Effects of Exogenous Application of Plant Growth Regulators on Growth, Yield, and In Vitro Gynogenesis in Cucumber

The effects of exogenous application of plant growth regulators (PGRs) were evaluated on both field performance and in vitro gynogenesis of 'Chai Lai' and 'Big C' cucumber (Cucumis sativus L.). Plants were sprayed with two concentrations of N-6-furfuryladenine [kinetin (KIN); 2 and 20 ppm], 2,3,5-triiodobenzoic acid (TIBA; 1 and 10 ppm), naphthaleneacetic acid (NAA; 10 and 100 ppm), abscisic acid (ABA; 2 and 20 ppm), thidiazuron (TDZ; 1 and 10 ppm), and maleic hydrazide (MH; 10 and 100 ppm) to assess their effects on vegetative growth and floral and yield related traits in the Winter of 2013 and in the Summer of 2014 compared with distilled water control. Meanwhile, the effects of two PGRs (KIN and TIBA) on cucumber gynogenesis were also investigated in vitro. Growth parameters and floral and yield-related traits were significantly affected by the various PGRs in both cultivars during both seasons. In both cultivars, the highest yield was obtained with the application of 10 ppm NAA during the Winter of 2013 (1.5- to 1.8-fold over control) and with 1 ppm TIBA during the Summer of 2014 (2.1- to 2.2-fold over control). With regard to the ovary culture response, exogenous application of KIN and TIBA on floral buds tended to enhance callus formation in 'Chai Lai' cultured on 17 medium, whereas no effect was observed in 'Big C'. The embryo-like structure (ELS) formation efficiencies also tended to increase with 2 and 20 ppm KIN and 1 ppm TIBA application in 'Chai Lai' and with 20 ppm KIN and 1 ppm TIBA application in 'Big C' when cultured on 17 medium. Nevertheless, TIBA at high concentrations (10 ppm) decreased the percentages of ELS formation and the number of ELSs/piece in both cultivars. These results suggest that the polar auxin transport may play a major role on growth, floral and yield-related traits, yield as well as in vitro gynogenesis in cucumber. However, the success of exogenous applications of these PGRs depended on several factors including plant genotypes, growing seasons, types and concentrations of PGRs, and for ovary culture, the responses also varied according to the induction media used. Chemical names: abscisic acid (ABA); maleic hydrazide (Mh); naphthaleneacetic acid (NAA); N-6-furfuryladenine (kinetin; KIN); thidiazuron (TDZ); 2,3,5-triiodobenzoic acid (TIBA).