Temperature adaptation in Australasian populations of Puccinia striiformis f. sp. tritici

Abstract

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the major fungal pathogens of wheat. A new pathotype was introduced to Australia in 2002 and several derivative pathotypes were detected in subsequent seasons. It has been suggested that the severity of stripe rust outbreaks in Australia since 2002 could be as a result of traits other than virulence in the pathogen population. This study was conducted to investigate the hypothesis that the stripe rust pathogen population dominant in Australia since 2002 was better adapted to warm temperature conditions compared to previous pathogen populations. Sixteen pathotypes were selected to examine the influence of two contrasting temperature regimes during the 24 h incubation (10°C and 15°C) and the subsequent post-inoculation (17°C and 23°C) periods on latent period and infection efficiency on four susceptible wheat cultivars. In addition, the effect of two contrasting incubation temperatures on urediniospore germination was examined. The results indicated that pathotypes of P. striiformis f. sp. tritici detected after 2002 did not show evidence of adaptation to high temperatures, which suggests that other factors contributed to the observed increased aggressiveness.

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

“…Furthermore, Loladze et al . () found that thermal aptitude alone could not explain the development of the PstS1 clonal lineage in Australia since 2002. Australian PstS1 isolates did not perform better than pre‐2002 isolates under the warm regime.…”

“…PstS2 isolates also had the highest IEs of all the isolates tested at 20 °C on Cartago. This thermal adaptation trait can lead to dominance of PstS1/PstS2 strains in warmer geographic areas, as recently found in new areas for wheat yellow rust, with PstS1 in the southern United States (Milus et al ., ) and western Australia (Wellings, ; Loladze et al ., ), and PstS2 in southern France (de Vallavieille‐Pope et al ., ), the Mediterranean area (Bahri et al ., ) and Asia (Hovmøller et al ., ). However, the PstS2 isolates tested here under warm regime conditions did not perform as well as the S1 and S2 isolates (PstS3), previously found in the Mediterranean area.…”

“…The structure of the French Pst population before 2004 also demonstrated a local thermal adaptation: southern isolates persisted at high temperature under a warmer Mediterranean climate, whilst northern isolates showed an infective superiority at lower temperatures (Mboup et al ., ). Besides a varietal effect, the effect of temperature on Pst aggressiveness components can be dramatic, as noticed recently with North American and Australian PstS1 isolates (Milus et al ., ; Loladze et al ., ). The race Warrior is another exotic strain invading new regions; it appeared in 2011 in northwestern Europe and rapidly replaced the European Pst population.…”

“…High temperatures during the growing season have been considered a constraining factor for Pst development and its long-distance dissemination (Brown & Hovmøller, 2002). Despite this selective pressure and in the context of global climate change, many worldwide major epidemics occurred between 1999 and 2002 in the south-central United States (Milus et al, 2006(Milus et al, , 2009 and Australia (Wellings, 2011;Loladze et al, 2014). An incursion of a new aggressive strain, PstS1, at higher temperature occurred in regions previously considered too warm for the development of wheat yellow rust.…”

Exploring and exploiting the boundaries of host specificity using the cereal rust and mildew models

“…However, such isolate specificity also extends to other plant species that are closely related to wheat. The US-derived 134 E16 A+ pathotype evolved virulence for rye-derived resistance genes relative to the European-derived pathotype 104 E137 A-, resulting in adaptation to Triticale varieties including Jackie and Tobruk (Loladze et al, 2014). Furthermore, when the Chinese Spring-Imperial rye chromosome substitution lines were independently challenged with closely related pathotypes at the seedling stage, pathotype 134 E16 A+ (+Yr17 + Yr27) was comparatively more virulent relative to 108 E141 A-, suggesting a marked difference in virulence/avirulence and also host specificity (Fig.…”