Production of unreduced apomicts by diploidization of lines predisposed to reduced parthenogenesis --Tyrnov, VS, Smolkina, YV Maize lines, characterized by reduced pseudogamous parthenogenesis were produced (Tyrnov, MNL 71:73-74, 1997; Enaleeva, Tyrnov, 73-75). In these lines, we obtained haploids successively in 5-10 generations from kernels set on haploids. This was practically regular reproduction by haploid apomixis.This points to the principal possibility of production of unreduced apomicts. There is a probability, that this can be realized by the introduction of unreduction genes into parthenogenetical lines. But before starting work in this direction on a large scale, it was necessary to see if parthenogenesis manifests on a diploid level and how endosperm develops in that case. We checked this in a model system. We treated kernels and seedlings of the AT-3 line with colchicine to produce tetraploid plants. Colchicine-treated plants were pollinated by pollen of tetraploids, having genes a B Pl R or A B Pl R. The AT-3 line had gene A1, so all hybrid plants had a purple colour, and hybrid endosperm had a purple aleurone. Maternal diploids were green with white roots. By autonomous development, the endosperm must have a colour of maternal form.

1126 kernels were set on 42 colchicine-treated plants. Almost all of them appear larger than in the initial line AT-3. It has not been ascertained exactly if this is connected with polyploidy, heterozygosity or a small number of kernels on ears. Most of the kernels had purple colour. Only 8 yellow kernels were found. However, it is impossible for the present to confirm an apomictic origin. 1118 kernels were germinated on moist filter paper. Normal seedlings were developed from 423 kernels. 268 of them (63%) were diploids of the maternal type. Among the rest of the plants, 34 were abnormal in appearance. They did not produce ears. Weakly developed panicles did not form pollen. The rest of the plants were hybrid tetraploids. Part of the plants were analyzed in winter, another part in spring. Therefore, only 76 plants of the maternal type were grown in the field. Most of them were like plants of the initial line AT-3. However, 8 of them had some distinctions in height, form of panicle, and terms of blossom. It is possible that this could be a consequence of colchicine's mutagenic action. Part of the plants were self-pollinated, and another part pollinated by pollen of the embryo marker (ACR-nj:cudu, g11). More than 10% of haploids were discovered by kernel germination. Thus, this experiment allows the following conclusion: Parthenogenesis can manifest on diploid level as well as on a haploid level. Diploid apomicts, produced experimentally, do not lose the ability for reduced parthenogenesis. Hybrid endosperm is well-developed and is, probably, hexaploid. It is known that pollination of a tetraploid by reduced pollen gives a weakly-developed pentaploid endosperm. Defective endosperm is an extremely undesirable phenomenon. So, in further work, we plan to discover and use genes to provoke unreduction simultaneously in both female and male spheres. In line AT-3, the initial stages of endospermogenesis (some few nuclear divisions) can be realize without fertilization, but further development is blocked (Enaleeva, Tyrnov, MNL 71:74-75, 1997). Therefore, we plan work on intensification of the tendencies to autonomous endospermogenesis by selection, creation of optimal ploidy level, and overcoming the effect of imprinting.

This work was supported by a grant from the Russian Foundation for Basic Research (01-04-49385).
 
 

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