Metabarcoding Approach for Evaluation of Bacterial Diversity in Soft Rotting Potato Tubers and Corresponding Geocaulospheres

Plant pathogenic bacteria from the genera Pectobacterium and Dickeya in association with potato cause blackleg and tuber soft rot disease. A metabarcoding was used to analyze the microbial communities of soft-rotted tubers and their geocaulospheres. In September 2018, samples collected from the blackleg-infected field (58 ha) in the Backa region (Serbia) reached 45% disease incidence. Next-generation sequencing Illumina MiSeq platform was used to obtain 16S rRNA sequences from six tested tubers (with and without soft rot symptom) and the surrounding geocaulosphere. Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria were present in all samples, with Proteobacteria being the most prevalent, especially in tubers without soft rot symptoms. In all tested samples, species of the Pectobacterium (P. aroidearum, P. atrosepticum, P. carotovorum, and P. polaris) were detected but were more represented in tubers without symptoms. However, the genus Dickeya was at the limit of detection or not detected at all. Acinetobacter was the most dominant in tubers with soft rot, while Pseudomonas and Enterobacter were the most abundant in tubers without symptoms. The genera Bacteroides and Dysgonomonas with starch-degradable features were almost exclusively present in soft rotted tubers and their corresponding geocaulospheres. The most represented genera in the geocaulosphere sample associated with no-symptom tubers were Gaiella, Sphingomonas, Sphingobium, Gemmatimonas, and Geminicoccus, which include species with confirmed biocontrol potential. This study indicates that the soft rot maceration process arises due to complex interactions between plant pathogens and other endophytic bacteria.

Automated summary

This study analyzed the microbial communities of soft-rotted potatoes and their surrounding geocaulospheres using metabarcoding. The results showed that the plant pathogenic bacteria species Pectobacterium were more prevalent in tubers without soft rot symptoms, while the genus Dickeya was either at the limit of detection or not detected at all. Furthermore, starch-degradable bacteria species Bacteroides and Dysgonomonas were exclusively found in soft-rotted tubers.