Fusarium ear blight is widespread in Irish wheat crops. Control attempts using chemical fungicides have had only limited success; it is almost impossible to control the disease. It is caused by a complex of up to five species of fungi, all belonging to the fusarium genus, which thrive under the mild, moist conditions of the Irish landscape.
The fungi infect the wheat plant at flowering time, and in Ireland this can be prolonged under cool, moist conditions. Most fungicides do not have the persistence to control the disease, according to Dr Mike Cooke of UCD's department of environmental resource management, which is attached to the faculty of agriculture.
"In addition to causing substantial yield losses, the fungi can infect the grain of the plant and can cause the production of mycotoxins, which are harmful to human health and animals when consumed," he added.
Regular monitoring of mycotoxin levels is not carried out on grain in Ireland, Dr Cooke noted, despite the threat they pose.
Inevitably, resistance to fusarium species has a high priority in cereal breeding in the northern hemisphere. Conventional breeding for resistance to fusarium ear blight - the ear refers to the head of the plant - is expensive and time-consuming, Dr Cooke said. "At present their is little or no durable resistance to the disease available to farmers and breeders."
As a consequence, effective management of the disease relies on a combination of cultural practices, chemical control and the use of the least susceptible or tolerant wheat varieties available.
But research by Ms Helen Diamond and Dr Cooke has yielded a novel method for the early detection of possible sources of resistance to the blight.
Using a comparatively simple laboratory method, detached wheat leaves are infected with micro-droplets of one of the fungi responsible for the disease. Only one member of the fungal complex can infect leaves, and this method makes use of this by scoring specific parameters of leaf lesion development and comparing these with infection on whole wheat plants.
"Results show it is possible to significantly correlate leaf scores with whole plant reaction to the disease," said Dr Cooke.
This "detached leaf method" takes only four weeks to carry out and is therefore not only reliable but an extremely rapid bioassay for screening large numbers of wheat varieties. Moreover, results using one species of fungus will give an indication of resistance to all five species responsible for the blight.
Although only Fusarium (Microdochium) nivale is used to infect wheat leaves, results hold true for other fungi in the complex. The others cannot be used in the leaf test as they do not infect the leaf but infect the ear of the plant, he said.
The system relies on assessment of partial resistance components against the disease which are under the control of a series of polygenes in the wheat. This means resistance is caused by the cumulative effect of a number of related genes.
The genes control factors such as the time taken for the fungus to produce symptoms and spores. By scoring these factors an accurate record is make of disease development, which in turn can be related to disease development in the whole plant.
"The method is therefore more precise than conventional `disease scoring' under field conditions. And like all the best research, the discovery happened half by accident," he added.
The method is not likely to replace conventional plant breeding but will be complementary to it and facilitate rapid pre-screening of material before field evaluation. The work has aroused considerable interest at conferences in Ireland, Greece, Austria and Denmark, where papers were presented by Ms Diamond and Dr Cooke. Its merit is reflected in a decision by the European Journal of Plant Pathology, a leading journal, to publish their findings.
Meanwhile, the test will be fine-tuned to operate in different conditions, and, subject to more research funding, the team hopes to see if it applies equally to oats and barley.