Zheng-jin Xu

Genetical and Physiological Basis of Plant Type Model of Erect and Large Panicle Japonica Super Rice in Northern China

The historical changes in rice yields across China were explored. The physiological mechanisms and genetic basis of the erect and large panicle super-high-yield plant type model for breeding japonica super rice were analyzed mainly on the panicle type, number of large vascular bundles (LVB) in the panicle neck, and the panicle type index (PTI). In the production point of view, we suggested that, for the breeding of super-high-yield japonica rice, the erect panicle types with more LVB numbers in the panicle neck and superior upper grains in the secondary branches would be the key factors. The information has potential significance in the rice breeding and productivity not only in China but also throughout the rice production areas of the world.

Development of a highly informative microsatellite (SSR) marker framework for rice (Oryza sativa L.) genotyping.

Abstract To select highly informative microsatellite markers (SSRs) and establish a useful genetic SSR framework for rice genotyping, 15 rice (Oryza sativa L.) cultivars including six indica varieties and nine japonica varieties were used to analyze the polymorphism information content (PIC) value of 489 SSR markers. A total of 1 296 alleles were detected by 405 polymorphic markers with an average of 3.2 per locus. The PIC value of each chromosome was ranged from 0.4039 (chromosome 2) to 0.5840 (chromosome 11). Among the two rice subspecies, indica (0.3685-0.4952) gave a higher PIC value than japonica (0.1326-0.3164) and displayed a higher genetic diversity. Genetic diversity of indica was high on chromosome 12 (0.4952) and low on chromosome 8 (0.3685), while that for japonica was high on chromosome 11 (0.3164) and low on chromosome 2 (0.1326). A SSR framework including 141 highly informative markers for genotyping was selected from 199 SSR markers (PIC > 0.50). Ninety-three SSR markers distributed on 12 chromosomes were found to be related to indica-japonica differentiation. Of these 93 pairs of SSR primers, 17 pairs were considered as core primers (all the japonica varieties have the same specific alleles, while the indica varieties have another specific alleles), 48 pairs as the second classic primers (all the japonica or indica varieties have the same specific alleles, while the indica or japanica varieties have two or more other specific alleles) and 28 pairs as the third classic primers (all the japonica and indica varieties have two or more alleles, but the specific alleles are different between japonica and indica). Thirty-two SSR markers were selected to be highly informative and useful for genetic diversity analysis of japonica varieties. This work provides a lot of useful information of SSR markers for rice breeding programs, especially for genotyping, diversity analysis and genetic mapping.

Distribution of Rice Grains on Panicle Axis and Its Relationship with Seed-Setting Ability in Liaoning, China

Abstract Studies were conducted with rice varieties developed in recent years in Liaoning Province of China as test materials. Results showed that the varieties tested could be divided into three types: (1) the high-yielding (HYV), (2) the medium-yielding (MYV), and (3) the low-yielding (LYV). The panicle population was in the order of HYV

Comparison Between QTLs for Chlorophyll Content and Genes Controlling Chlorophyll Biosynthesis and Degradation in Japonica Rice

Abstract The objectives of this study were to understand the expression patterns of chlorophyll content-related genes at different growth stages of rice ( Oryza sativa L.) and to disclose the genetic mechanism of stay-green at later stage. Quantitative trait loci (QTLs) controlling chlorophyll content at tillering, heading, and maturity stages were located using 126 recombinant inbred lines (RILs) derived from a cross between 2 japonica rice cultivars, Shennong 265 and Lijiang Xintuanheigu. A total of 22 QTLs for chlorophyll content were identified, of which 5 loci were expressed at tillering stage, 7 at heading stage, and 10 at maturity stage. These QTLs were located on all the rice chromosomes except chromosome 5. According to the comparison between the locations of these QTLs and genes underlying the key enzymes of chlorophyll biosynthesis and degradation, relatively rich QTLs for chlorophyll biosynthesis and degradation at earlier stage were located in the regions harboring the loci for chlorophyll content. With the process of plant growth, more QTLs were detected but only a few of them were involved in chlorophyll biosynthesis and degradation. These results suggest that the expression levels of most genes/QTLs for chlorophyll biosynthesis or degradation were not different at earlier stage but the expression levels of specific key genes were increased at later stage. Therefore, the genetic basis for stay-green is proposed in 2 pathways: increase of transcripts for chlorophyll biosynthesis-related genes and decrease of expression for chlorophyll degradation genes.

Analysis of QTLs for Mesocotyl Length in Rice (Oryza sativa L.)

Abstract The objective of this study was to understand the genetic basis underlying the relationship between mesocotyl elongation and plant hormone gibberellin (GA) in rice (Oryza sativa L.). Using a recombinant inbred line (RIL) population derived from a cross between 2 japonica rice cultivars, Shennong 265 (long mesocotyl) and Lijiang Xintuan Heigu (short mesocotyl), quantitative trait loci (QTLs) for mesocotyl length were detected under both water and GA germination conditions. The treatment of 1.50 μmol L−1 of GA dramatically stimulated the mesocotyl elongation of rice. A total of 5 QTLs for mesocotyl length were identified on chromosomes 1, 2, 3, 6, and 11 under water and GA germination conditions, which accounted for 7–33% of the phenotypic variance, respectively. The LOD value of each QTL ranged from 3.65 to 15.52. Among the 5 QTLs, qML3, qML6, and qML11 were common in both germination conditions, whereas qML1 and qML2 were detected only under water germination condition. qML3 was usually detected in several experiments using different populations, indicating that it might be a major QTL for mesocotyl elongation of rice.

Erect panicle super rice varieties enhance yield by harvest index advantages in high nitrogen and density conditions

Abstract The erect panicle (Ep) type is an important characteristic for japonica super rice in Northeast China and plays a significant role in enhancing yield. The Ep type is considered to be a genetic ideotype resource to the japonica super rice group by virtue of its agronomic advantages such as grain number per panicle and biomass. This study addresses the effects of nitrogen and planting density conditions on yielding performance regarding panicle type (PT) using the recombinant inbred line (RIL) population derived from the cross between an Ep variety Liaogeng 5 and non-Ep variety Wanlun 422. The genetics underlying the Ep type proved to be robust not only for panicle-type optimization but also plant height, panicle length, flag leaf length and seed density. We also found that regardless of nitrogen and density, correlation between harvest index (HI) and plant height was not significant in Ep type whatever the nitrogen and density. The application of Ep type provides a potential strategy for yield improvement by increasing biomass through HI maintainable in rice.

Advances and prospects of super rice breeding in China

Abstract Super rice breeding in China has been very successful over the past 3 decades, and the Chinese government has made great efforts to support breeding and cultivation of both conventional and hybrid super rice. In this review, we focus on the progress in and potential of super rice breeding. After the establishment of the breeding theory and strategy of “generating an ideotype with strong heterosis through inter-subspecies hybridization, by using gene pyramiding to combine elite traits through composite-crossing to breed super rice varieties with both ideotype and strong hybrid vigor”, a series of major breakthroughs have been achieved in both conventional and super hybrid rice breeding. A number of new genetic materials with ideotype have been created successfully, and the Ministry of Agriculture of China has approved 156 novel super rice varieties and combinations for commercialization. During the Developing the Super Rice Varieties Program, great attention has also been paid to the integration and demonstration of the rice production technology. Collaboration between industry and university researchers has led to technological innovations and initiation of a demonstration system for super hybrid rice. With widespread cultivation of super rice with higher quality and yield, as well as resistance or tolerance to abiotic or biotic stresses, the yield of rice production per unit has reached a new level. In addition to increased quality and yield, hybrid rice breeding has also led to improvements in many other agronomic traits, such as resistance to pests and diseases, resistance to lodging, and optimized light distribution in population. Achievements in super rice breeding and innovation in rice production have made major contributions to the progress in rice sciences and worldwide food security.

Effect of Indica-Japonica Hybridization on Grain Quality of Rice Cultivars in Northeast China

Most cultivated varieties were bred from indica–japonica hybridization in Northeast China.In this study,we collected major japonica rice varieties widely cultivated in Northeast China and Japanese varieties as research materials,using subspecies-specific InDel and SSILP markers determined the proportion of indica pedigree in japonica cultivars,compared the morphological differentiation with the Chengs index,and measured 10 rice quality traits to study the relationship of indica pedigree,morphological differentiation and grain quality with correlation analysis.The results indicated that the indica-type allele frequency of Northeast japonica cultivars was 4.71% and extremely higher than that of Japanese varieties(0.30%);Indica-type loci frequency of Northeast japonica cultivars among 12 rice chromosomes was greatly different,that of chromosomes 5,6,10,and 11 was more than 5%,indica-type loci frequency of chromosome 5 was the most(9.83%),while chromosomes 7 was the least(0.59%).Indica-type allele frequency of rice cultivars in Northeast China showed an order of Liaoning(6.17%) Jilin(3.92%) Heilongjiang(3.44%),with significant different between Liaoning and Jilin,Heilongjiang,and no great difference between Jilin and Heilongjiang.The subspecies type of the Northeast cultivated varieties and Japanese varieties was japonicalinous and typical japonica respectively identilgied by Chengs index,and vascular bundle characters also greatly differred too.Rice milling quality of Japan preceded than that of Northeast China.Chengs index had very significantly positive correlations with rice milling quality.Indica-genotype frequencies had very significantly or significantly negative correlations with milling quality and taste score.The chalky grain rate was very significantly and positively correlated with indica-genotype frequencies.The main reason of lower chalkiness traits of japonica in Northeast China than in Japan was that the chalky grain rate and chalkiness were very low in Heilongjang.

Advances and Prospects in Breeding Japonica Rice for Super High Yield in the Northern China

Abstract In this paper, advances and prospects in breeding japonica rice for super high yield in the northern China were analyzed comprehensively in terms of breeding theories, techniques and practices. The author holds that developing and spreading super rice is an important way to enhance the overall yielding ability of japonica rice and attaining immense expansion of rice production. After theories and technical guidelines for super rice breeding were formulated, which involved the creation of new plant morphology and strong hybrid vigor through crossing indica with japonica subspecies, the optimization of combination of desirable traits via multiple crossing or backcrossing, the assemblage of favorable genes and the integration of ideal plant morphology with the utilization of vigor-major breakthroughs have been made in conventional breeding of japonica super rice. A batch of new super rice varieties marked by superior rice quality and high disease resistance, such as Shennong 265, Shennong 606, and Jijing 88, etc., have been developed and released. In comparison with the advancement in conventional breeding of super rice, progress in hybrid japonica super rice breeding is slower because of climatic and ecological constraint in northern China. Therefore, solving the contradictions between vigor and growth duration, between yield and rice quality, and boosting vastly seed production are still serious challenges for breeders of hybrid japonica rice. Physiological and genetic problems in japonica super rice breeding are also discussed in this paper.

Altered Expression of Transcription Factor Genes in Rice Flag Leaf under Low Nitrogen Stress

The response of transcription factor genes to low nitrogen stress was studied to provide molecular basis for improving the absorption and utilization efficiency of nitrogen fertilizer in rice. The agilent rice genome arrays were used to study the varied expression of transcription factor genes in two rice varieties (SN 196 and Toyonishhiki) with different chlorophyll contents under low nitrogen stress. The results showed that a total of 53 transcription factor genes (35 down-regulated and 18 up-regulated genes at the transcription level) in flag leaves of super-green rice SN196 and 27 transcription factor genes (21 down-regulated and 6 up-regulated genes at the transcription level) in flag leaves of Toyonishiki were affected by low nitrogen stress. Among those nitrogen-responsive genes, 48 transcription factor genes in SN196 and 22 in Toyonishiki were variety-specific. There were overlapped transcription factor genes responded to low nitrogen stress between SN196 and Toyonishiki, with 1 up-regulated and 4 down-regulated at the transcription level. Distributions of low nitrogen responsive genes on chromosomes were different in two rice varieties.