Effect of Temperature and Air Humidity on Multiplication of Xanthomonas campestris pv. undulosa and Symptom Expression in Susceptible and Field‐Tolerant Wheat Genotypes uri icon

abstract

  • Multiplication of Xanthomonas campestris pv. undulosa in the leaf tis sues of susceptible and field-tolerant wheat genotypes was determined at the seedling stage, under different incubation conditions of temperature and air humidity. Dry air conditions did not hamper the multiplication of the bacteria in the leaf tissues, and temperature had a direct effect on the population trend. Symptoms were not observed at 15 degrees C. The occurrence of lesions coincided with populations of bacteria that had reached an estimated threshold of 10(8) colony forming units/ leaf. Differences in populations between genotypes Alondra and Pavon were only noticeable at 25 degrees C and dry air conditions, without correlation to differences in symptom expression. Considering these two genotypes, resistance to bacterial leaf streak did not seem to operate at the seedling stage when plants were inoculated by infiltration. In both genotypes, lesions did not extend significantly. An active mechanism stopping bacterial growth which is apparently temperature-dependent or a saturation of the target sites was possibly involved, as shown in the different experiments by the fit-curves calculated for Alondra and Pavon. This study provided information on the role of climatic factors in relation to epidemics. Temperature appeared to have a major effect on the disease and results confirmed that the risk of bacterial leaf streak prevails in warmer non-traditional wheal growing areas. Several types of resistance are likely to exist in the X. c. pv. undulosa/wheat system.

publication date

  • 1995
  • 1995