First report of bacterial wilt disease caused by Pantoea agglomerans on the ornamental perennial Oxalis articulata in China.

Abstract

Oxalis articulata is now widely cultivated in China as an ornamental species, and thus found in abundance in agricultural farms, gardens, and lawns. In December 2021, some severely infected Oxalis articulata were observed at many places at Zhejiang Normal University (29°8'4″N, 119°37'54″E) in Jinhua City, Zhejiang Province, China. Yellow was first observed on the margin of the leaves, leading to light brown and wilting at a later stage. To identify the pathogen, symptomatic leaves were collected and cut into small pieces, surface disinfected in 1% sodium hypochlorite solution for 3 min, followed by 75% alcohol for 0.5 min, then rinsed in sterile distilled water thrice. Then they were transferred onto Luria-Bertani medium and incubated at 28°C for 3 days. The colonies were round, yellow, viscous and smooth, which was consistent with the characteristics of Pantoea agglomerans (Li et al. 2020; Zhang et al. 2022). The bacteria tested gram-negative, negative for indole test and Voges-Proskauer reaction, and positive for methyl red reaction, lysine decarboxylase and ornithine decarboxylase. In addition, the bacteria can utilize D-xylose, sorbitol, adonitol, and glucose, but can't utilize raffinose, urea, and Simmons. Meanwhile the bacteria can not produce H2S, and can not produce gas from D-glucose as well. These results of physiological and biochemical characteristics were consistent with those of Pantoea agglomerans (Gavini et al. 1989). To identify the strain, the 16S rDNA gene fragment was amplified by polymerase chain reaction (PCR) using universal primers 8F and 1510R, and sequenced. The BLAST results indicated that the 16S rDNA sequence of the strain OAPB-1, deposited under GenBank accession LC709256, showed 99.93%(1376/1377) and 99.49% (1370/1377) identitytothecorresponding sequence of Pantoea agglomerans FC2948 (MH532498.1) and the type strain Pantoea agglomerans DSM 3493 (AJ233423) respectively. The Neighbor-Joining phylogenetic tree generated using MEGA11 indicated that it formed a clade with the other P. agglomerans. Furthermore, the phylogenetic analysis based on sequences of housekeeping genes (atpD, rpoB and infB; GenBank accession LC722492 to LC722494) showed the same result. Based on the above results, the strain OAPB-1 from Zhejiang was identified as P.agglomerans. To test the Koch's postulates, bacterial suspensions (2×108CFU/mL) were injected into the middle of healthy leaves of mature plants with sterile water as a control. Then the plants were placed at 28°C in a light incubator with 12-h-light/12-h-dark photoperiod and approximately 60% humidity. Leaves in the inoculated group showed symptoms similar to those observed on the naturally infected leaves, while leaves in the control group showed no symptoms. The pathogen was reisolated from inoculated leaves, and its morphological characteristics and molecular identification results were consistent with those of the original isolate. P. agglomerans is a bacterium associated with plants, and also infects humans and animals (Dutkiewicz et al. 2016). In China, it has been reported to infect many kinds of plants (Fan et al. 2022; Guo et al. 2020; Han et al. 2020; Li et al. 2020; She et al. 2019; Zhang et al. 2022). As far as we know, this is the first report of P. agglomerans causing bacterial wilt on Oxalis articulata in China. These results further expand the range of plants that can be infected by P. agglomerans, and help to establish an effective control strategy against the disease.