Visual Starch Stain Procedure Assists Cycad Propagation Decisions

Abstract

Stem cuttings are often exploited for asexual propagation of cycad plants, and impaired health of the source plants may reduce success. A reliable procedure that screens potential source plants for predicted success would benefit conservationists. The cut surfaces of Cycas revoluta stem cuttings obtained from source plants that had endured 0–39 weeks of Aulacaspis yasumatsui herbivory were stained with potassium triiodide to determine if this visual test could predict asexual propagation success. The stem cuttings were sorted into three groups based on stain intensity, then specific gravity and starch concentration of pith and cortex tissue were measured. The cuttings were maintained in a propagation nursery for 27 weeks, then root growth was quantified as dry weight. Specific gravity ranged from 1.01 to 1.11 and scaled linearly with starch concentration, which ranged from 16 to 195 mg·g−1. The group of cuttings with the darkest stain intensity exhibited 100% propagation success with 23 g of roots per cutting, and the group with the least stain intensity exhibited 30% success with 2 g of roots per cutting. The group of stems with intermediate stain intensity exhibited intermediate values of every metric. These results indicated that cycad cuttings may be stained with iodine to estimate starch content in the field to provide an accurate instantaneous visual test for selection of the source plants that reliably generate the greatest level of asexual propagation success.