DETECTION AND DESCRIPTION OF SPATIAL PATTERNS OF BACTERIAL BROWN SPOTOF SNAP BEANS USING CYCLIC SAMPLES

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 p lan, only 6 of every 31 plants were sampled, but sampled plants were s paced such that pairs of plants that were 1, 2, 3, 4,..., 1,525 plants apart could be identified within each sample. Every leaflet on every sampled plant was assessed for bacterial brown spot, and the proportio n of disease leaflets per plant was determined. Arcsine square-root-tr ansformed disease incidence values were analyzed for spatial patterns by autocorrelation and spectral analyses. Disease patterns were detect ed at several different scales within a single snap bean row, at dista nces that ranged from similar to 20 to similar to 100 m. Approximately 23 to 53% of the disease variability in the samples could be describe d by sine and cosine curves, indicating a substantial component of reg ularity in the disease patterns. Possible origins for these regular pa tterns, including cultural practices and seed infestation, are discuss ed.