Chong Huang, and
Zhanhong Ma, Department of Plant Pathology, China Agricultural University, Beijing 100193, P. R. China
Stripe rust of wheat, caused by Puccinia striiformis f. tritici, is of worldwide significance. Quantification of latent infection level is critical to estimate the potential for disease epidemics. In this study, field distribution of latent infection and the corresponding observed disease were studied in two growing seasons from 2009 to 2011 in Gangu, Gansu Province and Shangzhuang, Beijing, China. A previously developed real-time polymerase chain reaction (PCR) assay was applied to obtain the molecular disease index (MDX) to quantify the level of latent infection. At 1 to 3 weeks after leaf sampling, the observed disease indices (DX) were assessed in the corresponding experimental sites. The computer software SURFER showed that the spatial distribution patterns of MDX had a linear relationship with DX in field plots with P = 0.01. The aggregation levels of MDX correlated with those of DX in the fields. The disease foci which were correctly detected for latent infections with the real-time PCR for the Gangu and Shangzhuang field plots were 71.4 and 85.7%, respectively. The triadimefon fungicide treatment focused on the detected latent infection foci reduced both the initial inoculum and disease development, resulting in an average reduction in disease area in the field plots of 73 to 81%.