Bacterial Leaf Streak Diseases of Plants: Symptom Convergence in Monocot Plants by Distant PathogenicXanthomonasSpecies

Abstract

Bacterial leaf streak (BLS) is a disease of monocot plants caused by Xanthomonas translucens on small grains, X. vasicola on maize and sorghum, and X. oryzae on rice. These three pathogens cause remarkably similar symptomology in their host plants. Despite causing similar symptoms, BLS pathogens are dispersed throughout the larger Xanthomonas phylogeny. Each aforementioned species includes strain groups that do not cause BLS and instead cause vascular disease. In this commentary, we hypothesize that strains of X. translucens, X. vasicola, and X. oryzae convergently evolved to cause BLS due to shared evolutionary pressures. We examined the diversity of secreted effectors, which may be important virulence factors for BLS pathogens and their evolution. We discuss evidence that differences in gene regulation and abilities to manipulate plant hormones may also separate BLS pathogens from other Xanthomonas species or pathovars. BLS is becoming an increasing issue across the three pathosystems. Overall, we hope that a better understanding of conserved mechanisms used by BLS pathogens will enable researchers to translate findings across production systems and guide approaches to control this (re)emerging threat.

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

“…Bacterial leaf streak (BLS) is a disease caused by Xanthomonas species on monocotyledonous plants and is characterized by watersoaked and later chlorotic interveinal streaks. Although there is limited reporting, BLS can lead to significant yield losses [5][6][7][8][9][10][11][12]. Limited research suggests that BLS pathogens are seedborne but can spread locally in the form of exudates via wind and water [6,7,[9][10][11]13].…”