Varietal Screening Can Help Fight Yellow Stripe Rust Disease

Serbian farmers will remember 2023 as the year when yellow stripe rust disease (Žuta rđa in Serbian) endangered their wheat crops.

What is yellow stripe rust disease (and why should you care)?

Yellow stripe rust disease can be recognized by the parallel strips of yellow-orange pustules on the leaves of mature plants. The disease initially affects individual plants, often in the fall, leading to the formation of infected plant clusters by early spring, and then rapidly spreading to entire fields and changing their color from bluish-green to yellow.

Yellow rust is a disease that can harm the amount and quality of wheat grains. If it shows up early, it can completely wipe out the wheat harvest for certain types of wheat. 

Usually, it leads to yield losses ranging from 10% to 70%, depending on the wheat variety, when the infection happens, how far the disease has spread, and how long it sticks around.

How can farmers protect their wheat against Yellow Stripe Rust?

Farmers can employ various strategies to protect their wheat crops against the damaging effects of yellow stripe rust disease:

1. Chemical or biological treatments: Farmers can use chemical or biological agents to control the spread of the disease. These treatments can help manage and reduce the impact of yellow stripe rust on wheat plants. Because we grow crops organically, and biological treatments aren’t (yet) available, chemical methods weren’t a suitable solution.
2. Genetic tolerance: Genetic tolerance is a crucial approach in combating yellow stripe rust. We pick plants that have an advantage against Yellow Stripe Rust built in their DNA. Two types of genetic tolerance are often employed:
   1. R Genes (Pathogen Race Genes): R genes refer to specific genes in wheat varieties that provide tolerance to certain races of the yellow stripe rust pathogen. Planting wheat varieties with these R genes can be an effective way to protect crops against particular strains of the disease.
   2. APR Genes (Adult Plant Resistance Genes): APR genes are associated with a tolerance that develops in the adult stage of wheat plants. By selecting wheat varieties with these genes, farmers can bolster the plant’s natural ability to fend off yellow stripe rust as it matures.

These strategies help farmers safeguard their wheat crops from yellow stripe rust, ensuring healthier yields and better quality grains.

How did we find the most tolerant wheat varieties?

We decided to run a screening trial to find the most tolerant wheat variety to select varieties that can grow in organic production environments without the need for chemical corrections.

What did we do?

1. We picked 22 different wheat varieties that showed potential for genetic tolerance in sustainable conditions.
2. To avoid uncontrolled variability biasing our results, we grew the wheat varieties according to a randomized trial design. Wheat varieties were randomly split according to the row-column design with three replications for each variety, and across two different locations.

3. We scouted the fields to determine their natural infection by wheat variety using our internal protocol for scoring disease severity.
   1. 9 – No presence
   2. 7 – 25% of the field affected with yellow stripe rust
   3. 5 – 50% of the field affected with yellow stripe rust
   4. 3 – 75% of the field affected with yellow stripe rust
   5. 1 – 100% of the field affected with yellow stripe rust

We used Cultivar Ranker – an app that helps you visualize and pick the best variety for your use cases, to determine which varieties were most tolerant to yellow stripe rust.

This helped us identify many varieties that showed a genetic tolerance to yellow stripe rust, including Flavor, Obiwan, Tenor, etc.

It’s not just about disease tolerance

A wheat variety can be tolerant to yellow stripe rust, but not to another disease (Powdery mildew, Fusarium head blight, etc.) or it can show disease tolerance, but produce insufficient yields or seed proteins.

This is why in every screening research we do, we compare the target metric (in this case a tolerance to yellow stripe rust) to 30+ metrics that indicate successful growth (yield, seed protein content, abiotic tolerance, weed competition, etc.). To find the best trade-offs across all the different metrics.

Are you curious about how our crop selection team runs screening experiments? Stay tuned to find out what we learned in our wheat screening trials.