Abstract:

This study took sugar beet and its root rot as the research objects, and analyzed the changes of soil microbial community composition, structure and function of different sugar beet varieties with different degrees of disease, so as to obtain the relationship among resistant varieties, degree of disease and rhizosphere microorganisms, and reveal the soil microbial mechanism of disease-resistant varieties. In this paper, two kinds of sugar beet varieties including the disease-resistant and disease-susceptible types were employed, and two different sugar beet varieties with low and high disease severity were separately selected to measure bacteria and fungi communities in their rhizosphere by Illumina MiSeq high-throughput sequencing technology. The results showed that the rhizosphere microbial (bacteria and fungi) diversity of sugar beet with lower disease symptom were relatively higher than that with higher disease severity, at the same time, the fungal diversity of disease-resistant sugar beet rhizosphere soil was higher than that in disease-sensitive types. NMDS analysis demonstrated that resistance breeding could significantly affect the community structure of soil fungi, and the community structure of both bacteria and fungi could be notably distinguished from different disease status. In terms of the enrichment of rhizosphere microorganisms, disease-resistant sugar beets enriched some beneficial bacteria such as Pseudomonas, Arthrobacter and Bacillus, while susceptible sugar beets enriched more plant pathogenic microorganisms-Fusarium oxysporum. In addition, the samples with lower disease severity tended to have more beneficial bacteria, including unclassified Acidobacteria, Bacillus, Rubrobacter, unclassified Actinomycetes, Streptomyces, and Nocardioides. Furthermore, FUNGuild functional prediction showed that more plant pathogens were detected in susceptible sugar beets and samples with higher disease severity. In conclusion, although disease-resistant varieties and healthy plants differ in microbial species, a large number of beneficial microorganisms gather in their rhizosphere, while disease-susceptible types and the plants with higher disease severity are more likely to be colonized by pathogenic microorganisms around the roots. One of the microbial mechanism of resistance formation in a disease-resistant sugar beet variety is that plants recruit more beneficial bacteria as the first line to defense against pathogen infection when the plants grow. This study clarifies the resistance mechanism of disease-resistant varieties from the perspective of soil microbiome and enriches the theoretical mechanism of resistance generation of disease-resistant varieties.

Key words: resistance breeding, plant pathogen, bacterial community, fungal community, high-throughput sequencing