Breeding at the 2x level and sexual polyploidization

Summary

INTRODUCTION

The breeding strategy advocated in this paper is based on genetic diversity. By diversity we mean both the many valuable traits available in the wild and cultivated relatives of the 4x potato (Solanum tuberosum ssp. tuberosum (hereafter, Tuberosum)), and the allelic diversity present in these relatives that provides the opportunity to approach maximum heterozygosity in developing new 4x cultivars. The breeding strategy contains three essential components; 1) the wild and cultivated relatives are the source of genetic diversity, 2) haploids (2n = 2x = 24) of Tuberosum (2n = 4x = 48) are effective tools in capturing the genetic diversity (putting the germplasm in a usable form), and 3) 2n gametes, gametes with the sporophytic chromosome number, are the basis of an efficient method of transmitting the genetic diversity to the cultivated 4x potato (Peloquin 1982).

An essential for the third component is that there are 2n pollen producing 2x hybrids from crosses between haploids of Tuberosum and the cultivated 2x species S. phureja (hereafter, Phureja) and S. stenotomum or the 2x wild species. The 2n pollen can be formed by either the genetic equivalent of first division restitution with crossing-over, FDR-CO (parallel spindles mutant, ps) or FDR without crossing-over, FDR-NCO (parallel spindles in combination with the synaptic 3 mutant, sy 3). The significance of the mode of 2n pollen formation resides in the genetic consequences.