二十一世纪水稻育种新战略Ⅱ.利用远缘杂交和多倍体双重优势进行超级稻育种

A New Strategy of Rice Breeding in the 21st Century Ⅱ. Searching a New Pathway of Rice Breeding by Utilization of Double Heterosis of Wide Cross and Polyploidization

本文论述了远缘杂交和多倍体化结合利用基因组间和多倍体杂种优势，开创水稻育种新途 径的策略。纵观水稻育种的历史，无论是常规杂交育种，还是杂交稻育种，其研究战略都是建立在有 性生殖和二倍体基础上的，归根结底，都是利用栽培稻同一基因组（Ａ基因组）内优良基因的重组以及 从野生稻向栽培稻引入少数优良基因。从作物进化趋势看，水稻是二倍体，基因组小、ＤＮＡ含量低、 染色体小，增加基因组数，提高倍性水平，利用异源多倍体杂种优势将是水稻育种新途径。针对同源 四倍体水稻结实率低的关键问题，可采取拉大亲缘关系距离、减少多价体形成，应用广亲和、无融合 生殖基因等措施，从遗传机理上提高多倍体水稻结实率。按三步实施战略；一、选用极端类型籼粳稻、 爪哇稻，诱导亚种间杂种多倍体；二、诱导亚洲栽培稻和非洲栽培稻以及非洲野生稻种间杂种多倍体； 三、诱导 ＡＡ基因组的栽培稻与其它不同基因组野生稻（ＢＢ、 ＣＣ、 ＢＢＣＣ、 ＣＣＤＤ、 ＤＤ、 ＥＥ、 ＦＦ、 ＧＧ、 ＨＨＪＪ）的种间多倍体。在实施过程中发挥一些特殊基因材料的特殊作用，如广亲和基因对于克服籼便 杂种一代不育性、特别是雌败育的作用，无融合生殖缺乏减数分裂发生和受精过程对于克服染色体配

This is the second one of a series of papers about the new strategies of rice breeding in the 21st century. It is suggested that the tactics of new pathway of rice breeding by utilization of wide cross and polyploidization, i. e using heterosis of intergenomes and polyploid and the role of some special genes. Making a general survey of the history of rice breeding, their research strategies were based on sexual reproduction and diploid, in general, all used the combination of superior genes of cultivated and wild rice in the same genome (AA). Reviewing on the tendance of crop evolution, rice is a diploid with smaller genome, DNA content and chromosome size. Increasing the number of its genomes, getting up its ploidy level, using heterosis of allopolyploid will be a new pathway of rice breeding. To counter the key problem of low percentage of filled seeds in autotetraploid , such measures can be used to raise seed fertility by genetic principle, as enlarging their relative distance of parentages, reducing the formation of polyvalent chromosome and utilizing apomixis, wide compatibility and Ph genes. There are three steps to realize the strategy. First, selecting terminal type of Orysa sativa ssp indica, japonica and javanica involved American cultivars cross each other to induce intersubspecific polyploid. Second, inducing O. sativa, O. glaberrima and O. barthii to form interspecific polyploid. Third, inducing cultivated rice with AA genome and wild rice with different genomes in other 8 genomes from B to J to form interspecific allopolyploid. Some germplasms with special genes such as wide compatibility, apomixis and Ph genes will be taken part of important role in the cross. Wide compatibility will be useful to overcome male sterility and female abortion of F1 of intersubspecies. The characteristic of apomixis without meiosis and fertilization will be helpful to avoid segregation of progeny because of chromosome pairing. And Ph gene as in wheat with impression of the pairing o f partial homologeous chromosomes, can be used to prevent the pairing of partial homologeous chromosomes in intergenomes of allopolyploid and formation of multivalent, chromosomal bridge, lag chromosome. These will ensure for their progenies with high rate of seed set and good stability in utilization of selecting allopolyploid rice and apomictic rice. Recent progress in this experiment have provided a good results. Using apomictic lines as a parent to cross with O. satva ssp indica and japonica and cross between O. sativa ssp Asian and American cultivars had obtained some superier polyploid plant lines with powerful heterosis and high up to 85 % seed set. It has provided a very good background to realize the new breeding strategy.