacturing industry and fresh fruit marketplace. In spite of having good fruit quality under sub–tropical scenario and early market availability when other fruits are not accessible, only a few rootstock studies for ‘Satluj Purple’ have been executed in India. Consequently, a field study was conducted at Punjab Agricultural University, Ludhiana state, to assess the horticultural output of ‘Satluj Purple’ Japanese plum grafted on four rootstocks: ‘Kala Amritsari’ (Prunus salicina L.), ‘Kabul Green Gage’ (Prunus salicina L.), Sharbati (Prunus persica Batsch) and Flordaguard (Prunus persica Batsch) over two consecutive seasons. The experimental grove was planted in 2015 using a 6 × 6 m and 6 × 1.5 m spacing, in a randomized block design, with three replications and two trees per replication under climate conditions typical of a semi–arid and sub–tropical area. Fruiting, yield and fruit quality were assessed for each rootstock at different spacing. Reproductive growth (fruit set, fruit retention and fruit yield per tree) was found to be higher on ‘Kala Amritsari’ rootstock. Fruits harvested from trees grafted on ‘Kala Amritsari’ were superior in fruit quality (fruit weight, fruit colour, total soluble solids (TSS), titratable acidity (TA) and ripening index (TSS/TA). Irrespective of the rootstocks, the performance of plum trees in terms of fruiting, yield and fruit quality was better in 6 × 6 m planted trees as compared to trees planted at 6 × 1.5 m distances. Yield was found to be positively correlated with fruit weight, chroma, TSS, ripening index, fruit set and retention while it was negatively correlated with the TA values. Overall, the results from this study indicated that the rootstocks ‘Kala Amritsari’ and ‘Kabul Green Gage’ are the most suitable rootstocks for ‘Satluj Purple’ under the conditions investigated herein. Finally, the ‘Satluj Purple’ trees at spacing of 6 × 6 m performed better as compared to 6 × 1.5 m planted trees regardless of the rootstocks.

Evaluation of different deficit irrigation strategies in the late-maturing Japanese plum cultivar 'Angeleno'

In stone fruits, the pit hardening period is usually one of slow fruit growth that is considered relatively insensitive to an imposed moderate water stress. For this reason, this period is commonly employed for a first phase of reduced water input in regulated deficit irrigation (RDI) strategies. However, in previous studies with the Japanese plum cv. 'Angeleno', the identification of a period of slow growth just before harvest suggested the need to reconsider the most suitable RDI strategy for this cultivar. In this 3-year study (2014, 2015 and 2016) three irrigation strategies were compared: Control (CON) designed to meet tree water requirements throughout the season; Regulated Deficit Irrigation (RDI) with two separate periods of water deficit, one preharvest with no irrigation inputs during an intermediate period of fruit growth (pit hardening period), and the other postharvest with a 30 % reduction of the CON inputs; and Preharvest + Regulated Deficit Irrigation (RDP) with a single period of deficit irrigation initiated before harvesting and extended until the end of the irrigation campaign. Both deficit irrigation treatments were found to be effective at controlling tree vigor, with lower trunk cross-sectional area growth and pruned wood weight than in the CON treatment. Average water savings with the RDI and RDP strategies over the three years of the study were 24 % and 18 %, respectively, compared to CON, with no impact on yield and no carry-over effect. Fruit size in the RDP treatment was similar to the CON. The differences in fruit firmness, soluble solids concentration (SSC), acidity, lightness (L), hue (ho) and chroma (C*) of the skin were only slight or inconsistent over the three years. Our results confirm the suitability of moderate pre- and postharvest water stress (RDP strategy) in this cultivar, with greater water productivity than the traditional RDI strategy.

Construction of an SNP-based high-density genetic map for Japanese plum in a Chinese population using specific length fragment sequencing

The Japanese plum (Prunus salicina Lindl.) is one of the most important stone fruit crops in China. High-density linkage map is valuable resources which enhance functional genomics and genetic breeding studies. So far several Japanese plum linkage maps have been reported using different kinds of molecular markers; however, the marker numbers and chromosome coverage are limited. Recently, a newly developed strategy which genome sequencing towards specific-locus amplified fragments (SLAF) markers, has been proven to be powerful for rapid genotyping of genome-wide markers and for high-density genetic map construction. In this study, SLAF was used to genotype markers with 114 F1 seedlings from the ‘09–16’ × ‘Fortune’ cross. Suitable SLAF markers (160,344 out of 343,436,902 pair-end reads) were chosen to conduct genetic map construction, 16.31% of which were polymorphic. The overall integrated map contained 3,341 high quality SLAFs and 720 loci that were grouped in eight genetic linkage groups with a total length of 869.9 cM and an average distance of 1.21 cM, and only five gaps with a genetic distance > 5 cM between adjacent markers occurred in linkage group (LG) 3 and LG6. The number of markers with each LG ranged from 82.3 cM (LG3) to 138.3 cM (LG1). Aligning the map against the peach reference genome sequence (Prunus persica L.) indicated a strictly co-linear relationship between the LGs and peach genome, demonstrating the markers on ours LGs were well ordered. Overall, our studies identified large-scale of genetic markers and constructed high-density linkage maps for Japanese plum, which will obviously provide a solid foundation for marker-assisted selection and sequence assembly of the Japanese plum reference genome.

A New Sawfly Pest, Monocellicampa pruni Wei (Hymenoptera, Tenthredinidae) Attacking Fruitlets of Japanese Plum in South Korea

A larval attack leading to severe loss to fruit production of Japanese plum (Prunus salicina Lindl.) was reported in the orchards in Gwangyang, Jeonnam province, South Korea during the spring seasons of 2018 and 2019. As the result of investigation, the damage was identified to be caused by Monocellicampa pruni Wei of the family Tenthredinidae. In this study, we present the first report of this pest in Korea and describe the damage caused by the larvae as well as taxonomic information by illustrating the characteristics of male genitalia.

Book review

Plum is a significant temperate fruit and a very important fruit species in Hungary as well. Cultivation has moved beyond the area boundaries of the Northern Hemisphere many centuries ago. Domestic (European) plum production has been particularly affected by the pandemic-scale destruction of the Sharka virus and worldwide breed changes. According to FAOSTAT (2016) data, world plum production is 12 million tones, with 36% from Eurasian, 63% from Japan and other Asian varieties. The share of American plums is only 1%. Domestication and dissemination of plums is „multi-stepped” because homemade (taste) plums are hybrids of two nature species in the first place, but Japanese plums (hybrids with Chinese plums or Prunus cerasifera) are not uniform; the role of the American plum species is much smaller, though their prospects cannot to predict with certainly. The book consists of 19 chapters, finding a complex way of summing up linguistic, historical, floristic, historical-botanical, cultivation, and morphological and anatomical knowledge.

Brown rot caused by Monilinia fructicola on Japanese plums in Turkey

Brown rot caused by Monilinia fructicola on Japanese plums in Turkey

First Report of Necrotic Disease Caused by Pantoea agglomerans on Plum (Prunus salicina) in China

Prunus salicina L., commonly called Chinese plum or Japanese plum, is a small deciduous tree native to China and widely distributed in the world. Since spring of 2018, an unknown disease has affected commercial plums grown in an orchard located in Dazhou, Sichuan Province, China (31°40′41″N, 107°43′57″E). Disease symptoms in plum trees include water-soaked lesions on immature fruits, brown necrotic spots, and holes with a yellow halo in leaves, as well as dark brown oily cankers on twigs. To isolate the causal agent, surface-disinfested tissues from three separate symptomatic fruits, leaves, and twigs were placed onto nutrient agar (NA) plates and were incubated at 28°C. Pale yellow colonies with smooth margins and mucoid texture appeared after 12 h of incubation. Individual colonies were transferred two times to NA plates using the conventional streak plate techniques to obtain pure cultures. Purified bacteria cells were rod shaped, 1.5 to 3.0 μm long, and 0.5 to 1.0 μm wide. Three isolates (named CdjP1, CdjP2, and CdjP3) were used for further characterization. Biochemical tests using Gram stain, MacConkey agar, and Kovacs’s indole kit (Solarbio, Beijing, China) indicated that the three isolates were gram negative, lactose positive, and indole negative. The 16s rDNA fragment was amplified for the three strains using universal primers 27F and 1492R (Lane 1991) and sequenced (GenBank accession nos. MN542182, MN542183, and MN542184). BLASTn analysis revealed the nearly full-length (about 1,400 bp) 16S rDNA sequences of CdjP1, CdjP2, and CdjP3 shared over 99% identity with Pantoea agglomerans (MH101508) (identities 1,400/1,406, 1,407/1,412, 1,405/1,413), P. vagans (CP038853) (identities 1,397/1,406, 1,403/1,412, 1,402/1,414), and P. ananatis (KC178592) (identities 1,399/1,406, 1,405/1,412, 1,404/1,414), respectively. Multilocus sequence analysis has been shown to be a powerful molecular method for delineation of Pantoea species (Deletoile et al. 2009; Tambong et al. 2014). To identify the species of CdjP1, CdjP2, and CdjP3, six housekeeping genes (fusA, gyrB, leuS, pyrG, rlpB, and rpoB) of each strain were amplified and sequenced (GenBank accession nos. MN549363 to MN549380). Then a phylogenetic tree was constructed using Bayes inference methods based on fusA-gyrB-leuS-pyrG-rlpB-rpoB concatenated fragments (2,997 bp), which showed that CdjP1, CdjP2, and CdjP3 are most closely related to P. agglomerans. To fulfill Koch’s postulates, pathogenicity tests were conducted on 3-year-old plum trees (cv. Qinba) grown in Sichuan Province, China (31°40′53″N, 107°44′2″E). Immature plum fruits, leaves, and twigs were wounded with a sterile toothpick and were inoculated with 20 µl of bacterial suspension (10⁸ CFU/ml) of each isolate. Plants inoculated with sterile water were used as a control. All treatments and the control were repeated three times. The trees were then grown under natural conditions (monthly mean maximum temperature 32°C, monthly mean minimum temperature 23°C). After 2 weeks, all test-isolate-inoculated plum fruits, leaves, and twigs developed symptoms similar to those of the natural infections observed. No lesions were observed on the controls. Bacteria reisolated from the infected plum fruits, leaves, and twigs were similar in colony appearance to the original isolates, and the 16s rDNA fragments were identical to their original isolate sequences, thereby fulfilling Koch’s postulates. Based on colony morphology, biochemical tests, 16S rRNA gene sequencing data, and phylogenetic analysis, the pathogen was identified as P. agglomerans. In China, P. agglomerans has been reported to infect cotton, walnut, Vigna angularis, and Ziziphus jujuba (Lu et al. 2015; Ren et al. 2008; She et al. 2019; Yang et al. 2011). To our knowledge, this is the first report of P. agglomerans causing bacterial necrosis of plum in China or worldwide. This report expands the host range of P. agglomerans and will help to develop effective disease control strategies, as the etiology is known.

Rootstocks modulate the physiology and growth responses to water deficit and long-term recovery in grafted stone fruit trees

The effects of climate change have forced to search quickly new strategies to achieve sustainable agriculture in the context of a growing demand for food. Rootstocks have shown to have a key role in the resistance and tolerance to biotic and abiotic stresses in horticultural and fruit trees species, being a way to incorporate these strengths to the cultivated varieties. Here, we report the assessment of physiological parameters and growth responses of two commercial interspecific hybrid Prunus rootstocks contrasting in their tolerance to water deficit: ‘ROOTPAC®40’ (tolerant) and ‘ROOTPAC®20’ (sensitive); grafted with the almond cultivar Non Pareil or the Japanese plum cultivar Angeleno. Plants were subjected during 35 days to two irrigation treatments, well-watered and water deficit (drought period), followed by a recovery period of 44 days. On each period, biomass accumulation, stomatal density, water-use efficiency at the whole plant level and root hydraulic conductivity were determined in both irrigation treatments. Also, in the drought period, the fraction of transpirable soil water when the relative transpiration drops and the expression of seven aquaporins belonging to plasma membrane intrinsic proteins subfamily was assessed. In the drought period, ‘ROOTPAC®20’ had a decrease in the aquaporin gene expression in roots and also had an early decline in transpiration, independent of the grafted scion. Also, on this rootstock, the biomass was more severely affected. On the other hand, ‘ROOTPAC®40’ induced a late decline in transpiration and increased the water-use efficiency, keeping less affected the biomass accumulation. Contrasting with the above, in the recovery period, ‘ROOTPAC®20’ improved the water-use efficiency, reaching higher biomass accumulation in the grafted plants. Also, we observed some interesting interactions between rootstocks and scions. ‘ROOTPAC®20’ induced a higher stomatal density in both, almond and plum scions, and ‘Angeleno’ plum induced a bigger root hydraulic conductivity in both rootstocks, in comparison to almond ‘Non Pareil’, in the drought period.

Self-(in)compatibility, S-RNase allele identification, and selection of pollinizers in new Japanese plum-type cultivars

Japanese plum (Prunus salicina Lindl.) exhibits gametophytic self-incompatibility, a prezygotic reproductive barrier that inhibits the growth of self-pollen tubes in the style, preventing self-fertilization. This reaction of incompatibility is genetically controlled by a multiallelic locus (S). When the S allele in the pollen grain is the same as either of the two S alleles expressed in the pistil, the pollen tube arrests its growth in the style preventing fertilization. Most Japanese plum-type cultivars are self-incompatible and need cross-pollination with compatible cultivars coincident at flowering. In the last years, an important renewal of plant material is taking place, with the introduction of a number of new cultivars from breeding programs of different countries whose objectives include self-compatibility. In South Africa, the ARC Infruitec/Nietvoorbij program has released a series of new cultivars that are being introduced in the main producing countries. However, their adaptability to other areas with different climatic conditions is unknown. In this work, the pollination requirements of twelve cultivars from ARC-Infruitec program is determined, analyzing their behavior in Extremadura (Spain), one of the main producing areas in Europe. For this purpose, for each cultivar, pollen viability has been evaluated through in vitro pollen germination, self(in)compatibility has been determined by the observation of pollen tube growth in self-pollinated flowers under the microscope, and S-alleles have been identified by PCR analysis. The time of flowering has been monitored over five years. The selection of adequate pollinizers were done by assigning the cultivars to their corresponding incompatibility group and comparing their time of flowering. These results can be extrapolated to other areas where these cultivars are newly introduced, although additional data of flowering dates may be required for each zone.

Silencing of one copy of the translation initiation factor eIFiso4G in Japanese plum (Prunus salicina) impacts susceptibility to Plum pox virus (PPV) and small RNA production

BackgroundIn plants, host factors encoded by susceptibility (S) genes are indispensable for viral infection. Resistance is achieved through the impairment or the absence of those susceptibility factors. Many S genes have been cloned from model and crop species and a majority of them are coding for members of the eukaryotic translation initiation complex, mainly eIF4E, eIF4G and their isoforms. The aim of this study was to investigate the role of those translation initiation factors in susceptibility of stone fruit species to sharka, a viral disease due to Plum pox virus (PPV).ResultsFor this purpose, hairpin-inducing silencing constructs based on Prunus persica orthologs were used to generate Prunus salicina (Japanese plum) 4E and 4G silenced plants by Agrobacterium tumefaciens-mediated transformation and challenged with PPV. While down-regulated eIFiso4E transgenic Japanese plums were not regenerated in our conditions, eIFiso4G11-, but not the eIFiso4G10-, silenced plants displayed durable and stable resistance to PPV. We also investigated the alteration of the si- and mi-RNA profiles in transgenic and wild-type Japanese plums upon PPV infection and confirmed that the newly generated small interfering (si) RNAs, which are derived from the engineered inverted repeat construct, are the major contributor of resistance to sharka.ConclusionsOur results indicate that S gene function of the translation initiation complex isoform is conserved in Prunus species. We discuss the possibilities of using RNAi silencing or loss-of-function mutations of the different isoforms of proteins involved in this complex to breed for resistance to sharka in fruit trees.

Fruit aroma and sensorial characteristics of traditional and innovative Japanese plum (Prunus salicina Lindl.) cultivars grown in Italy

Plums are climacteric fruits with reduced shelf life and they represent a very appreciated product for fresh consumption. European consumers can find several plum cultivars that offer different organoleptic characteristics, flavor and aroma. In this study, chemical properties, such as total soluble solids (TSS), pH, titratable acidity, total phenolic and anthocyanin contents, aroma profile and sensory evaluation of seven plum cultivars were investigated. Significant differences in chemical properties were found in ‘Settembrine’ and ‘Angeleno’, the late ripening European plums that showed the highest TSS content and the lowest acidity values. As expected, a high level of anthocyanins was detected in red pulp and red flesh plums such as ‘Dofi Giudy’ and ‘Black Diamond’, though significant differences in their total phenolic amount were observed. ‘Dofi Giudy’, ‘Black Diamond’ and ‘Laroda’ showed the highest aroma profile among the investigated cultivars. Finally, a discrimination among the cultivars was obtained by combining the volatile profiles with a back-propagation neural network analysis (BPNN). The results showed that C6 compounds such as esters and aldehydes were strongly related to flavor perception of the panelists. ‘Dofi Giudy’ was the mostly appreciated plum due to its juiciness, sweetness and flavor intensity; furthermore, when compared to the other cultivars, it also showed remarkable levels of total soluble solids, total phenolic and anthocyanin contents.

Using Soil Moisture Sensors for Automated Irrigation Scheduling in a Plum Crop

The growing scarcity and competition for water resources requires the urgent implementation of measures to ensure their rational use. Farmers need affordable irrigation tools that allow them to take advantage of scientific know-how to improve water use efficiency in their common irrigation practices. The aim of this study is to test under field conditions, and adjust where required, an automated irrigation system that allows the establishment of regulated deficit irrigation (RDI) strategies in a stone fruit orchard. For this, an automated device with an algorithm which combines water-balance-based irrigation scheduling with a feedback adjustment mechanism using 15 capacitive sensors for continuous soil moisture measurement was used. The tests were carried out in 2016 and 2017 in Vegas Bajas del Guadiana (Extremadura, Spain) on an experimental plot of ‘Red Beaut’, an early-maturing Japanese plum cultivar. Three irrigation treatments were established: control, RDI and automatic. The control treatment was scheduled to cover crop water needs, a postharvest deficit irrigation (40% crop evapotranspiration (ETc)) strategy was applied in the RDI treatment, while the Automatic treatment simulated the RDI but without human intervention. After two years of testing, the automated system was able to “simulate” the irrigation scheduling programmed by a human expert without the need for human intervention.

Progress in the Japanese plum (Prunus salicina L.) breeding program developed by CEBAS-CSIC and IMIDA in Murcia, Spain

Progress in the Japanese plum (<i>Prunus salicina</i> L.) breeding program developed by CEBAS-CSIC and IMIDA in Murcia, Spain

Genotypic characterization of an F1 Japanese plum progeny through genotyping by sequencing (GBS) and preliminary quantitative trait locus (QTL) analysis for important agronomic traits

Genotypic characterization of an F₁ Japanese plum progeny through genotyping by sequencing (GBS) and preliminary quantitative trait locus (QTL) analysis for important agronomic traits

Morphological characteristics and germination of pollen in European and Japanese plum cultivars

Morphological characteristics and germination of pollen in European and Japanese plum cultivars

Sugar homeostasis in Japanese plum fruits with contrasting ripening behavior

Sugar homeostasis in Japanese plum fruits with contrasting ripening behavior

Differences and similarities between some European and Japanese plum cultivars

Differences and similarities between some European and Japanese plum cultivars