Spatial and Temporal Distribution of Iris yellow spot virus and Thrips in Colorado Onion Fields
Tables 1 and 2 from:
Schwartz, H. F., Gent, D. H., Fichtner, S. M., Khosla, R., Mahaffey, L. A., Camper, M. A., and Cranshaw, W. S. 2010. Spatial and temporal distribution of Iris yellow spot virus and thrips in Colorado onion fields. Online. Plant Health Progress doi:10.1094/PHP-2010-0820-01-RS.
Table 1. Summary of field, plant, edaphic, thrips and Iris yellow spot virus data (low to high) collected from six onions fields in western and northeastern Colorado during 2005 and 2006.
w Relative area under the disease progress curve (rAUDPC) = AUDPC values divided by the total area of the graph (21). AUDPC = ∑[(xi+n1 + xi)/2] [ti+1+1 – ti)] where xi is incidence of IYS at the ith observation, ti = time in days at the ith observation, and n = total number of observations. IYS incidence measured as number of symptomatic/total plants in a 3-m section at each sampling point.
x t-days = Thrips-days calculated by dividing the average number of thrips/plant by the number of days between the first and last sample for each experiment (38).
y Total marketable yield = combined weight of medium, jumbo, and colossal bulbs (32).
z CL = clay loam, L = loam, LS = loamy sand, SL = sandy loam, SiL = silt loam. Soil texture for 2006 was obtained from Soil Survey Staff (39).
Table 2. Pearson’s correlation coefficients for plant population, yield, thrips density, Iris yellow spot disease incidence, and edaphic characteristics for six commercial onion fields in western and northeastern Colorado during 2005 and 2006.
x Number of onion plants/3 m of one row/sample site/field.
w Yield of colossal and jumbo grade bulbs estimated from 3 m of one row/sample site/field.
x Thrips-days were calculated as:
where xi is the mean number of thrips/plant at time ti.
y Incidence (%) of plants with iris yellow spot (IYS) symptoms on the final disease assessment near crop maturity.
z rAUDPC is relative area under the disease progress curve (21). rAUPDC was
where xi is IYS incidence at time ti.
* = significant at P < 0.05.
** = significant at P < 0.01.
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