Sustainable management of rust diseases in wheat

Rust diseases pose a serious threat to wheat production in Norway. New races of yellow rust have recently caused serious damage, and several popular wheat cultivars on the Norwegian market are susceptible. The overall aim of this project is to take a holistic approach to disease management by considering epidemiology, breeding of resistant cultivars and strategies for optimal use of fungicides when the resistance in the cultivars is not sufficient. In order to monitor the race composition of yellow rust in Norway, we have collected 38 samples with rust symptoms during the 2021 field season and sent them to the Global Rust Reference Center (GRRC) at Aarhus University for race identification. Results from 30 analyzed samples show that the race composition in Norway reflect that of other Northern European countries with yellow rust race 'Warrior-' dominating the rust population. This 'Warrior-' race that was first observed in Europe in 2013 and has since 2015 been the dominating yellow rust race in Norway. Other European races like 'Triticale 2015', 'Kranich' and 'Warrior' are also found at lower frequencies over the last years. To study the potential for overwintering, 5-7 winter wheat fields with yellow rust infections were registered in autumn 2020 and 2021. Due to poor survival of winter wheat, no living yellow rust was found in spring 2021. Winter wheat fields with yellow rust infection registered in autumn 2021 will be visited again in the spring to check whether the rust infections have survived the winter. To study the genetics of resistance in relevant wheat breeding material we are using a collection of 300 spring wheat lines. It consists of the current and historically important spring wheat cultivars in Norway, crossing parents and new breeding lines. This collection is being tested in field trials at three locations in Norway in addition to Mexico, China, Turkey and Kenya by our international collaborators. The set has also been genotyped with high density SNP (Single Nucleotide Polymorphism) markers, which makes it possible to map resistance genes using association mapping. Based on yellow rust data from field trials in Norway, China, Germany and Austria we have identified several consistent chromosome areas with effects across locations and years. The most important locus that can explain differences in yellow rust resistance in Norwegian spring wheat is located on chromosome 6A. This resistance is found in the spring wheat cultivars Mirakel and Caress. We are now looking further into the genetic origin of this resistance, and the planned seedling tests with selected rust races will likely determine whether it is race specific or race non-specific. In 2020 we observed for the first time in several decades natural infection of stem rust on wheat in Norway. This was repeated in 2021 with quite severe infections in a late plated spring wheat trial at Vollebekk. This has given highly useful data on the resistance levels in Norwegian cultivars. Together with field trial data from Kenya we have now confirmed that Norwegian spring wheat in general has a high degree of susceptibility to this devastating pathogen, but that gradual differences in quantitative resistance exists. When it comes to leaf rust, we so far only have data from one field trial in China. More testing for this disease will be conducted in both Mexico and China in 2022. Fungicide treatment is, in addition to growing resistant cultivars, an important tool of integrated management of yellow rust. As in 2020 we carried out field trials in 2021 at three locations (Ås and Apelsvoll at NIBIO, Sarpsborg at NLR) with fungicide treatments using three cultivars (Bjarne, Seniorita, Zebra) with different levels of disease resistance. The cultivars were treated with fungicides using ½ or ¾ dose at first sign of infection, and thereafter based on the disease development in relation to the developmental stages of the plants. The goal is to optimize timing and doses of fungicide treatments to control yellow rust and leaf blotch diseases, and to assess whether Danish thresholds for the control of yellow rust is applicable to Norwegian conditions. Only small natural yellow rust infections were observed at the start of the growth season, and the planting of pre-inoculated wheat plants grown in greenhouse was hardly successful this year. The yellow rust prevalence increased towards the end of the season, but the Danish threshold was not achieved at Apelsvoll or in Sarpsborg during the time period when fungicides could be applied. Yields were measured and yield samples from all plots will be analysed for grain quality in December 2021.

Sustainable and effective disease control is necessary in order to secure Norwegian wheat yields and achieve the goals of increased domestic food production. New races of stripe rust have in recent years caused severe epidemics on both spring and winter wheat in Norway. Several popular market cultivars are susceptible, which has caused a 30% rise in the use of fungicides. Stem rust and leaf rust are also threatening Norwegian wheat production. It is urgent to provide farmers with sustainable and effective control strategies, which should combine resistant cultivars with integrated fungicide strategies. We need knowledge about host-pathogen interactions specific to our local cultivars and climatic conditions. In this project we will i) answer fundamental questions about rust epidemiology in Norway, ii) identify resistance genes that can provide effective field resistance, iii) deliver effective tools for resistance breeding, iv) develop sustainable disease management strategies integrating optimal fungicide dose and timing with cultivar-specific disease thresholds. In the end, v) practical recommendations will be delivered to the wheat growers. While focusing on wheat rusts, the project will take a holistic approach that also considers other major wheat diseases. Our aim is to deliver solutions that support the implementation of integrated pest management (IPM) in Norwegian wheat production. The project will bring together the national expertise on wheat genomics, plant pathology, breeding and agronomy at NMBU, NIBIO, Graminor and NLR, and collaborate closely with the world-leading expertise on rust diseases in wheat and statistical modelling. Disease management recommendations will be disseminated to farmers through the agricultural extension service (NLR) and key private actors in seed sales and grain handling (FK Agri, Strand Unikorn and Fiskå Mølle) and plant protection (Bayer, BASF and Syngenta).