Artificial Alkalizing Drought Signals As Potential Growth Retardants.

 

Excessive growth is detrimental in crops by increasing lodging and disease, and reducing light penetration into the canopy. These effects lead to management problems and reduce yield and quality of produce. Synthetic growth retardants can be used to reduce these problems. In some crops, however, it is not common practice to apply growth retardants because either: there are no approved active substances; the retardants available are expensive; or application of synthetic active substances may not be permitted in the retailer produce specifications. There is thus scope for lower-cost growth retardants that are acceptable to retailers.

Basic research into the control of leaf growth has shown that, in some species, retardation of leaf growth during drought may result from an alkalizing signal moving from the roots to the leaves. Experiments with detached shoots of canola (oilseed rape; Brassica napus L.) and barley (Hordeum vulgare L.) have shown that both species respond to artificial alkaline xylem sap with reduced leaf expansion. Spray applications of alkaline pH buffers to intact plants of canola have, however, been variable in effects on leaf expansion. This may be a result of either, difficulty in penetrating the thick layer of epicuticular wax on canola, or efficient internal buffering. Application of either alkaline pH buffers, or of solid calcium carbonate (lime), to field-grown barley has, however, retarded canopy expansion for a short period.

These results, together with those from recent experiments on cilantro (coriander; Coriandrum sativum L.), indicate that the greatest commercial potential for alkalizing growth retardants may be with short duration crops, and possibly with crops that also do not have a thick layer of epicuticular wax.