A Preliminary Study On Embryonic Development And Embryo Culture Of Casava

Embryonic development and immature embryo culture of Cassava have been studied with Manihot esculenta crantz cv. South China5(SC5) and Manihot esculenta Crantz cv. South China7(SC7). The developmental processes of embryo, seed and fruit of cassava have been observed by means of paraffin section and anatomic observation. The culture conditions of young embryos in different developmental phases and the inducing methods of young embryos in the middle and late period are reseached in detail.The chief results from the study on the developmental processes of embryo, seed and fruit of Casava are presented as follows:(1) The dormant period of zygote of SC5is about10days. The embryo develops into multicellular proembryo, globular embryo, the early dicotyledonous embryo and complete embryo at12d,14d,19d,37d respectively. The division of fertilized polar nucleus is earlier than the zygote. On the3rd day, there are free nuclei of endosperm in the ovule of SC5. While on the12th day, few endosperm cells and free nuclei of endosperm are existing together in the ovule. Two pieces of thin cotyledons are packaged by thick endosperm when the seed becomes mature.(2) After fertilization, ovules and ovaries gradually expand, with increment of their lengths and weight. The increment scale of length is larger than the weight's in the early stage. There is no significant difference on the development of embryo, seed and fruit between SC5and SC7. The development rate of SC5is faster than SC7's. SC5has grown for105days and SC7for113days from blooming to complete maturing. The development of embryo, seed and fruit are positively correlated.A further study on the culture conditions of young embryos in different developmental phases and the inducing methods of young embryos has brought about the following results.(1) In the early period (5-15d), the material near the caruncle about1/3of the ovule's length carries the best effect for culture. The influence on immature embryo culture with different concentration of sucrose and NAA has been studied with SC5and SC7. The optimal culture medium is MS+0.5mg.L-1CuSO4+0.01mg.L-1NAA+0.5mg.L-16-BA+6%sucrose for the materials of5days and10days after pollination; however, the optimal culture medium becomes MS+0.5mg.L-1CuSO4+0.1mg.L-1NAA+0.5mg.L-16-BA+6%sucrose for the materials of15days after pollination. The culture of early young embryo is obviously influenced by embryo age and genetic type. Therefore, younger the embryo is, more difficult for it to be cultured. And it is much easier to culture the immature embryo culture of SC5than the immature embryo culture of SC7at the same stage. (2) The study on the immature embryo is carried out with SC5, aiming to probe the influence of different Concentration of coconut water and different proportion of MS on the culture of the immature embryo. In the medium of1/2MS+0.5mg.L-1CuSO4+0.5mg.L-16-BA+0.01mg.L-1NAA+3%sucrose+20.0%coconut water, the embryo development rate and seedling rate reach the highest level. At5d,10and15d after fertilization, the embryo development rates are10.53%,23.53%and26.32%respectively, and the seedling rates are10.53%,17.65%and26.32%respectively.(3) In the middle and late period (20-45d), the vivo embryo has been cultured. The influence on immature embryo culture with different concentration of sucrose and NAA is studied with SC5and SC7. In MS+.5mg.L-1CuSO4+0.01mg.L-1NAA+0.3mg.L-16-BA+3%sucrose, the effect tends to be most prominent. The germination and seedling rate of SC5could amount to100%on the35th day after pollination.(4) In the middle and late period, the vivo embryo has been cultured to obtain embryoid with SC5and SC7. A study is made on the influence of different Concentration of2,4-D and Picloram. The best Concentrations of2.4-D and of Picloram for embryoid induction are6mg.L-1and12mg.L-1respectively. The immature embryo of SC530days after pollination have the highest rate of88.00%of breeding embryoid in the culture medium MS+0.5mg.L-1CuSO4+12mg.L-1Picloram+3%sucrose. Then, by adding different Concentration of6-BA, the plantlet regeneration is further studied. In MS+0.5mg.L-1CuSO4+0.5mg.L-16-BA+3%sucrose, the seedling rate of the embryoid becomes highest, up to66.67%.