Correlations of the Characteristics of Photosynthates between Female Parent and F_1 Inter-subspecific Hybrids of Rice

The utilization of hybrid rice heterosis between subspecies is an important way to prove rice breeding programs, but the low matter conversion rate of inter- subspecific hybrids becomes the bottleneck to get high yield. To further explore the reasons for the low conversion rate of dry matters, and the coordination mechanism between biological yield＇s potential and grain yield＇s potential, we evaluated the correlations of the agronomic characters between the female parent and F1 inter subspecific hybrids, using a male parent R292, three female parents Y58S, Peiai 64S and 83S, and their hybrid combinations Y58S/292, 64S/292 and 83S/292 as experimental materials, Yueyou 9113 as the control. The results indicated that the contents of both soluble sugar and starch of all the experimental materials varied at different growth stages, and the highest starch content appeared at pre-ripening stage while soluble sugar content was the lowest. Notable positive correlations in a- gronomic characteristics were observed between the female parents and their F1 hybrids. The soluble sugar content in stem was the highest, followed by that in panicle, and the soluble sugar content in sheath and flag leaf was lower. The re- sults provide a theoretical basis for the research on heterosis and yield coordination mechanisms of inter-subspecific hybrids of rice.

Correlation and Regressive Model Between Spikelet Fertilized Rate and Temperature in Inter-Subspecific Hybrid Rice

To study the sensitivity of inter-subspecific hybrid rice to climatic conditions, the spikelet fertilized rate （SFR） of four types of rice including indica-japonica hybrid, intermediate hybrid, indica and japonica were analyzed during 2000-2004. The inter-subspecific hybrids showed lower SFR, and much higher fluctuation under various climatic conditions than indica and japonica rice, showing the inter-subspecific hybrids were sensitive to ecological conditions. Among 12 climatic factors, the key factor affecting rice SFR was temperature, with the most significant factor being the average temperature of the seven days around panicle flowering （T7）. A regressive equation of SFR-temperature by T7, and a comprehensive synthetic model by four important temperature indices were put forward. The optimum temperature for inter-subspecific hybrids was estimated to be 26.1-26.6℃, and lower limit of safe temperature to be 22.5-23.3℃ for panicle flowering, showing higher by averagely 0.5℃ and 1.7℃, respectively, to be compared with indica and japonica rice. This suggested that inter-subspecific hybrids require proper climatic conditions. During panicle flowering, the suitable daily average temperature was 23.3-29.0℃, with the fittest one at 26.1-26.6℃. For an application example, optimum heading season for inter-subspecific hybrids in key rice growing areas in China was as same as common pure lines, while inferior limit for safe date of heading was about a ten-day period earlier than those of common pure lines.

Effect of Temperature on Pollen Fertility in Inter-Subspecific Rice Hybrids

Seventeen rice varieties and hybrids of different types (indica, japonica, javanica, indica hybrid, japonica hybrid and inter-subspecific hybrid) were evaluated to determine the effect of temperature on pollen fertility in inter-subspecfic hybrids. The pollen fertility of inter-subspecific hybrids was greatly reduced when average daily temperature dropped to 22.0 - 23.0℃ at meiosis stage, and the extent of pollen fertility reduction varied greatly with respect to different hybrids. However, the pollen fertility reduction of indica and japonica hybrids and conventional varieties was not obvious under the same regime of temperature conditions. When the average daily temperature dropped to 20℃, the pollen development of conventional varieties and hybrids was also affected. Correlation analysis revealed that there existed a positive correlation between pollen fertility and average daily temperature. A significant difference (P<0.01) was also found between the two correlation coefficients i.e. inter-subspecific hybrids and conventional varieties. Temperature at meiosis stage of pollen mother cell was a key factor in pollen developing, and the pollen fertility of inter-subspecific hybrids was more sensitive to low temperature than that of traditional variety.

Comparative Embryological Studies on Infertility of Interspecific Hybridizations Between Oryza sativa with Different Ploidy Levels and O. officinalis

As maternal parents, diploid （L202-2x） and autotetraploid （L202-4x） of Oryza sativa cv. L2O2 were crossed with O. officinalis. Embryo development and fertilization in these two crosses were comparatively studied. There were no mature hybrid seeds obtained because all the hybridized spikelets died 30 days after pollination. The main reasons for no seed set were abnormal fertilization and development of the embryos and endosperms in the interspecific hybrids. There were doublefertilization, egg cell single-fertilization and non-fertilization in these crosses. Although 59.45% and 54.87% of hybrid embryos produced in the crosses of L202-2x/O. officinalis and L202-4x/O. officinalis, respectively, hybrid embryos ceased to develop or degenerated and plenty of free endosperm nuclei were in disaggregating state without developing cellular endosperms three days after pollination. Besides, some embryological differences in these two crosses were found, that is, the rate of double-fertilization and total rate of doubleand single-fertilization in L202-2x/O. officinalis were higher than those in L202-4x/O. officinalis. The embryo and endosperm of hybrids developed more slowly, and embryos and free endosperm nuclei were more severely degenerated in L202-4x/O. officinalis than in L202-2x/O. officinalis. Five days after pollination, a few of embryos in L202-2x/O. officinalis developed into pear-shaped ones, however, embryos in L202-4x/O. officinalis were all degenerated. Therefore, it is more difficult to obtain interspecific hybrids by wide crosses between autotetraploid of O. sativa and O. officinalis.

同源四倍体水稻亚种间杂种胚囊的结构及受精特点

利用激光扫描共聚焦显微术对11份同源四倍体水稻亚种间杂种的胚囊结构和双受精特点进行研究，结果表明，所有四倍体杂种均存在一定频率的败育胚囊，败育频率因组合而异，最高的败育率为23．8％，最低为5．5％，平均14．3％。败育胚囊主要有胚囊退化、异常小胚囊、无卵器、无雌性生殖单位和极核位置异常等5种类型。杂种在双受精过程中也存在一定频率的异常，包括胚囊结构正常但未能受精和受精停滞等，其中未能受精的频率为3．5％～11．9％。平均7．9％，受精停滞的频率为1．1％～6．2％，平均3．7％。另外，还存在低频率（平均4．7％）的胚乳发育受阻。认为部分胚囊败育和受精异常（包括未能受精和受精停滞）是导致同源四倍体水稻亚种间杂种结实率降低的主要原因。

不同倍性水稻亚种间杂种小孢子发生的细胞学观察

利用塑料半薄切片对水稻同源四倍体亚种间杂种F1及其对应的二倍体杂种F1小孢子母细胞减数分裂过程的细胞学变化进行观察研究。结果表明,同源四倍体水稻亚种间杂种造孢细胞期和小孢子母细胞期已经表现出较高频率的异常;减数分裂过程中,小孢子母细胞出现异常更加复杂,主要包括小孢子母细胞液泡化和退化两大类,这些异常是导致杂种花粉败育和花粉低育性的重要原因之一;此外,绒毡层异常也是导致杂种的花粉育性降低的因素。二倍体杂种小孢子母细胞在减数分裂过程的异常类型与水稻同源四倍体亚种间杂种基本相似,其绒毡层异常频率较低,对其花粉低育性影响不大。

同源四倍体水稻与非洲栽培稻杂交的后效性研究

利用亚洲栽培稻中的4份同源四倍体水稻(O.sativa,2n=4x=48)和相应的4份二倍体水稻(O.sativa,2n=2x=24)为母本,以4份非洲栽培稻(O.glaberrima,2n=2x=24)为花粉供体进行远缘杂交后,对其杂种后代的分离动态进行了研究。结果表明,不同倍性的普通栽培稻与非洲栽培稻之间杂交后代的结实率以二倍体普通栽培稻的较高。在配制的32个杂交组合中,其杂种第1代群体均表现出明显的营养生长优势。从群体的生长势来看,杂种第2代群体比杂种第1代群体要弱一些;在杂种第2代群体中,以同源四倍体水稻为母本的杂交组合的分离现象比以二倍体水稻为母本的杂交组合的分离现象更明显。在各杂交组合的第3代群体中,从植株的株叶形态和生育期来看,株系间的差异和株系内的变异依然很明显,变异频率更宽,变异种类更多。在普通栽培稻与非洲栽培稻的杂交组合中,育性变异、生长势变异、株叶形态变异、染色体变异和结实性变异等是较易发现的变异现象。

同源四倍体水稻与非洲栽培稻杂交的效果

以4份同源四倍体水稻(Oryzasativa,2n=4x=48)和4份二倍体水稻(Oryzasativa,2n=2x=24)为母本,以4份非洲栽培稻(Oryzaglaberrima,2n=2x=24)为父本进行远缘杂交配组,共配制32个杂交组合。研究结果表明,非洲栽培稻分别与亚洲栽培稻中的两种倍性水平的水稻品系进行杂交均表现出一定的可交配性,生殖隔离并不很严格。然而,不同倍性的亚洲栽培稻与非洲栽培稻杂交,其结实率表现出明显的差异。二倍体水稻与非洲栽培稻不容易杂交,其结实率比较低(0.32%～1.93%),而同源四倍体水稻与非洲栽培稻较容易杂交,其结实率比较高(1.22%～8.86%)。由此认为,利用同源四倍体水稻为母本与非洲栽培稻杂交更容易将后者的遗传物质引入亚洲栽培稻。

同源四倍体水稻与非洲栽培稻杂交的胚胎学观察

以同源四倍体水稻 (Oryzasativa ,2n =4x=48)和二倍体水稻 (Oryzasativa ,2n =2x =2 4)为母本 ,以非洲栽培稻 (Oryzaglarri,2n=2x =2 4)为父本进行远缘杂交配组 ,对其杂交结实的胚胎学机理进行了研究。结果表明 ,非洲栽培稻的花粉粒能在二倍体水稻的柱头上萌发 ,但萌发频率仅为 0 .18%～ 0 .5 6% ,花粉管在花柱内的伸长速度比较慢 ,发生受精的频率比较低 ,因而二倍体水稻与非洲栽培稻杂交的结实率比较低。然而 ,非洲栽培稻的花粉粒在同源四倍体水稻的柱头上萌发频率高达 12 .81%～ 14 .65 % ,花粉管在花柱内的伸长速度比较快 ,发生受精的频率比较高 ,因而同源四倍体水稻与非洲栽培稻杂交的结实率比较高。在同源四倍体水稻与非洲栽培稻的杂交中发现 ,其受精作用比较特殊 ,其中包括精细胞与卵细胞的单受精作用 ,精细胞与次生极核的单受精作用和正常的双受精作用 ,总受精率和总成胚率分别为 7.49%～ 9.2 8%和 6.61%～ 8.64 %。

同源四倍体籼粳亚种间杂种第2代的结实特性研究

以2个同源四倍体籼稻IR361（4）和11128（4）和2个同源四倍体粳稻[紫粳（4）和新稻10（4）]及其对应的二倍体水稻[即IR36（2），11128（2），紫粳（2）和新稻10（2）]为材料，研究了具有不同染色体组倍性（同源四倍体和二倍体）的籼粳亚种间杂种第2代群体在花粉育性和结实率上的差异。结果表明，在雄配子和雄配子体的发育过程中同源四倍体水稻籼粳亚种间杂种第2代群体表现正常，花粉育性变幅为90．01％-95．60％，结实率变幅为71．22％～95．78％；而二倍体水稻籼粳亚种间杂种第2代群体花粉育性差（9．60％～11．20％）．结实率低（0～19．45％）。