Comparing methods of ploidy estimation in potato (Solanum spp.)

Authors: KRAMER, LYDIA - University Of Wisconsin; Bamberg, John

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2019
Publication Date: 6/12/2019
Citation: Kramer, L.J., Bamberg, J.B. 2019. Comparing methods of ploidy estimation in potato (Solanum spp.). American Journal of Potato Research. 96:419-426. https://doi.org/10.1007/s12230-019-09729-4.
DOI: https://doi.org/10.1007/s12230-019-09729-4

Interpretive Summary: Potato is the top US vegetable crop with the most exotic germplasm resources for breeding. Making hybrids efficiently often depends on knowing the number of chromosomes in the intended parents, but standard methods for counting chromosomes can take considerable skill, expensive equipment, or involve toxic chemicals. We compared seven variations of simplified microscopic methods for estimating chromosome numbers. The accuracy was similar with most methods, but the quicker preparation and scoring time for measurement of cells on the underside of leaves made it the method recommended. This improved method is important because it helps potato researchers and breeders more efficiently make improved potato varieties that are more profitable for potato farmers and more nutritious for the consumer.

Technical Abstract: Ploidy manipulation and the resulting need for rapid ploidy screening can be important in potato research and breeding programs. We tested three predictors of ploidy, particularly seeking the quickest, simplest, and most reliable: Chloroplast number per guard cell (C#), guard cell length (GC), and pollen diameter (P), with a total of seven variations in methods of preparation. Time required for each preparation was assessed, and a panel of inexperienced volunteers compared these methods for accuracy using a standard set of coded samples of known ploidy. The common method of counting C# with iodine stain took longer and was no more accurate than observing C# or GC in tap water. GC from tape impressions of the underside of leaves was reliable and has the advantage of permanent slides for later reference. We recommend GC, whether in water, stained, or as tape impressions. GC is significantly different in diploids and tetraploids, but the distributions do overlap, so experience and care in selecting a representative sample of cells contributes to accuracy. The standard measurement of P after staining with aceto-carmine was faster to prep and just as reliable as epidermal methods for some technicians, even with no previous experience. Pursuit of ultra-simplified methods led us to measure P in plain water. Diameters of pollen in plain water are significantly larger, but only for living pollen, suggesting this method might also be developed into a rapid and reliable way to estimate pollen viability.