Improving Forage Grass Disease Resistance

UK - The Forage Grasses breeding programme at the Agri-Food and Biosciences Institute (AFBI), Loughgall, Northern Ireland was established in the 1950s and has produced an extensive portfolio of varieties, such as Dunluce and Tyrella, for use on UK farms. For almost 20 years, the breeding programme has been jointly funded by seed specialists Barenbrug, who have made the varieties widely available across the UK and Ireland.
calendar icon 20 September 2010
clock icon 3 minute read

While the main grass breeding objectives at Loughgall are to improve dry-matter yield, persistency and herbage quality, in recent years increasing effort is going into breeding for improved disease resistance. The main diseases occurring on perennial ryegrass in the UK and Ireland are mildew, crown-rust and leaf spot. These diseases are weather-related and more intense in some years than others.

Contrasting with the hot, dry summer weather, in 2005 and 2006, the excessive rainfall in summer months during the last three years created serious problems for grass farmers across the country. Perfect spring weather, allowing good early grazing and providing optimal conditions for first cut silage, was often followed with heavy rain accompanied by low levels of sunshine and poor drying conditions, resulting in very wet fields with severe poaching on many farms and a delay in taking second cut silage.

Grass swards are most susceptible to diseases when growth is slowed down by extreme weather conditions. Furthermore, when grass growth has slowed down due to reduced fertiliser applications, diseases tend to be more of a problem. In the south and east of England, during periods of drought, swards are often affected by crown rust, a disease that has distinctive orange pustules and reduces palatability to grazing animals. However, in the north and west of the country, leaf spot is more common and was particularly prevalent during the last three years.

Leaf spot disease on perennial ryegrass is caused by the fungus Drechslera siccans. Temperature and humidity play an important role in the development of leaf spot and the transfer of the disease within the sward. Above average air temperatures, along with the high rainfall, created perfect conditions for this disease and in recent years, many pastures, from as far south as Cornwall and right up into Aberdeen were affected.

Farmers reported that swards were unproductive and unpalatable to grazing livestock. The initial symptoms of leaf spot infection are black speckles on the leaf. Diseased leaves eventually became chlorotic and die, effectively lowering grass quality for both silage and grazing. Leaf separations carried out by AFBI found that in the most severely affected varieties, up to 30 per cent of the leaf tissue was severely chlorotic or dead.

In Northern Ireland the climatic conditions in late summer are often perfect for the development of leaf spot. Severe infections are frequently seen on perennial ryegrass in September and October resulting in poor quality pasture and some varieties are much more resistant than others. Subsequently this has given the grass breeding team at Loughgall good opportunity to identify disease resistant plants which can be crossed to make new varieties.

The next stage in the selection process involves testing on several sites where different environmental conditions expose the grasses to various disease pressures. As well as using the main trial site at Loughgall, trials provided by Barenbrug in Aberdeen, Evesham, the Netherlands and France add valuable extra information.

Breeding for improved leaf-spot resistance by AFBI has been further enhanced by the recent introduction of new assessment techniques. Near Infra-red Reflectance Spectrometric (NIRS) assessment and the development of image analysis technology using digital photography are just two of the new techniques which are being used to ensure that future AFBI grasses will have high resistance to diseases such as leaf spot which affect production and palatability.

The first new perennial ryegrass with improved leaf spot resistance to be released from the AFBI programme is the intermediate tetraploid variety Malone. In addition to having significantly improved leaf spot resistance, Malone produces high yields of quality herbage and has a prominent position on Recommended Lists throughout the UK and Ireland.

As a high percentage of the agricultural output in the UK is dependent upon grass, a steady supply of improved, high yielding and disease resistant varieties, able to cope with changes in farm management or environmental factors, is essential to the future of the industry.

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