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Abstract SUMMARY The present work was conducted in the Horticultural Department, Texas A&M University, Texas, USA through Channel System with Agricultural Botany Department, Genetics Branch, Faculty of Agriculture, Zagazig University, Banha Branch as an attempt to produce haploid onion plants (n) through anther and ovary culture techniques. Effects of some factors and their combinations and modifications were studied for haploid induction. The two onion genotypes used in this study were TGY1015 and 1025 were taken from Texas A&M University farm to find out their ability to produce haploid plants through androgenic and parthenogenic techniques using two types of media; MS medium (Murashige and Skoog, 1962) and B5 medium (Gamborg et al., 1968). Before culturing anthers or ovaries, they were exposed to cold temperature pretreatment at 4°C for different periods. Also, three sucrose concentrations were applied at different ages of cultured anthers and ovaries. a. Induction of Haploid Plants through Anther Culture in Onion (Allium cepa L.) The anthers of the two onion genotypes used in the present study did not respond to any factor, factor combination or modification. Accordingly, no haploid plantlets were obtained from onion anther culture technique. b. Induction of Haploid Plants through Ovary Culture in Onion (Allium cepa L.) During the first 2 to 3 weeks, most of onion cultured ovaries swelled and turned to dark brown, then died. Simultaneously, the rest of the onion cultured ovaries swelled at the base and turned into white. Eight to ten weeks later, ovary walls had split out and the plantlets started to emerge. 56 Eight to ten more weeks later, the emerging plantlets grew on a shootsuitable medium and increased in size, in spite of the remarkable low incidence of regeneration (about 0.43% haploid out of the actual initial number of the cultured onion ovaries). After four to five more months, haploid plantlets were transferred to a misttint over a sterile potting soil under the natural environmental conditions. Those expressed regular development concurrent with clear differences compared to the diploid ones (2n). Haploids were less in size and growth. Factors affecting in vitro ovary culture 1. Genotype The potential of the genotype 1025 was greater than that of 1015 in producing haploid plantlets through ovary culture technique under all other applied treatments. 2. Ovary age The highest average number of regenerated plantlets was achieved when onion ovaries were excised from flowers three to five days before anthesis. The minimum average number of regenerated plantlets occurred when the onion ovaries were excised six to ten days before anthesis. These results were recorded for both onion genotypes used in this study. 3. Temperature pretreatment The exposure of unpollinated onion ovaries to 4°C for four days as a cold temperature pretreatment proved to be the most favorable in production the highest number of regenerated plantlets, irrespeet of genotype and suaose application. 57 4. Media type Murashige and Skoog basal medium (MS) was better than that of Gamborg (B5) in increasing the response rate of the cultured onion ovaries for development into haploid plantlets. 5. Sucrose concentration Sucrose concentration of 10%, was significantly better than the 5% and 15% in increasing the average number of survivals of regenerated plantlets from cultured onion ovaries. 6. Interaction between sucrose concentration and genotype Irrespect of sucrose concentration, genotype 1025 produced significantly more rehenerated plantlets than did 1015. At 5% or 15% sucrose, no significant difference was recorded in the average number of survival regenerated plantlets derived from the cultured onion ovaries of the two genotypes used. 7. Interaction between sucrose concentration and ovary age At the level 10% sucrose, the highest number of the regenerated plantlets was obtained when the onion ovaries were excised three to five days before anthesis from genotypes 1015 and 1025. 8. Interaction between sucrose concentration and temperature pretreatment A significant increase in the average number of onion cultured ovaries which differentiated into plantlets occurred when the unfertilized ovaries were exposed to 4°C for 4 days as a temperature pretreatment in the presence of 10% suaose. Insignificant inaease in the response of the onion cultured ovaries to be differentiated into haploid plantlets was recorded because of the combination effect. Findings of the present study show that maximum haploid production from ovaries had been achieved with the genotype 1025, 10% sucrose, temperature pretreatment at 4°C for a period of four days, MS medium and ovary age of three to five days before anthesis. |