Sunday, April 20, 2014

Wheat Rust: "The Death of Grass"?

In an echo of "The Death of Grass", the 1956 novel whose theme is the progressive razing of the world's food production by a marauding and mutating virus, with apocalyptic consequences for humankind, the spectre of "wheat rust" is now raised. Wheat rust is said to be a similarly devastating condition, in fact a fungus, described as the "polio of agriculture", which has spread from Africa to South and Central Asia, the Middle East and Europe, causing severe yield losses of the most important staple crop next to rice In writing his novel, Sam Youd, using the pseudonym John Christopher, may have been inspired by the major epidemic of wheat rust that engulfed the North American wheat belt in the 1950s, in which 40% of the harvest was destroyed. In 1999, in Uganda, the disease resurfaced, due to mutation of the fungus, despite millions of pounds that have been spent in creating rust-resistant strains of wheat. It is thought that some 90% of all types of wheat in Africa are vulnerable to wheat rust.

Properly termed "wheat leaf rust", this is a fungal disease that affects wheat, barley and rye stems, leaves and grains, with crop yields being further diminished by dying leaves which feed the fungus. The pathogen is Puccinia rust fungus: P.triticina causes 'black rust', P.recondita causes 'brown rust' and P.striiformis causes 'yellow rust'. While farmers have used strain selection over centuries to improve wheat yields, so doing to provide disease-resistant crops has proved equally important in maintaining adequate crop production. The use of a single resistance gene against various pests and diseases plays a major role in resistance breeding for cultivated crops, and many single genes for leaf rust resistance have been identified.

Wheat leaf rust spreads via airborne spores, of which 5 different kinds are produced over the life cycle: uredospores, teleutospores, and basidiospores develop on wheat plants and pycnidiospores and aeciospores develop on the alternate hosts. Moisture is a key element for successful germination, for which optimum conditions are 100% humidity and a temperature of 15-20 degrees Centigrade. Within 10 – 14 days of infection, the fungi begin to sporulate and symptoms become visible on the wheat leaves, while the plants are entirely without symptoms prior to sporulation. In the Asian subcontinent, the spores cannot survive the hot dry weather but are re-introduced year on year from the Himalayas or surrounding hills, originating, so it is thought, from Berberis spp, Thalictrum flavum and Muehlenbergia huglet, which is a major cause of bread moulds.

Rust epidemics have been compared to a forest fire, in that once they take hold, the loss of crops is rapid and widespread, since millions of wind-borne spores are produced by the fungus, each of which has the capacity to initiate a fresh infection. The race is on to find new disease-resistant seed varieties of wheat, for which the legacy nations are better provided than developing countries such as those in Africa. A central part of this strategy is the use of Genetically Modified (GM) crops, including cloning resistance from wild grasses and barley, as opposed to using ever more virulent chemical pesticides. Mathematical models are being developed to predict potential outbreaks of wheat rust in African and Middle Eastern nations, to determine which may be most vulnerable.

Part of the problem is blamed on climate change, and the spread of two types of the fungus is thought to be a result of its adaptation to a warmer environment. Thus, outbreaks have been born in regions with no history of the disease, stretching from North Africa to South Asia, transmitted via spores carried by wind and through the soil. Such crop infestations can be added to the nexus of other afflictions upon the human capacity to survive and thrive, and most likely are exacerbated by modern industrialised agriculture and its practice of monoculture cropping. By default or more desirably by design, humankind may find itself steered onto the path of agro-ecology, regenerative agriculture and permaculture, and away from a global food production system which is patently unsustainable.


Anonymous said...

> the spectra of "wheat rust" is now raised.

I think you mean "spectre".

Anonymous said...

Specter actually. Spectre sounds better bit really only refers to the arch enemy of James Bond

Professor Chris Rhodes said...

"Specter" is U.S. spelling; I'm writing British English, so it's "spectre". Thanks for pointing out the original typo as in "spectra".