Population fluctuations of Xanthomonas translucens in wheat seeds and its effect on some quality characteristics of seed and disease emergence in the next generation

Infected seeds play considerable role in establishment of bacterial leaf streak disease caused by Xanthomonas translucens on cereal, which can onset disease outbreaks under favorable environmental conditions. The population of this pathogenic bacterium fluctuates over time in the seed. The present study investigated these changes and their effects on the disease establishment and seed quality. The bacterial population in the seeds harvested from the infected fields with progressed symptoms up to the flag leaves, had at least 104 to a maximum of 4×105 CFU/gr at harvest time. Ten months later the population was reduced to 102 to a maximum of 4×104CFU/gr and 24 months after harvest, the pathogen was not isolated from the seeds (except for one sample). The seed contamination evaluated in this study is higher than the seed contamination threshold (103CFU/gr) but disease transmission in the experimental field occurred from zero to a maximum of one percent. Although this rate of transmission is low, the same number of diseased plants in favorable environmental conditions can trigger an epidemic. Also, bacterial population on seed even after storage time did not have significant effects on germination and natural seedlings emergence, although on some characteristics related to longitudinal growth had significant effects. The effect of X. translucens on physiological and biochemical changes of seeds needs to be further investigated.