To cite this paper: Tantasawat, P.A., A. Sorntip, O. Poolsawat, W. Chaowiset and P. Pornbungkerd, 2015. Evaluation of factors affecting embryo-like structure and callus formation in unpollinated ovary culture of cucumber (Cucumis sativus AbstractThe effects of various factors including genotypes of donor plants, induction and differentiation media, and thermal shock pretreatment were evaluated on embryo-like structure (ELS) and callus formation in an unpollinated ovary culture of cucumber. All five cucumber cultivars, which were used as donor plants, produced ELSs and calli, although their ELS and callus formation potentials varied significantly. The addition of 1 mg/L thidiazuron (TDZ) and 1 mg/L 6-benzylaminopurine (BA) into the induction medium resulted in the highest percentage of ELS formation, ranging from 42.3 to 91.4% with an average of 60.4%. However, the highest percentage of callus formation was observed in an induction medium containing 2 mg/L BA, 0.5 mg/L indole-3-acetic acid (IAA), 1 mg/L gibberellic acid (GA 3 ) and 32 mg/L putrescine (70.8%). By contrast, differentiation media had no significant effect on the formation potentials of both ELSs and calli. Thermal shock pretreatment reduced the percentage of ELS formation ca. 1.3-fold, but had no significant effect on callus formation. These results can be implicated for the efficient production of cucumber doubled haploids in the future.

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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Four culture media were evaluated for their ability to induce Phytophthora palmivora growth and produce culture filtrate (CF), and to determine a CF concentration and culture period effective for in vitro screening of black rot resistance in Dendrobium cv. ‘Earsakul’. Mycelial fresh weights of P. palmivora cultured in potato dextrose broth (PDB; the most commonly used medium for fungi), pea sucrose broth (PSB; a medium frequently used for Phytophthora spp.), and Murashige and Skoog broth (MSB; the most popular plant tissue culture medium) were found to be significantly higher than that in the newly developed modified oat meal broth (MOMB). When the total proteins of CFs were analysed with SDS-PAGE, a protein band of 10.5 kDa MW was found in CFs from all media with the highest level in PSB. LC-MS/MS analysis identified this protein as α-elicitin that had an identical amino acid sequence to the α-elicitin hibernalin of P. hibernalis and syringicin from P. syringae. The optimum conditions for in vitro selection of Dendrobium for black rot resistance using α-elicitin-containing CFs were also determined by evaluating the CF toxicity on Dendrobium protocorm-like bodies (PLBs) when cultured in all media supplemented with 0, 30, 50 and 100% CFs for seven, 14 and 21 d. The levels of PLB necrosis varied according to medium types, CF concentrations and culture periods. The maximum percentage of PLB necrosis (100%) was obtained in PSB supplemented with 50 and 100% CFs, and the severity of PLB necrosis was highest when treated with 100% CF for 14 and 21 d.

The effects of culture media on growth and proliferation of ‘Earsakul’ dendrobium (Dendrobium) protocorm-like bodies (PLBs) were evaluated in a two-step culture. After culturing on each of the four first step media for 4 months and on each of the four second step media for 4 months, the greatest total PLB fresh weight, increase in number of PLBs and growth rates were obtained when using Vacin and Went medium 1 (VW1) in both culture steps compared with those in 15 other medium combinations. Starting from 0.5 g of PLBs, culturing on VW1 for 8 months achieved a total of 415.25 g of PLBs, a multiplication rate of 830-fold. The supplementation of tomato (Solanum lycopersicum) and substitution of ‘Hom Thong’ banana [Musa acuminata (AAA group)] with ‘Khai’ banana [M. acuminata (AA group)] in this new medium promoted growth and proliferation of dendrobium PLBs 2.4-fold over the control medium, suggesting its usefulness in commercial micropropagation.