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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]

Replant problem in agriculture is popular and has restricted the development of tobacco industry. To identify the key soil factors affecting replant problem of tobacco, rhizosphere soils and flue-cured tobacco plants were sampled from continuous planting fields for 1 year (CK), 3 years (3a), 5 years (5a), and 7 years (7a). The pH value, nutrient, autotoxic compounds and microbial community in soils and the yield and quality (economic characters) of tobacco were determined. Then the correlations between soil factors and economic characters of tobacco were analyzed by Mantel test. Results showed that the economic characters, soil pH, organic matter (SOM), total nitrogen (TN), available potassium (AK), microelements (Ca, Mg and Fe), bacterial richness and diversity decreased significantly, total potassium (TK), total phosphorus (TP), available phosphorus (AP) changed unevenly, while autotoxic compounds, fungal diversity and richness increased under the long-term continuous cropping system. Mantel test showed that the economic characters always had the highest positive correlation with bacterial community. In addition, when continuous cropping for 3 years, there was a high positive correlation between economic characters and major elements content (R = 0.5649, P = 0.003). After continuous cropping for 3 years, there was a high positive correlation between the economic characters and soil major elements (5 years: R = 0.6195, P = 0.001; 7 years: R = 0.4761, P = 0.001), microelements (5 years: R = 0.7214, P = 0.001; 7 years: R = 0.6427, P = 0.001). Therefore, in Central Henan tobacco growing areas, bacterial community dysbiosis together with nutrient imbalance cause the replant problem. However, the accumulation of rhizosphere autotoxic compounds contributes less to the 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]

Replant problem is a situation resulting in suppression of growth and poor productivity of the trees planted on old orchard sites and makes the plantations un-economical. It is a serious malady throughout the world in some fruit crops where the new plantations are done at the old orchard sites. Although replant problem is known to exist for many decades but greater attention was paid to this phenomenon only when Thompson (1959) while working at East Malling Research Station, United Kingdom observed poor growth of apple and cherry on old plantation sites. This observation strongly stimulated replant research in different parts of the world. Western Himalayan states of India are also facing the replant problem where majority of apple orchards have out lived their economic life and new plantations are being done at the same site. The incidence of apple replant disease on various sites has been observed 25-70 per cent. It is comparatively easy to prevent the replant problem than to control it because of unknown exact etiology and complex nature of malady due to the presence of different biotic and abiotic factors associated with the problem. Nature and intensity of the incidence is highly variable from country to country and even region to region and there is lack of quick diagnostic methods. The problem is difficult to control with one method and require integrated management practices for effective control. [ABSTRACT FROM AUTHOR]

Highlights • Kiwifruit leaf extracts inhibited the test plant growth in a dose dependent manner. • The kiwifruit roots were more sensitive to the leaf extracts than the hypocotyls. • (-)-Epicatechin was identified as a phytotoxic substance in kiwifruit leaves. • (-)-Epicatechin inhibited seedling growth of kiwifruit in a dose dependent manner. Abstract When aged kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson) plants are replaced with young ones, the growth and productivity of the young plants were occasionally lower than expected. This symptom is typical of the replant problems reported in several fruit trees. Phytotoxic substances released from the plant are assumed to be involved in the replant problems. Although some substances contained in kiwifruit leaves have been reported to have phytotoxic activity, little is known about phytotoxicity and phytotoxic substances in kiwifruit leaves on the growth of the kiwifruit itself. Therefore, this study determined the phytotoxic activity of kiwifruit leaf extracts and soil extracts and identified a phytotoxic substance in kiwifruit leaves. Extracts of kiwifruit leaves inhibited the growth of Lepidium sativum , Lactuca sativa , Medicago sativa , Phleum pratense , Lolium multiflorum , Echinochloa crus-galli , and kiwifruit seedlings. The soil extracts also inhibited the growth of L. sativum. These results suggest that kiwifruit leaf extracts and soil extracts may possess phytotoxic substances. (-)-Epicatechin was isolated from the extracts with bioassay-guided separations using chromatography. The concentrations of (-)-epicatechin required for 50% growth inhibition of the hypocotyls and radicles of L. sativum were 27.9 and 10.7 mM, respectively, and those for the hypocotyls and radicles of kiwifruit were 13.9 and 7.6 mM, respectively. This substance may contribute to the phytotoxic activity of kiwifruit leaf extracts and may be involved in the kiwifruit replant problem. [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.

At present, replant disorder and peach (Prunus persica (L.) Batsch) short life has become an important problem in peach production, and it has seriously restricted the development of the peach industry in Chahar Mahal va Bakhtiary province. During 2014-2017, 108 samples of plant tissues and rhizosphere were collected from the peach orchards of this province. Samples were investigated to isolation and identification microorganisms and pathogens associated with symptoms of peach replant problem. Symptoms including: yellowing, stunting, abscission of leaf, leaf discoloration and chlorosis, crown and root rot, canker and death of young trees. From plant and soil samples, the frequency respectively, isolates of Bacillus sp, Fusarium sp, Pseudomonas flourescens, Mesocriconema xenoplax, Aspergillus sp, Alternaria sp, Pantoea agglomerans, Arthrobacter sp, Phytophthora sp, Pseudomonas syringae, Pseudomonas putidae, Verticillium dahliae, Dematophora necatrix, Trichoderma sp, Streptomyces sp, Meloidogyne sp, Pratylenchus sp, Paratylenchus sp, Stenotrophomonas maltophilia, Pythium sp and Rhizoctonia sp were isolated and identified. About 11% of isolates were unknown. The amount of replant disorder and isolation of these microorganisms in orchards that were planted immediately after the destruction of previous trees or planted the same previous species was about 30% more than the orchards that had not been cultivated (fallow) for at least one year. On this basis canbe say these microorganisms are the most important agents associated with replant problem and life short in peach orchards in Chahar Mahal va Bakhtiary province. Koch's postulates investigations are necessary to determine the role of these microorganisms in this replant disease. [ABSTRACT FROM AUTHOR]

Asparagus ( Asparagus officinalis L.) is a widely cultivated perennial veritable and can be harvested more than ten years. However, the crop quality and yield decline after a few year’s cultivation, which is called “asparagus decline”. Even though those asparagus plants were replaced with new young asparagus plants, the productivity and quality of the crop remain relatively low, which is known as a “asparagus replant problem”. One of the possible reasons for “asparagus decline” and “asparagus replant problem” is thought to be autotoxicity of asparagus. However, the compounds involved in the autotoxicity is not clear. The objective of this study was therefore to determine the potential role of autotoxicity in the “asparagus decline” and “asparagus replant problem”. An aqueous methanol extract of 10-year-asparagus-cultivated soils inhibited the growth of asparagus seedlings and other two test plants with concentration dependent manner. The result confirmed that the asparagus soils have autotoxic activity. The extract was then purified by several chromatographies with monitoring the inhibitory activity and a potent growth inhibitory substance causing the autotoxic effect was isolated. The chemical structures of the compound was determined by spectral data to be trans -cinnamic acid. trans -Cinnamic acid inhibited the growth of asparagus seedlings at concentrations greater than 10 μM. The concentrations required for 50% growth inhibition of asparagus (IC 50 ) were 24.1–41.6 μM. trans -Cinnamic acid accumulated 174 μM in the 10-year-asparagus-cultivated soils, which may be enough levels to cause the growth inhibition on asparagus considering its IC 50 value. Therefore, trans -cinnamic acid may contribute to the autotoxic effect of asparagus soils, and may be in part responsible for “asparagus decline” and “asparagus replant problem”. [ABSTRACT FROM AUTHOR]

Rehmannia glutinosa Libosch. is a medicinal plant cultivated at a commercial scale in China. However, replanting problems result in a severe decline in both the biomass and quality of its roots, which are of greatest medicinal value. This study attempted to remediate the replant soil using spent Pleurotus eryngii Quel substrate for alleviating this issue, and to investigate the underlying mechanisms. Results showed that R. glutinosa grew successfully in fresh soil and remedial replant soil, while no roots were harvested in the unremedied replant soil. Overall, the nutritional status in the remedial soil was higher than that of the unremedied and fresh soil, while the concentration of allelopathic phenolic acids was lower. When planted in unremedied soil, the growth of five plant pathogens was induced and one beneficial fungus was suppressed. When planted in remedied soil, four out of the five pathogens were suppressed, while two beneficial fungi were identified in the remedial soil. This study suggests that the spent P. eryngii substrate significantly alleviates the replant problem of R. glutinosa, and that the alleviatory function reflects a synergetic effect, including the supplementation of soil nutrition, the degradation of allelochemicals, and the remediation of unbalanced microbial community. [ABSTRACT FROM AUTHOR]

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]

Abstract: Italy and Spain are Europe''s main peach-producing countries. Since the mid-90s, however, peach-growing areas have decreased in Italy thus causing its loss of European leadership. One of the reasons for the decline is the presence of replant disorders in peach orchards. As soil-borne pathogens are one of the biotic components of aetiology, a study was performed in an intensively cultivated area of southern Italy, to investigate the use of soil fungi as indicators of soil health when planting new peach orchards. Soil sampling was carried out in five replanted peach orchards and five horticultural sites in the “Piana del Sele”, a peach and vegetable-growing valley in the Campania region. Three different soil fungi communities were recorded: soil-inhabiting filamentous fungi; endophytic root fungi, based on cultural methods; and uncultured soil fungi, based on nucleotide sequences of internal transcribed spacers (ITS1 and ITS2) and rDNA gene fragments. Soil health was evaluated with a greenhouse bioassay, using young plants of peach rootstock GF677. Diversity and composition of fungal communities were compared using PAST, a software which includes several functions commonly used in paleoecology. Each peach tree orchard was characterized by a significantly higher diversity score than horticultural crops. The two cultivation systems differed widely for species composition suggesting that vegetative cover and cultivation practices strongly affected fungal community composition. The bioassay to evaluate soil health showed a significant growth reduction in horticultural sites compared to peach sites. This finding was supported by the high abundance of Cylindrocarpon destructans and Thielviopsis basicola, two aggressive root rot agents, within endophytic fungal communities in horticultural sites. In this survey, greatest fungal diversity corresponds to best plant growth. From a practical point of view, when deciding to replant a new fruit tree orchards in intensively cultivated areas, a greenhouse bioassay with the target crop, combined with a quantitative analysis of endophytic root fungal communities, may help in deciding the best soil use. [Copyright &y& Elsevier]

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.)