Research Objective 2

Left: Three dihaploids extracted from Russet Norkotah. By choosing vigorous, fertile dihaploids such as the one on the right, and against plants with poor vigor, such as the ones on the left and in the middle, we will concentrate desirable genes and remove deleterious ones from diploid breeding stock. Right: Chips from dihaploids extracted from White Pearl. Each pair came from a different dihaploid. Variation in tuber size and chip color is evident. Potatoes were stored at 38 ˚F prior to chip processing. Chips from White Pearl are in the lower right.

As we develop diploid germplasm for breeding, we must capture the desirable alleles from tetraploid cultivars and existing breeding lines, while discarding the deleterious alleles. We will do this by crossing tetraploid potatoes with pollen from special diploid lines of Solanum phureja, a cultivated potato in South America. When a tetraploid potato plant is pollinated with the Phureja dihaploid inducer, seeds containing dihaploid embryos are produced. Each seed carries two of the four copies of each of the 12 chromosomes in the tetraploid female parent and no genes from the male Phureja parent. Since the two copies of each chromosome are randomly chosen, each seed carries a different complement of chromosomes. Also, since the seeds are products of meiosis, recombination has exchanged segments between each chromosome pair, adding to genetic variability among dihaploids extracted from the same tetraploid. Consequently, no two seeds are genetically identical to each other or to the mother plant. The potato breeding community in the U.S. will contribute to this objective by extracting dihaploids from their favorite breeding lines and selecting them for vigor and fertility.

By extracting dihaploids from elite U.S. cultivars and advanced breeding lines, we make use of the last 100 years of breeding and selection efforts in potatoes. We propose to develop diploid potato germplasm for the three major U.S. potato market classes – fresh and processing russets, round white chippers, and fresh market reds. Dihaploids from these three groups will serve as a starting point for future commercial diploid potato breeding efforts.

Once we have dihaploid plants, breeders will create self-compatible offspring by crossing selected dihaploids to diploid parents that carry genes that allow for self-fertility.