Study On Germplasm Creation And Identification Of Apomixis Induced By Chemicals In Cassava

Apomixis can not only avoid the spread of complex pathogens in the process of crops vegetative propagation but also can be used to fix heterosis and preserve specific genotypes;and ovule unisexual apomixis(parthenogenesis)that occurrs in the embryo sac during meiosis is the main source of haploid or homozygous diploid materials.Cassava(Manihot esculenta crantz)is an important economic and energy crop in tropical regions of China,the research on apomixis has significant meaning in breeding and molecular biology for cassava production.The apomixis of cassava can be obtained through interspecific hybridization,but the frequency is very low(1%-2%).Chemical induction is an important way to obtain apomixis.In this study,three main kinds of chemicals includes DMSO,Col,Ory has been used to induce cassava female flowers during the four nuclear embryo sac to the mature embryo sac.Apomictic germplasms was obtained for the first time by the induction of chemicals.Its apomixis types and genetic characteristics of the germplasms were identified and analyzed by EST-SSR and SRAP molecular markers.The main results are as follows:1.Chemicals were used to induce apomixis on female flowers of cassava,then isolated with a bag,and a percentage of fertility rate and fruit rate can be obtain.The highest fertility rate was up to 72.66%;the highest fruit rate was up to 2.44%.Among the three chemicals,DMSO had the best effect.The fruit rate induced by DMSO reached a extremely significant level compared with Col and Ory,and the three apomictic offsprings were all induced by DMSO in this research.It can be seen that the pathways of using chemicals to induce apomixis in cassava is effective,but different chemicals had extremely different effects when induced apomixis of cassava.2.The effects inducted by DMSO showed that,under the same conditions,the fruit rate of apomixis induced by different concentrations in cassava had significant differences.In this study,the concentration of 1%,1.5%,2%DMSO has been used on the cassava female flowers to induce apomixis with the method of cotton dip for 6 hours,among them,the fruit rate induced by the concentration of 1.5%DMSO was the highest,up to 1.74%,which was extremely significant higher than that induced by the concentration of 1%and 2%DMSO.Therefore,using chemicals for appropriate concentration can improve the rate of apomixis in cassava.3.The induction rate of apomixis was different in different species of cassava.The induction rate was different when using chemicals to induce apomixis on different genotypes of cassava.The results showed that:When inducing apomixis of three varieties,SC5 had the best effect and the highest fruit rate of 2.44%by 1.5%DMSO.The induction rate of SC5 was significantly higher than that of SC 10 and SC8.The results indicated that the material of different genotypes lead to different frequency of apomixis in cassava.It is necessary to select different genotypic materials during the process of induction.4.This experiment obtained a total of 67 fruits,70 seeds,and 34 offsprings seedlings after sowing which induced by chemicals.All 34 offsprings seedlings were identified as diploid through the cytological identification and flow cytometry analysis and the haploid and polyploid were undetected.The co-dominant EST-SSR molecular markers were used to detect the homozygosity,the results showed that all 34 induced offsprings were heterozygous.Furthermore,the heterogeneous heterozygosity or homogenous heterozygosity of 34 offsprings seedlings was identified by SRAP molecular markers,it was found that three of them had homozygous heterozygosity with their parents,indicating that there were three cassava apomixis germplasms of apospory or double sporophyte type we have obtained,the induction rate of apomixis accounted for 8.82%of the induction of offsprings.