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Title: DETECTION AND DESCRIPTION OF LARGE SCALE SPATIAL PATTERNS OF BACTERIAL BROWN SPOT OF SNAP BEANS USING CYCLIC SAMPLES

Author
item HUDELSON, B.
item CLAYTON, M.
item SMITH, K.
item Upper, Christen

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Snap bean plants within row segments from 65 to 147 m long were sampled using a cyclic sampling plan. Only six of every 31 plants were sampled, but in a way that pairs of plants that were 1, 2, 3, ..., 1525 plants apart could be identified within each sample on every leaflet on every sampled plant. The proportion of leaflets per plant with bacterial brown spot disease was determined. Disease incidence values were analyzed for spatial patterns. Patterns of disease were detected at several different scales within a single snap bean row at distances that ranged from approximately 20 to approximately 100 m. Disease patterns were extremely regular. Several of these regular patterns occurred at distances that corresponded to distances associated with known cultural practices such as fungicide application. These results indicate that previous culture conditions would be considered as possibly influencing subsequent disease development. Furthermore, this knowledge could lead to procedures to minimize such "memory" effects.

Technical Abstract: Snap bean plants within seven row segments that ranged from 65 to 147 m were sampled using a cyclic sampling plan. In the cyclic sampling plan, only six of every 31 plants were sampled, but sampled plants were spaced such that pairs of plants that were 1, 2, 3,..., 1525 plants apart could be identified within each sample. Every leaflet on every sampled plant was assessed for bacterial brown spot and the proportion of diseased leaflets per plant was determined. Arcsine square root-transformed disease incidence values were analyzed for spatial patterns using autocorrelation and spectral analyses. Disease patterns were detected at several different scales within a single snap bean row at distances that ranged from approximately 20 to approximately 100 m. Approximately 23 to 53% of the disease variability in the samples could be described by sine and cosine curves indicating that disease patterns were extremely regular. Several of these regular patterns occurred at distances that corresponded to distance associated with known cultural practices (such as fungicide application).