![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgdegQ_2erk9GttcbVYJzhz4D_Ilj8j7d92fAqftQlRCnN34y591_33n3wrZGSXLb1slxU_RYadBDQFmSm7TLBaO3GdFPd_Afoz_Jg5tDkSm0IeaNwlcfxMShpxVfhiqLPUzaHGMQMCffO1/s200/08102009_rust.jpg)
Luckily, there was a plant pathologist in center field.
The softball field was infected with a rust fungus, most likely Puccinia graminis. This fungus grows invisibly inside the grass blades until it's ready to reproduce, when it bursts through the epidermis with structures called uredinia, covered in the appropriately named (and bright orange) urediniospores.
These fungi are famous for their very complicated lifecycles, which often require different host plants at different spore stages. The stages of P. graminis are shown in the figure
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgAIRz0IPv4lgAmESj-F4J42mHC29RTg2zeXScvD6qS7TMqYU8Y9gGvPQix4lOr5tmJt08bFpcqqyV6u5aqkUUbbBBj3OhYg2JXkRwQHVsskQBZ1rTc3cK_WV6nxd0s-9fK8JhAuRwo5rU2/s200/PgLifecycle.jpg)
Rust fungi often don't hurt their hosts very much, at least until they burst through the epidermis to produce spores, which interrupts photosynthesis and makes the plant susceptible to dehydration. It's pretty much just a cosmetic problem on lawns, but causes major diseases on crops like wheat. It was such a problem for the ancient Romans that they invented a special god who presided strictly over rust epidemics, Robigo. Every spring, they celebrated the holiday of Robigalia, when they sacrificed red dogs and sheep in hope of appeasing him!**
According to Purdue Extension, lawn rust fungi rarely survive the cold winters of Indiana, but blow up north from warmer climates in the late summer and early fall. The same thing happens with wheat rust - urediniospores are carried on the wind along the "puccinia pathway," from the southern U.S., where it successfully overwinters, north into Canada, infecting progressively later and more northerly wheat crops along the way each summer.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvfP1XL8ofBMMWXQYLCg5XyhXY0CPuyR47ktlfaZO87JLuWNdoEbL729tbD8FWdobRlWy6yiz4cv8mq-yyswNtq2jJa9HZbDQl9W7YGiRymvkLbtpxWh4YYFmLsE2CZQgMfiYLwuUBNE-v/s200/puccinia_pathway.jpg)
"Alternate hosts" of rust diseases simply refer to the required host that we don't care about. In the devastating forest disease, white pine blister rust, the alternate hosts include gooseberries and currents (Ribes spp.). Unlike the previous example though, this rust attacks our host of interest as basidiospores and severely damages trees with the repeated production of bark-rupturing aecia. Although the aeciospores can travel for hundreds of kilometers to infect Ribes plants, the basidiospores that cycle back to attack pines are very fragile and short-lived. So, unlike these grass rusts, an infected pine can only sicken its neighbors if there are Ribes plants within range. For awhile, the New Deal's Works Progress Administration tried to take advantage of this by eradicating this alternate host from mountain forests of North America. To some extent, eradication of alternate hosts is still used today. And in fact, this tactic was one of the first recorded descriptions of people dealing with plant pathogens.***
Agrios, G.N. 1997. Plant Pathology. Academic Press.
*I'm impressed that Wikipedia correctly names these spores "urediniospores" and not "uredospores." This common misspelling has been tracked back to a single typo in a scientific article from many years ago. Unfortunately, they go on to state that this asexual spore stage produces basidia...
**Not to be confused with Robannukah.
***As early as the 1600 and 1700's, farmers in France and Connecticut independently noticed that wheat rust appeared to be worse near barberry bushes. Correctly deducing that the rust somehow fed on barberry, they convinced their towns to eradicate the bush as a way of controlling the disease.
Great post. You have to submit this to Berry go Round.
ReplyDeleteHi Matt, Attempts to stop rust by obliterating its hosts go on and on. During and after the First World War, E.C. Stakman at the University of Minnesota spearheaded a ferocious campaign to eradicate every single barberry bush in the wheat belt -- because he and his team had discovered that wild barberry was a site for genetic recombination by sexual reproduction for wheat rust fungi. (See pp. 19-22, "Dr. Stakman and the Rust Demon" in The Viking in the Wheat Field.) The campaign worked. For a while. But just this past year, U of M's Yu Jin has identified new strains of Ug99 as originating in the barberry bush.
ReplyDeleteA few years ago, in a monumentally wet summer, my garlic had rust so badly the foliage died right back. The crop was a little low, but OK.
ReplyDeleteThanks for the extra info, Susan!
ReplyDeleteJeremy, I've heard of berry go round but don't know exactly what it is. Where do I go to submit this?
Oh God I hate rust. You should really write a book, since gardners really need to know the why and how of what goes on with their plants. Once again, great article.
ReplyDeleteIt's also fun when a smut fungus invades lawn grasses and everyone's feet turn black, another gift from the rotten world around us.
ReplyDeleteOoh! I haven't seen a smutted lawn but I'll definitely be on the look out!
ReplyDelete