Peihua Du

Apple (Malus domestica Borkh.) is a major fruit crop of global economic importance, and China ranks first worldwide in both apple cultivation area and total production. With the large-scale renewal of aging orchards, apple replant disease (ARD) has become increasingly prevalent in major apple-producing regions. ARD is typically characterized by severe growth suppression, impaired root development, increased incidence of soil-borne diseases, and, in severe cases, seedling mortality. These symptoms substantially constrain orchard renewal, limit improvements in fruit yield and quality, and threaten the sustainable development of the apple industry. The etiology of ARD is complex and involves the synergistic interaction of three factors: soil microbial dysbiosis characterized by pathogen enrichment and the depletion of beneficial microorganisms; allelopathic autotoxicity caused by the accumulation of phenolic acids, especially phloridzin; and degraded soil physicochemical properties, including acidification, compaction, and nutrient imbalance. Current management strategies mainly include the use of ARD-tolerant rootstocks, microbial regulation, chemical and physical soil disinfection, and agronomic practices such as crop rotation and organic amendment application. Among these approaches, biological regulation mediated by beneficial rhizosphere and endophytic microorganisms has attracted increasing attention because of its environmental compatibility and sustainability. This review summarizes the occurrence patterns, regional characteristics, core pathogenic mechanisms, and integrated management strategies of ARD, with particular emphasis on the functional roles of rhizosphere and endophytic microbiomes in disease alleviation. The review provides a theoretical basis and practical reference for the development of green, efficient, and sustainable strategies for ARD control and apple orchard management.

Bacterial wilt caused by Ralstonia solanacearum (R. solanacearum) poses a severe threat to pepper production. However, resistant cultivars can recruit root-associated microbial communities to cope with soil-borne pathogen infection. In this study, we analyzed the physiological traits, rhizosphere soil and root endosphere bacterial communities of the resistant cultivar HR01 and the susceptible cultivar HS03 under R. solanacearum stress. Infection significantly reduced the root biomass and altered the bacterial composition in HS03 compared with HR01, particularly in root endophytic bacteria. Biomarker analysis showed that Ralstonia dominated both the rhizosphere soil and roots of HS03_T, whereas HR01_T was enriched with taxa such as Ellin6067 in the rhizosphere and Acidovorax in the roots. Notably, Pseudomonas abundance decreased in HS03 but increased in HR01 after inoculation. Among 80 bacterial isolates obtained from HR01, strain P1202 was identified as Pseudomonas aeruginosa (P. aeruginosa), exhibiting the largest inhibition zone against R. solanacearum in dual-culture assays; its cell-free fermentation filtrate also showed strong inhibitory effects. Pot experiments demonstrated that strain P1202 application effectively alleviated the disease symptoms of HS03 and also promoted pepper growth, enhanced antioxidant enzyme activities, and improved early-stage photochemical activity of photosystem II (PSII). Transcriptomic and quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed activation of defense-related pathways (e.g., plant–pathogen interaction) and upregulation of key genes (WRKY33, CNGC, CaM, and MPK3). These results suggest that P. aeruginosa enhances pepper resistance to bacterial wilt through direct antimicrobial activity and induction of pepper defense responses, highlighting its potential as an effective biocontrol agent.

Fruit cracking in jujube is a major constraint on the sustainable development of the jujube industry. In this study, 60 mg L⁻¹ of 6-Benzylaminopurine (6-BA) was foliar-sprayed at the early fruit stage. Fruit cracking incidence was recorded during the green and white fruit periods, and these observations were integrated with transcriptomic and metabolomic analyses to explore the potential mechanisms by which 6-BA influences fruit cracking. The results showed that the fruit cracking in the treatment groups was 53% and 18% of that in the control group during the green period and the white period, respectively. In jujube peel, catalase (CAT) activity was significantly increased in the treated peel during both periods. In the peel metabolites, compounds belonging to the cytokinin (CTK) category exhibited significant accumulation in both periods. Transcriptomic analysis showed that differentially expressed genes (DEGs) were enriched in pathways related to starch and sucrose metabolism, plant hormone signal transduction, and cellular polysaccharide metabolism. These findings suggest that 6-BA treatment may alleviate jujube fruit cracking by enhancing antioxidant capacity, modulating hormone homeostasis, and upregulating genes associated with carbohydrate and cell wall metabolism.

This study investigates the effects of 1-methylcyclopropene (1-MCP) treatment on postharvest storage of winter jujube. The results indicate that after 1-MCP treatment, the pyruvate (PA) content in winter jujube decreased by 20% at 30 days compared to the control. The energy charge (EC), ATP, and ADP levels increased by 7%, 17%, and 27%, respectively. Activities of key enzymes involved in energy metabolism, including succinate dehydrogenase (SDH), cytochrome c oxidase (COX), H ⁺ -ATPase, and Ca ²⁺ -ATPase were elevated. Furthermore, the activities of acid invertase (AI) and neutral invertase (NI) were 27% and 26% lower, respectively, than those in the control. Sucrose synthase (SS) activity increased by 52%, while the activities of hexokinase (HK) and phosphofructokinase (PFK) decreased by 19% each. Activities of key antioxidant enzymes-superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione reductase (GR)-were significantly enhanced. Non-enzymatic antioxidants, including vitamin C (VC), flavonoids, total phenols, and reduced glutathione (GSH) contents, were effectively retained, and suppressing the accumulation of the hydrogen peroxide (H ₂ O ₂ ) and malondialdehyde (MDA). These findings suggest that 1-MCP treatment preserves the postharvest quality of winter jujube by enhancing energy metabolism, delaying sugar metabolism, and improving antioxidant capacity.

Nutrient stress harms plant growth and yield. Melatonin is a biologically active, multifunctional hormone that relieves abiotic stress in plants. Although previous studies have shown that melatonin plays an important role in improving nutrient-use efficiency, the mechanism of its regulation of nutrient stress remains unclear. In this study, melatonin was applied to apple plants under nutrient stress, and morphological indices, physiological and biochemical indices, and stomatal morphology were evaluated. The response of apple plants to nutrient deficiency and the melatonin mechanism to alleviate nutrient stress were analyzed by combining ionome, transcriptome, and metabolome. The results showed that exogenous melatonin significantly alleviated the inhibitory effect of nutritional stress on the growth of apple plants by regulating stomatal morphology, improving antioxidant enzyme activity, promoting ion absorption, and utilizing and changing the absorption and distribution of minerals throughout the plant. The transcriptome results showed that melatonin alleviated nutrient stress and promoted nutrient absorption and utilization by regulating glutathione metabolism and upregulating some metal ion transport genes. The metabolome results indicated that levels of oxalic acid, L-ascorbic acid, anthocyanins (cyanidin-3-O-galactoside), lignans (lirioresinol A and syringaresinol), and melatonin significantly increased after exogenous melatonin was applied to plants under nutrient stress. These differentially expressed genes and the increase in beneficial metabolites may explain how melatonin alleviates nutrient stress in plants.