First Incursion of the Warrior Race of Wheat Stripe Rust (Puccinia striiformis f. sp. tritici) to Turkey in 2014

Abstract

Stripe rust caused by Puccinia striiformis f. sp. tritici is the most common disease of wheat in Turkey. During the 2014 season, an unusual stripe rust infection occurred in winter-wheat-growing areas of the Thrace region in northwest Turkey. Some of the commercial cultivars (Enola, İzgi 2001, etc.) known to be resistant to the previously characterized races of P. striiformis f. sp. tritici in Turkey were recorded as fully susceptible. The first major infection was observed in a farmer’s field in Edirne (41°12′6.34″ N; 26°24′44.04″ E) on cultivar Enola, and the disease then spread to Kirklareli and Tekirdağ provinces. Trace infections of stripe rust was later observed on some Yr genes previously known to be resistant, such as Yr1, Yr3, and Yr4, in a yellow-rust trap nursery at Sakarya, northern Turkey. Independent race analysis of collected samples from Thrace and Sakarya undertaken at the Central Research Institute for Field Crops in Ankara and the Regional Cereal Rust Research Center in Izmir confirmed the detection of a new P. striiformis f. sp. tritici race in Turkey. Standard procedure for raising seedlings, inoculation, and incubation protocols were followed in seedling assessments of stripe rust differential sets (McIntosh et al. 1995). Seedling infection types of line combinations from World and European differential sets and Near Isogenic lines for Yr-genes in Avocet ‘S’ background were recorded 17 days after inoculation. Compatible infection types of 7 to 9 on Yr1, Yr2, Yr3, Yr4, Yr6, Yr7, Yr9, Yr17, Yr25, Yr32, and YrSp were recorded for the samples collected in 2014 from Thrace and Sakarya. In recent years, a stripe rust race commonly termed “Warrior,” first identified in 2011 in the United Kingdom, has already spread at high frequencies in most European countries and North Africa (Hovmøller et al. 2015). The virulence spectrum of collected samples from Thrace and Sakarya was identical to the Warrior race which is identically different from characterized races in Turkey by carrying virulence combination for Yr1, Yr3, Yr4, Yr17, Yr32, and YrSP and is avirulent on Yr8 and Yr27. Except for Yr8 and Yr27, the common races in Turkey are generally avirulent on Yr1, Yr3, Yr4, Yr17, Yr32, and YrSP. This is the first confirmed report of the Warrior race in Turkey. In 2015, the same race was redetected with high infection in the Thrace region and Sakarya provinces. Initial assessment of Turkish wheat cultivars and winter wheat germplasm from the International Winter Wheat Breeding Program showed vulnerability of some of the winter wheat cultivars whereas the spring wheat cultivars were more resistant to the Warrior race. This difference is a result of the Warrior race being avirulent on Yr27, a common resistance gene carried by the spring wheat cultivars in Central and West Asia and North Africa (CWANA), the Caucasus region, and East Africa. Considering the predominant west-east wind trajectory of rust spores and striking combination of virulence factors for important Yr-genes, it is expected that the spread of the Warrior race will be the next challenge of wheat growers in CWANA, the Caucasus, and East African countries. Future acquisition of virulence for Yr27 by the Warrior race would be a concern and therefore monitoring for the potential development of virulence for Yr27 in the Warrior race in this region is very crucial.