4. Management of Poppy (Papaver somniferum l.) Stand Height using Growth Regulators

Plant growth regulators (PGRs) are synthetic compounds used to reduce shoot length of plants. This is achieved primarily by diminishing cell elongation but also by decreasing cell division. In their effect on the morphological structure of plants, PGRs are antagonistic to gibberellins and auxins, the plant hormones primarily responsible for shoot elongation. The first synthetically derived PGR applied to wheat, chlormequat chloride (CCC), had been found to decrease height and increase stem diameter. With cereal crop varieties in the 1960s being predominantly tall in stature, subsequent studies focused on the ability of CCC to reduce lodging. Another PGR, ethephon, achieved similar results and was widely tested in cereals during the 1980s. With breeding of cereals reducing the tendency to lodge, subsequent studies largely focused on earlier application of PGRs to influence yield components in wheat and barley. More recently, with a trend towards earlier sowing dates and general adoption of complete crop management packages, in particular higher nitrogen and fungicide inputs, crop lodging has again become more problematic and the use of PGRs commonly beneficial. New PGRs, termed by Grossmann (1992) as the second (in particular triazoles) and third (acylcyclohexanedione) generation, are now applied to a number of agricultural and horticultural crops to reduce vegetative growth and potentially modify yield, its components, and quality. An array of other compounds with growth-regulating effects is used in cereals and oil crops. The most widely used preparations in oilseed rape are metconazole and tebuconazole, which are applied in autumn to improve overwintering and in spring to reduce stand height. Lovett and Campbell (1973) studied the effects of three growth regulators – paclobutrazol, mepiquat chloride, and CCC – on sunflower plant height, yield, and number of achenes in flower heads. Mepiquat chloride and paclobutrazol reduced plant height after application until maturity. The height reduction was very pronounced, ranging from 9.5% to 11.7% of the control and was due to shortening of internodes length. Supported by the Ministry of Agriculture of the Czech Republic, Projecct No. RO0211. studied the effects of foliar application of paclobutrazol, mepiquat chloride, and CCC in single or double applications on sunflower plant morphology, growth, achene yield, and oil content. They determined that paclobutrazol and mepiquat chloride under a single application scheme can reduce plant height in sunflowers without adverse effects on achene and oil yields, thereby providing a basis for reducing the risk of plant lodging. Spitzer et al. (2011) found similar results also in sunflower. Elkoca and Kantar (2006) investigated the effects of different doses of mepiquat chloride on growth, lodging control, seed yield, and yield parameters in pea (Pisum sativum L.) under field conditions in Turkey. Application rates of 25, 50, 75, and 100 g a.i./ha significantly reduced stem height, increased stem width, and thereby reduced the tendency of the crop to lodge. There is very little research on the possibilities of using PGRs in poppy. The only substance currently approved for use with poppy in the Czech Republic is metconazole, primarily used as a fungicide, however affecting plant growth, too.

III. HORTICULTURE