Comparative Transcriptomic Analyses of Different Jujube Cultivars Reveal the Co-Regulation of Multiple Pathways during Fruit Cracking

Fruit cracking is a common physiological disorder in many fruit species. Jujube (Ziziphus jujuba Mill.) is an economically valuable fruit in which fruit cracking seriously affects fruit yield and quality and causes significant economic losses. To elucidate cracking-related molecular mechanisms, the cracking-susceptible cultivars ‘Cuizaohong’ and ‘Jinsixiaozao’ and the cracking-resistant cultivar ‘Muzao’ were selected, and comparative transcriptome analyses of cracking and non-cracking ‘Cuizaohong’ (CC and NC), cracking and non-cracking ‘Jinsixiaozao’ (CJ and NJ), and non-cracking ‘Muzao’ (NM) were conducted. A total of 131 differentially expressed genes (DEGs) were common to the CC vs. NC and CJ vs. NJ comparisons. To avoid passive processes after fruit cracking, we also mainly focused on the 225 gradually downregulated DEGs in the CJ, NJ, and NM samples. The functional annotation of the candidate DEGs revealed that 61 genes related to calcium, the cell wall, the cuticle structure, hormone metabolism, starch/sucrose metabolism, transcription factors, and water transport were highly expressed in cracking fruits. We propose that expression-level changes in these genes might increase the turgor pressure and weaken mechanical properties, ultimately leading to jujube fruit cracking. These results may serve as a rich genetic resource for future investigations on fruit cracking mechanisms in jujube and in other fruit species.

Calibration and Tests for the Discrete Element Simulation Parameters of Fallen Jujube Fruit

Discrete element method (DEM) simulation is an important method to analyze the interaction relationship between materials and equipment, and to develop machinery and/or equipment. However, it is necessary to input specific simulation parameters when establishing a DEM simulation model. In this study, the interval values were measured through angle of repose tests of fallen jujube fruit (FJF), and the simulation angle of repose tests for FJF were established with EDEM software (DEM Solutions Ltd. Edinburgh, Scotland, UK). Then, the Plackett-Burman design, steepest ascent search experiment, and center composite design experimental methods were utilized to obtain the specific values of the simulation parameters from the interval values. The results showed that significant influencing factors in the simulation angle of repose include the Poisson’s ratio, the static friction coefficient between FJF, and the static friction coefficient between FJF and the steel plate, for which the optimal values were 0.248, 0.480, and 0.309, respectively. The angle of repose tests’ results showed that the error was 0.53% between the simulation angle of repose (29.69°) and the angle of repose (29.85°). In addition, the flow rate test results showed that the average error was 5.84% between the physical and simulation tests. This indicated that the calibrated parameters were accurate and reliable, and that the simulation model can accurately represent the physical tests. Consequently, this study provides an EDEM model of FJF that was essential in designing machinery and equipment through the EDEM simulation method.

Nutrient Composition, Antioxidant Activities and Anti-Inflammatory Effect of Jujube Fruit

Jujube (Ziziphus jujuba) fruit belongs to the Rhamnaceous family and is widely located in the tropical and subtropical regions of Asia as well as in the Mediterranean regions including Jordan. Therefore, the aim of this review was to illustrate the nutritional value of jujube fruit and its importance in human health protection as antioxidant and anti-inflammatory agent. Recently, several scientific reports have been carried out about the presence of many biologically active compounds from Z. jujuba, which may have high potential benefit in human nutrition, health, and disease. Based on previous studies, jujube fruit can possess good antioxidant and anti-inflammatory activity rendering it a functional food. Since jujube fruit has diverse biological activity, further biological studies including clinical-based studies are recommended to explore the health promoting effect of jujube.

Integrative Morphological, Physiological, Proteomics Analyses of Jujube Fruit Development Provide Insights Into Fruit Quality Domestication From Wild Jujube to Cultivated Jujube

Jujube (Ziziphus jujuba) was domesticated from wild jujube (Z. jujuba var. spinosa). Here, integrative physiological, metabolomic, and comparative proteomic analyses were performed to investigate the fruit expansion and fruit taste components in a jujube cultivar ‘Junzao’ and a wild jujube ‘Qingjiansuanzao’ with contrasting fruit size and taste. We revealed that the duration of cell division and expansion largely determined the final fruit size, while the intercellular space in the mesocarp dictated the ratio of mesocarp volume in mature fruits. The high levels of endogenous gibbereline3 (GA) and zeatin in the growing fruit of ‘Junzao’ were associated with their increased fruit expansion. Compared with ‘Junzao,’ wild jujube accumulated lower sugars and higher organic acids. Furthermore, several protein co-expression modules and important member proteins correlated with fruit expansion, sugar synthesis, and ascorbic acid metabolism were identified. Among them, GA20OX involved in GA biosynthesis was identified as a key protein regulating fruit expansion, whereas sucrose-6-phosphate synthase (SPS) and neutral invertase (NINV) were considered as key enzymes promoting sugar accumulation and as major factors regulating the ratio of sucrose to hexose in jujube fruits, respectively. Moreover, the increase of Nicotinamide adenine dinucleotide-Malate dehydrogenase (NAD-MDH) activity and protein abundance were associated with the malic acid accumulation, and the high accumulation of ascorbic acid in wild jujube was correlated with the elevated abundance of GalDH, ZjAPXs, and MDHAR1, which are involved in the ascorbic acid biosynthesis and recycling pathways. Overall, these results deepened the understanding of mechanisms regulating fruit expansion and sugar/acids metabolisms in jujube fruit.

First Report of Colletotrichum fructicola Causing Anthracnose on Indian Jujube (Ziziphus mauritiana) in Taiwan

Ziziphus mauritiana Lamarck known as Indian jujube is one of the most popular and delicious fruit crops in Taiwan. This crop is mainly planted in southern Taiwan and their fruit are harvested for providing fresh fruit. In March 2015, an anthracnose-like disease was observed on Indian jujube fruit (cv. Candied date) planted in an orchard in Yanchao District (22°46'33" N, 120°21'37" E) in Kaohsiung City. The disease was quickly distributed around the orchard after rain and caused great loss (around 40% of fruit infected). The diseased fruit would completely rot and lose its market value. Symptoms could be observed on all the developmental stages of fruit. On ripe fruit, symptoms were round, brown, water-soaked lesions covered with salmon-colored spore masses. Four fungal isolates from diseased fruit in the same orchard were collected by single spore isolation with hand-made glass needle. They were grown on potato dextrose agar (PDA) at 24 to 28°C with diffused light. All four strains produced white to gray, aerial, and cottony mycelia scattered with abundant salmon-colored conidial mass on the center of the colony on PDA. The conidia were hyaline, single celled, round cylindrical on both ends, thin walled, and the contents guttulate. The sizes of conidia were 15.2 (17.5 to 13.0) × 5.0 (5.5 to 4.5) μm (length/width ratio = 3.03, n = 40). DNA was isolated from JC1 and used for amplification of partial sequences of the internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), β-tubulin 2 (TUB2), chitin synthase 1 (CHS-1), manganese-superoxide dismutase (SOD2) and the intergenic region of apn2 and MAT1-2-1 gene (ApMat) genes (Silva et al. 2012; Weir et al. 2012). A BLAST search against the NCBI database revealed that JC1 gene sequences [GenBank accession nos. MT197188 (ITS), MT199871 (GAPDH), MT199872 (ACT), MT199870 (TUB2), MT815918 (CHS-1), MT815919 (SOD2) and MT221653 (ApMat)] displayed 100.0, 100.0, 99.1, 100.0, 99.7, 99.5 and 99.8% nucleotide identity to the respective gene sequences of Colletotrichum fructicola ICMP 18581 (JX010165, JX010033, FJ907426, JX010405, JX009866, JX010327, and JQ807838). Conidial suspension (1 × 106 conidia/mL) was prepared from JC1 isolate of C. fructicola and inoculated by spraying onto detached, ripe, healthy, non-wounded and surface-disinfected jujube fruit (cv. Candied date, n = 4). Four control fruit were sprayed with sterile water. Fruit were kept in a moist chamber (greater than 90% relative humidity, 24 to 28°C) for 24 h and maintained in the lab for additional 5 days. The inoculated fruit initially showed small light-colored spots in 5 to 7 days, which eventually developed into brown, sunken, water-soaked lesions 8 to10 days after inoculation, similar to the symptoms in the orchard. C. fructicola was re-isolated from symptomatic fruit showing similar morphological characteristics to those collected from the field, thus fulfilling Koch’s postulates. No symptom was observed on fruit treated with water and no pathogen was re-isolated. The experiment was performed twice. The JC1 isolate of C. fructicola with the identification number BCRC FU31437 has been deposited at Taiwan Bioresource Collection and Research Center. This pathogen has been found in many plant species in various countries (Weir et al. 2012). To our knowledge, this is the first report of C. fructicola causing Indian jujube fruit anthracnose in Taiwan and worldwide.

Identification of marker-trait associated SNPs for fruit weight and plant height in a wild and domesticated jujube fruit tree (Ziziphus spp.) collection using genotyping-by-sequencing

Ziziphus are economically and nutritionally important fruiting plants that were domesticated in China around 7000 years ago. We identified genetic diversity in 141 accessions of four, different species collected in Pakistan and in China, including wild species of Ziziphus mauritiana, Z. nummularia and Z. oxyphllya, and both wild and domesticated Z. jujuba Mill. Population structure, phylogenetic analysis and principal coordinates analysis based on 10,889 high-quality SNPs derived from genotyping-by-sequencing indicated that the accessions clustered into two major groups. The wild Pakistani Z. jujuba and Z. nummularia exhibited higher genetic diversity and polymorphic information content (0.37 and 0.23 respectively) than other species. We further conducted a genome-wide association study and discovered six highly significant marker-trait associations for fruit weight and plant height in this population. Our study provides important information for future breeding of Ziziphus species.