Thermal generalist behaviour of invasive Puccinia striiformis f. sp. tritici strains under current and future climate conditions

Abstract

Yellow rust is a devastating wheat disease. Since 2000, Puccinia striiformis f. sp. tritici strains PstS1 and PstS2 have become adapted to high temperatures and have spread worldwide. By 2011, Warrior strains had invaded both warm and cold areas of Europe. This study questioned whether thermal aptitude promoted the spread of Warrior strains, similar to PstS1/PstS2, by comparing infection efficiency (IE) at five temperatures and latent period (LP) under warm and cold regimes for Warrior isolates and pre‐2011 reference strains on two susceptible wheat varieties. The Warrior isolates showed a range of IE and LP responses to temperature that was intermediate between the northern reference isolates adapted to cold conditions and both the southern and invasive PstS2 isolates adapted to warm conditions. Warrior isolates had the highest IE under optimal temperatures of 10 and 15 °C, and displayed reduced infectivity under the warmest (20 °C) and coldest (5 °C) temperatures. Warrior strains acted as thermal generalists and the reference isolates acted as specialists. An IE thermal response was used to simulate the development of each isolate under future climate scenarios in a temperate and Mediterranean region. Isolates had the same ranking for yearly IE over the three 30‐year periods (1971–2000, 2021–2050, 2071–2100) and both locations, with a slight infection increase in the future. However, in the future IEs increased in earlier months. The thermal generalist profile of Warrior isolates for IE was confirmed, with an intermediate capacity to tolerate warming climate, whereas the southern isolates are better adapted to warm conditions, but do not have the virulences necessary to develop on current varieties.

Yellow rust does not like cold winters. But how to find out which temperature and time frames could be decisive in vivo?

“…The first period between 21 and 28 DAS corresponds to the end of October and could be related to the establishment of the disease on the newly sown, emerging crop (Zadocks plant growth stages between 11 and 19). This hypothesis is supported by the fact that the average temperature between 21 and 28 DAS was 10.79 ± 0.26°C which corresponds well with a recent study by de Vallavieille-Pope et al (2018), where the highest infection efficacies of various yellow rust strains were observed at 10°C. To the best of our knowledge, this is the first report providing evidence for a crucial effect of low temperature on yellow rust epidemics during the period of winter wheat emergence under field conditions.…”

“…The approach proposed here will produce the clearest result if fungal strains with identical temperature requirements were responsible for the epidemics within the period and region of observation. In reality, temperature requirements of fungal strains differ to some extent (see for example de Vallavieille-Pope et al, 2018). If, for instance, two populations of strains with extremely contrasting temperature requirements would be present, the variability of temperatures within the epidemic studies as well as within the non-epidemic studies will be large and the detection of significant differences between epidemic and non-epidemic cases will become increasingly unlikely with increasing differences in the temperature response of the two populations.…”

“…Both scenarios can result in similar numbers of degree days but epidemiological outcomes differ. Furthermore, the thermal behaviour of yellow rust strains differs, with significant shifts over time (de Vallavieille-Pope et al 2018). More precise and more recent information on relevant time frames and temperatures is needed to enhance yellow rust forecasts.…”

Weather-Based Predictive Modeling of Wheat Stripe Rust Infection in Morocco

“…Several disease models with variable levels of complexity and data requirements have been developed to predict WSR progress in wheat [15,[31][32][33][34][35][36][37]. For example, in Canada, an integrated model-based forecasting approach for WSR disease risk at the regional scale, which involves weather, airborne inoculum and satellite-based data, was developed and tested in Alberta [34].…”

A polyetic modelling framework for plant disease emergence

“…A third and recent example of strain introduction is that of Puccinia striiformis f. sp. tritici , the causal agent of stripe (yellow) rust of wheat, into north‐western Europe in 2011 (de Vallavieille‐Pope et al ., 2018), which has caused severe epidemics. The introduced strains differ from the preexisting population for several traits, including higher aggressiveness on wheat genotypes that carry genes encoding adult plant resistance (Hovmøller et al ., 2016).…”