2019: Response of Cotton Varieties to Inoculation with Xanthomonas citri pv. malvacearum, the Causal Organism of Bacterial Blight

Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist December 27, 2019 13:29

2019: Response of Cotton Varieties to Inoculation with Xanthomonas citri pv. malvacearum, the Causal Organism of Bacterial Blight

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Symptoms of bacterial blight include water-soaked lesions on leaves.

During 2019, two sets of the cotton varieties (52 entries) contained in the Mississippi State University Official Variety Trial were planted in Stoneville.  At flowering (7/19/2019), 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 and 30 days post-inoculation).  The results contained in the attached table (below) were based on the last observations made August 18, 2019.  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

No plot or variety exhibited an incidence of bacterial blight greater than 60% (observationally).  In all, the breakdown of variety responses within the OVT were: S = 35% of the entries, MS = 4% of the entries, MR = 4% of the entries, and R = 58% of the entries.

2019 OVT bacterial blight response

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Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist December 27, 2019 13:29
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