Controlled Humidification of Sweet Potato Stem-Cuttings in a Self-Sustaining Humidifier: Effects on Vigour, and Implications for Climate Change

Predictions of extreme weather associated with global warming signify potential extremes in soil water content, and extremes of soil water tension are inimical to early plant growth. Periderm tissue [cork cells], being waterproof, restricts root and stem waterlogging whilst the promotion of early roots better prepare stem cuttings for survival in dry soils. Sweet potato stem cuttings were stored for up to six days in a chamber humidifier. Humidification was achieved by evaporation up to saturation vapour pressure [SVP] in a closed system of capillary water evaporating from a fabric which enclosed the cuttings. Treatments included vine cuttings stored (1) under grass clippings (traditional treatment) and (2) inside a high humidity (100%) chamber. Root growth occurred on 90% of the cuttings in the root length sequence- 9-, 28-, 47 mm after 3, 6 and 9 days respectively in the 100% humidity chamber at an average ambient room temperature of 25 oC. Under traditional treatments, root growth occurred on only 10% of the cuttings and was 0.5-, 2-, and 3 mm after 3, 6 and 9 days respectively. Traditional treatment did not exhibit observable periderm (cork cells) growth at any stage of the study. Periderm thicknesses of 3-, 7-, and 9mm occurred on days 3, 6, and 9 for samples held at 100% humidity. No periderm was observed for the traditionally treated samples. For field trials, the most vigorous growth in a dry soil was observed for cuttings previously subjected to chamber humidification, an important asset when early season weed competition is evident and when rapid ground cover is important. In a broader perspective, these results can be used to optimize studies of other crops grown from cuttings.