An efficient system to identify virulence patterns in stripe rust in Canadian

Project Description

This research aims at facilitating the deployment of stripe rust resistance in Canadian wheat and to ease breeding efforts in finding unidentified resistance sources existing in our own Canadian adopted genotypes and cultivars.

The virulence of rust changes in over a short period of time, persistent looking for non-defeated resistance sources is critical. This is done by screening isolates on wheat genotypes, that each carries unique resistance gene, under controlled conditions. This project aims at doing so and also expanding these genotypes with regional lines that can translate to the benefit of Canadian producers.

Objectives

1. Expanding the differential lines to integrate regional sources that can distinguish virulence patterns that will translate to Canadian producers.
2. Ease breeding efforts in finding unidentified resistance sources existing in our own Canadian adopted genotypes and cultivars.
   1. Expand stripe rust differential lines to include other sources of resistance from regional wheat germplasm and other international land races
   2. Determine virulence spectrum of individual stripe rust isolates on the expanded differentials
   3. Release info in regard to defeated resistance sources in Canada in timely manner

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Results

Currently, stripe (yellow) rust is the most damaging wheat disease worldwide. It is transmitted by wind over very long distances. In Canada and worldwide, stripe rust became a significant threat to wheat production around 2000, due to the emergence of new virulent races. These races have a higher number of resistance genes and are adopted to cause infection under higher temperature. Alberta is a Canadian hot spot for stripe rust infection, due to its proximity to the Pacific Northwest where prevalent conditions favour the infection in the early spring. There is a scarcity of information about stripe rust virulence in Canada as there was not much need to study it.

In this project, we have evaluated a large collection of stripe rust isolates (140) originating from across Canada and tested their ability to defeat known stripe rust resistance genes, known as all stage (Yr-genes). The tested isolates represented a 33-year time period from 1984 to 2017. Some were stored in liquid nitrogen since 1984, but we were able to recover and compare them to a recent collection in order to trace the changes in virulence of stripe rust in Canada for the first time. As a result of this work, we generated a valuable collection of isolates that can be explored in later studies. We generated data on what virulent races are present, provided evidence for a shift toward increased virulence in Canadian stripe rust, and showed that this shift has occurred twice, once around the year 2000 and again around 2010. We also linked this data to the wheat cultivars (genetic) being used.

Over the past 33 years, we showed that stripe rust races in Canada have expanded its ability to defeat at least 13 additional resistance Yr-genes. Spring wheat is the most common type grown on the Prairie and the majority of cultivars are known to carry combinations of Yr6, Yr7, and Yr27. This explains the high virulence toward these genes in our results from the early years. Moreover, the results showed that before 2010, only 31 percent of isolates were identical to races in U.S.A, but since 2010, 64 percent matched races present in U.S.A and the rest were unique to Canada, indicating the ability of stripe rust to change virulence locally. We found that the rust populations in western Canada were similar to that in the western states of the U.S.A, and the pathogenic races in eastern Canada were similar to the eastern and/or central regions of the U.S.A, supporting that rust in North America travel through different wind trajectories.

Lastly, a total of 100 wheat cultivars were selected to represent Canadian wheat development over the past 100 years, of which these cultivars can be considered as the backbone of our wheat today. The reaction of these cultivars at the seedling stage to one of the recent and most virulent races showed that 11 of these cultivars were resistant, 29 were intermediate and the rest (60) were susceptible. However, many of these cultivars display adult plant resistance in the field. Remarkably, most of the durum cultivars tested here were found susceptible at the seedling stage, but these are known to be resistant at the adult stage in the field. This overall project has provided a better understanding of prevalent races of stripe rust in Canada, possible migration routes, and reaction of key cultivars to specific virulent race. This information altogether will assist guiding building the genetic resistance in wheat by providing what material are potential resistant parent.