Abstract
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.
Highlights
Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive disease of wheat throughout the world
Occurrence of stripe rust in most wheat growing areas in China relies on long-distance dispersal of urediniospores by wind (Li and Zeng 2002; Zeng and Luo 2006) because the pathogen Pst, not forming any resting structure and obligatorily parasitizing on living tissues, cannot survive summer and winter in most places where the average temperature is higher than 23 °C in the summer (Li and Zeng 2002) or where temperature is low in the winter and all expanded wheat leaves are frozen to death (Li and Zeng 2002; Zeng and Luo 2006)
Our results revealed that mountains in the junction area can serve as the barriers to migration, and high genetic differentiation exists between autumn subpopulations in this areas, the spring subpopulations at the conjunction area tended to be undifferentiated or unified, inferred based on low pair-wise φpt, similar genetic structure, and a large number of shared genotypes
Summary
Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive disease of wheat throughout the world. (2019) 1:25 wintering regions in China (Li and Zeng 2002; Zeng and Luo 2006; Wan et al 2007) In these provinces, south and east Gansu, northwest Sichuan, and west Shaanxi with high elevations and relatively low summer temperatures can serve as over-summering areas where Pst survives on late-maturing wheat and volunteer seedlings in the summer. The disease epidemic in the Huang-Huai-Hai winter wheat region can be greatly affected by the pathogen population structure ( emergence of novel races) in these three provinces (Wan et al 2007)
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