Virulence of Blumeria graminis f. sp. tritici in Brazil, South Africa, Turkey, Russia, and Australia

Abstract

The globally distributed causal agent of powdery mildew on wheat, Blumeria graminis f. sp. tritici (Bgt), is one of the most rapidly adapting plant pathogens and requires monitoring for shifts in virulence to wheat resistance (Pm) genes. Virulence frequencies were assessed in a total of 346 Bgt isolates from several countries that had either lately recorded increasing powdery mildew epidemics (Brazil, South Africa, and Australia) or not recently been surveyed (Turkey and Russia). The results were compared to previously published surveys of United States and Egyptian Bgt (390 isolates). Many of the Pm genes that have potentially been employed longer (Pm1a–Pm17) were shown to have lost effectiveness, and the complexity of virulence to those genes was higher among Brazilian isolates than those from any other country. Some cases of high virulence frequency could be linked to specific Pm gene deployments, such as the widespread planting of cultivar Wyalkatchem (Pm1a) in Australia. Virulence was also assessed to a set of Pm genes recently introgressed from diploid and tetraploid wheat relatives into a hexaploid winter wheat background and not yet commercially deployed. The isolate collections from Fertile Crescent countries (Egypt and Turkey) stood out for their generally moderate frequencies of virulence to both the older and newer Pm genes, consistent with that region’s status as the center of origin for both host and pathogen. It appeared that the recently introgressed Pm genes could be the useful sources of resistance in wheat breeding for other surveyed regions.

Two pathogen loci determine Blumeria graminis f. sp. tritici virulence to wheat resistance gene Pm1a

“…Turkey, Egypt, and Israel, with low frequencies of AVRPM1A.1 and AVRPM1A.2 isoforms causing an immune response, had higher levels of virulence to Pm1a , while Russia and the United States had higher frequencies of those same isoforms and lower levels of virulence to Pm1a . Frequencies of Pm1a virulence in the larger collection of isolates, of which present isolates were a subset, reflected these trends: Pm1a virulence was high in Turkey, Egypt, and Israel (65%, 61%, and 68%, respectively), and low to absent in Russia and the United States (0–9%; Ben‐David et al ., 2016; Kloppe et al ., 2022). Thus, the allele frequencies of AvrPm1a.1 and AvrPm1a.2 observed in this study may be representative of the larger Bgt populations of those countries.…”

“…14114. Entire plants were collected, and from each leaf that showed visible mildew pustules, one isolate of Bgt was obtained (Abdelrhim et al ., 2018; Kloppe et al ., 2022). Also phenotyped for this study were 25 isolates from a spring wheat region in Central Russia and Kazakhstan (grouped together for analysis purposes), and 89 isolates sampled from winter wheat fields in and around Turkey and Russia near the Black Sea (Tables 1, S1; Fig.…”

“…Nevertheless, a large 2013–2014 survey of Bgt from five US regions revealed that only one of 1017 isolates was virulent to Pm1a (Cowger et al ., 2018). This contrasts with the apparent maintenance of substantial percentages of Pm1a virulence (40–100%) in Bgt populations of other countries such as Egypt, Israel, Turkey, Brazil, and Australia (Ben‐David et al ., 2016; Kloppe et al ., 2022).…”

“…Shifts in virulence to Pm1a , Pm2 , Pm4a , and Pm6 have apparently occurred in Brazil within c . 15 yr (Kloppe et al ., 2022), and to Pm4b and Pm24 in Australia within just 4 yr (Golzar et al ., 2016).…”

“…The nine isolates from Russian Black Sea locations 15 and 16 were grouped with Turkish isolates because they are in a common winter wheat region, while Russian and Kazakh locations 17-19 are in a spring wheat region (Fig. 1; Kloppe et al, 2022). It is noteworthy that the EFRSN (D103N) virulence variant in AVRPM1A.1 was found only in the United States, while the KLGCD and KLGSD virulence variants were found commonly in the other five countries and not in the United States.…”