Subtropical Fruit Tree Research Articles

Identification of Key Genes Controlling Sugar and Organic Acid Accumulation in Wampee Fruit (Clausena lansium) via Genome Assembly and Genome-wide Association Analysis.

Wampee (Clausena lansium) is an economically significant subtropical fruit tree widely cultivated in Southern China. To provide high-quality genomic resources for C. lansium, we report a chromosome-level genome sequence for the "JinFeng" cultivar. The 297.1 Mb C. lansium genome contained nine chromosomes with a scaffold N50 of 29.2 Mb and encoded 23,468 protein-coding genes. Selective sweep analysis between sweet and sour C. lansium varieties and genome-wide association analysis identified 14 candidate genes putatively involved in sugar and acid accumulation. ClERF061, encoding an ethylene response factor, and ClSWEET7, encoding a Sugars Will Eventually be Exported Transporters (SWEET) family protein, were proposed as key regulators of the sweet and sour tastes of the wampee fruit. ClERF061 and ClSWEET7 overexpression in tomatoes increased the total sugar and acid content in fruits. ClSWEET7 promoter activation by ClERF061 was confirmed via Nicotiana benthamiana transient expression. Our study provides valuable genomic resources for C. lansium genetics and breeding.

Fabrication of bio-inorganic metal nanoparticles by low-cost lychee extract for wastewater remediation: a mini-review.

This review article gives an overview of the biogenic synthesis of metal nanoparticles (mNPs) while using Litchi chinensis extract as a reducing and stabilizing agent. The subtropical fruit tree i.e lychee contains phytochemicals such as flavonoids, terpenoids, and polyphenolic compounds which act as reducing agents and convert the metal ions into metal atoms that coagulate to form mNPs. Different methodologies adopted for the synthesis of lychee extract and its use in the fabrication of mNPs under different reaction conditions such as solvent, extract amount, temperature, and pH of the medium have also been discussed critically in detail. Different techniques such as FTIR, UV-visible, XRD, SEM, EDX, and TEM adopted for the analysis of biogenic synthesis of mNPs have also been discussed in detail. Applications of mNPs: Applications of these prepared mNPs in various fields due to their antimicrobial, antiinflammatory, anticancer, and catalytic activities have also been described in detail.

Identification and Comprehensive Analysis of OFP Genes for Fruit Shape Influence in Mango.

OVATE family proteins (OFPs) are a class of plant-specific proteins with a conserved OVATE domain that play fundamental roles in fruit development and plant growth. Mango (Mangifera indica L.) is an economically important subtropical fruit tree characterized by a diverse array of fruit shapes and sizes. Despite extensive research on OFPs across various species, there remains a scarcity of information regarding OFPs in mango. Here, we have successfully identified 25 OFP genes (MiOFPs) in mango, each of which exhibits the conserved OVATE domains. The MiOFP gene exhibit a range of 2-6 motifs, with all genes containing both motif 1 and motif 2. Phylogenetic analysis on 97 OFPs (including 18 AtOFPs, 24 SlOFPs, 25 MiOFPs, and 30 OsOFPs) indicated that MiOFPs could be divided into three main clades: clade I, II, and III. Comparative morphological analysis identified significant variations in fruit longitudinal diameter, fruit transverse diameter, and fruit shape index between two distinct shaped mango cultivars ('Hongxiangya' and 'Jingpingmang') at DAP5, DAP7, and DAP10 stages. The subsequent examination of paraffin sections revealed distinct patterns of cell elongation. The majority of MiOFP genes exhibited predominantly expressed in developing organs, specifically flowers and immature fruits, while displaying distinct expression patterns. RNA-Seq analysis revealed significant disparities in the expression levels of several OFP genes, including MiOFP5, MiOFP11, MiOFP21, MiOFP22, MiOFP23, and MiOFP25, between the two mango cultivars. These findings suggest that these six genes may play a crucial role for fruit shape in mango, especially the MiOFP22. The findings of this study have established a basis for future investigations into MiOFPs in mango, offering a solid foundation for further research in this field.

Florida Plant Disease Management Guide: Guava (Psidium guajava)

Guava is a popular subtropical fruit tree grown commercially in south Florida. Production is affected by multiple diseases of different origin. This guide provides information about the most common diseases, including disease biology and management. Written by Romina Gazis, Jonathan Crane, and Jeff Wasielewski, and published by the UF/IFAS Plant Pathology Department, revised April 2024.

Water Use Efficiency in a Deficit-Irrigated Orange Orchard

Citrus is a subtropical fruit tree with high water requirements. This study aimed to determine the effects of water deficit on an orange orchard subjected to different water-saving strategies. The study was realised in an orange orchard in a semiarid area by adopting four different water management techniques: 100% crop evapotranspiration (control); SSDI—subsurface sustained deficit irrigation; RDI—regulated deficit irrigation; PRD—partial rootzone drying treatment during five growing seasons. The experimental design foresaw a randomised block design with six replicates per treatment (24 index plants). The results of the study showed that the water-saving strategies reduced irrigation water consumption by 25% (SSDI), 33% (RDI), and 49% (PRD) compared to the fully irrigated treatment without yield reduction, thus increasing water use efficiency. Mineral nutrition of the trees was slightly affected by irrigation treatments; element concentration in leaves was generally in the optimal range; only potassium showed values below the recommended leaf concentrations. Regarding fruit quality parameters, the vitamin C concentration in RDI showed significant differences with a value of 62.7 mg 100 mL−1 compared to 58.5 mg 100 mL−1 in the control. Plants subjected to SSDI and PRD strategies showed increased levels of pulp colour index with significant values of 10 and 9.90, respectively, compared to the control (8.44). By implementing targeted water management, citrus growers could save water and increase the ascorbic acid and sugar concentration in the fruits; anthocyanins also increased but not significantly. These findings open new market opportunities for citrus growers in marginal areas, where they cannot rely solely on producing citrus fruits to remain competitive.

Impact of flowering temperature on litchi yield under climate change: A case study in Taiwan

Litchi is a subtropical fruit tree that undergoes flower bud differentiation under low-temperature conditions. However, climate change has affected litchi production in Taiwan, causing litchi farmers to experience economic losses. This study explored the influence of flowering temperature on litchi yield under climate change in Taiwan by analyzing litchi production data from 2001 to 2020 and observation data from meteorological stations in litchi-producing areas. Historical observed data were used to construct several regression models relating temperature to yield, with the performance of the models used to determine critical temperature thresholds for litchi flower bud differentiation. Analytical climate data (CMIP5) were used to project yield changes in Taiwan’s litchi-producing regions under anticipated low-temperature conditions for the mid- (2036–2065) and late- (2071–2100) 21st century. The variable that exhibited the highest correlation with yield changes was the number of days with an average flowering temperature below 16 °C. The production yield, in terms of yield variation per hectare, is expected to decrease by 12 % to 35 % by the end of the 21st century (2071–2100). Given the projected decline in the number of cooler days due to climate change, existing litchi cultivars may become unsuitable for cultivation in production areas in southern Taiwan. Practical ImplicationsSome fruit trees require a period of low temperature before their flowering stage. Climate change is expected to cause warming of winter temperatures in Taiwan, which is likely to lead to reduced litchi flowering. The current study assessed the potential effects of climate change on litchi flowering in the future.Historical observed data were used to establish models, and critical temperature thresholds for litchi flowering were determined on the basis of model performance. Days with average temperatures below 16 °C exhibited the highest correlation with litchi yield among the tested thresholds. According to our results, farmers can use this 16 °C threshold to evaluate the potential effects of future climate change at their current farm locations and to identify other areas with similar or more favorable conditions for litchi cultivation. For agricultural researchers, this temperature threshold could provide a target for new litchi variety breeding and a reference basis for research on optimal cultivation methods.Notably, because climate change projection data have a high degree of uncertainty, the results of this study may differ from those of studies using different databases. In this study, we used an ensemble of CMIP5 projections incorporating data from models from various research centers around the world, which can provide more robust results based on an ensemble mean than those obtainable from a single model or a few models. In addition, rainfall is a crucial factor during the flowering growth stage. Future studies should consider the effects of rainfall and temperature on yield and should consider using a model with yield being considered a function of both of these variables to improve model accuracy.To conclude, the present study provides researchers, policymakers, and other stakeholders with insights into the primary effects of climate change on litchi production. It also lays the groundwork for future climate adaptation strategies in Taiwan’s litchi industry.

Climate Change Challenges in Temperate and Sub-Tropical Fruit Tree Cultivation

In the last few years, the world has experienced the impacts of climate change, such as elevated mean annual temperature, extreme weather events, drought, etc. Among living organisms, perennial plant species are the ones mostly exposed to climate change impacts, as they may experience different extreme events within the same year, such as flooding during some periods and drought in summer months, extremely low temperatures in winter but excessively high temperatures in summer, etc. Climate change affects a range of physiological functions of temperate fruit and nut tree species, such as their phenophases, bud dormancy release and vernalization, pollination and fruit set, fruit growth and quality, as well as bud sprouting and growth initiation. Besides these, the impact of climate change on pests, diseases, and weeds may generate significant negative interactions with tree physiology, threatening food production, food safety, and human welfare. In the present manuscript, a general aspect of climate change impacts on fruits’ and nut trees’ physiological functions is described and commented on.

Identification and characterization of novel drought-responsive lncRNAs in stone apple (Aegle marmelos L.) through whole-transcriptome analysis

Stone apple (Aegle marmelos L.) is a subtropical fruit tree of the Rutaceae family, highly valued in traditional medicine across the Indian subcontinent. We conceived this study with the objective of developing a comprehensive transcriptome dataset, identifying SSRs for marker-assisted breeding, and delineating regulators of gene expression, with a specific emphasis on non-coding RNA (ncRNA), particularly related to drought stress. To achieve this, RNA-seq was conducted using RNA pooled from various tissues, including roots, leaves, inflorescence, and developing seeds from stone apple, and the clean reads were assembled into 40,886 unigenes. Subsequently, the unigenes were categorized into gene ontology categories encompassing biological processes, molecular functions, and cellular components. Within the unigenes, we identified a total of 9174 perfect simple sequence repeats (SSRs), 2167 transcription factors (TFs) distributed among 69 families, and 415 transcription regulators (TRs) across 27 families. Additionally, 19 microRNAs (miRNAs) from 12 families, 16,811 potential long noncoding RNAs (lncRNAs), and six functional endogenous target mimics (eTMs) were detected. Analysis of lncRNA-miRNA-mRNA interactions unveiled multiple regulatory nodes, elucidating lncRNA/miRNA-driven gene expression control in stone apple. The increased co-expression of selected drought-related lncRNAs and their cognate target mRNAs supported the aforementioned findings under drought conditions. Overall, this study significantly advances our understanding of stone apple genomics and lays a foundation for future omics-based studies, thereby facilitating the deployment of climate-resilient strategies in the species.

Experimental study on cold tolerance thresholds in field grown subtropical fruit trees

Experimental study on cold tolerance thresholds in field grown subtropical fruit trees

Effects of Covering Mature Avocado ‘Pinkerton’ Trees with High-density Shading Nets during Cold Winters on Microclimate, Chlorophyll Fluorescence, Flowering, and Yield

Avocado (Persea americana Mill.) is a subtropical fruit tree with high commercial value and increasing global demand. Most avocado cultivars are vulnerable to cold climates, which may reduce yields and restrict their geographical expansion. This includes the green-skinned avocado cultivar Pinkerton, which accounts for 45% of the avocado cultivated in northeastern Israel. Shading nets can protect agricultural crops from cold environments. Therefore, we evaluated the effect of covering mature ‘Pinkerton’ trees with high-density shading nets during the winter. Trees were covered with silver-colored 50% or 70% shading nets during three consecutive winters, and uncovered trees served as controls. Photosynthetically active radiation in plots covered with the silver 50% or 70% nets was significantly lower than that for the control by 52% and 90%, respectively. The minimum air temperature was similar between treatments. The maximum air temperature was generally lower under the shading nets compared with that of the control. The ratios of variable fluorescence to maximum fluorescence (Fv/Fm) measured in February 2019 and February 2020 were 0.72 and 0.8 for the control trees, 0.79 and 0.83 for the silver 50% trees, and 0.81 and 0.84 for the silver 70% trees, respectively. Flowering intensity of the net-covered trees was lower than that of the control by up to 42%. Interestingly, the 3-year average yield of trees covered with the silver 50% or 70% nets was insignificantly higher by 27% and 38%, respectively, compared with the control trees. These results suggest that the reduction of daytime solar irradiance in the winter by the shading nets may mitigate adverse effects of cold and increase yield. Additional long-term studies should examine the effects of shading nets and other shading strategies on different avocado cultivars.

Morphological and pathological characterization ofColletotrichumspecies causing anthracnose of litchi leaves in Guangxi, China

AbstractLitchi (Litchi chinensisSonn.) is an evergreen subtropical fruit tree native to southern China. Litchi is vulnerable to a wide range of diseases affecting yield and fruit quality. Anthracnose is one of the main diseases during the period of growth and storage, which has a serious impact on the quality and production of litchi. In December 2020 to May 2021, typical anthracnose symptoms were observed on litchi leaves in different orchards in Qinzhou City, Guangxi Province, Southern China. According to colony features, conidial and appressorial morphology, and sequence analysis of several genomic regions (internal transcribed spacer (ITS) region, chitin synthase (chs‐1), actin (act), calmodulin (cal), glyceraldehyde‐3‐phosphate dehydrogenase (gapdh), β‐tubulin (tub2) and the intergenic region of apn2 and MAT1‐2‐1 (ApMat)), 44 isolates were obtained, and 26 were identified as threeColletotrichumspecies:C. fructicola(50%),C. siamense(42.31%),C. gigasporum(7.69%). The pathogenicity tests were performed with conidial suspension and mycelia plugs to inoculate wounded litchi seedlings. The results of pathogenicity tests showed that the virulence ofC. gigasporumwas the weakest, and the virulence ofC. fructicolawas the strongest. This is the first report ofC. gigasporumcausing anthracnose of litchi worldwide.

Antioxidant and Antiproliferative Activities of Phenolic Extracts of Eriobotrya japonica (Thunb.) Lindl. Fruits and Leaves.

Increasing interest in new sources of secondary metabolites as biologically active substances has resulted in an advanced study of many plant species. Loquat (Eriobotrya japonica (Thunb.) Lindl. = Rhaphiolepis bibas (Lour.) Galasso & Banfi, Rosaceae family), an evergreen, subtropical fruit tree, native to China and Japan, but cultivated in southern countries of Europe, is a species commonly used in folk medicine and may be an excellent source of bioactive compounds. Therefore, the aim of the present study was to evaluate the profile of the phenolic constituents of E. japonica fruits and leaves originating from Tuscany (Italy), as well as their in vitro antioxidant and chemopreventive activities on human cancer cell lines breast adenocarcinoma (MCF-7), colon adenocarcinoma (Caco-2 and HT-29), and glioblastoma (U87MG). Results revealed that the extract of leaves displayed higher antioxidant and anticancer potential than the fruit extract and contained 25 individual phenolic compounds that have been characterized and quantified by the UPLC-PDA-MS method. The antiproliferative activity was correlated with the content of polyphenolic compounds indicating that both fruits and leaves are a good source of antioxidants and may be exploited as nutraceuticals enriching food or as components for the cosmetic/pharmaceutical industry.

Impact of waterlogging on fruit crops in the era of climate change, with emphasis on tropical and subtropical species: A review

Incidents of flooding in tropical and subtropical fruit trees have increased as a result of climate change. Because of flooding, the anaerobic conditions of the rhizosphere increase the conditions for phytotoxicity and infection by pathogenic fungi and bacteria. Due to oxygen depletion in waterlogged soils, growth, functions of the roots and of the entire plant are impaired. The decrease in the photosynthetic rate is considerable because of the reduced functional leaf area because of chlorosis, necrosis, leaf drop and stomatal closure, as well as chlorophyll degradation. Plants have developed different morphological, physiological, and biochemical adaptations to survive hypoxic stress. Some fruit trees form an aerenchyma in roots for the diffusion of oxygen from the aerial parts. Induced aerenchyma-containing adventitious roots, rapidly elongate stems into deeply flooded soils; or they form hypertrophied lenticels, like some mango varieties. Measures for better adaptations and tolerance of tropical fruit trees to climatic impact include the following: adaptations of the cultivated terrain, selection of varieties, rootstocks more tolerant to hypoxic stress, pruning to reestablish the balance of the aerial part/roots, and foliar applications (e.g., of glycine betaine or hydrogen peroxide (H2O2)). Mycorrhizal colonization of roots can increase tolerance to waterlogging, while the application of fertilizers, such as CaO or MgO, can improve the redox potential of flooded soils. We present results of studies on this problem for the following fruits: yellow passion fruit (Passiflora edulis f. flavicarpa) and purple passion fruit (P. edulis f. edulis), cape gooseberry (Physalis peruviana), lulo or naranjilla (Solanum quitoense), tree tomato (Solanum betaceum), citrus (Citrus spp.), guava (Psidium guajava), papaya (Carica papaya), and mango (Mangifera indica).

Comparative transcriptome profiling unveils the potential key genes involved in peel coloration between Ziziphus mauritiana Lam. and Z. jujuba Mill

Ber (Ziziphus mauritiana Lam.) is one of the important tropical and subtropical fruit trees of the genus Ziziphus Mill. Most cultivars of Ber keep green throughout fruit development while its close relative Chinese jujube (Z. jujuba Mill.) changes the color from green to red in all cultivars. However, the lack of transcriptomic and genomic information limits our insights into the molecular mechanisms underpinning fruit coloration in Ber. Here, high-throughput RNA sequencing (RNA-Seq) was used for the first time to de novo assemble and characterize the transcriptome of Ber fruit. Over 20 million clean reads were produced, and 62,029 unigenes with an average length of 1078.76 bp were assembled. The differentially regulated genes that are responsive to fruit color were also studied in Ber. Eight structural genes, ZmC4H1, ZmBIA1, ZmLDOX, and ZmUGT (UTG6, UFGT13 UFGT14, UFGT15, and UFGT16), were found to be significantly differentially expressed and downregulated in Ber fruit peel, indicating that these genes may be involved in no color formation in the fruit peel of Ber. Furthermore, transcription factors such as bHLH and ZmMYB (MYB13, 14 15, and 16) were found to be downregulated at five developmental stages of Ber fruit, suggesting an important interconnection with flavonoids like anthocyanin biosynthesis-related genes. The expression of these selected genes was also checked at all fruit developmental stages in the Chinese jujube transcriptome. All the selected genes were significantly up-regulated in the fruit developmental stages of Jujube. The expression pattern of these selected genes encoding flavonoid or anthocyanin biosynthetic enzymes and transcription factors in the Ber and Jujube fruit peels were confirmed using quantitative real-time PCR. This study provided insights into the diversity of fruit coloration in Ziziphus Mill. and will serve as a new starting point for further functional investigation of these genes.

Genome-wide analysis of the GLP gene family and overexpression of GLP1-5–1 to promote lignin accumulation during early somatic embryo development in Dimocarpus longan

Longan (Dimocarpus longan Lour.) is an economically important subtropical fruit tree. Its fruit quality and yield are affected by embryo development. As a plant seed germination marker gene, the germin-like protein (GLP) gene plays an important role in embryo development. However, the mechanism underlying the role of the GLP gene in somatic embryos is still unclear. Therefore, we conducted genome-wide identification of the longan GLP (DlGLP) gene and preliminarily verified the function of DlGLP1-5–1. Thirty-five genes were identified as longan GLP genes and divided into 8 subfamilies. Based on transcriptome data and qRT‒PCR results, DlGLP genes exhibited the highest expression levels in the root, and the expression of most DlGLPs was upregulated during the early somatic embryogenesis (SE) in longan and responded to high temperature stress and 2,4-D treatment; eight DlGLP genes were upregulated under MeJA treatment, and four of them were downregulated under ABA treatment. Subcellular localization showed that DlGLP5-8–2 and DlGLP1-5–1 were located in the cytoplasm and extracellular stroma/chloroplast, respectively. Overexpression of DIGLP1-5–1 in the globular embryos (GEs) of longan promoted the accumulation of lignin and decreased the H2O2 content by regulating the activities of ROS-related enzymes. The results provide a reference for the functional analysis of DlGLPs and related research on improving lignin accumulation in the agricultural industry through genetic engineering.

Supra-optimal temperatures induce photochemical leaf damage and reduce photosynthetic O2 evolution in Carica papaya L.

Carica papaya L. is a tropical and subtropical fruit tree. In such climatic regions, cultivation frequently includes exposure to supra-optimal temperatures, which may affect the leaf photosynthetic capacity. Two papaya genotypes, 'Candy' and 'Golden THB', were used to study the effects of supra-optimal temperatures on photochemical responses. The seedlings were cultivated in a greenhouse in 40 L pots. After 100 days, excised leaf discs were incubated at 25, 35, 40, 45, 50 or 55 °C, for 15, 30, 45 or 60 min. Emissions of chlorophyll a fluorescence and photosynthetic O 2 evolution rates were measured. In both genotypes, F 0 increased, while F m decreased after 15 min at 45 °C or above, indicating photochemical damage. An increase in non-photochemical dissipation in relation to photochemical dissipation (F v /F 0 ) was noted, resulting in decreased maximum (ΦP 0 ) and effective (QY Lss ) quantum yields of the PSII. A reduction in the probability of the electrons being transported beyond Q A - (Ψ 0 ), and in the efficiency of electron transport through the chain (ΦE 0 ) were observed, indicating an increase in the quantum efficiency of energy dissipation (ΦD 0 ). The high rate of reaction center deactivation (increase in RC/CS 0 ) in supra-optimal temperatures resulted in elevated absorption (ABS/RC), capture (TR 0 /RC), transport (ET 0 /RC), and dissipation (DI 0 /RC) of energy per active reaction center. An increase in energy absorption by the PSII antenna complex (ABS/CS 0 ) occurred above 40 °C. However, this additional energy was not effectively captured (TR 0 /CS 0 ), or transported (ET 0 /CS 0 ), resulting in high excess energy dissipation (DI 0 /CS 0 , NPQ Lss , NPQ D ). An increase in ΔV/Δt 0 reflected a reduction in the rate of photosynthetic O 2 evolution rate at temperatures above 30 °C. The reduction of three key parameters PI Abs , SFI abs and Rfd Lss occurred in leaf disks incubated at 40 °C for a period of 15 min, indicating a reduction in photochemical efficiency in both genotypes. Therefore, severe damage to the photosynthetic capacity of C. papaya L. can be observed at temperatures above 40 °C. • Temperatures higher than 40 °C cause photochemical damage to papaya leaves. • Chlorophyll fluorescence images show heterogeneity of photochemical damage. • Energy capture and transport are more sensitive than absorption by the LHCII. • Moderate temperatures excite PSI and optimize electron transport. • Reduction in the rate of evolution of photosynthetic O 2 from 35 °C.

Sunburn disorder in tropical and subtropical fruits. A review

The increase in solar radiation and temperature as a result of climate change and variability has increased sunburn damage to fruits, which highly affects quality and yield in tropical and subtropical fruit plants. Solar injuries increase because of conditions with low relative humidity, fruits left uncovered by foliage, and plantations at higher altitudes as a result of increased UV radiation. Three different types of sunburn on fruits are distinguished: photooxidative sunburn, sunburn browning, and necrosis on the epidermis. Fruits employ self-protection mechanisms against this stress through the production of enzymatic and non-enzymatic antioxidants. Fruit growers try to mitigate the impact of sunburning by planting species and varieties that are tolerant to this stress, pruning and training plants, leaving enough leaves above the fruit, efficient irrigation and intercropping for shading. More technical sunburn mitigation strategies include 1) improving the microclimate (shading nets, fruit bagging, evaporative cooling), 2) suppressors (kaolinite clay particle films, calcium carbonate) or 3) chemical protection (tocopherol, abscisic acid, ascorbic acid, anti-transpirants). This paper presents the state of research and its results for this abiotic stress in some tropical and subtropical fruit trees, such as avocado, banana, citrus, mango, pineapple and pitaya, along with observations for other fruit trees in tropical altitude zones. Continued research is recommended for this stress in different varieties with the use of environmentally friendly protective materials, along with studies on molecular mechanisms that direct the acclimatization of plants to a combination of these two types of stress, excessive radiation and temperature.

Suppressive Effect of Soil Microbiomes Associated with Tropical Fruit Trees on Meloidogyne enterolobii.

Plant-parasitic nematodes are one of the main biotic factors limiting agricultural production worldwide, with root-knot nematodes (Meloidogyne spp.) being the most damaging group. This study was conducted to evaluate the efficacy of soil microbiomes, associated with various subtropical fruit trees, on the management of a Meloidogyne enterolobii population. Of 14 soil microbiomes tested for nematode suppression, 9 samples in the first experiment and 10 samples in the repeat experiment had significantly (p ≤ 0.05) lower numbers of eggs and J2 compared to the untreated control. The highest nematode suppression was recorded for SA12 extracted from a papaya orchard with a 38% reduction in the nematode population density. In addition, the presence of some bacteria (Bacillus aryabhattai, B. funiculus and B. simplex) and fungi (Metarhizium marquandii, Acremonium sp. and Mortierella sp.) was correlated to a higher suppression potential in some samples. Substantial variations were observed for the diversity of bacterial and fungal isolates among the samples collected from various crop hosts and regions. This suggests that the nematode suppression potential of different soil microbiomes highly depends on the abundance and diversity of fungal and bacterial strains present in the soil. The study confirmed that among all variables, soil dryness, pH, Fe, Zn, organic matter, altitude, and crop cultivar strongly influenced the soil microbial composition.

Investigating the Mechanism of Unilateral Cross Incompatibility in Longan (Dimocarpus longan Lour.) Cultivars (Yiduo × Shixia).

Longan (Dimocarpus longan Lour.) is an important subtropical fruit tree in China. Nearly 90% of longan fruit imports from Thailand are from the cultivar Yiduo. However, we have observed that there exists a unilateral cross incompatibility (UCI) when Yiduo is used as a female parent and Shixia (a famous Chinese cultivar) as a male parent. Here, we performed a comparative transcriptome analysis coupled with microscopy of pistils from two reciprocal pollination combinations [Shixia♂ × Yiduo♀(SY) and Yiduo♀ × Shixia♂(YS)] 4, 8, 12, and 24 h after pollination. We also explored endogenous jasmonic acid (JA) and jasmonyl isoleucine (JA-Ile) levels in pistils of the crosses. The microscopic observations showed that the UCI was sporophytic. The endogenous JA and JA-Ile levels were higher in YS than in SY at the studied time points. We found 7,251 differentially expressed genes from the transcriptome analysis. Our results highlighted that genes associated with JA biosynthesis and signaling, pollen tube growth, cell wall modification, starch and sucrose biosynthesis, and protein processing in endoplasmic reticulum pathways were differentially regulated between SY and YS. We discussed transcriptomic changes in the above-mentioned pathways regarding the observed microscopic and/or endogenous hormone levels. This is the first report on the elaboration of transcriptomic changes in longan reciprocal pollination combination showing UCI. The results presented here will enable the longan breeding community to better understand the mechanisms of UCI.

Genomic insights into longan evolution from a chromosome-level genome assembly and population genomics of longan accessions.

ABSTRACTLongan (Dimocarpus longan) is a subtropical fruit tree best known for its nutritious fruit and regarded as a valuable tonic and traditional medicine since ancient times. A high-quality chromosome-scale genome assembly is valuable for functional genomic study and genetic improvement of longan. Here, we report a chromosome-level reference genome sequence for the longan cultivar JDB. The assembled genome is 455.5 Mb in size and anchored to fifteen chromosomes, representing a significant improvement in contiguity (contig N50 = 12.1 Mb, scaffold N50 = 29.5 Mb) over a previous draft assembly. A total of 40 420 protein-coding genes were predicted in the D. longan genome. Synteny analysis suggests that longan shares the widespread gamma event with core eudicots but has no other whole genome duplications. Comparative genomics showed that the D. longan genome experienced significant expansions of UDP-glucosyltransferase and phenylpropanoid biosynthesis-related gene families. Deep genome sequencing analysis of longan cultivars identified longan biogeography as a major contributing factor to its genetic diversity and revealed clear population admixture and introgression among cultivars of different geographic origins, suggesting a likely migration trajectory of longan that is confirmed by existing historical records. Finally, genome-wide association studies (GWAS) of longan cultivars identified quantitative trait loci (QTLs) for six different fruit quality traits and revealed a shared QTL that contained three genes for total soluble solids and seed weight. The chromosome-level reference genome assembly, annotation, and population genetic resources for D. longan will facilitate the molecular studies and breeding of desirable longan cultivars in the future.