The potato is an autotetraploid plant, multiplied vegetatively in most instances, with many clones being male sterile, or even completely sterile. The potato was brought into France by only two introductions of a limited number of clones, and was subsequently severely selected to change photoperiod sensitivity. Genetic variability is thus restricted, and this is serious since there is evidence of a correlation between heterozygosity and vigour.

CURRENT SELECTION PRACTICES

Potato breeding practice is in part dictated by the peculiarities of the species. Selection is applied to the products of crosses between plants, and while there are data on the progeny, they are of limited value given the incomplete genetic information for the species. Selection is thus largely ineffective. The sheer mass of vegetative material imposes drastic selection in the early stages, with few representatives per clone. The risk of discarding worthwhile material is high. Hougas and Peloquin (1958) proposed using diploids (dihaploids) as a means of overcoming these difficulties.

USE OF DIPLOIDS IN BREEDING PROGRAMMES

Production of diploids

The first diploids were obtained by Hougas and Peloquin (1957) using Solanum phureja to provoke parthenogenesis. Dunwell and Sunderland (1973) obtained diploids by anther culture and Irikura (1972) cultured anthers of diploids to produce haploids. It is worth investigating several methods of haploid production because, as San (1977) has shown for barley, plants produced by androgenesis, gynogenesis and interspecific crosses can be different from one another.