Evidence for a Novel Phylotype ofPseudomonas syringaeCausing Bacterial Leaf Blight of Cantaloupe in China

Abstract

Bacterial leaf blight (BLB) has caused severe yield losses in cantaloupe (Cucumis melo L.) in the major melon-growing regions of China since the beginning of the twentieth century. Historically, Pseudomonas syringae pv. lachrymans was considered to be the causal agent of BLB of cantaloupe and angular leaf spot of cucumber. In the process of characterizing bacteria isolated from cantaloupe, we observed that putative P. syringae pv. lachrymans yielded negative results in P. syringae pv. lachrymans-specific PCR assays. This suggested that the P. syringae pv. lachrymans-like strains from cantaloupe were distinct from those recovered from cucumber. To investigate the differences between P. syringae pv. lachrymans-like strains isolated from cantaloupe and cucumber, 13 P. syringae strains isolated from cantaloupe [12 from China and 1 from Zimbabwe (NCPPB2916)] and 7 additional P. syringae reference strains were analyzed by catabolic profiling, phylogenetic analysis by multilocus sequence analysis (MLSA) and pathogenicity tests on cantaloupe leaflets. Catabolic profiling and MLSA based on 10 housekeeping genes and 2 hypersensitive response and pathogenicity (hrp) genes allowed us to differentiate strains isolated from cantaloupe and cucumber. Pseudomonas syringae pv. lachrymans strains isolated from cucumber clustered with genomospecies 2, and 13 P. syringae strains isolated from cantaloupe belonged to genomospecies 1. While all cantaloupe strains were closely related to P. syringae pv. aptata, they could be differentiated from this pathovar based on metabolic tests and MLSA. Pathogenicity tests showed that all strains isolated from cantaloupe and cucumber were only pathogenic on their original hosts. Based on these observations we conclude that P. syringae pv. lachrymans strains recovered from cantaloupe in China represent a novel phylotype.

Bacterial Leaf Spot of Cucurbits

“…lachrymans. However, recent research implicates multiple P. syringae pathovars, including pathovars syringae and aptata (Langston Jr. et al 2003;Newberry et al 2018;Tian et al 2017), as well as other Pseudomonas species, including P. alliivorans, P. capsici, P. cichorii, and P. viridiflava (Fullem et al 2024;Newberry et al 2016;Obradovic and Arsenijevic 2002), as causal agents of the disease. This publication is intended to provide information on the disease bacterial leaf spot of cucurbits, its epidemiology, and management to cucurbit growers in the southeastern United States.…”

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

“…Meanwhile, it can be found in diverse agricultural environments and is one of the most studied bacterial plant pathogens worldwide (Yan et al, 2008). In recent years, some researches have reported that P. syringae can cause various plant diseases, such as bleeding canker of Aesculus hippocastanum (Webber et al, 2010), bacterial canker of Actinidia chinensis Planch (Everett et al, 2011), bacterial brown spot of Avena storigosa Schereb (Ishiyama et al, 2013), leaf spots of Cucurbita pepo (Balaz et al, 2014), leaf blight of Cucumis melo (Tian et al, 2017), bacterial blister bark of Malus pumila (Gasic et al, 2018), halo blight of Avena sativa (Persson and Sletten, 2001), leaf streak and black chaff of Triticum aestivum (Amanifar, 2019), etc. However, some studies found that P. syringae pv.…”