Pseudomonas syringae pv. coronafaciens, causing a new bacterial halo blight disease on oat (Avena sativa L.) in China

Abstract

Pseudomonas syringae pv. coronafaciens (Ps-c) is a pathogenic bacterium species that can be found in agricultural environments that causes diseases in plants. During a survey in 2019–2020 of different areas, bacterial halo blight (BHB) caused by Ps-c in oat (Avena sativa L.) was observed in many oat fields in Huan county, Gansu Province of China. Average leaf disease incidence was approximately 1 to 14%. The symptoms of BHB were mainly observed on leaves of oat and appeared as white to yellow streaks. After 20–30 d, the streaks became yellow necrotic lesions and spread to whole leaves, eventually causing leaves to wilt and decline. Symptomatic leaves of affected oats were collected from locations to investigate the etiology of BHB disease, and a group of 32 bacterial isolates (HK7) phenotypically similar was consistently isolated from the necrotic lesion margins in all samples. Pathogenicity tests of this group isolates by wounding and injection inoculations in greenhouse demonstrated that the symptoms induced by them on oat were similar to those observed in the field. HK7 isolates were identified as Ps-c based on Biolog Gen III MicroStation, morphological, physiological and biochemical characterization, 16S rRNA and gyrB gene sequence analysis, which compared with a reference strain (Ps-c ATCC 19608). Furthermore, Ps-c had a narrow host range and was host specific. After inoculation of Ps-c on A. sativa (B7) and A. nuda (B2) in greenhouse, effective tillers, plant height, flag-leaf length, flag-leaf width, fresh weight, dry weight, panicle length, grains per spike, reproductive branches number and thousand grains weight of infected oat were averagely decreased by 19.44%, 11.49%, 11.34%, 9.23%, 11.61%, 7.57%, 6.11%, 9.73%, 9.31% and 4.15% compared with that of healthy oat, respectively. Therefore, BHB (Ps-c) is a new bacterial disease on oat in China and has negative influences on plant growth, forage and grain yield of oat, and these negative effects are enhanced with the increase of disease severity.