Towards a sustainable whole-farm approach to the control of Ergot

Abstract

The aims of this project were i) to establish whether grass margins act as a source of ergot infection for wheat crops ii) identify low risk grass species for use in margin mixtures and iii) determine whether wheat varieties differ in susceptibility to ergot.

Extensive sampling was carried out on farms to investigate the incidence of ergot in grass margins and compare the infectivity of ergots from different grass species on wheat. Ergots were found in 37 grass species and were more common in areas of weedy grass and natural regeneration than in sown margins. Ergots from different grass species differed in their infectivity for wheat, but there was also variation between ergots from the same grass species. It was concluded that grass species which combine low infectivity for wheat with late flowering should minimise the risk of spread of ergot to adjacent crops. It may be possible to identify ergot populations that are highly infective to wheat by alkaloid profiling.

In epidemiological studies, primary infections in wheat, caused by ascospores, were rare. Secondary infections, caused by conidia, occurred frequently on late tillers of wheat around the edges of plots and along tramlines and also within black-grassinfested areas of the crop. There was no evidence that grass margins produced gradients of infection into wheat crops, such as might be attributable to primary inoculum. They do however contribute to the overall reservoir of ergot inoculum in the arable environment. They may also provide a local source of secondary inoculum from infected grasses and this poses a risk to wheat at the crop / margin interface.

In an investigation of the susceptibility of wheat varieties to ergot, contrasting methods of inoculation were used to reveal a) 'field resistance' i.e. the combined effects of 'escape' and tissue resistance and b) tissue resistance on its own. Flowering traits which might confer escape from infection were also examined. Despite a high degree of variation in field resistance between sites and years, certain varieties showed consistently low levels of infection whereas a number of others tended to be heavily infected. There was also evidence of differences in tissue resistance. No variety was immune, but some exhibited a greater degree of partial resistance than others. This is evidence of genetic resistance to C. purpurea in the North European winter wheat gene pool. A range of flowering characteristics that might influence openness of flowering were identified and assessed. Little consistency emerged, with seasonal variation in temperature or rainfall apparently having a much greater influence than variety. It was concluded that varietal differences in openness of flowering are unlikely to be a major determinant of their relative susceptibility to ergot in the field and that tissue resistance is of more importance.