Speaker
Description
Introduction
Rhynchosporium leaf scorch (causal agent Rhynchosporium graminicola) is a devasting disease of barley. To control the diseases, fungicides are used heavily to maintain grain yield and quality. To prevent the overuse and unnecessary application of pesticides, farmers are being encouraged to adopt Integrated Pest Management (IPM) strategies that combines a range of management options to manage diseases. However, adoption of these strategies requires reliable information on the contribution of varietal resistance for plant disease management. Selecting varieties based on their disease resistance rating has long been regarded as a cornerstone of IPM. However, for growers to be able to use varietal resistance as a means of reducing fungicide inputs they must be know when and how to do so and be confident in their decision-making ability.
Environmental conditions, such as temperature and rainfall, can alter the relationship between pathogen and host and hence affect disease levels, which can influence the efficacy of pest management tools and techniques. Unless the grower is confident that combining chemical and non-chemical management techniques will reduce the fungicide requirement and protect the yield for that crop, then pesticide usage practices are unlikely to change. This study examined the effectiveness of variety resistance in the management of barley leaf scorch across years and sites in the UK.
Materials and Methods
Three field trials were sown in each of three years in Scotland and Northern Ireland, providing a total of nine winter barley trials. Nine varieties were sown and grouped according to their resistance rating for Rhynchosporium on a 1-9 scale (1=highly susceptible and 9=highly resistant). The crops were treated with fungicide to control the powdery mildew (Blumeria graminis) and Ramularia leaf spot (Ramularia collo-cygni). Routine treatments of fertiliser, herbicides and insecticides were applied over the whole trial site. The trials were assessed for disease levels at several crop growth stages during the growing season. At harvest, grain yields for individual plots were measured and recorded. As there were no weather stations at the three sites, the seasonal precipitation and average daily temperature data for the local region were obtained from the UK Met Office.
For the statistical analysis, the treatment means for the early-season and mid-season disease scores, and yield were calculated from the plot level data. The impact of weather on the disease was analysed using the beta regression, and therefore the percentages were transformed to proportions for the analysis. To assess the effect of resistance rating on the mid-season disease score and the yield, the difference in disease between varieties with resistance rating 8 averaged across all treatments, and the other resistance ratings were calculated.
Results
The regression analysis (pseudo R2 = 0.75, Figure 1) identified that the interaction of the resistance rating with both the cumulative rainfall for the previous autumn, winter and spring, and the winter temperature had a significant impact on early disease levels, which is before the most important foliar fungicidal spray (applied at stem extension) for Rhynchosporium control. The level of disease was increased by elevated winter temperature and total rainfall. In addition, higher spring temperatures reduced disease levels while increased autumn temperature increased disease levels. Similar patterns for environmental influence on disease were observed for the mid-season disease assessment. The effect of these environmental factors on visually observable Rhynchosporium symptoms was moderated by the varietal resistance rating with the trend showing fewer disease symptoms in varieties with higher resistance ratings (Figure 1). Varieties with higher resistance ratings also displayed less variation in disease symptom expression between years (Figure 1).
Figure 1. Boxplot of the Rhynchosporium symptoms observed early-season (GS25-30, pre stem extension) in fungicide untreated plots of winter barley (red boxes). The prediction of disease severity based on temperature and rainfall (black boxes).
Discussion
Through examination of the various environmental factors that influence Rhynchosporium disease levels in Scotland and Northern Ireland we have identified the conditions in which the benefits of growing highly resistant varieties are likely to be achieved. Such information will allow growers to make more informed decisions regarding varietal choice and pesticide usage in their winter barley crops. This work highlights the importance of early disease surveillance to identify crops at risk.
| Keywords | IPM; barley; resistance; Rhynchosporium |
|---|
