Wheat’s powdery spots

Abstract

European wheat crops are affected by powdery mildew, a major disease that is caused by the ascomycete fungus Blumeria graminis forma specialis tritici (Bgt). We have lacked good understanding of the population biology of Bgt, but writing in PLoS Biology, Jigisha et al. have now analysed newly sequenced genomes of 276 Bgt strains collected in 2022 and 2023 from over 90 locations that span Europe and neighbouring regions. The samples group into five populations: northern Europe, southern Europe, Turkey and northern Caucasus, Middle East and a population with individuals that fall between northern and southern Europe. The northern Europe population shows high rate of gene flow, whereas the southern Europe population shows strong spatial structure. Wheat powdery mildew spores are transported by wind, and the authors showed that wind connectivity primarily shapes population structure across Europe; climate and geography have a secondary role. Genome scans also identified several loci that are putatively under recent positive selection in different populations, including one fungicide target and several genes that prevent Bgt from causing disease when matched with specific genes in wheat (avirulence genes). This suggests that fungicide treatment and resistance breeding pose a strong selective pressure for Bgt. One such case is the avirulence gene AvrPm17, which encodes an effector recognized by the wheat receptor Pm17. Several variants of AvrPm17 that can partially escape recognition by Pm17 are circulating in Europe. The authors found evidence for a selective sweep on standing genetic variation. Moreover, they found multiple virulent variants that were circulating in Europe before Pm17 was introduced to the continent in the early 2000s as well as a more-recent virulent variant that remains rare but might increase in frequency, given that it can completely evade recognition by Pm17.

Original reference: PLoS Biol. 23, e3003097 (2025)