Changes in temperature alter the ability of wheat to resist yellow rust

Some good news from me: I passed my PhD viva yesterday with minor corrections, hooray! I now have a few weeks to sort out the corrections my examiners have asked for and then I will be able to submit the final version of my thesis. The speed in which my viva was organised caught me a bit by surprise (its only three weeks since I submitted my thesis for the first time) but it meant that my work was still fresh in my mind so that was good.

I would love to be able to talk more about the work that went into my thesis but that will have to wait until its been published as a journal article. Instead, this week’s post is about some research done by a friend of mine who studied the effects of temperature on wheat disease resistance during her PhD.

Changes in temperature alter yellow rust disease resistance in wheat

Yellow (stripe) rust is an economically important wheat disease. It is caused by the fungus Puccinia striiformis f. sp. tritici (Pst for short). Pst infects the leaves of wheat plants, entering through pores in the surface (stomata). As the fungus spreads throughout the leaf, yellow pustules form stripes on the leaf surface. The disease is becoming more common and there is a lot of interest in research that could help reduce crop losses. Many commerical wheat varieties have some level of resistance to Pst infection. However, in recent years some of these disease resistance traits have become less effective as forms of the fungus that can overcome the plant resistance emerge.

Some of the wheat genes that encode for yellow rust resistance traits have temperature dependent effects. For example the resistance gene Yr18 is more effective in wheat grown at lower temperatures, whereas Yr36 provides enhanced resistance at higher temperatures.

Figure 1: A temperature shift from high to low temperature decreases wheat resistance to yellow rust. Images of wheat leaves showing disease symptoms (yellow pustules) after inoculation with Pst. Plants were grown under 4 regimes: 18  or 25 degrees throughout, 18 to 25 degrees temperature shift or 25 to 18 degrees temperature shift. Image from reference 1 (CC BY 2.0)

A recent study published in the open access journal BMC Plant Biology grew wheat line UC1041 under controlled conditions (controlled light, humidity, temperature etc.) to study the effect of temperature shifts on resistance to yellow rust (2). They grew the plants in 4 different daytime temperature regimes and inoculated the plants with Pst. The regimes were: 18 °C throughout, 25 °C throughout, 18 °C then shift to 25 °C at point of inoculation, and 25 °C then shift to 18 °C.

Figure 2: Scoring of yellow rust disease symptoms on wheat leaves. The percentage of the leaves covered in yellow pustules is shown for each of the 4 temperature regimes. Image from reference 1 (CC BY 2.0)

They found that there was no difference in the levels of resistance between plants grown at 18 °C or 25 °C throughout the experiment (Figure 1 and 2) (1). However, the plants grown at 25 °C then shifted to 18 °C when inoculated with Pst showed decreased levels of resistance (more severe disease symptoms visible in Figure 1, scored in Figure 2). Conversely, the plants grown at 18 °C then shifted to 25 °C upon Pst inoculation showed increased levels of resistance. The researchers found that the effect of the temperature shift was independent of the resistance gene Yr36 (1).

The mechanisms underlying the effect of temperature shift on resistance in these wheat plants is not yet known. With our changing climate, understanding how temperature can affect disease resistance in plants could aid the development of more stable disease-resistance in crops.

References:

1. Bryant et al (2014) A change in temperature modulates defence to yellow (stripe) rust in wheat line UC1041 independently of resistance gene Yr36. BMC Plant Biology

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