2024: Response of Cotton Varieties to Inoculation with Xanthomonas citri pv. malvacearum, the Causal Organism of Bacterial Blight

Bacterial blight symptoms on a cotton leaf post-inoculation.

During 2024, two sets of the cotton varieties (50 entries) contained in the Mississippi State University Official Variety Trial were planted (5/21/24) in Stoneville.  At flowering (7/19/2024), 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 (21 and 32 days post-inoculation).  The results contained in the attached table (below) were based on the observations made August 20, 2024 (32 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 bacterial blight severity greater than 58% (observationally).  In all, the breakdown of variety responses within the OVT were: S = 32% of the entries, MS = 2% of the entries, MR = 2% of the entries, and R = 64% of the entries.

2024 Cotton OVT Bacterial Blight response table