Distribution of Pectobacterium Species Isolated in South Korea and Comparison of Temperature Effects on Pathogenicity

Abstract

Pectobacterium, which causes soft rot disease, is divided into 18 species based on the current classification. A total of 225 Pectobacterium strains were isolated from 10 main cultivation regions of potato (Solanum tuberosum), napa cabbage (Brassica rapa subsp. pekinensis), and radish (Raphanus sativus) in South Korea; 202 isolates (90%) were from potato, 18 from napa cabbage, and five from radish. Strains were identified using the Biolog test and phylogenetic analysis. The pathogenicity and swimming motility were tested at four different temperatures. Pectolytic activity and plant cell-wall degrading enzyme (PCWDE) activity were evaluated for six species (P. carotovorum subsp. carotovorum, Pcc; P. odoriferum, Pod; P. brasiliense, Pbr; P. versatile, Pve; P. polaris, Ppo; P. parmentieri, Ppa). Pod, Pcc, Pbr, and Pve were the most prevalent species. Although P. atrosepticum is a widespread pathogen in other countries, it was not found here. This is the first report of Ppo, Ppa, and Pve in South Korea. Pectobacterium species showed stronger activity at 28°C and 32°C than at 24°C, and showed weak activity at 37°C. Pectolytic activity decreased with increasing temperature. Activity of pectate lyase was not significantly affected by temperature. Activity of protease, cellulase, and polygalacturonase decreased with increasing temperature. The inability of isolated Pectobacterium to soften host tissues at 37°C may be a consequence of decreased motility and PCWDE activity. These data suggest that future increases in temperature as a result of climate change may affect the population dynamics of Pectobacterium.

Keywords: Pectobacterium; pathogenicity; plant cell-wall degrading enzymes; soft rot; temperature.

Fig. 1

Incidence of soft rot on potato and napa cabbage in seven areas of Korea during 2016-2017. Incidence of soft rot on potato and napa cabbage in Pyeongchang, Gangneung, Taebaek and Hongcheon was evaluated in the summer; in Miryang, Boseong, and Jeju, evaluation was done in the fall.

Fig. 2

A concatenated neighbor-joining phylogenetic analysis of 225 Pectobacterium strains based on 16S rRNA and recA gene sequences. This analysis was performed with 225 isolated strains and 48 reference strains. This collection was divided into 6 clades including P. odoriferum, P. carotovorum subsp. carotovorum, P. brasiliense, P. versatile, P. parmentieri, and P. polaris.

Fig. 3

The diameter of macerated tissue in potato and napa cabbage inoculated with Pectobacterium species. The inoculated tissues of potato (A, B) and napa cabbage (C, D) were incubated at four different temperatures: 20°C, 28°C, 32°C, and 37°C. Pod, Pectobacterium odoriferum; Pcc, P. carotovorum subsp. carotovorum; Pbr, P. brasiliense; Pve, P. versatile; Ppa, P. parmentieri; Ppo, P. polaris; Pa, P. atrosepticum. Different letters indicate significant difference according to ANOVA with Duncan test at **P < 0.01.

Fig. 4

Comparison of swimming motility of Pectobacterium species at four different temperatures. Pod, Pectobacterium odoriferum; Pcc, P. carotovorum subsp. carotovorum; Pbr, P. brasiliense; Pve, P. versatile; Ppa, P. parmentieri; Ppo, P. polaris; Pa, P. atrosepticum. Different letters indicate significant difference according to ANOVA with Duncan test at **P < 0.01. This test was performed with 7 Pectobacterium species including a reference strain of P. atrosepticum.

Fig. 5

Comparison of pectolytic activity with Pectobacterium species at 28°C and 37°C. The assessment of pectolytic activity was performed with diameter of a cavity on crystal violet pectate (CVP) medium. Different letters indicate significant difference according to ANOVA with Duncan test at *P < 0.05.

Fig. 6

Comparison of plant cell-wall degrading enzyme activity of Pectobacterium species at 24°C, 28°C and 37°C. The diameter of halo response was measured for each enzyme activity: protease (Prt) (A), cellulase (Cel) (B), pectate lyase (Pel) (C), and polygalacturonase (Peh) (D). Pod, P. odoriferum; Pcc, P. carotovorum subsp. carotovorum; Pbr, P. brasiliense; Pve, P. versatile; Ppa, P. parmentieri; Ppo, P. polaris. Different letters indicate significant difference between species in an enzyme activity test according to ANOVA with Duncan test at *P < 0.05 or **P < 0.01.