The responses of virus-free and virus-infected lily ‘Enchantment’ to the retardants ancymidol, chlormequat chloride, mepiquat chloride and BTS 44 584, a ternary sulphonium carbamate

Abstract

The new growth retardants mepiquat chloride (a quaternary ammonium compound of the piperidinium type, coded BAS 083 00W) and a ternary sulphonium carbamate (coded BTS 44 584) were compared with ancymidol (A-Rest or Reducymol) and chlormequat chloride (Cycocel) for their ability to dwarf virus-free and virus-infected (ordinary) Mid-Century Hybrid lily cultivar ‘Enchantment’. Single compost drenches were given 3 weeks after transferring plants to the glasshouse. Compared with the virus-infected control plants, virus-free controls were 62% taller and 33% greater in leaf spread; floret number was approximately doubled and floret diameter was increased by 12%, but flowering was delayed by 6.5 days. The length of the lower stem bearing dead leaves was 15% of the total in virus-infected controls and 3% of the total in virus-free controls. Ancymidol, chlormequat chloride and mepiquat chloride were all effective growth retardants, and were without adverse side-effects. On a concentration basis, mepiquat chloride was 2–2.5 times as active as chlormequat chloride in reducing stem extension, but ancymidol was several orders of magnitude more active than both those compounds. With BTS 44 584, the maximum reduction in stem length obtained was 16% compared to controls. The decreases in stem extension were more pronounced, in both percentage and absolute terms, in the virus-free bulbs. Nevertheless, for a given retardant treatment, plants of the virus-free stock remained taller than those of the virus-infected stock. As a result, 2–3 times the amount of an active retardant was required by virus-free than by virus-infected plants in order to produce similar stem lengths at flowering. Effects of the retardants on the time of flowering, flower number, floret diameter and leaf spread were small, but increasing concentrations of all chemicals progressively increased the proportion of the stem bearing dead leaves. The effects of ancymidol, chlormequat chloride and mepiquat chloride persisted in the year after treatment.