2019 ASHS Annual Conference

Quantifying herbaceous cutting root development can be difficult and time consuming. Conventional methods include dry weights, ordinal ratings, root counts, root lengths, and root area calculations. Dry root weights are often considered the best measure of root growth; however obtaining these values requires washing, drying, and weighing the roots. This is a lengthy and tedious process, and it requires an accurate and precise scale. It is also difficult to connect dry weights to commercial value, such as transplant-ready status. The use of an ordinal rating scale is subjective, but if the assessor is experienced in plant propagation it may provide the most meaningful data relative to commercial value. The use of root scans allows researchers to obtain images of roots, then quantify root development without storing or handling the roots a second time. Scans may be used to generate root counts, root area calculations, and root length calculations. In this study I grew herbaceous cuttings of 6 species (Achillea ‘Moonshine,’ Ajuga ‘Chocolate Chip,’ Iberis ‘Purity,’ Leucanthemum ‘Western Star Leo,’ Phlox ‘Purple Beauty,’ Salvia ‘May Night’) using 7 substrate treatments [1:2 (v/v) Sphagnum peat and coarse perlite or that substrate amended with biochar or sand (0%, 20%, 40%, or 80%; v/v)]. Then I quantified root development via 5 methods [dry root weight, 0-5 ordinal rating (0 = cutting dead, 1 = cutting alive but no root development, 2 = minimal root development, 3 = moderate root development but insufficient for transplanting, 4 = good root development and sufficient for transplanting, 5 = optimal root development), and three methods from excised root scans using ImageJ (primary root count, primary root length, and two-dimensional root area)], then I examined and correlated the metrics and mean comparisons. Calculation of two-dimensional area was very quick and easy. Relationships between quantification methods varied by species. All species had strong positive correlation between root area and root weight (r = 0.99 to 0.73) as well as primary root length and root weight (r = 0.93 to 0.61), but primary root count did not correlate consistently with root weight (r = 0.66 to -0.07). Mean separation (P ≤ 0.05) of the substrate treatments groups with root weight, root length, root area, and rooting rating measurements showed only minor differences between quantification methods. Excised root scans can quickly and effectively quantify root growth and provide a lasting record.