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Autotoxicity is known as a critical factor in replanting problem that reduces land utilization and creates economic losses. Benzoic acid (BA) is identified as a major autotoxin in peach replant problem, and causes stunted seedling growth or even death. However, the physiological and molecular mechanisms of peach response to BA stress remain elusive. Here, we comprehensively studied the morphophysiological, transcriptional, and metabolic responses of peach plants to BA toxicity. Results showed that BA stress inhibited peach seedlings growth, decreased chlorophyll contents and fluorescence levels, as well as disturbed mineral metabolism. The contents of hydrogen peroxide, superoxide anion, and malondialdehyde, as well as the total antioxidant capacity, were significantly increased under BA stress. A total of 6,319 differentially expressed genes (DEGs) were identified after BA stress, of which the DEGs related to photosynthesis, redox, and ion metabolism were greatly changed; meanwhile, numerous stress-responsive genes (HSPs, GSTs, GR, and ABC transporters) and transcription factors (MYB, AP2/ERF, NAC, bHLH, and WRKY) were noticeably altered under BA stress. BA induced metabolic reprogramming, and 74 differentially accumulated metabolites, including amino acids and derivatives, fatty acids, organic acids, sugars, and sugar alcohols, were identified in BA-stressed roots. Furthermore, an integrated analysis of genes and metabolites indicated that most of the co-mapped KEGG pathways were enriched in amino acid and carbohydrate metabolism, which implied a disturbed carbon and nitrogen metabolism after BA stress. The findings would be insightful in elucidating the mechanisms of plant response to autotoxicity stress, and help guide crops in alleviating replant problem. [ABSTRACT FROM AUTHOR]

As aged kiwifruit trees often reduce the fruit productivity and quality, those aged kiwifruits are replaced with juvenile vigorous plants. However, the productivity and quality of the replaced kiwifruits remain relatively low. In the present research, autotoxicity and allelopathy of kiwifruit roots were evaluated. Aqueous methanol extracts of kiwifruit roots inhibited the growth of cress, lettuce, alfalfa, Lolium multiflorum, Phleum pretense and Echinochloa crus-galli. The extracts of kiwifruit roots also showed an inhibitory effect on the growth of kiwifruits themselves. These results suggest that kiwifruit roots may contain allelopathic and autotoxic substances. The accumulation of autotoxic substances in orchard soil may occur by continuous exudation of autotoxic substances from kiwifruit roots over the long-term cultivations, and by liberation of the substances from the root residues. Accumulated autotoxic substances may suppress the fruit productivity and quality of the replaced kiwifruits. Therefore, autotoxicity may be involved in the replant problem of kiwifruits. [ABSTRACT FROM AUTHOR]

Long-term changes of soil nematode diversity and distribution patterns in replant peach orchard (RPO) and continuous-planting peach orchard (CPPO) were assessed to evaluate different effects on nematode community and function by RPO and CPPO, in relation to peach replant problem from the point of soil fauna. Observations were conducted on a silt loam soil, and soil sampling was performed four times through the growing season of peach trees in the period from 2006 to 2008 in Pinggu, Beijing. The result showed that RPO differed from CPPO by its higher abundance of plant feeding nematodes but lower abundance of bacterivore nematodes, as well as significantly higher values of plant parasite index but lower nematode biodiversity. Obviously, the absolute abundance of Paratylenchus in RPO was higher than that in CPPO, which could be a key factor for the peach replant problems from the part of soil nematode. Nematode function indices and weighted nematode fauna profile analysis were no significantly different in the two peach ecosystems, but they represented an indication of high disturbance, N-enriched, bacterial decomposition pathway.

Productivity decline of monospecific forest plantations has remained a serious problem. Despite increasing knowledge of the problem involved in the build-up of soil-borne pathogens and allelopathy, relatively little is known about tree-derived allelochemicals and their impacts on the soil microbial community and root growth. Therefore, the objective of this study was to examine a novel allelochemical cyclic dipeptide in relation to the soil microbial community and phytotoxicity to tree roots in 25-year-old monospecific Chinese fir ( Cunninghamia lanceolata ) forest plantations. We sampled soils and fine roots in situ and quantified soil cyclic dipeptide, microbial and root characteristics along with their correlation analyses. When compared with soil from a plantation established following removal of natural forest vegetation, soil from a replanted plantation contained a greater amount of cyclic dipeptide. Furthermore, increased soil potentially pathogenic fungi and reduced root biomass, root surface area and root length density were observed in the replanted plantations. There were negative relationships among cyclic dipeptide concentration, microbial community composition and root biomass in given plantations. Phospholipid fatty acid profiling showed that the signature lipid biomarkers of soil bacteria and fungi, and soil microbial community structure were affected under cyclic dipeptide application. Soil degradation dynamics indicated that cyclic dipeptide declined rapidly. The results demonstrated that allelochemical cyclic dipeptide not only had direct phytotoxicity to tree roots but also indirectly altered soil microbial community compositions, suggesting that productivity decline of continuous Chinese fir monocultures may be a negative feedback interaction between allelochemical-mediated soil microbial community and root phytotoxicity. [ABSTRACT FROM AUTHOR]

Replant diseases often occur when pome and stone fruits are grown in soil that had previously been planted with the same or similar plant species. They typically lead to reductions in plant growth, crop yield and production duration. In this project, greenhouse assays were used to identify a peach orchard soil that caused replant disease symptoms. Biocidal treatments of this soil led to growth increases of Nemaguard peach seedlings. In addition, plants grown in as little as 1% of the replant soil exhibited reduced plant growth. These results suggest that the disease etiology has a biological component. Analysis of roots from plants exhibiting various levels of replant disease symptoms showed little difference in the amounts of PCR-amplified bacterial or fungal rRNA genes. However, analysis using a stramenopile-selective PCR assay showed that rRNA genes from this taxon were generally more abundant in plants with the smallest top weights. Nucleotide sequence analysis of these genes identified several phylotypes belonging to Bacillariophyta, Chrysophyceae, Eustigmatophyceae, Labyrinthulida, Oomycetes, Phaeophyceae and Synurophyceae. Sequence-selective quantitative PCR assays targeting four of the most abundant phylotypes showed that both diatoms ( Sellaphora spp.) and an oomycete ( Pythium ultimum) were negatively associated with plant top weights. [ABSTRACT FROM AUTHOR]

Field experiment was conducted to study the replant problems of grapevine and apple. Plantings were in three different fields: on virgin soil, on apple replant soil and on vine replant soil. Each field was planted with 60 pieces of grafted vine (variety Bianca on rootstock Berl. X Rip. T.K. 5BB) and 60 pieces of grafted apple (variety Gloster on rootstock MM. 106). Fungicide (BUVICID K with 50 % captan agent, 0.5 g/1 1 soil) and nematocide (VYDATE 10 G with 10 % oxamil agent, 0.03 g/1 I soil) treatments were used in the soil in order to identify the causal factor of the problem. Biological soil test was conducted to test 17 soil samples of II wine districts and vine growing fields in plastic pots, under shading net. No root pieces were left in the soil. Two bud-cuttings of the Bed. X Rip. T 5C rootstock varieties were used as test plants. In each case, samples were taken from the vineyard and from the virgin soil. One fourth of the soil from the vineyard was left untreated and the other three part was treated with nematocide, fungicide or heat. The results of the field experiment suggest that there was no problem growing grapevine after apple and apple after grapevine, but both species had been inhibited growing after itself. The fungicide and nematocide treatments did not succeed in determining the casual factor of the problem. Heat treatment of replant soil (in pot test) was useful in AS and VNS soils. Results of biological soil test suggest, that grapevine replant problem do not occur in every vineyard. In fifty percent of soils, no significant differences between the treatments for shoot length, weight of cane, length, diameter and wood:ratio of the fourth internode were observed. In one case, difference was not found in any of the measured characters. However, fruiting bodies of Roesleria pallida (Pers.)Sacc. and the mycelium of Rosellinia necatrix Prill. were observed in this sample. In other samples, there was no significant difference between the treatments, but nematode and fungus infection appeared to be involved in increased shoot growth in nematocide and fungicide treated plants (mycelium of Rosellinia necatrix was detected). In other samples, the fungus infection caused significant difference between the virgin, untreated and fungicide treated soils and infection of Rosellinia necatrix was observed.

Field experiment was conducted to study the replant problems of grapevine and apple. Plantings were in three different fields: on virgin soil, on apple replant soil and on vine replant soil. Each field was planted with 60 pieces of grafted vine (variety Bianca on rootstock Berl. X Rip. T.K. 5BB) and 60 pieces of grafted apple (variety Gloster on rootstock MM. 106). Fungicide (BUVICID K with 50% captan agent, 0.5 g/1 1 soil) and nematocide (VYDATE 10 G with 10% oxamil agent, 0.03 g/1 1 soil) treatments were used in the soil in order to identify the causal factor of the problem. Biological soil test was conducted to test 17 soil samples of 11 wine districts and vine growing fields in plastic pots, under shading net. No root pieces were left in the soil. Two bud-cuttings of the Berl. X Rip. T 5C rootstock varieties were used as test plants. In each case, samples were taken from the vineyard and from the virgin soil. One fourth of the soil from the vineyard was left untreated and the other three part was treated with nematocide, fungicide or heat. The results of the field experiment suggest that there was no problem growing grapevine after apple and apple after grapevine, but both species had been inhibited growing after itself. The fungicide and nematocide treatments did not succeed in determining the casual factor of the problem. Heat treatment of replant soil (in pot test) was useful in AS and VNS soils. Results of biological soil test suggest, that grapevine replant problem do not occur in every vineyard. In fifty percent of soils, no significant differences between the treatments for shoot length, weight of cane, length, diameter and wood:ratio of the fourth internode were observed. In one case, difference was not found in any of the measured characters. However, fruiting bodies of Roesleria pallida (Pers.) Sacc. and the mycelium of Rosellinia necatrix Prill. were observed in this sample. In other samples, there was no significant difference between the treatments, but nematode and fungus infection appeared to be involved in increased shoot growth in nematocide and fungicide treated plants (mycelium of Rosellinia necatrix was detected). In other samples, the fungus infection caused significant difference between the virgin, untreated and fungicide treated soils and infection of Rosellinia necatrix was observed.

Autotoxicity is known as a critical factor in replanting problem that reduces land utilization and creates economic losses. Benzoic acid (BA) is identified as a major autotoxin in peach replant problem, and causes stunted seedling growth or even death. However, the physiological and molecular mechanisms of peach response to BA stress remain elusive. Here, we comprehensively studied the morphophysiological, transcriptional, and metabolic responses of peach plants to BA toxicity. Results showed that BA stress inhibited peach seedlings growth, decreased chlorophyll contents and fluorescence levels, as well as disturbed mineral metabolism. The contents of hydrogen peroxide, superoxide anion, and malondialdehyde, as well as the total antioxidant capacity, were significantly increased under BA stress. A total of 6,319 differentially expressed genes (DEGs) were identified after BA stress, of which the DEGs related to photosynthesis, redox, and ion metabolism were greatly changed; meanwhile, numerous stress-responsive genes ( HSPs , GSTs , GR , and ABC transporters ) and transcription factors ( MYB , AP2/ERF , NAC , bHLH , and WRKY ) were noticeably altered under BA stress. BA induced metabolic reprogramming, and 74 differentially accumulated metabolites, including amino acids and derivatives, fatty acids, organic acids, sugars, and sugar alcohols, were identified in BA-stressed roots. Furthermore, an integrated analysis of genes and metabolites indicated that most of the co-mapped KEGG pathways were enriched in amino acid and carbohydrate metabolism, which implied a disturbed carbon and nitrogen metabolism after BA stress. The findings would be insightful in elucidating the mechanisms of plant response to autotoxicity stress, and help guide crops in alleviating replant problem., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Shen, Zeng, Zhang, Zhu, He, Zhu, He, Li and Liu.)