Effect of growth retardant chemicals on stock plant growth and subsequent rooting of verbenA (Verbena hybrida) cuttings

Verbena hybrida and its cultivars are some of the most popular bedding plants in the landscape and are in the best top ten of bedding plants in terms of annual sale and market acceptance. Like several bedding plants, Verbena hybrida may begin to stretch, developing thin, long and less branched stems after transplanting which forces growers to use some sort of growth retardation. Chemical growth retardation is the most commonly used method for commercial greenhouse production. Effects of chemical growth retardants may vary by location, species, and variety. Growth retardants are widely used in cutting producing farms in Ethiopia without any scientifically justified concentration levels. Consequently a two phase greenhouse experiment was conducted at Florensis Ethiopia plc situated at Koka from November 2009 to February 2010 with the objective of determining the growth response of stock plants and subsequent rooting of cuttings of Verbena hybrida cultivar Vegas Scarlet to individual and combined application of Cycocel and Alar. The experiment was laid down as 4x4 factorial experiment involving two different growth retardants as factor, with four different levels in a complete randomized design (CRD) with three replications. The two growth retardants used were Alar at concentrations of 0g L-1, 1g L-1, 2g L-1, and 3g L-1and, Cycocel at concentrations of 0ml L-1, 0.5ml L-1, 1ml L-1, and 1.5ml L-1. On stock plants it was vividly observed that interaction of Alar and Cycocel considerably affected most of the parameters except average leaf area, stem diameter and number of cuttings. Combination of 1ml L-1 CCC and 2g L-1 Alar significantly produced the maximum number of main branches (14.35). However, combined application of 1.5ml L-1 CCC and 3g L-1 Alar resulted in the minimum internode length (3.88cm), stem length (10.15cm), canopy diameter (48.44cm), root dry weight (12.39g), root fresh weight (72.86g), shoot fresh weight (196.74g), and shoot dry weight (35.81g). Conversely, maximum values for internode length (7.56cm), stem length (21.35cm), canopy diameter (60.33cm), shoot fresh weight (229.80g), and shoot dry (57.84g) were obtained from stock plants without any treatment. Application of 1ml L-1 CCC with 0g L-1 Alar resulted in the maximum root fresh weight (82.01g), whereas maximum root dry weight (16.17g) was obtained from application of 1.5ml L-1 CCC with 0g L-1 Alar. As the concentration of Cycocel increased from 0ml L-1 to 1.5ml L-1 average leaf area revealed a decline trend from 8.26 cm2 to 6.97 cm2 . The same trend has also been observed from Alar applications (8.16cm2 to 6.83cm2 ). Significantly maximum number of cuttings was achieved at a concentrations 1ml L-1 CCC (75.0) and 2g L-1 Alar (70.4). Regarding stem diameter, 1.5ml L-1 CCC and 3g L-1 Alar showed the maximum value (1.45mm and 1.40mm, respectively). The minimum stem diameter was obtained from 0ml L-1 CCC (1.27 mm) and 0g L-1 Alar (1.37mm). Significant persistent effect of the treatments on subsequent rooting was observed only on number of roots per cutting. Maximum number of roots per cutting (9.37) was recorded from cuttings collected from stock plants treated with the combination of 0.5ml L-1 CCC and 2g L-1 Alar. Whereas cuttings collected from non treated stock plants produced less number of roots per cuttings (7.80). Generally, the investigation verified the influence of Alar and Cycocel on growth of Verbena hybrida and cutting yield without causing a significant reduction on rooting performance of cuttings. Hence, application of 1ml-1L Cycocel, which demonstrated positive influence on cutting production, can be recommended for use by commercial growers. However, further researches are imperative regarding the economic aspects and other production factors like type of media used for rooting purpose, time and type of application of retardants to come up with pertinent and comprehensive recommendations.