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 wheat varieties on the Norwegian market are susceptible. The aim of this project has been 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. We have during the project period collected infected leaf samples from the wheat growing areas of Norway that were sent to the Global Rust Reference Center (GRRC) at Aarhus University for race identification. Not surprisingly, the race composition in Norway reflects that of other Northern European countries with 'Warrior-' as the dominating yellow rust race. Other European races like 'Triticale 2015', 'Kranich' and 'Warrior' were also found. Inoculation experiments were carried out to test whether couch grass could function as a host of the most common yellow rust race on wheat in Norway, with the conclusion that this is unlikely. To study the potential for overwintering in Norway, infected winter wheat plants were identified in the autumn and checked again in the following spring. For the three years we did these observations, no surviving yellow rust infections could be detected. Since yellow rust often occur together with septoria nodorum blotch (SNB) we used inoculation experiments to test how infection with one pathogen affected the disease development of the other. The results showed that the severity of SNB increased when plants were infected with yellow rust either one week before or after the SNB infection. Both variety and plant developmental stage was important for the disease developments of yellow rust and SNB. To study the genetics of resistance in Norwegian wheat breeding material we use a collection of 300 spring wheat lines of relevance for Norwegian wheat breeding. These were together with new breeding lines from Graminor tested in field trials at three locations in Norway in addition to Mexico, China, Turkey, Kenya, Germany and Austria by our international collaborators. The field data was together with high density SNP markers used in association mapping to identify the most important resistance genes in Norwegian spring wheat. We identified a total of nine quantitative trait loci (QTL) with effects across years and continents. Of these, we found a highly consistent QTL on chromosome 6A with stable effect across growing environments and yellow rust races. Inoculation experiments confirmed that it is likely based on race non-specific resistance. KASP markers were developed and validated for this QTL that Graminor can use as a selection tool in their breeding program. The field trials also gave valuable data on leaf rust and stem rust resistance in the Norwegian spring wheat. While most varieties are susceptible, we have documented quantitative differences in resistance that can be utilized in the breeding of new varieties with better protection against these rust diseases that are expected to increase in importance over the coming years. Fungicide treatment is an important part of integrated yellow rust management. During the years 2021 to 2023, we carried out field trials at three locations (Ås, Apelsvoll, Sarpsborg) using three varieties (Bjarne, Seniorita, Zebra) with different levels of disease resistance. The varieties were treated with fungicides using ½ or ¾ dose at first sign of infection, and thereafter based on the disease development in relation to plant developmental stages. The goal was 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. The disease developments differed between the growing seasons, and it was only the trials from Ås and Apelsvoll that had sufficient infection levels to be used in the analyses. The results showed clearly that the choice of resistant variety is the most effective management strategy, but that spraying with fungicides in susceptible varieties can reduce the risk of yield losses. Fungicide dose was less important than the timing of the applications. The most effective protection was achieved by either spraying both early and late or only with a late spray (BBCH 55). This highlights not just the importance of resistant varieties, but also that it is possible to avoid yield losses in more susceptible varieties even with a reduced dose and number of fungicide applications. The project has received good publicity in media and the agricultural press throughout the project period. We have also disseminated results to wheat growers and advisors through webinars and participation in field days and conferences targeting the grain sector in Norway. A successful final seminar with active participation from target stakeholders was held in June 2024.

Direct outcomes: - Knowledge about the current race composition of yellow rust in Norway, and resistance levels of current varieties - Identified the most important resistance genes/QTL in Norwegian spring wheat breeding material - KASP markers developed for a large-effect QTL on chromosome 6A - Locally adapted management strategies for yellow rust provided to farmers in Norway - Postdoctoral fellow trained in plant pathology and genomics-based breeding Impacts on research and plant breeding: - Strengthened national competence on rust diseases in wheat - New insights into the synergistic and antagonistic effects between yellow rust and septoria nodorum blotch Impacts on society: - More productive wheat cultivation with less environmental footprint through more effective disease management

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).