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Wheat stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici, is one of the most destructive plant diseases in China. Gansu and Ningxia Provinces are considered to be the key areas for over-summering of this pathogen in China. In this study, 283 P. striiformis f. sp. tritici isolates were collected in these two provinces. Amplified fragment length polymorphism (AFLP) was used to analyze the population genetics and to infer the chance of population exchanges between different geographic locations and seasons. The genotypic diversity of the Gansu population (0.514) was slightly higher than that of the Ningxia population (0.489). The occurrence of frequent population exchanges between these two regions was observed, showing that 40 AFLP genotypes were shared by the populations of the two provinces. Gene flow between these two regions in autumn and spring subpopula-tions was also detected. The genotype distribution in three populations of Ningxia from opposite sides of the Liupan Mountains revealed possible significant effects of the mountains on limiting gene flow and population exchange. Phylogenetic analysis confirmed the possibility of recom-bination in some of the studied subpopulations in both provinces. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]