Introgression in certain wild potato species

Abstract

It is pointed out that no variations in the cultivated potato have hitherto been interpreted as due to introgression, even though the necessary prerequisites for introgressive hybridization are often present. Certain geographical regularities in respect of disease resistance genes may be interpretable as due to natural selection of random mutations rather than to a flow of genes from a resistant species into a susceptible one.

Introgression of genes from the diploid species Solanum stenotomum to the tetraploid S. tuberosum and vice versa seems to be very probable, though it is difficult to obtain exact proof of this.

The evidence for introgressive hybridization between the Argentine wild potato species S. chacoense and S. microdontum is rather better. From measurements of a number of distinct characters in a wide range of specimens of S. chacoense it seems fairly certain that introgression is taking place in the mountains of N.W. Argentina. In consequence, S. chacoense, which was originally a low-altitude species, adapted to open places in the Argentine plains, has been able, as a result of contamination with germ-plasm from S. microdontum, to extend considerably its ecotypic range. Thus it now colonizes areas and extends into altitudes where the pure species is probably quite unable to penetrate.