Epidemiology, Host Resistance, and Genomics of the Small Grain Cereals PathogenXanthomonas translucens: New Advances and Future Prospects

Abstract

Bacterial leaf streak (BLS) primarily affects barley and wheat and is mainly caused by the pathogens Xanthomonas translucens pv. translucens and X. translucens pv. undulosa, respectively. BLS is distributed globally and poses a risk to food security and the supply of malting barley. X. translucens pv. cerealis can infect both wheat and barley but is rarely isolated from these hosts in natural infections. These pathogens have undergone a confusing taxonomic history and the biology has been poorly understood making it difficult to develop effective control measures. Recent advancements in the ability and accessibility to sequence bacterial genomes have shed light on phylogenetic relationships between strains and identified genes that may play a role in virulence, such as those that encode Type III effectors. In addition, sources of resistance to BLS have been identified in barley and wheat lines and ongoing efforts are being made to map these genes and evaluate germplasm. While there are still gaps in BLS research, progress has been made in recent years to further understand epidemiology, diagnostics, pathogen virulence, and host resistance.

Barley variety Quest exhibits broad-spectrum, moderate quantitative resistance against diverseXanthomonas translucenspathovar translucens

“…Clade Xt-I includes the two pathovars which are typically found infecting barley: translucens and undulosa [14]. Barley is threatened primarily by the pathovar translucens (Xtt) [11,[16][17][18][19]. The pathovar undulosa mainly infects wheat along with a wide range of alternative hosts but has also been documented to occasionally cause BLS in barley [20,21].…”

“…BLS is a sporadic disease [17]. The incidence of BLS is associated with high temperatures and humidity with these conditions favoring the replication and spread of Xtt [12,13,17,23]. In the recent decade the threat and prevalence of BLS in barley has increased especially in the Northern Great Plains of the USA [17].…”

“…Therefore, this is unlikely to be a sustainable technique. In line with this challenge to manage Xanthomonas species in general, there are currently no available control methods for BLS pathogens [17]. The gold standard for prevention of losses due to Xanthomonas BLS pathogens could be genetic resistance [33].…”

“…BLS is a sporadic disease [17]. The incidence of BLS is associated with high temperatures and humidity with these conditions favoring the replication and spread of Xtt [12,13,17,23].…”