Avoiding the use of plant growth regulator in geranium production by application of a cyclic deficit irrigation strategy

Abstract: Plant growth regulators (PGRs) are commonly used in ornamental plant production to improve the decorative value of the plants and to meet marketable targets. The PGRs mostly used in ornamental plant culture are chemical growth retardants that control the size of plants, improve compactness and enhance flowering. However, the use of PGRs has been restricted under current legislation, and modified culture practices should be implemented to produce the desired quality of plants. Ornamental plant quality traits are determined by the genetic background of the plant and environmental conditions such as water availability. In the present study, the responses of growth and flower production in geranium (Pelargonium peltatum L.) subjected to cyclic deficit irrigation (CDI) were characterized to evaluate the technique as an alternative to the application of a plant growth regulator (daminozide). The leaf water potential of plants under CDI was lower than in control and PGR-treated plants. Moreover, the aerial dry mass, stem dry mass, leaf number, leaf blade area, specific leaf area and stem number of plants under CDI and PGR-treated plants were similar. However, the percentage of plants with at least one opened flower and the number of inflorescences per plant were increased by CDI. The marketable quality of the plants subjected to CDI was higher than that of the PGR-treated plants. Moreover, the water use efficiency of plants under CDI was 21% higher than that of PGR-treated plants, leading to a 10% reduction in the total water consumption during production.