Multiline varieties and disease control. II. The ‘dirty crop’ approach with components carrying two or more genes for resistance

Abstract

The effects of multilines, where each component carries two or more genes for resistance, on the long-term racial composition of a pathogen population were investigated using simple theoretical models. It was found that multilines in which the components carried overlapping sets of genes (of the type AB, BC, AC, etc.) were less likely to stabilize the racial composition of the pathogen population with simple races predominant than multilines composed of lines each with a single gene for resistance. On the other hand, multilines in which the components carried disjoint sets of genes (of the type AB, CD, EF, etc.) were as, or more, effective in preventing the development of complex pathogen biotypes than mixtures with a single resistance gene per component. These findings are discussed in relation to the question of the optimum constitution of a multiline variety, in terms of the number of resistance genes per component, for stable and effective disease control.