Designation of Pathotypes of Plant Pathogens

For evaluation and communication of data on populations of plant pathogens a sensible code to name pathotypes can be extremely helpful. Starting from a coding system proposed by Habgood in 1970, a system, called “coded triplets” is developed which has the same advantages but is easier to understand and to use. This is especially useful as, in the meantime, pathotypes did become increasingly complex due to the increased number of genes conferring race specific resistance in the host. An important advantage of the coded triplets is that codes change only at one digit if, for example, a new differentia) is added or if the pathotype changes from avirulence to virulence or vice versa on a single differential. In this way evoluationary patterns and changes in the pathogen population can be visualized easily. The system is used to describe complex data on haplotypes of the barley mildew pathogen, but it is suited equally well for designation of pathotypes of other pathogens. Some basic principles of coded triplets are similar to octal notation, described by Gilmour in 1973, which has, however, not become widely known. Reasons for this are discussed. – There is a fourth system belonging to the same group of mathematical, condensing codes. As there is reason to believe that the evolution of condensing codes is drawing to an end, the systems are compared extensively, and the benefits of a generally accepted designation are outlined.