In Vitro Gynogenesis In Summer Squash (Cucurbita Pepo L.) And Plant Regeneration

Haploid breeding has advantages because of the high purity of doubled haploid plants. These plants are ture breeding for all the characters and the selection efficiency is greatly enhanced. It requires only single selection generation thereby improving breeding efficiency. Summer squash (Cucurbita pepo L.) is one of gourd vegetables , and now its planting area in vegetable protective planting takes second place to cucumber. Summer squash has obvious hybrid vigor. But it is very difficult to obtain its self-bred lines. Because the selection of self-bred lines needs long time and lots of work. Haploid breeding technique can provid a quick way to obtain a self-bred lines. In vitro culture of unpollinated ovules in plant is one of important haploid breeding technique , and the embryoid sac plants can be obtained rely on this method .There are many plant styles among the embryoid sac plants ,such as haploid , double haploid (DH), polyploid and aneuploid . These haploid and double haploid plants are the valuable source materials to select good self-bred lines. In addition , the plant regeneration system can also be used as the new acceptor system in genetic engineering . And the DH lines obtained by this technique are ideal lines to RFLP and the establation of the genetic map. This research studied five donator materials 1-SxG1,15xG1,15x23,20-3-9x17 and "shuang feng "(F1) and established an efficient , stable, and repeatbal system for summer squash embryod sac plants(R0) production via in vitro unpollinated ovules culture , investigated the factors affecting gynogenesis, established a technique which is simple , practical and has high survival rates for tansplanting of the regenerated plants. And then , depending on these results, the main agronomic characters of R0 and R1 (self-bred progeny of R0) were also studied. The main results were as follows: 1 An efficient, stable, and repeatbal system for summer squash plants regeneration system via in vitro unpollinated ovules culture for the first time. Three high inductivity medium were selected. This research gave an embryoid inductivity range of 9-30% relied on genotype and the in vitro culture conditions. 2 The embryological results indicated that the gynogenic plants regenerated from the embyoid. And the origin of the gynogenic embyoid was the egg apparatus which locating the micropyle end. 3 This study showed that there were many factors which significantly influenced the embryoid inductivities.These factors included the embryoid sac maturity when inoculated on the media, the media compositions, the genotypes and the planting seasons of the donator materials, the mode of light and the mode of inoculation ,etc. Among these main factors, the embryoid sac maturity, the media compositions and the donator genotypes had significantly interaction. And the results on embryoid sac maturity ×medium, embryoid sac maturity ×donator genotypes, donator genotypes ×medium, and embryoid sac maturity ×medium ×donator genotypes interaction were both higly significant. The order according to the effection of the main three factors was : the embryoid sac maturity when inoculated ﹥the media compositions ﹥the donator genotypes.The interaction order was embryoid sac maturity ×donator genotypes ﹥embryoid sac maturity ×medium ﹥donator genotypes ×medium ﹥embryoid sac maturity ×medium ×donator genotypes. The most materials showed that the ovules one day before anthesis and the same day anthesis had high inductivities. So, different donator materials need different medium and different embryoid sac maturity. 4 A lot of regenerated plants were obtained in this research. Several plant styles were found in these R0 plants.1/3 plants died in the course from test tube plantlet to transplanting into field. 2/3 plants survivled after transplanted, and had vigorous growth, and their femal flowers , male flowers and flowering were both normal. Most of these flowering plants could obtain self-bred seeds. But another ones had sterility. It is difficult to fructuate for them. Results from the sterile plant indicated that their pollen had lower vigour. Therefore, ovules culture can produce abundant variants and provid valuable source materials for summer squash breeding. 5 Genetic studies showed that the self -bred progeny R1 lines of the regenerated embryoid sac plants (R0) hadn't observed characters separation. The main agronomic characters displayed no differences. This result proved that the fertile R0 plants were pure diploid plants ,...