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Comparing Methods of Ploidy Estimation in Potato (Solanum) Species

  • Lydia J. Kramer
  • John BambergEmail author
Article
  • 22 Downloads

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 tap 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.

Resumen

La manipulación de la ploidía y la necesidad resultante de prueba rápida de ploidía puede ser importante en investigación en papa y en programas de mejoramiento. Probamos tres predictores de ploidía, particularmente buscando el más rápido, simple y confiable: El número de cloroplástos por célula guardia (C#), longitud de la célula guardia (GC) y diámetro del polen (P), con un total de siete variaciones en métodos de preparación. Se evaluó el tiempo requerido para cada preparación, y un grupo de voluntarios inexpertos compararon estos métodos para precisión usando un juego estándar de muestras codificadas de ploidía conocida. El método común de conteo C# con tinción de iodo tomó más tiempo y no fue más preciso que la observación de C# o GC en agua corriente. La GC de impresión en cinta del envés de las hojas fue confiable y tiene la ventaja de preparaciones permanentes para referencia posterior. Recomendamos GC, ya sea en agua, teñida, o como impresiones en cinta. GC es significativamente diferente en diploides y tetraploides, pero la distribución se traslapa, de manera que la experiencia y el cuidado en la selección de muestra representativa de células contribuyen a su precisión. La medida estándar de P después del teñido con aceto-carmín fue más rápida de preparar y justo tan confiable como los métodos epidermales para algunos técnicos, aún sin experiencia previa. La búsqueda de métodos ultrasimplificados nos condujo a medir P en agua corriente. Los diámetros del polen en agua simple son significativamente más grandes, pero solo para polen vivo, sugiriendo que este método debería también desarrollarse de una manera rápida y confiable para estimar la viabilidad del polen.

Notes

Acknowledgments and Perspectives

Thanks to USPG staff Mrs. Renee Sauer, ploidy-scoring volunteers, and the University of Wisconsin Peninsula Agricultural Research Station (PARS) for their help. We observe that even a simple study like this reveals several related facets which deserve more focused attention-- for example, the question of how subliminal perception affects the ploidy verdict when the researcher selects and measures only a few cells among many thousands in the field of view. Unrelated ideas, sometimes even more interesting that the original theme may be suggested, like using pollen swelling as an indicator of viability or guard cell size distributions to separate taxa. Isaac Asimov remarked that scientific discovery springs more from a “that’s funny” moment than “Eureka!” Similarly, the late legendary UW potato germplasm researcher and former genebank director Stan Peloquin remarked that while we pursue carefully planned-out hypotheses, just being busy working with germplasm and noticing unexpected phenomena that appear is often actually the start of the path to important scientific discoveries.

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Copyright information

© The Potato Association of America 2019

Authors and Affiliations

  1. 1.USDA/Agricultural Research Service, US Potato GenebankSturgeon BayUSA

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