Meiotic mutants in potato breeding : (haploids, 2n gametes, germplasm transfer)
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Three factors provide unusual opportunities for potato improvement: (1) The wild and cultivated tuber-bearing relatives of the potato represent a large source of valuable germplasm. This genetic diversity can be incorporated into commercial cultivars. The gemzplasm is valuable in providing both specific desirable traits, such as disease and insect resistance, and for broadening the genetic base; (2) Haploids (2n=24) of cultivars (2n=48) can be readily obtained and used. They offer the advantages of simpler inheritance patterns (disomic vs. tetrasomic), and more important, a direct approach to germplasm transfer from the numerous 24-chromosome, tuber-bearing relatives of the potato. They provide us with a unique means of capturing genetic diversity; and (3) The discovery of meiotic mutants which give rise to 2n gametes provide unique and exciting opportunities to increase yield and genetic diversity. It is estimated that 2n gametes formed by first division restitution (FDR) transfer intact 80 percent of the genotype of diploids to their tetraploid progeny in 4x-2x and 2x-2x crosses. The meiotic mutant parallel spindles (ps) is an FDR mechanism that accomplishes this transfer in the production of 2n pollen. Recently, two new meiotic mutants, sy2 and sy3, have been discovered. They prevent normal crossing over, and thus the result is mainly univalents at metaphase I and high male sterility. However, when a synaptic mutant is combined with the parallel spindles mutant, fertile 2n pollen is produced. The genetic significance of this combination of meiotic mutants is that it makes possible the incorporation of the intact genotype of the parent into the gamete. Thus, a truly exceptional opportunity is possible - transmitting 100[percent] of the heterozygosity and epistasis of the parent to the offspring. The meiotic mutants provide, therefore, a powerful breeding method for maximizing heterozygosity and epistasis, and a very efficient method of transferring germplasm from diploids to tetraploids.