Study On Production Of Common Wheat Doubled Haploids Through Wheat×Maize Crosses

Doubled haploid (DH) system is a biotechnological tool which has been widely applied in wheat breeding programmes. The system is developed through haploid production, followed by chromosome doubling, to produce homozygous plants in a single generation. For self-pollinated common wheat, a process of genetic fixation for uniformity of agronomic traits after hybridisation is necessary to increase variation. In conventional breeding, six or seven generations are required to achieve homozygosity and genetic stability. This long process renders the system inconvenient, and there is need for an alternative process, which takes a shorter time span. If well utilised, DH would be a useful breeding tool for meeting this urgent need. Although haploid and doubled haploid wheat plants have been repeatedly produced successfully through wheat × maize crosses(embryo rescue system), there were some problems when used in wheat breeding program. In order to use wheat × maize crosses under Yangling conditions, some problem of wheat × maize crosses were study in Yangling from 2003 to 2005. The results are as follows:1. Sticky corn hybrid, sweet and sticky corn hybrid, sweet corn hybrid and common corn hybrid were seeded in four periods in room on January 27 to February 7. They were transplanted in garden shed on March 1 and corn pollen was obtained until the last twenty-day of April.2. Embryo production frequency was 6.73%, 8.35% and 6.61% when wheat spike was pollinated before disseminating pollen and treated twice with 2 , 4-D of 100mg/L> 200mg/L and 300mg/L after pollination. While embryo production frequency was 2.78%, 4.70% and 2.67% when spike was pollinated after disseminating pollen. The results showed that there was the highest embryo production frequency when wheat spike was treated with 2 , 4-D of 200 mg/L.3. Embryos of were cultured in the medium of l/2MS+0.1% IAA+0.1% 6-BAP+2% sucrose+7.5% agar(PH=5.8). The results showed that there was the best effect when embryos of 470～510μm were cultured and the frequency of seedling production was 59.1%～61.9%.4. Through analysis on 400～600nm embryos cultured in 8 mediums based on 1/2 MS, we could find that the average frequency of seedling production was 63.35% when seedlingwas cultured with PH=5.8 medium of 1/2MS, 0.2%(IAA), 0.2%(6BAP), 2% sucrose and 7.5% agar, far more than the frequency (28.6%~57.1%) of seedling production when embryos were cultured in the other 7 mediums.5. Chromosome doubling frequency was 83.2% and doubling treatment frequency was 68.8% when it was treated with 500mg/L colchicines and supplied with O2 continuously. While they respectively were 72.7%#1 62.2% without O26. Chromosome doubling frequency respectively were 51.7%% 83.2%* 84.1%^0 83.0% and doubling treatment frequency correspondingly were 46.2%> 68.8%> 71.2%fO 70.9% when it was treated with 250 mg/Lx 500 mg/L> 750 mg/L #1 1000 mg/L colchicines. The results showed that it was the best way when embryo were treated with 750 mg/L colchicines on condition of continuous supply of O2.