Bacterial wilt – a puzzling disease of forage grasses

Bacterial wilt of forage grasses is caused by the bacterium Xanthomonas translucens pv. graminis (Xtg) and leads to major damage in meadows and pastures. To support the breeding of resistant cultivars, we are studying the genetic bases of the interaction between bacteria and plants. In doing so, we have learnt that this interaction exhibits a number of unique features when compared with other diseases of rice, tomatoes or lemons caused by Xanthomonas species. For one thing, no indications were found of a strain-specific interaction between individual bacterial isolates and plant genotypes, as is characteristic for typical resistance genes. The sequencing of the Xtg genome has shown that this pathogen possesses an unusually high number of insertion sequences. In addition, the organisation of an important virulence factor differs noticeably from other Xanthomonas species. Although knock-out mutation of this virulence factor led to a significant reduction of virulence, the bacteria were still able to reproduce in the plant. These findings provide valuable bases for the further development of efficient breeding methods.