2020: Response of Cotton Varieties to Inoculation with Xanthomonas citri pv. malvacearum, the Causal Organism of Bacterial Blight

Symptoms associated with bacterial blight of cotton as observed on the underside (abaxial) side of the leaf.

During 2020, two sets of the cotton varieties (56 entries) contained in the Mississippi State University Official Variety Trial were planted in Stoneville.  At flowering (7/15/2020), 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 two separate occasions (17, 26, and 34 days post-inoculation).  The results contained in the attached table (below) were based on the last observations made August 20, 2020.  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 60% (observationally).  In all, the breakdown of variety responses within the OVT were: S = 39% of the entries, MS = 4% of the entries, MR = 5% of the entries, and R = 52% of the entries.

UPDATED 2020 bacterial blight cotton OVT table