Diversity of Bacterial Soft Rot-Causing Pectobacterium Species Affecting Cabbage in Serbia

Abstract

The aim of this work was to identify and characterize the pectolytic bacteria responsible for the emergence of bacterial soft rot on two summer cabbage hybrids (Cheers F1 and Hippo F1) grown in the Futog locality (Bačka, Vojvodina), known for the five-century-long tradition of cabbage cultivation in Serbia. Symptoms manifesting as soft lesions on outer head leaves were observed during August 2021, while the inner tissues were macerated, featuring cream to black discoloration. As the affected tissue decomposed, it exuded a specific odor. Disease incidence ranged from 15% to 25%. A total of 67 isolates producing pits on crystal violet pectate (CVP) medium were characterized for their phenotypic and genotypic features. The pathogenicity was confirmed on cabbage heads. Findings yielded by the repetitive element palindromic-polymerase chain reaction (rep-PCR) technique confirmed interspecies diversity between cabbage isolates, as well as intraspecies genetic diversity within the P. carotovorum group of isolates. Based on multilocus sequence typing (MLST) using genes dnaX, mdh, icdA, and proA, five representative isolates were identified as Pectobacterium carotovorum (Cheers F1 and Hippo F1), while two were identified as Pectobacterium versatile (Hippo F1) and Pectobacterium odoriferum (Hippo F1), respectively, indicating the presence of diverse Pectobacterium species even in combined infection in the same field. Among the obtained isolates, P. carotovorum was the most prevalent species (62.69%), while P. versatile and P. odoriferum were less represented (contributing by 19.40% and 17.91%, respectively). Multilocus sequence analysis (MLSA) performed with concatenated sequences of four housekeeping genes (proA, dnaX, icdA, and mdh) and constructed a neighbor-joining phylogenetic tree enabled insight into the phylogenetic position of the Serbian cabbage Pectobacterium isolates. Bacterium P. odoriferum was found to be the most virulent species for cabbage, followed by P. versatile, while all three species had comparable virulence with respect to potato. The results obtained in this work provide a better understanding of the spreading routes and abundance of different Pectobacterium spp. in Serbia.

Phylogeographic Analysis of Soft-Rot-Causing Pectobacterium spp. Strains Obtained from Cabbage in Serbia

“…strains, namely P. carotovorum (Pc2321, Pc3821, Pc4821, Pc5421, and Pc8321), P. odoriferum (Po7521), and P. versatile (Pv6321), obtained from two cabbage hybrids [Cheers F1 (Takii Seed) and Hippo F1 (Sakata Seed)] grown in Futog (Vojvodina, Serbia) in 2021 were retrieved from the NCBI database. These seven Serbian cabbage strains were considered representative of each species based on their phenotypic and genotypic features determined previously by Jelušić et al [ 13 ]. In order to reconstruct their phylogeographic relatedness, sequences of other 19 Pectobacterium spp.…”

“…However, such investigations require assessment of many strains that originate from different countries and hosts. Given that changes in metabolic genes may be related to the adaptation of strains to specific environmental niches and host plants, typing and analysis of protein-coding loci (multilocus sequence typing and analysis, MLST/MLSA) can provide sufficient data for distinguishing closely related species [ 12 , 13 ]. Moreover, since the process required for obtaining strains from culture collections is often prohibitively expensive, and permits for some bacterial pathogens can be difficult to acquire, multilocus phylogenetic analysis can be a viable alternative, given that it exploits the information that can be derived from genomic sequences that are already deposited in the public databases [e.g., the National Center for Biotechnology Information (NCBI) database and the Plant Associated and Environmental Microbes Database (PAMDB)].…”

“…In Serbia, different Pectobacterium spp.— P. atrosepticum , P. brasiliense , P. carotovorum , P. odoriferum , P. punjabense , P. zantedeschiae, and P. versatile —have been isolated from various hosts [ 13 , 16 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Three of these species ( P. carotovorum , P. odoriferum , and P. versatile ) were recently described as causal agents of soft rot in cabbage in this region [ 13 ].…”

“…In Serbia, different Pectobacterium spp.— P. atrosepticum , P. brasiliense , P. carotovorum , P. odoriferum , P. punjabense , P. zantedeschiae, and P. versatile —have been isolated from various hosts [ 13 , 16 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Three of these species ( P. carotovorum , P. odoriferum , and P. versatile ) were recently described as causal agents of soft rot in cabbage in this region [ 13 ]. To substantiate the findings presented in this unique report, in the present study, we aimed to conduct more extensive research on their genetic heterogeneity, as well as their spread routes and origin by performing phylogeographic analysis.…”

Bacterial secretion systems contribute to rapid tissue decay in button mushroom soft rot disease

“…The agricultural sector continually suffers severe economic losses due to the adverse effect of Gram-negative bacterial soft rot pathogens on the yields of vegetable, fruit, and mushroom farming ( 1 - 4 ). These bacteria exert their devastating effects by releasing multiple virulence factors, lytic enzymes, and toxins to exploit eukaryotic host cells, thereby degrading the crop to mush ( 5 - 7 ).…”