2022: Response of Cotton Varieties to Inoculation with Xanthomonas citri pv. malvacearum, the Causal Organism of Bacterial Blight

Severe bacterial blight symptoms on the underside of a cotton leaf approximately 9-days post-inoculation.

During 2022, two sets of the cotton varieties (39 entries) contained in the Mississippi State University Official Variety Trial were planted (5/18/22) in Stoneville.  At flowering (7/25/2022), plants were inoculated with a bacterial suspension that contained the bacterium that causes bacterial blight (Xanthomonas citri pv. malvacearum).  Plots were inoculated in 15 gallons of water/Acre.  Following inoculation, plots were observed for the presence of bacterial blight on three separate occasions (9, 25, and 42 days post-inoculation).  The results contained in the attached table (below) were based on the observations made September 5, 2022 (42 days post-inoculation) .  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.  Eight total replicate plots of each variety were evaluated, four receiving inoculum (inoculated) and four that did not receive inoculum (non-inoculated).  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

Only one variety exhibited an incidence of bacterial blight greater than 58% (observationally).  In all, the breakdown of variety responses within the OVT were: S = 38% of the entries, MS = 5% of the entries, MR = 3% of the entries, and R = 54% of the entries.

2022 bacterial blight cotton OVT table