In vitro sugar and water use in diploid and tetraploid genotypes of daylily (Hemerocallis spp.) in liquid medium as affected by density and plant growth regulators

Abstract

Two tetraploid and two diploid genotypes of Hemerocallis spp. were micropropagated on an orbital shaker in Murashige and Skoog liquid medium in a factorial combination of two sucrose concentrations (90 mM and 180 mM), two 6-benzylamino-purine (benzyladenine) concentrations (0.32 μM and 3.2 μM), at two densities (57 explants/L and 171 explants/L), in the presence (0.32 μM) and absence of α-cyclopyl-α-[4-mehtoxyphenyl]-5- pyrimididinmethanol (ancymidol). There were linear relationships between fresh weight and water use (R2 = 0.800, P < 0.0001), dry weight and sucrose use (R2 = 0.636, P < 0.0001), and relative dry weight (dry weight/fresh weight = relative dry weight) to concentration of sucrose residual in medium after culture (R2 = 0.553, P < 0.0001). Eighty-five percent of the water used and 74% of the sucrose used were incorporated as plant fresh weight and dry weight, respectively. A 1% increase in percent sucrose residual (mass/volume in spent medium) was correlated to an increase of 1.8% relative dry weight over the range 7% to 22% relative dry weight. In vessels with 90 mM initial sucrose, where the most growth had occurred (>15 g fresh weight), sucrose was depleted (<0.2% sucrose) and plantlets had the lowest relative dry weight (≈6.9%). In vessels from 180 mM initial sucrose, with similarly high fresh weight, plantlets had 12.0% relative dry weight with 2.1% sucrose residual in medium. Fresh weight, dry weight, or relative dry weight of plantlets in the laboratory did not correlate with subsequent survival or growth in the greenhouse. Plantlets grown without ancymidol at the lower benzyladenine concentration acclimatized to the greenhouse with 93% survival. However, greenhouse survival of plants grown with ancymidol and a higher level of benzyladenine was only 4%. 'Barbara Mitchell' was the largest plant in the laboratory, but often had poorest growth in the greenhouse. When optimizing a liquid micropropagation protocol for larger vessels, sucrose and water requirements may be directly related to targeted biomass yield, but each genotype needs to be handled independently with ex vitro validation of plant vigor.