Workneh F, Jones D C, Rush C M
Phytopathology. 2009 Apr;99(4):432-40. doi: 10.1094/PHYTO-99-4-0432.
Wheat streak mosaic virus (WSMV), vectored by the wheat curl mite Aceria tosichella, is one of the major limiting factors in wheat production in the Texas Panhandle. The mites are blown by wind into wheat fields from nearby volunteer wheat fields or fields supporting vegetation which harbor virulent mites. Consequently, gradients of wheat streak severity are often observed stretching from the edges of wheat fields into the center or beyond. To describe the magnitude of the spatial relationships between grain yield and wheat streak intensity across the field, studies were conducted in 2006 and 2007 in three infected fields. Wheat streak severity was quantified with reflectance measurements (remote sensing) at 555-nm wave length using a hand-held radiometer. Measurements were taken in several equally spaced 1 m(2) locations along a total of eight transects and grain yield was assessed from a 0.8 m(2) area of each location. State space analysis was used to describe the relationships in which yield data and reflectance values were used as dependent and explanatory variables, respectively. A structural time series model was formulated as a state space model where the unobserved components were modeled explicitly. In the analysis the state of yield at current location (d) was related to the state of wheat streak intensity either at current locations (d) or lagged locations with autoregressive values of the first order (d-1) or greater. There were significant cross-correlations between yield and wheat streak intensity up to distances of 150 m (P < or = 0.05). Grain yield at the current position was significantly correlated with reflectance values at the same location and/or at lagged locations. The spatial aspects of the yield-reflectance relationships were best described by state space models with stochastic trends without slopes or deterministic trends with or without slopes. The models correctly predicted almost all of the observed yield values as a function of wheat streak intensity across the field within the 95% confidence interval. Results obtained in this study suggest that state space methodology can be a powerful tool in the study of plant disease spread as a function of other variables.
由小麦曲叶螨传播的小麦线条花叶病毒（WSMV）是德克萨斯狭长地带小麦生产的主要限制因素之一。这些螨虫被风吹到附近自生麦苗田或有带毒螨虫的植被田，再进入麦田。因此，经常能观察到从小麦田边缘延伸到田中心或更远区域的小麦条斑严重程度梯度变化。为描述田间谷物产量与小麦条斑强度之间空间关系的程度，2006年和2007年在三块感染田进行了研究。使用手持式辐射计在555纳米波长下通过反射率测量（遥感）对小麦条斑严重程度进行量化。沿着总共八条样带在几个等间距的1平方米位置进行测量，并从每个位置0.8平方米的区域评估谷物产量。状态空间分析用于描述产量数据和反射率值分别作为因变量和解释变量的关系。构建了一个结构时间序列模型作为状态空间模型，其中未观测成分被明确建模。在分析中，当前位置的产量状态（d）与当前位置（d）或具有一阶（d - 1）或更高自回归值的滞后位置的小麦条斑强度状态相关。产量与小麦条斑强度之间在150米距离内存在显著的交叉相关性（P≤0.05）。当前位置的谷物产量与同一位置和/或滞后位置的反射率值显著相关。产量 - 反射率关系的空间方面通过具有无斜率随机趋势或有或无斜率确定性趋势的状态空间模型能得到最佳描述。这些模型在95%置信区间内正确预测了几乎所有作为田间小麦条斑强度函数的观测产量值。本研究结果表明，状态空间方法可成为研究植物病害随其他变量传播的有力工具。
