Effects of synthetic brassinolide on the yield of onion grown at two irrigation levels

• Synthetic brassinolide effectively increased the yield.
• Effective concentration is 1 nM.
• Onion cultivars differ in response to synthetic brassinolide

Field experiments were conducted in two seasons to investigate the influence of a synthetic brassinolide on the growth and yield of onion grown at two irrigation levels. The onion plants were treated with a synthetic brassinolide analogue (2α, 3α, 17β-trihydroxy-5α-androstan-6-one) at concentrations of 100 nM, 1 nM and 0.01 nM. These were sprayed to foliage of two long-day cultivars (cv. Lusy and cv. Alice). The height of the part aboveground and the diameter of the neck were measured in the plants. After harvesting, the marketable yield, parameters of the individual bulbs and the amount of dry matter and ascorbic acid were assessed. Under conditions with optimal irrigation the influence of the treatments with 1 nM and 0.01 nM synthetic brassinolide in the cultivar Alice was proven on the mass of the individual bulbs and yield in 2013. In the case of reduced irrigation, the treatment with a concentration of 1 nM had a statistically significant positive influence on the mass of the individual bulbs (2013) and yield (2012) in the cultivar Alice. With the cultivar Lusy, the treatments with a concentration of 1 nM and 0.01 nM significantly increased the marketable yield relative to the control variant in 2012.The results confirm that it was possible to reduce the negative impact of the water deficit in the cultivation of onions with synthetic brassinolide. It is, however, necessary to bear in mind which parameter of the plants should be affected and last but not least also the varying sensitivity of the cultivars to the treatment.