With FHB, Resistance does not equal immunity!

In fall of 2014, the first winter wheat variety to be rated Resistant (R) to Fusarium Head Blight (FHB) will be available to producers – a variety named Emerson.

However, it is imperative that farmers know that resistance or an R rating does not equal immunity. In fact, plants don’t have immune systems and therefore can’t be immune to any disease. Depending on the level of disease pressure, varieties that are rated as resistant will be infected to some degree. If disease pressure is high (i.e. high inoculum levels, conducive environmental conditions for a long period of time), yield loss due to FHB can still occur in R-rated varieties.

In Table 1, FHB reaction data collected in the cooperative registration system is provided illustrating how Emerson performed relative to other winter wheat check varieties and supplementary checks. Emerson showed a consistent improved reaction to FHB comparative to the resistant supplementary checks, hence the R rating. But as the table also illustrates, the R rating does not equal immunity as FHB was still measurable in each of the three years.

Table 1: Fusarium head blight (FHB) reaction of Emerson, the check cultivars and supplementary checks, Western Winter Wheat Cooperative Registration trials (2008-2010).

Picture2

z Visual rating index = % incidence x % severity / 100.
y Disease response category: R = resistant, MR = moderately resistant, I = intermediate, MS = moderately susceptible, S = susceptible.
x Supplementary checks were chosen to assist in the differentiation of resistance levels based on long term data collection.

Field surveys are being conducted in winter wheat and in the MCVET winter wheat trials to measure level of FHB infection.  To date, all fields and all varieties have symptoms of FHB in 2014.

Use Multiple Management Practices!

This is why it is still important to use more than one management practice. Extensive research over the past 20 years have shown that using multiple management options, including crop rotation, fungicide application, tillage, and variety selection, is the best way to mitigate the risk of FHB. But unfortunately, FHB infection will always be highly influenced by environment. Under high levels of the disease, all varieties will sustain damage.

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

Source:  Graf, R. J., Beres, B. L., Laroche, A., Gaudet, D. A., Eudes, F., Pandeya, R. S., Badea, A. and Randhawa, H. S. 2013. Emerson hard red winter wheat. Can. J. Plant Sci. 93: 741-748.
Respond
Have a follow-up question?

Why do we see disease in varieties that are rated “R” or “MR”?

Prepared by Holly Derksen, MAFRI Field Crop Pathologist

It is important to remember that resistance does not equal immunity.

In fact, plants don’t have immune systems so you can’t expect them to be immune to any disease. Depending on the level of disease pressure varieties that are rated as resistant will be infected to some degree. If disease pressure is high (ie. high inoculum levels, conducive environmental conditions for a long period of time) then you can still see yield loss due to disease in R-rated varieties.

 The infection that we see on the R-rated varieties is caused by the part of the pathogen population on which that type of resistance is not effective. If we grow varieties with the same type of resistance over a widespread area and in a tight rotation we select for that part of the pathogen population (sometime referred to as a different race). This is when we really begin to see issues, now the majority of the pathogen population cannot be controlled with resistant varieties. This is why it is important to use more than one management technique – do not just depend on variety resistance. It varies from disease to disease, but other management options include crop rotation, rotation of variety, fungicide application(s), tillage, etc.

Respond
Have a follow-up question?