Previous work has shown that long-term (>40 years) time series of wheat stripe rust disease from North China contain a signal related to the Southern Oscillation Index (SOI). However, no cause-and-effect relationships or direct links between SOI and disease have been established. Because mid-latitude teleconnection patterns form important links between global atmospheric variations and regional weather anomalies, such as the Southern Oscillation, studies of such patterns could result in a better physical and biological interpretation for the SOI-disease association observed previously. We used cross-spectral analyses to determine if and on which time scales severity of stripe rust in five regions of North China between 1952 and 1990 was associated with fluctuations in four Northern Hemisphere teleconnection patterns. These included the Pacific/North American, the Western Atlantic. the Western Pacific, and the Eurasian patterns. The analysis showed consistent and significant (P less than or equal to 0.10) coherence relationships between the Western Atlantic (WA) pattern and stripe rust severity at a periodicity of 3.00 years. The phase relationships showed that, at the 3.00-year periodicity, the WA series and the disease series were out of phase by about half a period in all five regions. This phase difference indicated that peaks in the WA series. which are associated with below-normal winter temperatures over much of China, coincided with troughs in the disease series (i.e. low disease severity), presumably because of the negative effect of low winter temperatures on survival of the stripe rust pathogen. The analysis further showed that the WA series and the SOI series were highly significantly (P less than or equal to 0.01) coherent at a periodicity of 4.33 years, which could explain the association between SOI and stripe rust severity reported previously.
