Excessive nitrogen (N) application is widespread in Southern China. The effects of N fertilization on soil properties and crop physiology are poorly understood in tropical red loam soil. We conducted a field experiment to evaluate the effect of nitrogen fertilization rates on physiological attributes (chlorophyll, plant metabolic enzymes, soluble matters) on banana leaves, soil properties (soil enzymes, soil organic matter (SOM), soil available nutrients) as well as banana crop yield in a subtropical region of southern China. The N rates tested were 0 (N₀), 145 (N₁₄₅), 248 (N₂₄₈), 352 (N₃₅₂), 414 (N_FT), and 455 (N₄₅₅) g N per plant. The correlations among soil factors, leaf physiological factors and crop yield were evaluated. The results indiated that the high rates of N fertilization (N_FTand N₄₅₅) significantly decreased soil available potassium (K) content, available phosphorus (P) content, glutamine synthetase (GS) activity, and soluble protein and sugar contents compared with lower N rates. The N₃₅₂treatment had the highest crop yields compared with higher N rates treatments, followed by the N₄₅₅treatment. However, there were no significant differences in crop yields among N fertilization treatments. Factor analysis showed that the N₃₅₂treatment had the highest integrated score for soil and leaf physiological factors among all treatments. Moreover, the N₃₅₂treatment was the most effective in improving carbon and nitrogen metabolism in banana. Crop yield was significantly and positively linearly correlated with the integrated score (r= 0.823,p< 0.05). Path analysis revealed that invertase, SOM and sucrose synthase (SS) had a strong positive effect on banana yield. Canonical correspondence analysis (CCA) suggested that available K, invertase, acid phosphatase and available P were the most important factors impacting leaf physiological attributes. Cluster analysis demonstrated distinct differences in N application treatment related to variations in soil and leaf factors. This study suggested that excessive N fertilization had a negative effect on soil fertility, crop physiology and yield. The lower N rates were more effective in improving crop yield than higher rates of N fertilization. The N rate of 352 g N per plant (N₃₅₂) was recommended to reduce excess N input while maintaining the higher yield for local farmers’ banana planting.

Banana wilt disease, caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4), is one of the most devastating diseases in banana (Musa spp.). Foc is a soil borne pathogen that causes rot of the roots or wilt of leaves by colonizing the xylem vessels. The dual RNA sequencing is used to simultaneously assess the transcriptomes of pathogen and host. This method greatly helps to understand the responses of pathogen and host to each other and discover the potential pathogenic mechanism. Plantlets of two economically important banana cultivars, Foc TR4 less susceptible cultivar NK and susceptible cultivar BX, were used to research the Foc-banana interaction mechanism. Notably, the infected NK had more significantly up-regulated genes on the respiration machinery including TCA cycle, glyoxylate, glycerol, and glycolysis compared to BX at 27 h post inoculation (hpi). In addition, genes involved in plant-pathogen interaction, starch, sucrose, linolenic acid and sphingolipid metabolisms were uniquely more greatly induced in BX than those in NK during the whole infection. Genes related to the biosynthesis and metabolism of SA and JA were greatly induced in the infected NK; while auxin and abscisic acid metabolisms related genes were strongly stimulated in the infected BX at 27 hpi. Furthermore, most of fungal genes were more highly expressed in the roots of BX than in those of NK. The fungal genes related to pathogenicity, pectin and chitin metabolism, reactive oxygen scavenging played the important roles during the infection of Foc. CCP1 (cytochrome c peroxidase 1) was verified to involve in cellulose utilization, oxidative stress response and pathogenicity of fungus. The transcriptome indicated that NK had much faster defense response against Foc TR4 than BX and the expression levels of fungal genes were higher in BX than those in NK. The metabolisms of carbon, nitrogen, and signal transduction molecular were differentially involved in pathogen infection in BX and NK. Additionally, the putative virulence associated fungal genes involved in colonization, nutrition acquirement and transport provided more insights into the infection process of Foc TR4 in banana roots.

Soil microorganisms play an important role in regulating the responses of plants to disease, but little is known regarding the role of the microbial community in rhizosphere soil in the response to diseases in papaya. To clarify how the abundance and composition of the microbial rhizosphere community of papaya change with viral infection, papaya plants resistant and susceptible to papaya ringspot virus (PRSV) were inoculated with PRSV in the field, and differences in rhizosphere soil microbial communities between healthy and susceptible papaya were analyzed. The physiochemical properties of the soil surrounding the root system were strongly affected by microbial taxa, but this did not have a significant effect on plant health. 16S rRNA and ITS sequencing revealed that disease stress increased the microbial diversity of bacteria and decreased the diversity of fungi. The analysis of soil microbial community shows that the abundance of Nitrospirae was significantly higher in HN soil (1.35 ± 0.41) than in NC soil (0.83 ± 0.13) and YK soil (0.79 ± 0.27); the abundance of Paenibacillus was higher in HN soil (0.83 ± 0.38) than in NC (0.35 ± 0.12）and YK soil (0.58 ± 0.19); the abundance of Acremonium was higher in HN soil (0.71 ± 0.37) than in NC soil (0.21 ± 0.18) and YK soil (0.48 ± 0.43). Nitrospira, Paenibacillus, and Acremonium were all beneficial microorganisms, and they were significantly higher in healthy papaya soil than in susceptible papaya soil may help viral resistance. We show for the first time that a non-soil-borne disease may influence the microbiomes of papaya rhizosphere soil. When resistant papaya was infected with PRSV, beneficial microorganisms could be recruited in the rhizosphere soil to resist viral infection. Although these results are only preliminary insights into the potential role of beneficial microorganisms in supporting plant health under viral stress, our research provides new insights with implications for the prevention and control of papaya ringspot disease, furthermore, microorganisms that promote viral resistance could expediate the development of biopharmaceuticals or green fertilizers.