Sunflower morphology and yield as affected by foliar applications of plant growth regulators

Plant height of sunflower is a major agronomic trait affecting crop performance in the field and its adaptation to mechanical harvest. Field experiments were conducted to study the effect of foliar application of paclobutrazol (PBZ) at 12.5 g ai/ha, mepiquat chloride (MPC) at 25.0 g ai/ha and chlormequat chloride (CCC) at 1,500 g ai/ha in single or double applications on sunflower plant morphology, growth and achene yield and oil content. Single applications of PBZ or MPC reduced sunflower plant height at maturity by 11.1% and 11.7%, respectively. Single applications of PBZ, MPC or CCC did not reduce the above ground dry weight of the plants, provided similar achene yield per plant and 100-achenes weight compared with those of the non-treated control, whereas increased the total number of achenes as well as the number of filled achenes per capitulum. Double applications of PBZ, MPC or CCC reduced plant height by 13.9%, 15.6% and 13.4%, respectively, but proved in certain cases to have a phytotoxic effect on achene and oil production. Double application of PBZ resulted in lower achene and oil yield than the non-treated control, whereas double application of MPC resulted in lower above ground dry weight at maturity, achene yield and 100-achenes weight. Double application of CCC resulted in reduced 100-achenes weight. Overall, PBZ and MPC under the single dose scheme applied can reduce plant height in sunflower without adverse effects on achene and oil yields, thus providing a basis for reducing the risk of plant lodging.