The replant disease refers to abnormal crop growth caused by continuous cultivation of the same or related species on the same soil, and often occurring in crops and orchards. Recently, replant disease have become a major factor constraining the sustainable development of global agriculture and fruit trees. The causes of replant disease include biological and abiotic factors, but in the final analysis, they are caused by changes in the soil environment. Soil environment is closely related to soil productivity. A decline of soil quality results in poor crop growth and reduced yield. The causes of soil environment changes mainly include intensive soil tillage, rapid industrialization, soil pollution, destruction of soil micro-ecosystem and substances secreted by plants under replant condition. Biochar, a porous carbon material prepared from pyrolysis of biomass (agricultural waste, etc.), is widely used as an amendment and adsorbent. To understand the role of biochar in alleviating replant disease, we summarized the previous research results of biochar application in replant soil. The following points are summarized: (1) soil problems and their effects on plants; (2) effects of biochar on replant soil environment; and (3) effects of biochar on alleviating replant disease. Overall, the literature suggests that biochar is an effective measure to amendment soil environment and alleviates replant disease. Further studies on biochar will enhance our understanding of biochar–soil interactions, and its long-term impact of biochar on soil environment.

Phloridzin is a phenolic acid associated with the genus Malus (Mill.) that causes apple replant disease. The removal of phloridzin is of great significance to alleviate this condition, and hence biochar was investigated for this purpose. The goal of this study was to improve the adsorption capacity of biochar for phloridzin by chemical modification. Biochar from apple branches and biochar modified with chitosan to were characterized by elemental analysis, Brunauer Emmett Teller analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. Batch adsorption experiments were employed to select the optimal biochar dosage and adsorption time. The results showed that biochar treated for 24 h at 6 g L⁻¹ achieved best adsorption properties and that the chitosan-modified biochar provided a higher adsorption capacity than the unmodified material. The influence of pH upon the adsorption was studied and the results were fitted with isotherm and kinetic equations. The results showed that adsorption process corresponds to a Langmuir isotherm and pseudo-second-order kinetics. The q_max of the biochar was increased from 15.93 to 28.96 mg g⁻¹ by modification with chitosan. The pH was shown to play an important role in the adsorption process. The adsorption of phloridzin to biochar was demonstrated to be a single-layer multiple component adsorption process based on chemisorption. This study provides a theoretical basis to alleviate apple replant disease.

Background: The rhizosphere microbiome, as the second genome of plant immunity, forms a critical ecological barrier in plant-pathogen interactions. However, its functional mechanism in resisting the replanting disease pathogenic Fusarium proliferatum MR5 in apples has not been systematically elucidated. This study employed an integrated multi-omics approach to investigate the rhizosphere mechanisms of resistant (CG935) and sensitive (M9T337) apple rootstocks, aiming to uncover the metabolic and microbial interactions underlying apple replant disease resistance. Results: Multiple omics joint analysis found that the infection of Fusarium proliferatum MR5 triggered the activation of a specific lysine biosynthesis pathway in resistant rootstocks, and the expression levels of key rate limiting enzymes aspartate kinase and dihydrodipicolinate synthase were significantly upregulated by 2.79 ~ 6.81 times compared to M9T337. Along with the metabolic reprogramming process, the efflux of lysine from the rhizosphere increased, and Bacillus with broad-spectrum antibacterial activity were specifically recruited, increasing its relative abundance by 40.73%. In vitro assays demonstrated that the recruited Bacillus suppressed Fusarium spore germination and disrupted mycelial growth through the production of antifungal compounds, including 2,4-di-tert-butylphenol and bacillomycin. Potted experiments have confirmed that the synergistic treatment of Bacillus and lysine significantly reduces the number of pathogenic Fusarium in the rhizosphere, increases soil enzyme activity, and reshapes a more stable rhizosphere bacterial community structure by enhancing the modularity (the degree of modularity in microbial network structure) of the microbial network. This collaborative strategy effectively alleviates the physiological damage of apple seedlings under replanting stress, resulting in a 31.18% increase in plant fresh weight. Field validation experiments further demonstrate that this strategy can promote the growth of replanted apple saplings and reduce the occurrence of apple replant disease. Conclusions: Our findings elucidate an apple replant disease resistance mechanism in apple rootstocks involving lysine-mediated recruitment of protective Bacillus , which enhances rhizosphere microbiome stability and suppresses soil pathogenic Fusarium . Developed a technology for synergistic control of apple replant disease using Bacillus -lysine. The research results provide theoretical basis and practical solutions for green control of apple replant disease based on precise regulation of rhizosphere microbiome.

Apple replant disease (ARD) is seriously hindering the development of the apple industry. This experiment assessed the effects of two different root-growth-promoting agents (Indoleacetic acid and nutrient elements) on the microbial environment of apple-replanted soil and the growth of apple rootstock Malus hupehensis Rehd. seedlings after fumigation with crystal lime sulfur. The results showed that the simultaneous application of crystal lime sulfur, indoleacetic acid, and nutrient elements (T4) improved the biomass of Malus hupehensis Rehd. seedlings. It also enhanced the activities of soil enzymes and root antioxidant enzymes (SOD, POD, CAT). Their activities were significantly higher than in the individual treatments and resulted in a decrease in malondialdehyde (MDA) content. The T4 treatment significantly increased the net photosynthetic rate and chlorophyll content of the plant, thus effectively increasing the plant growth status. After fumigation, the amount of soil microorganisms was reduced, and the amount of bacteria and actinomycetes was increased after mixed application with the root-growth-promoting agent. The abundance of different species such as Pseudallescheria, Guehomyces, Trichoderma, Bacillus, Gaiella, and Sphingomonas was effectively increased, and the amount of Fusarium oxysporum was reduced. Through correlation analysis between different species and plant and soil enzymes, we found that the different species were positively correlated with root respiration rate and SOD activity and negatively correlated with MDA content. The differentially accumulated microbial species may be the key microorganism that promotes plant growth. Therefore, the simultaneous application of crystal lime sulfur, indoleacetic acid, and nutrient elements can optimize the apple replant soil environment and promote the growth of Malus hupehensis Rehd. seedlings, and can be used to control apple replant disease.

Apple is an important horticultural crop in China and its production consumes large amounts of Chemical fertilizers. In a survey of more than 300 Chinese apple growers, we found that small farmers’ fertilizer inputs are blind. Current research lacks a comprehensive evaluation of fertilizer inputs and soil nutrient status for apple production in China, but the evaluation work will play a supporting role in the macro management decision of nutrient resources. In this study, a database of fertilizer inputs and soil nutrients in five major apple producing areas in China was constructed by means of data integration. Two main conclusions can be drawn from the analysis of the database. Firstly, the chemical N and P fertilizer inputs exceed the recommended use in all five production areas, and secondly, the organic matter content of orchard soils in the five production areas only reaches a maximum of level 3. The research shows that China’s agricultural authorities should carry out macro management of nutrient resources in apple orchards, so as to guide different producing areas to adjust fertilizer input according to their soil environment, so as to improve the utilization rate of fertilizer.