Here, we report the complete genome sequence of Xanthomonas arboricola pv. juglandis DW3F3, a strong pathogenic strain isolated from blighted walnut immature fruit (Juglans regia L. cv. Qingxiang). The genome consists of a single chromosome (5,144 kb).

Walnut bacterial blight caused by Xanthomonas arboricola pv. juglandis (Xaj) has serious repercussions for walnut production around the world. Between 2015 and 2017, disease samples were collected from six counties (Danjiangkou, Baokang, Suizhou, Shennongjia, Zigui, and Xingshan) in Hubei province, China. Fifty-nine Xaj strains were identified by morphology and specific PCR primers from 206 isolates. The genetic diversity of 60 Xaj strains (59 from Hubei plus one from Beijing) was evaluated by Multilocus Sequence Analysis (MLST), and their resistance to copper ion (Cu2+) treatment was determined. A Neighbor Joining phylogenetic dendrogram was constructed based on four sequences of housekeeping genes (atpD-dnaK-glnA-gyrB). Two groups of strains were identified whose clustering was consistent with that of glnA. The minimal inhibitory concentration of copper ion on representative Xaj strain DW3F3 (the first genome sequenced Xaj from China) was 115 μg/ml. Setting the copper resistant threshold value to 125 μg/ml, 47 and 13 strains were considered sensitive and resistant to Cu2+, respectively. Furthermore, five strains showed Cu2+ resistance at 270 μg/ml. Compared to the copB from sensitive strains, the copB gene in resistant strains had a 15-bp insertion and eight scattered single nucleotide polymorphisms. Interestingly, the clustering based on MLSA was distinct between Xaj copper ion resistant and sensitive strains.

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Abstract. Zheng C, Zhu J, Yang X, Fu B. 2022. Short Communication: Genetic diversity of walnut blight-associated bacteria from China using rep-PCR. Biodiversitas 23: 5681-5686. Walnut blight is caused by the bacterium Xanthomonas arboricola pv. juglandis (Xaj), is one of the most serious diseases in walnut production around the world. Understanding the genetic diversity of walnut blight pathogen is of great significance to developing a scientific and reasonable prevention and control strategy. The rep-PCR (Repetitive Sequence Polymerase Chain Reaction) technique is a powerful tool for analyzing plant pathogens. In this paper, using three pairs of rep-PCR universal primers (ERIC, BOX, and REP), a genetic diversity analysis was carried out on walnut blight-associated bacteria mainly isolated from different counties of Hubei Province, China. A study of 60 walnut blight-associated bacteria isolated in 2016 found that they had a high genetic similarity among them. There is no clear correlation between the genetic diversity of these isolates and their geographical or tissue origins. Interestingly, these clusters can also distinguish copper-resistant isolates from sensitive ones. Therefore, rep-PCR is a powerful tool to study the population of walnut pathogenic bacteria.