以栽培稻(Oryza sativa)品种L202二倍体(L202-2x)及其同源四倍体(L202-4x)作母本分别与药用野生稻(Oryza of ficinalis)杂交,比较了两个杂交组合的杂交结实性及影响结实性的杂种胚胎发育细胞学。两个杂交组合所取得的一致结果是:杂交授粉后30d所有杂交小穗均干枯死亡,不能结实;种间杂交不结实的原因在于受精和杂种胚胎胚乳发育异常。两个杂交组合的受精和杂种胚胎胚乳发育虽然均存在双受精、单受精和未受精类型,但就受精率而言,L202-2x作母本的平均总受精率为59.45%,略高于L202-4x(54.87%);L202-4x的单受精率(24.60%)则高于L202-2x的单受精率(15.30%)。两个杂交组合的杂种胚胎胚乳发育均严重异常,虽然在授粉后1d形成小的球形胚;到授粉后3d,胚胎发育停滞并开始解体;至授粉后5d,只有二倍体杂交组合的极少数胚胎可发育到梨形胚时期,四倍体组合的胚胎则基本全部解体。双受精胚囊内胚乳发育更为异常,在授粉后1d,游离胚乳核就开始解体退化,到授粉后3d不能形成细胞化胚乳或细胞化过程异常。与L202-2x作母本的杂交相比,以L202-4x作母本所得杂种胚胎发育更为滞后,且退化严重,形成的游离胚乳核少,解体早,不能进行细胞化。因此,利用同源四倍体栽培稻与药用野生稻杂交获得种间杂种的难度更大。
Oryza officinalis is one of the important wild species in the tertiary gene pool of Oryza sativa. It has a number of elite genes for rice breeding in resistance or tolerance. However, breeding barriers are so serious that the gene transfer is much difficult by sexual cross method between O. sativa and O. officinalis. Characteristics of the breeding barriers were systemically studied in this paper. When both the diploid (AA, 2n=2x=24) and autotetraploid (AAAA, 2n=4x=48) cultivated rice were crossed as maternal parents with O. officinalis (CC, 2n=2x=24), none F1 hybrid seeds were obtained. The young hybrid ovaries aborted at 13-16 d after pollinations (DAP). By rescuing hybrid embryos, in vitro F1 plantlets were obtained in 2x×2x combinations with the crossabilities lower than 0.5%. Lower rates of double-fertilization and abnormal development of hybrid embryo and endosperm were mainly observed in both combinations of 2x×2x and 4x×2x. Free endosperm nuclei in hybrid degenerated early at 1 DAP in a large scale. Almost no normal endosperm cells formed at 3 DAP. Development of a lot of embryos ceased at globularor pear-shaped stage as well as some degenerated gradually. The hybrid plantlets were both male and female sterility. Due to the abnormal development, a diversity of abnormal embryo sacs formed in hybrids, and hybrid pollen grains were typically abortive. It showed that conflicts of genome A and C in hybrid induced abnormal meioses of meiocytes.
FU Xue-lin LU Yong-gen LIU Xiang-dong LI Jin-quan ZHAO Xing-juan
