RESUMEN
Previously we isolated three Fusarium strains (a F. sacchari strain namely GXUF-1, and another two F. commune strains namely GXUF-2 and GXUF-3), and we verified that GXUF-3 was able to cause sugarcane root rot to the chewing cane cultivar Badila. Considering that Fusarium spp. are a group of widely distributed fungal pathogens, we tested whether these three Fusarium isolates were able to cause root rot to Badila as well as sugar-making cane cultivar (Guitang42), using a suitable inoculation method established based on infection assays using Badila. We found that the three Fusarium strains were able to cause root rot symptoms to both Badila and Guitang42, to different extents. To better investigate the potential pathogenicity mechanisms, we performed Illumina high-throughput sequencing and analyzed the whole genomic sequence data of these three Fusarium strains. The results reveal that the assembly sizes of the three Fusarium strains were in a range of 44.7-48.2 Mb, with G + C contents of 48.0-48.5%, and 14,154-15,175 coding genes. The coding genes were annotated by multiple public databases, and potential pathogenic genes were predicted using proprietary databases (such as PHI, DFVF, CAZy, etc.). Furthermore, based on evolutionary analysis of the coding sequence, we found that contraction and expansion of gene families occurred in the three Fusarium strains. Overall, our results suggest a potential risk that the root rot disease may occur to the sugar-making canes although it was initially spotted from fruit cane, and provide clues to understand the pathogenic mechanisms of Fusarium spp. causing sugarcane root rot.
RESUMEN
To explore the causal pathogen and the correlated rhizosphere soil microecology of sugarcane root rot, we sampled the sugarcane root materials displaying different disease severity, and the corresponding rhizosphere soil, for systematic root phenotype and microbial population analyses. We found that with increased level of disease severity reflected by above-ground parts of sugarcane, the total root length, total root surface area and total volume were significantly reduced, accompanied with changes in the microbial population diversity and structure in rhizosphere soil. Fungal community richness was significantly lower in the rhizosphere soil samples from mildly diseased plant than that from either healthy plant, or severely diseased plant. Particularly, we noticed that a peculiar decrease of potential pathogenic fungi in rhizosphere soil, including genera Fusarium, Talaromyces and Neocosmospora, with increased level of disease severity. As for bacterial community, Firmicutes was found to be of the highest level, while Acidobacteria and Chloroflexi of the lowest level, in rhizosphere soil from healthy plant compared to that from diseased plant of different severity. FUNGuild prediction showed that the proportion of saprophytic fungi was higher in the rhizosphere soil of healthy plants, while the proportion of pathogenic fungi was higher in the rhizosphere soil of diseased plants. By co-occurrence network analysis we demonstrated the Bacillus and Burkholderia were in a strong interaction with Fusarium pathogen(s). Consistently, the biocontrol and/or growth-promoting bacteria isolated from the rhizosphere soil were mostly (6 out of 7) belonging to Bacillus and Burkholderia species. By confrontation culture and pot experiments, we verified the biocontrol and/or growth-promoting property of the isolated bacterial strains. Overall, we demonstrated a clear correlation between sugarcane root rot severity and rhizosphere soil microbiome composition and function, and identified several promising biocontrol bacteria strains with strong disease suppression effect and growth-promoting properties.