Effet de l’hôte et de la température sur la structure de la population de Puccinia striiformis f. sp. tritici, agent de la rouille jaune du blé au Moyen Orient

摘要

The adaptation of fungal pathogen to its hosts and to the climate variation, in particular to the temperature, was investigated on wheat stripe (yellow) rust, caused by the biotroph fungus Puccinia striiformis f. sp. tritici (Pst) in the Middle East, focusing on Lebanon and Syria. This disease is a major problem for the crop in the region. Specific resistance genes were postulated in 138 wheat genotypes including elite lines, grown varieties and local landraces, using an array of 11 French pathotypes. Resistance gene diversity for yellow rust in wheat elite lines was higher than in current, commercial varieties grown in Lebanon, with nine Yr genes detected singly or in combination. Some varieties were resistant to all tested pathotypes and might provide interesting sources of resistance. Most of the Lebanese landraces were susceptible but also heterogeneous by their number of plants susceptible and resistant to a specific pathotype in a same landrace.A field survey was conducted in Lebanon and Syria in 2010-2011 and 275 Pst isolates were collected. The pathogen population was genotyped with 20 microsatellite markers and was found to be clonal, although the alternate host Berberis libanotica is present in the region. The dominant multilocus genotype shared similarity with the new invasive strain PstS1/PstS2 dispersed worldwide since 2000. The population was clonal with 10 pathotypes detected in Lebanon and Syria. 50 MLGs were detected considered high for clonal population. The virulence profiles combining Vr2, Vr6, Vr7, Vr9, and Vr27 are typical of the Mediterranean area according to group (Bahri et al., 2009) and corresponded to the worldwide invasive pathotype described since 2000 (Milus et al., 2009). The Vr8 was not fixed in this population, whereas this virulence is frequent in the Mediterranean genetic group (Bahri et al., 2009).Recently Pst strains have been described for adaptation to warm temperature (Milus et al., 2009; Mboup et al., 2012). The question of temperature adaptation in this study was whether the strains adapted to warm temperature are found in few clones of invasive strains or if they are selected in different pathogen genotypes locally under specific climate conditions. We selected 26 Pst isolates from the Middle East, 13 isolates from warm and 13 isolates from cold areas. We assessed their infection efficiency and latent period under four temperature regimes (high and warm temperature for the spore penetration phase, and high and warm temperature for the latency period). The isolates differed for the thermal aptitude for infection efficiency and latent period, but no clear relationship was established between the climate of the origin location of the isolate and its thermal aptitude. Some isolates were able to infect at high temperature but had long latency at high temperature and vice versa, some isolates had low infection efficiency and short latent period at high temperature, and few isolates were efficient either at high temperature or cold temperature for infection efficiency. Latency period showed pattern of local adaptation. Warm dew temperatures retarded sporulation, but this effect was far less marked for isolates from warm climates when incubated under warm conditions.This study provides details about probable effective yellow rust genes present in different genotypes and the prevalent pathotypes in the region. Moreover, the thermal aptitude for infection efficiency and latent period of some isolates under contrasting temperature will help us to build a better integrated disease management in the highlight of global warming.