Response of Cotton Varieties to Inoculation with Xanthomonas citri pv. malvacearum, the Causal Organism of Bacterial Blight

Bacterial blight of cotton as indicated by the presence of water-soaked lesions on the underside of leaves.

During 2018, two sets of the cotton varieties (67 entries) contained in the Mississippi State University Official Variety Trial were planted in Stoneville. At flowering, plants were inoculated with a bacterial suspension that contained the bacterium that causes bacterial blight.  Plots were inoculated in 10 gallons of water/Acre initially, but were inoculated a second time as a result of rainfall that occurred less than 1-hour following the initial inoculation event.  Following inoculation, plots were observed for the presence of bacterial blight on two separate occasions.  The results contained in the attached table were based on the last observation made July 31, 2018.  Plots were evaluated using a percent scale (0-100%) for the incidence (percentage of leaves exhibiting symptoms), severity (percentage of the leaf surface area exhibiting symptoms) and for defoliation (0-100% of each plot) as a result of bacterial blight.  Four replicate plots of each variety were evaluated and each value averaged across all plots.  A response was assigned for each variety based on the values outlined below and the specific visual response to the bacterium.

Responses were assigned using a letter designation based on the numerical incidence response within a given range. Responses are defined as:

 S = susceptible

MS = moderately susceptible

MR = moderately resistant

R = resistant

No plot or variety exhibited incidence greater than 60% (observationally). In all, the breakdown of variety responses within the OVT were: S = 28% of the entries, MS = 12% of the entries, MR = 6% of the entries, and R = 54% of the entries.

2018 MSU Cotton OVT Bacterial Blight Response to Inoculation