Peach Roots Research Articles

Phosphorus-induced restructuring of the ascorbate-glutathione cycle and lignin biosynthesis alleviates manganese toxicity in peach roots.

Manganese (Mn) is indispensable for plant growth, but its excessive uptake in acidic soils leads to toxicity, hampering food safety. Phosphorus (P) application is known to mitigate Mn toxicity, yet the underlying molecular mechanism remains elusive. Here, we conducted physiological and transcriptomic analyses of peach roots response to P supply under Mn toxicity. Manganese treatment disrupted root architecture and caused ultrastructural damage due to oxidative injury. Notably, P application ameliorated the detrimental effects and improved the damaged roots by preventing the shrinkage of cortical cells, epidermis and endodermis, as well as reducing the accumulation of reactive oxygen species (ROS). Transcriptomic analysis revealed the differentially expressed genes enriched in phenylpropanoid biosynthesis, cysteine, methionine and glutathione metabolism under Mn and P treatments. Phosphorus application upregulated the transcripts and activities of core enzymes crucial for lignin biosynthesis, enhancing cell wall integrity. Furthermore, P treatment activated ascorbate-glutathione cycle, augmenting ROS detoxification. Additionally, under Mn toxicity, P application downregulated Mn uptake transporter while enhancing vacuolar sequestration transporter transcripts, reducing Mn uptake and facilitating vacuolar storage. Collectively, P application prevents Mn accumulation in roots by modulating Mn transporters, bolstering lignin biosynthesis and attenuating oxidative stress, thereby improving root growth under Mn toxicity. Our findings provide novel insights into the mechanism of P-mediated alleviation of Mn stress and strategies for managing metal toxicity in peach orchards.

Physiological and molecular mechanisms of melatonin to alleviate benzoic acid-induced autotoxicity stress in Prunus persica

Autotoxicity stress is well known as a critical factor in the replant problem that hinders the sustainable development of agriculture. Benzoic acid (BA) is identified as a major autotoxin in peach replant problem, and causes serious growth inhibition of peach plants. Melatonin is a multi-functional molecule that plays a key role in alleviating stress-induced damage in plants. However, the functions and the inherent molecular mechanisms of melatonin under autotoxicity stress remains largely elusive. Here, we found that application of melatonin significantly enhanced BA tolerance in peach seedlings. Exogenous melatonin mitigated the negative impact of BA stress on peach root growth. Melatonin pretreatment boosted flavonoid biosynthesis and increased soluble sugar content of peach plants under BA stress. In addition, melatonin also promoted the reactive oxygen species scavenging by enhancing the antioxidant capacity. Consistent with these alterations, transcriptome analysis demonstrated that up-regulations of flavonoid biosynthesis, starch and sucrose metabolism, and antioxidant-related genes were observed when melatonin applied under BA stress. Furthermore, we also observed that an induction in genes involved in xenobiotic transmembrane transport, cell wall organization or biogenesis, and α-linolenic acid metabolism, which might contribute to the melatonin-mediated BA tolerance. Collectively, our findings reveal that melatonin confers BA tolerance of peach seedlings, primarily attributed to increased flavonoid and soluble sugar levels, enhanced antioxidant capacities, and extensive transcriptome reprograming. This opens new avenues for utilizing melatonin to alleviate peach replant problem.

Transcription factor LBD16 targets cell wall modification/ion transport genes in peach lateral root formation.

LATERAL ORGAN BOUNDARIES DOMAIN/ASYMMETRIC LEAVES2-LIKEs (LBDs/ASLs) are plant-specific transcription factors that function downstream of auxin-regulated lateral root (LR) formation. Our previous research found that PpLBD16 positively regulates peach (Prunus persica) LR formation. However, the downstream regulatory network and target genes of PpLBD16 are still largely unknown. Here, we constructed a PpLBD16 homologous overexpression line and a PpLBD16 silenced line. We found that overexpressing PpLBD16 promoted peach root initiation, while silencing PpLBD16 inhibited peach root formation. Through RNA sequencing (RNA-seq) analysis of roots from PpLBD16 overexpression and silenced lines, we discovered that genes positively regulated by PpLBD16 were closely related to cell wall synthesis and degradation, ion/substance transport, and ion binding and homeostasis. To further detect the binding motifs and potential target genes of PpLBD16, we performed DNA-affinity purification sequencing (DAP-seq) analysis in vitro. PpLBD16 preferentially bound to CCNGAAANNNNGG (MEME-1), [C/T]TTCT[C/T][T/C] (MEME-2), and GCGGCGG (ABR1) motifs. By combined analysis of RNA-seq and DAP-seq data, we screened candidate target genes for PpLBD16. We demonstrated that PpLBD16 bound and activated the cell wall modification-related genes EXPANSIN-B2 (PpEXPB2) and SUBTILISIN-LIKE PROTEASE 1.7 (PpSBT1.7), the ion transport-related gene CYCLIC NUCLEOTIDE-GATED ION CHANNEL 1 (PpCNGC1) and the polyphenol oxidase (PPO)-encoding gene PpPPO, thereby controlling peach root organogenesis and promoting LR formation. Moreover, our results displayed that PpLBD16 and its target genes are involved in peach LR primordia development. Overall, this work reveals the downstream regulatory network and target genes of PpLBD16, providing insights into the molecular network of LBD16-mediated LR development.

Differential Gene Expression Patterns in Peach Roots under Non-Uniform Soil Conditions in Response to Organic Matter.

Organic matter (OM) amendments are often encouraged in sustainable agriculture programs but can create heterogeneous soil environments when applied to perennial crops such as peaches (Prunus persica (L.) Batsch). To better understand the responses of peach roots to non-uniform soil conditions, transcriptomic analysis was performed in a split-root study using uniform soil (the same soil type for all roots) or non-uniform soil (different soil types for each half of the root system) from either (1) autoclaved sand (S), (2) autoclaved sand with autoclaved compost (A), or (3) autoclaved sand with compost which included inherent biological soil life (B). Each uniform soil type (S, A, and B) was grouped and compared by uniform and non-uniform soil comparisons for a total of nine treatments. Comparisons revealed peach roots had differentially expressed genes (DEGs) and gene ontology terms between soil groups, with the S and B groups having a range of 106-411 DEGs and the A group having a range of 19-94 DEGs. Additionally, six modules were identified and correlated (p > 0.69) for six of the nine treatment combinations. This study broadly highlights the complexity of how OM and biological life in the rhizosphere interact with immediate and distant roots and sheds light on how non-homogenous soil conditions can influence peach root gene expression.

Comprehensive physio-biochemical and transcriptomic characterization to decipher the network of key genes under waterlogging stress and its recuperation in Prunus persica.

Waterlogging is a major abiotic stress that plants encounter as a result of climate change impacts. Peach is very sensitive to hypoxia during waterlogging, which causes poor tree vigor and huge economic losses. The molecular mechanism underlying the peach response to waterlogging and reoxygenation remains unclear. Here, the physiological and molecular responses of 3-week-old peach seedlings under waterlogged and recovery conditions were comprehensively analyzed. As a result, waterlogging significantly reduced plant height and biomass with inhibition of root growth when compared with control and reoxygenation. Similar results were observed for photosynthetic activities and gaseous exchange parameters. Waterlogging increased lipid peroxidation, hydrogen peroxide, proline, glutamic acid and glutathione contents, while superoxide dismutase, peroxidases and catalase activities were decreased. The glucose and fructose contents were accumulated, contrary to sucrose which was reduced remarkably throughout the stress periods. The level of endogenous indole acetic acid (IAA) was increased in waterlogging but decreased after reoxygenation. However, the change trends of jasmonic acid (JA), cytokinins and abscisic acid (ABA) levels were opposite to IAA. In transcriptomic analysis, there were 13,343 differentially expressed genes (DEGs) with higher and 16,112 genes with lower expression. These DEGs were greatly enriched in carbohydrate metabolism, anaerobic fermentation, glutathione metabolism and IAA hormone biosynthesis under waterlogging, while they were significantly enriched in photosynthesis, reactive oxygen species scavenging, ABA and JA hormones biosynthesis in reoxygenation. Moreover, several genes related to stress response, carbohydrate metabolism and hormones biosynthesis were significantly changed in waterlogging and reoxygenation, which indicated unbalanced amino acid, carbon and fatty acid pools in peach roots. Taken together, these results suggest that glutathione, primary sugars and hormone biosynthesis and signaling might play key roles in plant response to waterlogging. Our work provides a comprehensive understanding of gene regulatory networks and metabolites in waterlogging stress and its recuperation, which will facilitate peach waterlogging control.

Random forest analysis reveals taxa predictive of Prunus replant disease in peach root microbiomes

Successive plantings of Prunus species produce suboptimal growth and yield in many California soils due to a poorly understood soilborne disease complex, Prunus replant disease (PRD). We explored the hypothesis that PRD is mediated by microbial taxa in roots of Nemaguard peach, a rootstock for almond and other stone fruits. In a greenhouse bioassay, portions of 10 replant soils were treated with fumigation or pasteurization or left untreated as a control before being planted with peach seedlings. Ten weeks after planting, seedlings were considered PRD-affected if their top fresh weights in the control were significantly reduced, compared to the weights in pasteurization and fumigation treatments; plants with equivalent top weights in all treatments were considered to be non-affected. The roots were washed from the soil, frozen, extracted for total DNA, and used for metabarcoding of rRNA gene amplicons from bacteria, fungi, and oomycetes. High-throughput amplicon sequencing revealed that root microbial community shifts resulted from preplant treatments, and specific taxa were associated with PRD induction among controls. Random forest (RF) analysis discriminated effectively between PRD-affected and non-affected root communities. Among the 30 RF top-ranked amplicon sequence variant (ASV) predictors, 26 were bacteria, two were oomycetes, and two were fungi. Among them, only Streptomyces scabiei, Steroidobacter denitrificans, Streptomyces bobili, and Pythium mamillatum had root abundances ≥5% that were either associated positively (former two ASVs) or negatively (latter two) with PRD. Thus, our findings were consistent with microbial mediation of PRD in roots and suggested taxa that may be involved in the mediation.

Enhancement of plant growth, acclimatization, salt stress tolerance and verticillium wilt disease resistance using plant growth-promoting rhizobacteria (PGPR) associated with plum trees (Prunus domestica)

Plants interact with a great variety of microorganisms that inhabit the rhizosphere playing critical roles in several aspects of plant growth and protection against abiotic and biotic diseases. In this study, we performed a screening of bacteria associated with the rhizosphere of Prunus domestica trees to identify bacterial strains with plant growth-promoting activity. Ten strains isolated from the rhizosphere of P. domestica showed multiple in vitro plant growth promoting rhizobacteria (PGPR) activity such as the production of indole acetic acid, hydrogen cyanide, ammonia, solubilization of phosphates and antifungal activity against Verticillium dalhiae and Fusarium oxysporum f.sp. melonis. In planta, they significantly increased the growth (stem length, number of leaflets, leaf area and root weight) and biochemical (nitrate reductase activity, proline and chlorophyll content) parameters of tomato, as well as the rate of seed germination. Two selected strains (Pr7 and Pr8) with higher antagonistic activity against V. dalhiae and F. oxysporum f.sp. melonis protected tomato plants against Verticillium wilt and salt stress. In addition, they enhanced acclimatization of Vitis vinifera cv. Pinot noir and the peach root stock GF305 from in vitro to the greenhouse. 16S rRNA sequencing identified strains Pr7 and Pr8 as Pseudomonas stutzeri and Bacillus toyonensis, respectively. Since these two PGPR inoculants exhibited multiple traits beneficial to the examined host plants, they may be applied in the development of safe, and effective seed treatments as an alternative to chemical fungicides and fertilization but also for successful acclimatization of micropropagated plants.

Spatial changes of arbuscular mycorrhizal fungi in peach and their correlation with soil properties.

Arbuscular mycorrhizal (AM) fungi have beneficial effects on host plants, but their growth is influenced by various factors. This study was carried out to analyze the variation of AM fungi in soils and roots of peach (Prunus persica L. var. Golden Honey 3, a yellow-flesh variety) trees in different soil layers (0–40 cm) and their correlation with soil properties. The peach tree could be colonized by indigenous AM fungi (2.2–8.7 spores/g soil and 1.63–3.57 cm hyphal length/g soil), achieving 79.50–93.55% of root AM fungal colonization degree. The mycorrhizal growth, root sugars, soil three glomalins, NH4+-N, NO3−-N, available P and K, and soil organic matter (SOM) had spatial heterogeneity. Soil spores, but not soil hyphae contributed to soil glomalin, and soil glomalin also contributed to SOM. There was a significant correlation of soil hyphae with spore density, soil NO3−-N, and SOM. Root mycorrhiza was positively correlated with spore density, NH4+-N, NO3−-N, and easily extractable glomalin-related soil protein. Notably, spore density positively correlated with NO3−-N, available K, SOM, and root fructose and glucose, while negatively correlated with available P and root sucrose. These findings concluded that mycorrhiza of peach showed spatial distribution, and soil properties mainly affected/altered based on the soil spore density.

First Report of Xiphinema Diffusum from Pakistan.

SummaryThe population of Xiphinema americanum species group was detected from the soil surronding the roots of peach (Prunus persica) during a survey of plant-parasitic nematodes in Gilgit-Baltistan, Pakistan. From the results of the morphological study, the species was identified as X. diffusum. Morphometrics of X. diffusum generally agree with those of the type species and the topotype specimens. Molecular analysis of 18S rDNA of X. diffusum from Pakistan indicated two nucleotide differences and 99 % similarity with the Chinese (AM086669) and the Australian (AM086685) population of X. diffusum. Phylogenetic analysis of 18S rDNA placed the Pakistanis population close to X. diffusum from China and Australia. This species is reported for the first time from Pakistan

Regulation of growth in peach roots by exogenous hydrogen sulfide based on RNA-Seq

Hydrogen sulfide (H2S) has been shown to regulate many physiological processes of plants. In this study, we observed that 0.2 mM sodium hydrosulfide (NaHS), a donor of H2S, can regulate the root architecture of peach seedlings, increasing the number of lateral roots by 40.63%. To investigate the specific mechanisms by which H2S regulates root growth in peach, we used RNA sequencing and heterologous expression technology. Our results showed that exogenous H2S led to a 44.50% increase in the concentration of endogenous auxin. Analyses of differentially expressed genes (DEGs) revealed that 963 and 1113 genes responded to H2S on days one and five of treatment, respectively. Among the DEGs, 26 genes were involved in auxin biosynthesis, transport, and signal transduction. Using weighted correlation network analysis, we found that the auxin-related genes in the H2S-specific gene module were disproportionately involved in polar transport, which may play an important role in H2S-induced root growth. In addition, we observed that the expression of LATERAL ORGAN BOUNDARIES DOMAIN 16 (PpLBD16) was significantly up-regulated by exogenous application of H2S in peach. Overexpression of PpLBD16 in an Arabidopsis system yielded a 66.83% increase in the number of lateral roots. Under exposure to exogenous H2S, there was also increased expression of genes related to cell proliferation, indicating that H2S regulates the growth of peach roots. Our work represents the first comprehensive transcriptomic analysis of the effects of exogenous application of H2S on the roots of peach, and provides new insights into the mechanisms underlying H2S-induced root growth.

Cloning and Functional Determination of Ammonium Transporter PpeAMT3;4 in Peach.

Ammonium (NH4+) plays key roles in plant growth, development, fruit quality, and yield. In plants, NH4+ uptake and transport are facilitated by NH4+ transporters (AMT). However, molecular mechanisms and physiological functions of type-II AMT (AMT2) transporters in fruit trees are still unclear, especially in peach. In this study, we cloned and characterized an AMT2 family gene from peach, PpeAMT3;4, and determined its function in yeast mutant. Expression analysis showed that PpeAMT3;4 was majorly expressed in peach roots and significantly decreased by NH4+ excess but had no response to NH4+ deficiency. Functional determination and 15nitrogen-labeled NH4+ uptake assay in yeast cells implied that PpeAMT3;4 was a typical high-affinity transporter, with a Km value of 86.3 μM, that can uptake external NH4+ in yeast cells. This study provides gene resources to uncover the biological function of AMT2 transporters and reveals molecular basis for NH4+ uptake and nitrogen (N) nutrition mechanisms in fruit trees.

Mycorrhizal fungi enhance flooding tolerance of peach through inducing proline accumulation and improving root architecture

This study aimed to evaluate the effect of an arbuscular mycorrhizal fungus (AMF) Glomus mosseae on plant growth, root architecture, and proline metabolism in roots of peach (Prunes persica L.) under non-flooding and flooding conditions. The 12-day flooding dramatically inhibited root colonisation of G. mosseae, but induced a large number of extraradical mycelia. Although the flooding treatment also relatively inhibited growth and root architecture of peach, the mycorrhizal fungal inoculation dramatically increased shoot and root biomass, plant height, stem diameter, number of 1<sup>st</sup>- and 2<sup>nd</sup>-order lateral roots, root total length (mainly 0–1 cm and > 3 cm long), root surface area, and root volume under flooding. The study also revealed distinctly higher proline accumulation in the roots of mycorrhizal plants than non-mycorrhizal plants under both non-flooding and flooding conditions, accompanied by higher Δ<sup>1</sup>-pyrroline-5-carboxylate synthase (P5CS) activity and lower δ-ornithine transaminase and proline dehydrogenase activities. In addition, the PpP5CS1 gene expression was up-regulated by flooding and mycorrhization. This study concluded that mycorrhizal fungi enhanced flooding tolerance of peach through inducing proline accumulation and improving root architecture.

On characterizing root function in perennial horticultural crops.

While root-order approaches to fine-root classification have shown wide utility among wild plants, they have seen limited use for perennial crop plants. Moreover, inadequate characterization of fine roots across species of domesticated perennial crops has led to a knowledge gap in the understanding of evolutionary and functional patterns associated with different fine-root orders. We examined fine-root traits of common horticultural fruit and nut crops: Malus ×domestica, Prunus persica, Vitus vinifera, Prunus dulcis, and Citrus ×clementina. Additional roots were sampled from 33 common perennial horticultural crops, native to tropical, subtropical, and temperate regions, to examine variation in 1st- and 2nd-order absorptive roots. First-order roots of grape and 1st- and 2nd-order roots of apple and peach were consistently thin, nonwoody, mycorrhizal, and had high N:C ratios. In contrast, 4th- and 5th-order roots of grape and 5th-order roots of apple and peach were woody, nonmycorrhizal, had low N:C ratios, and were thicker than lower-order roots. Among the 33 horticultural species, diameter of 1st- and 2nd-order roots varied about 15-fold, ranging from 0.04 to 0.60 mm and 0.05 to 0.89 mm respectively. This variation generally was phylogenetically conserved across plant lineages. Collectively, our research shows that root-order characterization has considerably more utility than an arbitrary diameter cutoff for identifying roots of different functions in perennial horticultural crops. In addition, much of the variation in root diameter among species can be predicted by evolutionary relationships.

Peach PpSnRK1 Participates in Sucrose-Mediated Root Growth Through Auxin Signaling.

Sugar signals play a key role in root growth and development. SnRK1, as one of the energy centers, can respond to energy changes in plants and affect the growth and development of plants. However, studies on sugar signals and SnRK1 regulating root growth in fruit trees have not been reported. In this study, we found that 5% exogenous sucrose could increase the total volume and total surface area of the peach root system, enhance the number and growth of lateral roots, and promote the activity of SnRK1. When exogenous trehalose was applied, the growth of roots was poor. Sucrose treatment reversed the inhibitory effects of trehalose on SnRK1 enzyme activity and root growth. We also found that the lateral root number of PpSnRK1a-overexpressing plants (4-1, 4-2, and 4-3) increased significantly. Therefore, we believe that peach SnRK1 is involved in sucrose-mediated root growth and development. To further clarify this mechanism, we used qRT-PCR analysis to show that exogenous sucrose could promote the expression of auxin-related genes in roots, thereby leading to the accumulation of auxin in the root system. In addition, the genes related to auxin synthesis and auxin transport in the root systems of PpSnRK1a-overexpressing lines were also significantly up-regulated. Using peach PpSnRK1a as the bait, we obtained two positive clones, PpIAA12 and PpPIN-LIKES6, which play key roles in auxin signaling. The interactions between peach PpSnRK1a and PpIAA12/PpPIN-LIKES6 were verified by yeast two-hybrid assays and bimolecular fluorescence complementation experiments, and the complexes were localized in the nucleus. After exogenous trehalose treatment, the expression of these two genes in peach root system was inhibited, whereas sucrose had a significant stimulatory effect and could alleviate the inhibition of these two genes by trehalose, which was consistent with the trend of sucrose’s regulation of SnRK1 activity. In conclusion, peach SnRK1 can respond to sucrose and regulate root growth through the auxin signal pathway. This experiment increases our understanding of the function of fruit tree SnRK1 and provides a new insight to further study sugar hormone crosstalk in the future.

First report of the root-knot nematode, Meloidogyne morocciensis infecting peach in Southern Brazil.

The peach tree (Prunus persica) is the third most cultivated temperate fruit species in Brazil. In August 2017, peach seedling plants showing symptoms of stunting and multiple galls in the roots were detected in the municipality of Pelotas, state of Rio Grande do Sul, Brazil. Samples of peach roots were collected and they were subsequently processed to obtain eggs and second-stage juveniles (J2), to determine the number of nematodes per gram of roots and to proceed with morphological studies. Additionally, individual females were extracted from the peach roots and submitted to Meloidogyne species identification by electrophoresis using α-esterase (Est) and malate dehydrogenase (Mdh) phenotypes and perineal pattern. The nematode population density in the samples was 283 eggs + J2s per gram of fresh roots. The polymorphism analysis revealed the A3N1 phenotype, typical to Meloidogyne morocciensis. Perineal patterns of females showed oval squared shapes, with moderately high to high dorsal arches, streaks widely separated, generally continuous, sometimes broken; the phasmids were separate by 29.3 μm (25.43-31.94 μm), similar to M. arenaria and M. incognita, as observed by Hammah and Hirschmann (1990). The second-stage juveniles had the following morphometric characters: L = 389.3 ± 3.8 (377.5-425.1) μm, stylet = 13.9 ± 0.2 (12.7-14.9) μm, DGO = 3.6 ± 0.1 (3.3-4.2) μm, tail length 47.5 ± 0.6 (45.3-48.9) μm, hyaline tail terminus = 14.1 ± 0.3 (12.5-17.0) μm, a = 25.6 ± 0.4 (23.8-28.8) μm and c = 8.6 ± 0.1 (8.0-9.3). The known SCAR marker obtained for M. arenaria is the same as that amplified for M. morocciensis. Under greenhouse conditions, peach plants seedlings inoculated with 1,000 eggs (Pi) with M. morocciensis were evaluated 28 days after inoculation compared to non-inoculated plants. The inoculated peach plants showed a mean of 338 galls per root system, and a nematode reproduction factor of 10.3. Besides this plants exhibited a reduction in fresh weight of shoots and roots compared to the non-inoculated plants. These results confirm M. morocciensis pathogenicity on P. persica.

Effect of bag-controlled release fertilizer on nitrogen loss, greenhouse gas emissions, and nitrogen applied amount in peach production

In common nutrient management in peach orchards in China, a large amount of nitrogen fertilizer is used. However, low nitrogen absorption and utilization rate results in nitrogen loss and greenhouse gas emissions, which is not favorable for cleaner production in peach orchards. In this experiment, nitrogen leaching, ammonia volatilization, greenhouse gas emissions under bag-controlled release fertilizer (BCRF) were evaluated. In addition, the impact of BCRF on soil nutrient status in peach orchards, peach root system growth, nitrogen absorption and utilization rate, fruit quality, and the potential for using BCRF in major peach-producing areas in China to reduce the amount of nitrogen fertilizer application were also investigated. Results showed that BCRF maintained a stable supply of nutrients to soil, decreased nitrogen leaching, ammonia volatilization and greenhouse gas emissions while nitrogen loss was significantly reduced from peach orchard soil. Also, BCRF reduced the combined global warming potential at 20-, 100-, and 500-years. A 5-year study revealed that application of BCRF promoted the formation of a dense root system in peach trees by the development of fine roots and a more concentrated root distribution. This extended the lifespan of the root system and improved fruit quality. 15N tracer experiments showed that BCRF significantly increased the absorption and utilization rate of nitrogen by peach trees. BCRF reduced the amount of nitrogen fertilizers applied by 65–82% compared to common fertilizer application methods without decreasing peach yield, so it has huge potential for reducing the amount of nitrogen fertilizer used as well as fertilizer input costs in peach production. The results showed that BCRF has huge application potential as a new, environmentally friendly, low-cost, and efficient fertilizer for cleaner production in peach orchards.

Pseudomonas putida WH-B3 degrades benzoic acid and alleviates its autotoxicity to peach (Prunus persica L. batsch) seedlings grown in replanted soil

Autotoxins play important roles in problems with peach replanting. Benzoic acid (BA), one of the major autotoxins, is identified in peach root exudates and rhizosphere soil, leading to stunted seedling growth or even death. In this research, we aimed to screen the most efficient BA-degrading strain (BDS) from peach rhizosphere soil and assess its potential as a biodegradation strain that could relieve peach replant stress. In the work, three BDSs (WH-B1, WH-B2 and WH-B3) were isolated and identified as Pseudomonas denitrificans, Acinetobacter calcoaceticus and P. putida, respectively. Through bacterial growth and BA degradation tests, the strain WH-B3 was found to show the highest growth rate and the greatest degradation capacity and was selected for soil inoculation. Meanwhile, the phytotoxicity analysis revealed that the BA degradation products of the three BDSs were almost completely nontoxic to seedlings. Moreover, the pot experiments indicated that a high concentration of soil BA (≥ 40 mg kg−1) significantly restrained an increase in peach seedling height, stem diameter, and biomass, while the WH-B3 inoculum distinctly decreased the soil BA content and fully counteracted the BA-mediated inhibition of seedling growth. Furthermore, to investigate the performance of the potent strain under authentic replanted soil (RS) conditions, WH-B3 was inoculated into the RS for peach seedling growth. The results demonstrated that the WH-B3 inoculum degraded approximately 65% of the BA in RS and significantly improved replant-stressed seedling growth. Altogether, the characteristics of P. putida WH-B3 show that it is a potential strain for BA biodegradation and has promise for alleviating problems in peach replanting.

Insight into the Bacterial Endophytic Communities of Peach Cultivars Related to Crown Gall Disease Resistance.

Crown gall disease caused by Agrobacterium tumefaciens severely impacts the production of peach and other fruit trees. Several peach cultivars are partially resistant to A. tumefaciens, but little is known about the roles of endophytic microbiota in disease resistance. In the present study, the endophytic bacterial communities of resistant and susceptible peach cultivars "Honggengansutao" and "Okinawa" were analyzed using universal 16S rRNA gene amplicon sequencing in parallel with the cultivation and characterization of bacterial isolates. A total of 1,357,088 high-quality sequences representing 3,160 distinct operational taxonomic units (OTUs; Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes) and 1,200 isolates of 20 genera and 305 distinct ribotypes were collected from peach roots and twigs. It was found that factors including plant developmental stage, cultivar, and A. tumefaciens invasion strongly influenced the peach endophytic communities. The community diversity of endophytic bacteria and the abundance of culturable bacteria were both higher in the roots of the resistant cultivar, particularly after inoculation. Strikingly, the pathogen antagonists Streptomyces and Pseudomonas in roots and Rhizobium in twigs were most frequently detected in resistant plants. Our results suggest that the higher abundance and diversity of endophytic bacteria and increased proportions of antagonistic bacteria might contribute to the natural defense of the resistant cultivar against A. tumefaciens This work reveals the relationships between endophytic bacteria and disease resistance in peach plants and provides important information for microbiome-based biocontrol of crown gall disease in fruit trees.IMPORTANCEAgrobacterium tumefaciens as the causal agent of peach crown gall disease can be controlled by planting resistant cultivars. This study profiles the endophytic bacteria in susceptible and resistant peach cultivars, advancing our understanding of the relationships between endophytic bacterial communities and peach crown gall disease, with potential implications for other complex microbiome-plant-pathogen interactions. The resistant cultivar may defend itself by increasing the diversity and abundance of beneficial endophytic bacteria. The antagonists identified among the genera Streptomyces, Pseudomonas, and Rhizobium may have application potential for biocontrol of crown gall disease in fruit trees.

Effects of orchard floor management on the peach rhizosphere

A preliminary study examining soil microbiology and nutrient dynamics in year three of a peach orchard at the Sandhills Research Station‎, North Carolina, USA found that maintaining a 3.6-m vegetation-free strip in the tree row reduced microbial biomass and associated activities in the soil, compared with a 0 m strip, and that the use of under tree micro-sprinkler irrigation increased peach root colonization by endomycorrhizal fungi as well as microbial biomass and associated activities. The current study was conducted in years four and five of that orchard and examined vegetation-free strip widths of 0, 1.2, 2.4, and 3.6 m, with and without irrigation, to determine their effects on endomycorrhizal fungal colonization of peach roots, soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), soil microbial respiration (SMR), and net nitrogen mineralization (NNM). There were no significant differences between treatments for endomycorrhizal fungal colonization or MBC by year four. The 3.6 m vegetation-free strip had the lowest MBN and SMR in year four with no significant difference between strip treatments in year five. NNM decreased with greater vegetation-free strip widths in years four and five. Irrigated plots had significantly higher MBN and lower SMR in the spring of year five with no other significant differences due to irrigation. These important findings show that under standard commercial management of a bearing peach orchard there is little impairment of soil ecological function in the rhizosphere, allowing for maximum peach yield and quality while supporting the health of trees and soil.

Antagonistic potential of native agrocin-producing non-pathogenic Agrobacterium tumefaciens strain UHFBA-218 to control crown gall in peach

A non-pathogenic agrocin-producing native isolate of Agrobacterium tumefaciens strain UHFBA-218 was tested as a biological control agent against the peach crown gall. This strain was compatible with all the recommended pesticides used in stone fruits in the integrated pest management (IPM) module, except for copper oxychloride, which was detrimental to its growth. Upon artificial co-inoculation of 4-wk-old plants of tomato var. Solan Gola with A. tumefaciens strain UHFBA-218 and tumorigenic A. tumefaciens strain Peach 2E-10, out of the 27 isolates recovered, six were transconjugants showing selective acquisition of tumorigenic factors as made evident by amplification with ipt and virD2 primers, whereas the rest of the isolates did not acquire any of these tumorigenic factors. A white stone powder-based formulation of this isolate (103.3 × 108 cfu g-1) retained appreciable viability for up to 6 months at room temperature. When peach roots and seeds were soaked in cell suspensions of different doses of a white stone powder-based bioformulation of UHFBA-218 before planting in the field, the number of plants with tumours was reduced, with the lowest incidence of crown gall being observed in the 0.1% UHFBA-218 root dip treatment, i.e. 1.48% and 0.80% during the years 2013 and 2014, respectively. No incidence of crown gall was observed in the three seed dip treatments, i.e. 30-min dip in UHFBA-218 followed by 1 h of shade drying, stratified seeds dipped for 30 min in 0.1% suspensions of strains UHFBA-218 or K84 followed by 1 h of shade drying before sowing, as compared with 14.76% incidence in untreated plants.