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Piyada Alisha Tantasawat, Atitaya Sorntip, and Paniti Pornbungkerd

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 N6-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 I7 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 I7 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); N6-furfuryladenine (kinetin; KIN); thidiazuron (TDZ); 2,3,5-triiodobenzoic acid (TIBA).

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Anakkaorn Wannajindaporn, Chitpan Kativat, and Piyada Alisha Tantasawat

Dendrobium ‘Earsakul’ is an important commercial orchid in Thailand. Breeding new Dendrobium varieties for improved quality and yield is crucial. The objectives of this research were to perform in vitro mutagenesis of Dendrobium ‘Earsakul’ protocorm-like bodies (PLBs) using sodium azide (NaN3) and to select and evaluate the putative mutants using morphological characters, molecular markers, and the cytological method. The percentages of mortality of PLBs increased as concentrations of NaN3 increased. At 2 weeks, the lethal dose 30 (LD30) and LD50 were obtained with 0.1 and 0.5 mm NaN3, respectively. These two NaN3 concentrations were used for in vitro mutagenesis with reverse osmosis water (ROW; control 1) and 0 mm NaN3 (control 2) as controls. After the plants were cultured for 6 months, morphological differentiation was observed in some putative mutants: reduced height, higher numbers of nodes, reduced node length, shorter and thicker leaves, and shorter and fewer roots, compared with controls. When genetic profiles of 24 putative mutants were compared with controls, altered DNA profiles were found in 20 of 24 putative mutants (83.33%). Sixty-three polymorphic bands were produced from a total of 181 bands (34.81%) amplified by 10 polymorphic intersimple sequence repeat (ISSR) primers. When genetic diversity and relatedness, which were evaluated by ISSR analysis, and morphological characters were compared, the two markers were found to be uncorrelated. ISSR had a higher mutant differentiation capability than the morphological characters, indicating its higher efficiency. The chromosome numbers were similar in putative mutants and controls (2n = 2x = 24), suggesting that neither of the concentrations of NaN3 had any effect on the chromosome numbers in this experiment. These results indicate that NaN3 can be used effectively to mutagenize Dendrobium ‘Earsakul’ PLBs, and ISSR is a powerful tool for the identification of mutants. Chemical name: sodium azide (NaN3); reverse osmosis water (ROW).