Interaction Of Sterility Genes In Indic Rice CMS And TGMS And Sterile Stability Of The Two Types Of Male Sterile Lines

Hybrid rice technology is the most feasible and effective way of increasing the rice yield to meet the increasing populations in the world, especially in the developing countries in Asia. At present, hybrid rice occupies about 50% of the total rice field area but 58% of the total rice yield in China. It is well known that there are two genetically different types of hybrid rice breeding systems, which were termed as three-system and two-system. The use of cytoplasmic male sterility, namely three-system hybrid rice, which need cytoplasmic male sterile line(CMS-line), corresponding maintainer-line(B-line) and restorer-line(R-line), has been considered contribute great to the development of hybrid rice. And hybrid rice of the three-system is still planted in about 90% of the cultivated area of hybrid rice in China. But, the use of photo-thermo-sensitive genic male sterility(P/TGMS), namely two-system hybrid rice, in the development of rice hybrids, is an alternative to three-system.But comparison of heterosis of three-system hybrids and two-system hybrids has been regarded as one of the most different breeding programs and then, the sterile stability of CMS-lines and TGMS-lines in commercial hybrid seed. Exploitation of interaction of sterility genes in CMS-line and TGMS-line and difference of combining ability between CMS-line and TGMS-line may enable a better understanding of utilization of heterosis of three-system and two-system hybrid rice. On the other hand, studying on sterile stability of CMS-and TGMS-lines for increase of seed purity is important in commercial hybrid seed production. In this paper, the interaction of sterility genes in CMS-line and TGMS-line and sterile stability of the two types of male sterile lines were performed. The results were as follows.1 In order to evaluate the characters, inheritance and combining ability of 6311S, a new TGMS-line derived from Nongken 58S, the changes of fertile pollen and seed set of TGMS-line 6311S was investigated under controlled and natural temperature in Changsha, Hunan province, in Nanjing, Jiangsu province and in Lingshui, Hainan province. And then, the agronomic characters of the TGMS-line 6311S were investigated under eco-environments of different sowing dates in Nanjing. In order to study the allelic sterile gene, a half-diallel cross of three TGMS-lines, 6311S, Pei'ai 64S derived from Nongken 58S and 360S derived from Anxiang S-1 was conducted. The combining ability of 6311S and CK Pei'ai 64S was studied by using 7 restoring lines to pollinate 6311S and Pei'ai 64S. The results were as follows.1) 6311S, which is sterile when temperature is 23℃, during 4d after panicle initiation and fertile when temperature is 23℃, during 8 to 22d after panicle initiation, is a TGMS-line.2) Applying 6311S to cross restoring-lines and maintaining-lines to get F₂ and BC₁F₁ plants, the F₂ descendants from the F₁s segregated in the ratio of 3 fertile plants to one TGMS-plant and the progenies in BC₁F₁ populations segregated in the ratio of one fertile plants to one sterile plant, suggesting that the TGMS-trait of 6311S be governed by a single recessive gene.3) The F₁ plants of Pei'ai 64S×6311S, 6311S×Pei'ai 64S, Pei'ai 64S×360S and 360S×Pei'ai 64S were fertile under high temperature but the F₁ plants of 360S×6311S and 6311S×360S were sterile under high temperature and fertile under low temperature after panicle initiation, demonstrating that there be a single allelic sterile gene between 6311S and 360S but there be not any allelic sterile gene between 6311S(360S) and Pei'ai 64S.4) Using 7 restoring-lines to cross 6311S and CK Pei'ai 64S, the combining ability of 6311S and Pei'ai 64S was studied. The results showed that the yield per plant of 7 F₁s between 6311S×Restoring-lines was 34.94g, over the 7 CK F₁s by 13.3%, indicating that 6311S is a elite TGMS-line in development of hybrid rice.2 Gene-interaction is important in studying the genetic model of the sterile character. Fertility of generations of 51 F₁, 19 F₂ and 6 BC₁F₁ between Pei'ai 64S, 6311S and 360S, 3 TGMS-lines and three-lines including 7 indica CMS-lines, B-lines and 3 indica R-lines were investigated to study fertility expression of TGMS-genes in the backgrounds of the three-lines. The results confirmed that:1) The TGMS trait of Pei'ai 64S was governed by 2 pairs of independent recessive genes and Pei'ai 64S had stronger restoring fertility(Rf) genes for WA-CMS lines. The TGMS trait of 6311S was governed by a single recessive gene and 631S had weaker Rf-gene for WA-CMS lines. The TGMS trait of 360S was governed by a single recessive gene and 360S had no Rf-gene for WA-CMS lines.2) The F₂ generations from F₁ plants between CMS-lines and Pei'ai 64S and between CMS-lines and 6311S segregated in the ratio of 7.3～9.4 fertile plants to one sterile plant and in the ratio of 1.2～1.4 fertile plants to one sterile plant, respectively, but Xinxie A was continuously backcrossed to be sterile with TGMS 360S as a pollen donor, suggesting that inheritance of the TGMS-trait in the background of WA-CMS lines was significantly distinct from that of the TGMS-trait in the background of B-lines or R-lines. After studying on the fertility of F₁ plants between 5 CMS-lines and 4 F₃ generations with TGMS-gene selected from F₂ plants of 4 CMS-lines×6311S, we confirmed that the fertility expression of TGMS-gene was controlled by Rf-gene in the background of WA-CMS, but not affected by Rf-gene in the background of normal cytoplasm of fertility.3) The changes of pollen fertility of new TGMS-lines in WA-CMS background derived from CMS×6311S were investigated in Lingshui, Hainan and in Nanjing, Jiangsu. The preliminary results indicated that WA-cytoplasm could result in decreasing critical sterility inducing temperature of TGMS lines. Finally, the potential breeding strategies of TGMS-lines in the background of WA-CMS and WA-CMS lines with the nucleus of TGMS-genes were discussed.3 Honglian-CMS(HL-CMS), which is distinct from WA-CMS, is a gametophyte type. Pollinating HL-CMS Yuetai A and Yuetai B with 3 TGMS-lines, Pei'ai 64S, 6311S and 360S, fertility of generations of 6 F₁, 6 F₂ and CK(Yuetai A×R-lines) was investigated in order to study fertility expression of TGMS-genes in the backgrounds of the three-lines of HL-CMS system. The results were as follows.1) The pollen fertility and seed setting rate of the CK F₁s were 48.1% and 86.1%, respectively and the seed setting rate of F₂ plants was about 85%. The fertile pollen and seed setting ratio of the F₁s between Yuetai B×TGMS-lines were 88.1% and 86.1%, respectively, but the fertile pollen and seed setting rate of the F₁s between Yuetai A×TGMS-lines were 48.8% and 88.1%, respectively, showing that 3 TGMS-lines could be restored to be fertile by Yuetai B and had Rf-gene for HL-CMS Yuetai A.2) The F₂ descendants from the F₁s of Yuetai A×Pei'ai 64S segregated in the ratio of 15 fertile plants to one TGMS-plant and the progenies in F₂ populations of Yuetai A×6311S and Yuetai A×360S segregated in the ratio of 3 fertile plants to one sterile. Those results were similar to those of the F₂s between Yuetai B(or R-line)×TGMS-lines, demonstrating that fertility expression of TGMS-gene in HL-cytoplasmic background was controlled by Rf-geae for HL-CMS.4 In order to study the difference of combining ability between TGMS and CMS in similar genetic background, TGMS-line and it's NILs of CMS-line are developed. By backcrossing progeny without Rf-gene selected from F₂ population of Xinxiehuang B/6311S with recurrent parent'6311S' for 4 generations, we developed NIL 6311B of 6311S, which not only have the same genetic background, agronomic traits but maintain sterility of CMS-lines because of no Rf-gene. Furthermore, a new CMS-line'6311A' was developed by using 6311B as B-line to continuously backcross the CMS-line'Xieqingzao A' for 5 generations. At the same time, we developed NIL Pei'ai 64B of TGMS-line Pei'ai 64S and the CMS-line Pei'ai 64A by using the above method. Then, an incomplete diallel cross was conducted to study the combining ability of TGMS-lines and their NILs. 2 TGMS-lines(Pei'ai 64S and 6311S) and their NILs(Pei'ai 64A and 6311A) and 6 restorers used in hybrid rice production were used as parents. 24 combinations(4×6) were hand-pollinated in Lingshui, Hainan. The plots of F₁s were arranged in the field in a randomized complete block design with two replications in Nanjing. 8 agronomic characters were investigated. Research results were as follows.1) In 7 agronomic characters(plant height, days from sowing to heading, length of flag-leaf, length of panicle, length of enclosed panicle, spickelets per panicle and seed set), TGMS-lines were similar to their NILs but were distinct from their NILs in two characters of length of stigma and fertile pollen.2) The combining ability of yield and the other agronomic characters of Pei'ai 64S and it's NIL Pei'ai 64A was remarkably different from that of 6311S and it's NIL 6311A But the combining ability of yield and the other agronomic characters of TGMS-lines was similar to that of their NILs, suggesting that TGMS-lines and their NILs had the same combining ability. Obviously, yield and the other agronomic characters of a hybrid rice combination was influenced by its parents and gene-interaction between parents but not controlled by three-system or two-system hybrid rice.5 Sterile stability of CMS-lines and TGMS-lines is important in commercial hybrid rice seed production. With 7 representative indica rice male sterile lines in the Yangtze valley of China as materials, ecotypes and sterile stability of 5 CMS-lines and 2 TGMS-lines were studied under eco-environments of different sowing dates at Nanjing. The results were as follows.1) The 7 indica rice male sterile Lines were divided into early indica and middle indica eco-type. Eco-environment and genotype of varieties had a significant effect on panicle and spikelet number per plant of different rice male sterile lines and the effect of environment was stronger than that of variety. The middle indica male sterile lines had high spikelet number per plant, especially under eco-environment of the 1-2 sowing dates, as compared with the early indica ones. The variance of exertion stigma rate including single-and double-exertion rate was mainly due to variety and partly resulted from the interaction between variety and environment. Middle indica male sterile lines had higher and more constant exertion stigma rate than early indica ones, especially in the first sowing date for cytoplasmic male sterile(CMS) lines but in the third sowing date for themo-sensitive genic male sterile(TGMS) lines, respectively.2) Sterility of CMS-lines was stable under different eco-environment and sterility of TGMS-lines was stable under eco-environment of early-sowing but instable under eco-environment of lately-sowing.6 Yuetai A, which is an elite HL-CMS-line in the development of hybrid rice, has been demonstrated to have great potential for hybrid rice production. But the deterioration of HL-CMS Yuetai A and its' hybrids is serious. For this reason, samples of Yuetai A and Yuetai B were investigated to assess the seed purity and to analyze the cause of sterile un-stability of Yuetai A by imitating the biological contaminant to Yuetai A in Nanjing, Jiangsu and Lingshui, Hainan in 2004-2006. The results were as follows.Seed impurity of Yuetai A resulted mainly from genetic drift of restoring-gene(Rf-gene) after biological contaminant. All of maintaining lines, restoring lines and thermo-sensitive genic male sterile(TGMS-) lines used in this study could pollinate Yuetai A and Yuetai B to produce F₁ plants, resulting directly or indirectly in Rf-gene into Yuetai A and"iso-cytoplasm restoring-generations". Furthermore, Yuetai A's easily outcrossing and simultaneous heading with many varieties used in rice production were major factors to easily result in biological contaminant. After picking out all plants with Rf-gene mixed in Yuetai A and preventing Rf-gene drifting into Yuetai A, seed purity of Yuetai A and Yuetai B has been raised to 100%.After studying on the sterility of Yuetai A, we confirmed that the sterility of Yuetai A was stable under different eco-environment in Nanjing and Lingshui.