Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most destructive diseases of wheat in China. Conjunction area of Gansu, Sichuan and Shaanxi, acting as over-summering and over-wintering regions for the pathogen, plays a unique and critical role in epidemics of this disease in China. Because of the complexity in terrains and environmental conditions within this conjunction area, studies on the population structure, gene flow between local subpopulations and maintenance of genetic structure over time within this area are important to understand the epidemiology of this disease in China, and have practical significance in management of this disease at national scale. In this study, 461 isolates of Pst were collected from the junction area of Gansu, Sichuan and Shaanxi from 2013 spring to 2014 spring, and genotyped with amplified fragment length polymorphism markers. Results revealed that genotypic and genetic diversity were consistently high in Gansu and Shaanxi, but low in Sichuan, and a closer genetic relationship was found between Gansu and Sichuan than between them and Shaanxi illustrated by φpt, shared genotypes, Bayesian and nonparametric clustering methods. Genetic differentiation existed among autumn subpopulations, and genetic barriers were detected, although spring subpopulations were less differentiated. Subpopulations in Gangu of Gansu and Longxian of Shaanxi remained stable over the seasons studied. Potential migration events occurred at the junction area between successive seasons. The estimated frequency of sexual reproduction was 0.970 (s) (i.e. 97% of individuals being sexually derived during the yearly sexual cycle), suggesting the existence of sexual reproduction in this region. The main conclusions of this study are that genetic barriers exist at the junction area, and subpopulations in Gansu and Shaanxi are stable, and population exchange occurs mainly between Gansu and Sichuan.

Grapevine downy mildew (GDM) caused by Plasmopara viticola is a recurrent disease of wine grapes in the Ningxia Hui Autonomous Region (Ningxia) of northwestern China. However, the primary infectious pathogen in this region has not been thoroughly investigated. In this study, a multiplex real-time PCR assay was utilized to quantify P. viticola in soil, leaf residues, and asymptomatic leaf samples from ten commercial vineyards in two consecutive years to better understand the epidemiological significance of overwintering primary inoculum and its inoculum potential before the appearance of the first visual GDM symptoms. The DNA primers and multiplex real-time PCR assays that had been established exhibited specificity towards P. viticola within the test samples. The majority of the asymptomatic leaves (60%), leaf residues (80%), and soil samples (100%) tested positive for P. viticola. In addition, the amount of primary inoculum of P. viticola was found to be lower in soil than in leaf residues. The area under the disease progress curve in terms of the molecular disease index (AUDPC-MDI) was used to evaluate the overall latent P. viticola infection in asymptomatic leaves. Asymptomatic leaves were found to have different levels of P. viticola infection, and high AUDPC-MDIs correlated with a high AUDPC in terms of disease index (AUDPC-DI), with a significant correlation relationship between them (P < 0.01). Additionally, a well-correlated relationship was observed between the disease progress in the previous year and the MDIs of leaf residues and asymptomatic leaves in the following year, as well as the AUDPC-DI (Spearman’s correlation coefficient ρ = 0.643, 0.498, and 0.595, respectively) (P < 0.01). These findings provide valuable information for quantifying the primary infection of P. viticola in commercial vineyards.

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