Designated pathotype

A designated pathotype is one that matches the designated host. It is cultured on the designated host for the entire duration of the breeding program, and it is used both to identify the original parents, and to inoculate each screening generation.

Figure 7.1 The 'one-pathotype' technique

These two diagrams illustrate why it is essential to use only one designated vertical pathotype when screening for horizontal resistance. The circles are pathotypes and the rectangles are pathodemes. Green and thin lines represent matching, which is essential when screening for horizontal resistance, while red and thick lines represent non-matching, which prevents screening for horizontal resistance.

In the top diagram, there is only one vertical pathotype, and it has the two genes 1 and 2. When it is used to identify vertically susceptible pathodemes for use as the original parents, it will identify pathodemes 0, 1, 2, and (1 + 2). All other pathodemes (i.e., those with genes, 3, 4, etc.) will be resistant and will be discarded. With subsequent crossing among the hosts, all possible recombinations of the vertical resistance genes will be matched by this one vertical pathotype.

In the bottom diagram, there are two vertical pathotypes, one with gene 1, and the other with gene 2. When used together, these two pathotypes will identify vertical pathodemes 0, 1, and 2. However, this mixture of two vertical pathotypes will not identify pathodeme (1 + 2), which will be produced in subsequent generations by crossing pathodeme 1 with pathodeme 2.

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