This summer the wheat fields found in the southern end of MSU’s campus weren’t as green as usual. Stripe rust, Puccinia striiformis f. Sp. tritici had infected most of the plots leaving a yellow tinge to the field. This year stripe rust was much worse than usual in Michigan, perhaps due to environmental conditions that favored early development.
This disease gets its common name “stripe rust” because it develops in distinct lesion that are straight lines. Some people also refer to it as “yellow rust” because it’s spores are more a lighter yellow compared to other stem or leaf rusts of wheat.
These rust can be so devastating because of their polycyclic nature that allows them to produce a large amount of urediniospores that are readily transferred by wind. This rust is an obligate biotroph, meaning it needs to be infecting living tissue to survive. The life cycle of rusts is very complex, with many having up to six spore types. The orange spores pictured below are the urediniospores. Teliospores are the hardier spores that give rise to basidiospores, and are produced on the leaf in black pustules.
This rust produces tiny yellow to orange uredinia 0.3-0.5mm and each uredinium contains thousands of yellow orange spherical urediniospores 20-30µm in diameter, with thick echinulate walls and 6 to 12 scattered germ pores. The infection starts on leaves but can also spread to the wheat chaff.
Stripe rust has the ability to reduce yield significantly. The pustules reduce green leaf area which reduces photosynthesis; removing nutrients and water needed for the plant to thrive. This leads to reduced vigor, grain fill, and even root growth. This ultimately reduces yield, and can lower the crop’s forage value and palatability for cattle.
Agrios, G. N. (2005). Plant Pathology (Fith). Burlington: Elsevier Academic Press.
Bockus, W. W., Bowden, R. L., Hunger, R. M., Wendell, M. L., Murray, T. D., & Smiley, R. W. (2010). Compendium of Wheat Diseases and Pest (Third). St. Paul: APS Press.12.04.16