Bacterial leaf streak: Inoculation methodology determination

Information on inoculation methodologies and the phenological stage at which corn is susceptible to infection by Xanthomonas vasicola pv. vasculorum , the etiological agent of bacterial streak, are scarce. The objectives of the work were to model the calibration curve of the bacteria inoculum that allows the evaluation of the physiological damage in corn and determine its inoculation methodology. The calibration curve was obtained by dish counting the inoculum concentration. For the inoculation methodology, three sequential experiments were performed: inoculation method (absolute control, wind friction, steel wool, multi-needles and no injury, on the adaxial and abaxial sides of corn leaves), inoculum concentration (non-inoculated control, absorbances from 0.2 to 0.8 in a spectrophotometer at 580 nm) and phenological stage (non-inoculated control, inoculations via seed, in V 4 , in V 8 , in V T and in R 2 ). For the disease to express itself, around 1 × 10 8 CFU/mL were necessary. Multi-needle treatments and inoculation without causing injury differed significantly from the others, showing greater severity. Inoculation on the adaxial surface was more severe than on the abaxial surface. The symptoms of the disease started at a concentration of 0.4 and the severity of the bacterial streak was more intense at a concentration of 0.6, not differing from the higher concentration. Regarding the most susceptible phenological phase to the bacteria, the observed incubation period was 72 h and there were significant differences only in relation to the incidence expression. Stage V 8 was considered the most susceptible to infection.