· By Tom Allen and Brian Pieralisi ·
During 2021, two sets of the cotton varieties (44 entries) contained in the Mississippi State University Official Variety Trial were planted in Stoneville. At flowering (7/18/2021), 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 33 days post-inoculation). The results contained in the attached table (below) were based on the observations made Aug. 19, 2021 (33 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 60% (observationally). In all, the breakdown of variety responses within the OVT were: S = 30% of the entries, MS = 5% of the entries, MR = 2% of the entries, and R = 64% of the entries.
Tom Allen is an MSU Extension plant pathologist and Brian Pieralisi is the MSU Extension cotton specialist.