27 September 2004
Wheat monoculture may be sustainable after all, according to researchers in Washington State University, USA, speaking today at the 4th International Crop Science Congress in Brisbane. The Congress has brought together over 1000 delegates from 65 countries to focus on the key issues for cropping systems that provide food, feed and fibre for the world.
Cultivation of the same crop in the same field year after year – a practice called monoculture – has long been regarded as unsustainable because of declines in yields after about three years.
The yield loss is generally attributed to soil-borne pathogens that infect the roots of that crop, but that die out while the field is planted to a different crop.
However, recent research at Washington State University (WSU) has documented a remarkable and apparently widespread microbiological control of a root disease in wheat and barley when these crops are grown continuously in the same location.
“The root-associated microbes are responsible for the well-documented decline of the disease ‘take-all’ and a corresponding increase in yields following one or more outbreaks of the disease,” said R. James Cook, interim dean of WSU’s College of Agricultural, Human, and Natural Resource Sciences.
Dr Cook is a strong advocate for crop rotation for many reasons, but points out that crop monoculture also has advantages and can be achieved sustainably with the help of soil microbes.
Cook and his colleague David M. Weller studied the pathogens responsible for four major root diseases of wheat and barley grown in the inland Pacific Northwest.
“Breeding for host plant resistance has provided only useful tolerance for management of one of these, Fusarium crown rot, and no useful resistance or tolerance to take-all, Rhizoctinia root rot and Pythium root rot,” Cook said.
“Considering the fact that the forebears of modern wheat evolved as a virtual monoculture, the lack of genes for resistance to root diseases implies that some other defence mechanism exists. Such protection develops against take-all with wheat monoculture.”
He said that wheat and barley selectively stimulate and support populations of antagonistic microorganisms in the root zone. “Often four to six consecutive crops are required before the onset of take-all decline, but the exact number of consecutive crops may vary.”
Cook and Weller found that the disease suppression associated with take-all decline is transferable to non-treated conducive, fumigated or pasteurized soil. The decline in this disease is reduced when another crop is planted that is not susceptible to take-all.
However, Cook noted that a field with a long history of take-all decline generally will regain suppressive traits with resumption of wheat or barley monoculture following a non-host break crop.
He said that many different kinds of microorganisms are suppressive to take-all at different stages of the disease cycle, but only a very select and closely related group of root-associated bacteria are responsible for take-all decline. These bacteria team up with the roots of wheat and, through production of antibiotics inhibitory to the pathogen, provide the equivalent of host plant resistance to the disease.
“For field crops such as wheat and barley, control of soil-borne pathogens depends on integrated methods that make use of natural microbiological control, host plant resistance, plant nutrients made conveniently available to diseased roots, widening crop rows and timely elimination of volunteer and weed hosts to maximize the host-free period between harvest and planting,” he concluded.
4ICSC would like to thank all its supporters including the following major sponsors:
DIAMOND: ACIAR and GRDC
PLATINUM: AusAID, CSIRO, Pioneer Hi-Bred International and QDPI
GOLD: IRRI and USDA-ARS
Cathy Reade, Media Manager, 4th International Crop Science Congress
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