Studys On The Breeding Of Modified Single Cross Hybrid Of Indica Rice (Oryza Sativa L.)

The planting areas of indica hybrid rice was about 1.5×10⁷ hectares each year, occupied more than 50% of total areas of rice in China. The sterility of most indica rice CMS lines(A-lines) commercially used in China can be maintained by other maintainer lines(B-lines) except the Honglian type CMS-line. The male-sterile F₁ hybrids derived from the crosses between the A-lines and the other B-lines are named as binary CMS lines. In this paper, there are four types of binary CMS lines:(a) the binary CMS lines,in which two parents are distantly relationship are called non-sibling binary CMS lines,(b)and(c) the binary CMS lines which two parents are full sibling relationships or half sibling relationships are called full-sibling binary CMS lines and half-sibling binary CMS lines respectively,(d) if one of the two parents of the binary CMS lines was derived from the other one, these binary CMS lines are called backcross type binary CMS lines. The non-sibling binary CMS lines can be used as female parents to cross with rice restorer lines to produce three-way hybrids rice, and the other type binary CMS lines can be used to produce rice modified single-cross hybrids.The researches on three-way hybrid rice initiated in china in the late 1970s, and a consensus reached on this issue is that the three-way hybrid rice can be used to increase the yield of hybrid rice seeds production. Up to now, several combinations have been selected, but they were not put into practical use commercially. The main reason is the poor population uniformity of the three-way hybrids F₁ generation that was caused by the difference between the two parents of the binary CMS lines. The similar problem had been solved by selecting specific combinations especially using modified single-cross hybrids(MSHs) in maize breeding. The modified single-cross hybrid(A/A*//B) is a hybrid which was made by using a sister-line(A/A*) as female parent to cross with a inbred line(B), and the sister-line was produced from a cross between two highly related inbred lines(A and A*). It had been practical utilized in maize producing; however, there have been no any reports on the use of modified single-cross hybrids in rice breeding as yet.Just like in the maize breeding, in this study, three types' binary-CMS lines were made and three types rice MSHs were produced by using those binary-CMS lines to cross with the rice restorer lines; The male sterility, flowering habit, out crossing characters, heterosis and general combining ability(GCA) of all binary-CMS lines and the yields and the population uniformity of all MSHs were studied. The objectives of this study, for one thing, were to make an approach to the feasibility of the application of the MSHs in rice breeding, and for another, were to select high yield rice MSHs with good population uniformity to put into practical use commercially in rice producing.1. Three full-sibling binary CMS lines, 11 backcross binary CMS lines, 12 half-sibling binary CMS lines were made from 10 rice CMS lines and their maintainer lines, which have different sib ship. The male sterility, flowering habit, out crossing characters and some agronomic characters of all binary CMS lines and CMS lines and the heterosis of the corresponding F₁(B×B) were studied. The results were as follows:(1) All binary CMS lines were completely sterile and had no fertile seed. The percentage of stained pollen of binary CMS lines was similar to that of the corresponding parent CMS lines.(2) Majority of binary CMS lines were superior to the CMS lines in flowering habit, out crossing characters, and especially in double stigma exsertion rate.(3) There were distinct heterosis in plant height, flag-leaf length, flag-leaf width and panicle length in half-sibling binary CMS lines.(4) The results indicated that the grain weight per plant of the three types of F₁ of B×B crosses promoted with the increase of genetic difference between the parents of the corresponding binary CMS lines. 23 of 26 F₁ among B-lines were of yield superiorities to the elite parents, suggesting that the above three binary CMS lines could be used in increasing yield in rice hybrid seed production.2. Three full-sibling binary CMS lines, 11 back-cross binary CMS lines, 10 half-sibling binary CMS lines, 10 homozygous CMS lines and five restorer lines were chosen to make 50 single hybrids(SHs) and 120 modified single cross hybrids(MSHs) by the way of NCâ…¡design. The plots of F₁ were arranged in the field in a randomized complete block design with 2 replications and the combining ability of 7 characters were analyzed using random model. The results showed as follows:(1) The variance of general combining ability(GCA) and specific combining ability(SCA) were significant at 1% level in all characters.(2) The GCA of three types of MSHs and SHs were studied using analysis of variance of independent comparison of single degree of freedom in the grain weight per plant and the other yield traits. The result indicated that, three types of MSHs were higher than the SHs at 1% level in the grain weight per plant and the number of effective tillers per plant respectively, the back-cross binary CMS Lines and half-sibling binary CMS lines were higher than the SHs at 1% level in seed setting rate. There were no significant differences in other yield traits.(3) It suggested that the above three types of close-sibling binary CMS lines could be used increasing grain weight per plant, number of effective tillers per plant and seed setting rate in modified single cross hybrid rice breeding.3. The F₂ of B×B crosses and the three types of MSHs corresponding with the binary CMS lines were studied in the days from 10% to 80% plants heading in a plot(DPH), the days from the first plant heading to the latest plant heading in a plot(DFL), and the coefficient of variability of the plant height, flag-leaf length, flag-leaf width, number of effective tillers per plant, panicle length of main culms, days from sowing to initial heading(DIH). The correlation coefficients between the F₂ of B×B crosses and the three types of MSHs were investigated. The results showed that:(1) The mean values of the coefficient of variability of plant height of three types of MSHs were significantly higher than that of the single cross hybrids; there were no significant differences in that of other characters. The DPH, DFL, and the coefficient of variability of DIH have a tendency to increase from single cross hybrids, to full-sibling MSHs, backcross MSHs, and half-sibling MSHs. The mean population uniformity of some crosses in the full-sibling MSHs and backcross MSHs were close to the single cross hybrids.(2) There were highly significant positive correlations between the MSHs and the F₂ of the B×B crosses on the DFL, DPH, the coefficient of variability of DIH, plant height, and the correlation coefficients were 0.499,0.372,0.343 and 0.251 respectively. There were significant positive correlations on the coefficient of variability of flag-leaf width and panicle length of main culms, and the correlation coefficients were 0.226 and 0.196. The results indicated that the population uniformity of the three types of MSHs decreased with the increase of genetic difference between the parents of the corresponding binary CMS lines. It is necessary to reduce the genetic difference between the parents of the binary CMS lines in rice modified single cross hybrid breeding.(3) According to the population uniformity of there corresponding MSHs and the F₂ of the B×B crosses, the attention should be paid to the full-sibling binary CMS lines and the backcross binary CMS lines, especiallyâ…¡xie1A/â…¡xie2 B, JinxiehuangA/JinxieziB, Jin23A/JinxieziB, JinxiehuangA/Jin23B,â…¡-32A/â…¡xie1B,â…¡-32A/â…¡xie2B and XinxieziA/â…¡xie2B.4. Three full-sibling binary CMS lines, 11 back-cross binary CMS lines, 10 half-sibling binary CMS lines, 10 CMS lines and 5 restorer lines Nanhui 04, Minghui 86, Fuhui 838, Xianhui 207 and Milyang 46 were chosen to make 50 single cross hybrids(SHs) and 120 MSHs by the way of NCâ…¡design. The grain yields, DPH, DFL, and the coefficient of variability of DIH, plant height, flag-leaf length, flag-leaf width, number of effective tillers per plant and panicle length of main culms were studied respectively. The results showed that:(1) The grain yields of three types of MSH rice were higher than single cross hybrids on average. Among all MSHs, 74 of which had superiority to the two corresponding single cross hybrids in grain yield, including 9 full-sibling type MSHs, 37 back-cross type MSHs and 28 half-sibling type MSHs.(2) Some crosses of every types MSHs were similar to single hybrids in DBF, DFL, and the coefficient of variability of the plant height, flag-leaf length, flag-leaf width, number of effective tillers per plant, panicle length of main culms, days from sowing to initial heading.(3) A total of 10 good modified single cross hybrids were selected according to the grain yield and the population uniformity, and its grain yield increased from 10.43% to 26.39% compared with the corresponding higher single cross hybrids.5. 18 MSHs and 18 single cross hybrid, which were made from 9 binary CMS lines, 9 homozygous CMS lines and two restorer lines Nanhui 04, Milyang 46 were chosen. The characters investigated in this study include: chalky rice percentage(%), chalky area percentage(%), chalkiness degree(%), brown rice rate(%),milled rice rate(%),head rice rate(%), 1000-grain weight(g), grain length(mm), grain width(mm), length/width ratio, and the coefficient of variability of grain length, grain width, length/width ratio. The mean value of three types of MSHs and SHs were studied using analysis of variance of single degree of freedom in the appearance quality traits and milling quality traits.The results showed as follow:(1) The mean value of 1000-grain weight of the half-sibling type MSH was significantly higher than that of single cross and the backcross MSH at 0.01 levels. The mean value of the half-sibling type MSH and the full-sibling type MSH were significantly lower than that of single cross hybrid on the chalky rice percentage at 0.01 level, and the backcross type MSH was significantly lower than that of single cross hybrid at 0.01 level. The mean value of the half-sibling type MSH were significantly lower than that of the single cross hybrid and the other two types of MSHs at 0.05 level on the chalky area percentage,and significantly lower than the single cross hybrid and the backcross type MSH at 0.01 level on the chalkiness degree.(2)There were no significant difference between the three types of MSHs and single cross hybrids on the brown rice rate, milled rice rate, head rice rate, 1000-grain weight, grain length, grain width, length/width ratio. It suggested that there are no bad influence on the appearance quality and milling quality by using the modified single cross hybrid breeding method.(3) The mean and the range of coefficient of variability of the three types of MSHs were close to that of the single cross hybrid on grain length, grain width and length/width ratio.(4)The coefficient of variability of Xinxiehuang A/Xinxiezi B//Milyang 46 and Jin23A/JinxieziB//Nanhui04 were lower than there two corresponding single cross hybrids on the grain length, grain width and length/width ratio, and the coefficient of variability of another several MSHs were in the range of single cross hybrids on the three traits. The result indicated that the MSH with uniformity rice grain could be getting by selection.