Jiayu Wang

The contribution of intersubspecific hybridization to the breeding of super-high-yielding japonica rice in northeast China

Hybridization between indica and japonica rice combined with utilization of ideal plant type has led to the development of high-yielding japonica rice in northern China. However, the contribution at the genomic level of intersubspecific hybridization to the increased yield of northern Chinese japonica rice is uncertain. In this study, we analyzed the genomic pedigree of descendants of hybridization between indica and japonica rice grown in northeastern China between 1963 and 2008. Simple sequence repeat markers indicated that since 1990 the genetic diversity among northern japonica cultivars was enriched. Genome-wide analysis with subspecies-specific indel and intron length polymorphism markers showed indica-allele frequencies were significantly increased in cultivars bred after 1990, and were significantly positively correlated with spikelet number per panicle and significantly negatively correlated with panicle number per plant. Among eight genes controlling agronomic traits, GN1a and GS3 were partially fixed in the genome of northern japonica cultivars. In contrast, Waxy and qSH1 were eliminated, whereas DEP1 and qSW5 were retained. Indica germplasm is an important contributor to the increased yield of northern japonica rice. Breeding for high yield and grain quality in combination is a complicated process and difficult to achieve when relying on only one or several functional genes, thus the selection expertise of the breeder remains critical.

Characterization and fine mapping of thermo-sensitive chlorophyll deficit mutant1 in rice (Oryza sativa L.)

Chlorophyll content is one of the most important traits controlling crop biomass and economic yield in rice. Here, we isolated a spontaneous rice mutant named thermo-sensitive chlorophyll deficit 1 (tscd1) derived from a backcross recombinant inbred line population. tscd1 plants grown normally from the seedling to tiller stages showed yellow leaves with reduced chlorophyll content, but showed no significant differences after the booting stage. At temperatures below 22°C, the tscd1 mutant showed the most obvious yellowish phenotype. With increasing temperature, the yellowish leaves gradually turned green and approached a normal wild type color. Wild type and tscd1 mutant plants had obviously different chloroplast structures and photosynthetic pigment precursor contents, which resulted in underdevelopment of chloroplasts and a yellowish phenotype in tscd1. Genetic analysis indicated that the mutant character was controlled by a recessive nuclear gene. Through map-based cloning, we located the tscd1 gene in a 34.95 kb region on the long arm of chromosome 2, containing two BAC clones and eight predicted candidate genes. Further characterization of the tscd1 gene is underway. Because it has a chlorophyll deficit phenotype before the tiller stage and little influence on growth vigor, it may play a role in ensuring the purity of hybrids.

Effect of Biochar on Root Morphological and Physiological Characteristics and Yield in Rice

A pot experiment was conducted to clarify the effects of biochar on roots and yield of super japonica rice and the applicable value of biochar in rice production.In early growing stage,biochar application increased the main root length and volume and fresh weight of roots,leading to enlarged root total absorption area and active absorption area.In late growing stage,biochar application delayed root senescence in some extents and maintained relatively high activity of rice roots.Compared to the control,biochar treatments showed higher root physiological activity,which resulted in increased bleeding rate and root activity in the whole growing period.The average yield of biochar treatments was 25.28% higher than that of the control,due to improved panicle number per hill,grain number per panicle,and seed-setting rate.The optimal amount of biochar application was 20 g in one kilogram of dry soil,which produced the highest yield with 33.21% increase over the control.Therefore,biochar is favorable to optimize root morphology and physiological characteristics in rice.

Comparison and analysis of QTLs for grain and hull thickness related traits in two recombinant inbred line (RIL) populations in rice (Oryza sativa L.)

Abstract Grain traits are major constraints in rice production, which are key factors in determining grain yield and market values. This study used two recombinant inbred line (RIL) populations, RIL-JJ ( japonica/japonica ) and RIL-IJ ( indica/japonica ) derived from the two crosses Shennong 265/Lijiangxintuanheigu (SN265/LTH) and Shennong 265/Luhui 99 (SN265/LH99). Sixty-eight quantitative trait loci (QTLs) associated with 10 grain traits were consistently detected on the 12 chromosomes across different populations and two environments. Although 61.75% of the QTLs clustered together across two populations, only 16.17% could be detected across two populations. Eight major QTLs were detected on the 9, 10 and 12 chromosomes in RIL-JJ under two environments, a novel QTL clustered on the 10 chromosome, qGT10, qBT10 and qTGW10, have a higher percentage of explained phenotypic variation (PVE) and additive effect; 15 major QTLs were detected on the 5, 8, 9, and 11 chromosomes in RIL-IJ under two environments, a novel clustered QTL, qGT8 and qTGW8, on the 8 chromosome have a higher additive effect. Finally, the analysis of major QTL-BSA mapping narrowed the qTGW10 to a 1.47-Mb region flanked by simple sequence repeat markers RM467 and RM6368 on chromosome 10. A comparison of QTLs for grain traits in two different genetic backgrounds recombinant inbred line populations confirmed that genetic background had a significant impact on grain traits. The identified QTLs were stable across different populations and various environments, and 29.42% of QTLs controlling grain traits were reliably detected in different environments. Fewer QTLs were detected for brown rice traits than for paddy rice traits, 7 and 17 QTLs for brown rice out of 25 and 43 QTLs under RIL-JJ and RIL-IJ populations, respectively. The identification of genes constituting the QTLs will help to further our understanding of the molecular mechanisms underlying grain shape.

Identification of QTLs for seed storability in rice under natural aging conditions using two RILs with the same parent Shennong 265

Abstract Seed storability (SS) is an important trait for agronomic production and germplasm preservation in rice (Oryza sativa L.). Quantitative trait locus (QTL) for seed storability in three storage periods was identified using two sets of recombinant inbred lines (RILs) derived from the crosses with a common female parent Shennong 265 (SN265). Ten QTLs for seed storability were detected on chromosomes 1, 2, 3, 4, 6, 8, and 12 in SL-RILs (SN265/Lijiangxingtuanheigui (LTH)), and a total of 12 QTLs were identified on chromosomes 2, 3, 4, 6, 9, and 10 in SH-RILs (SN265/Luhui 99 (LH99)) in different storage periods. Among these QTLs, five major QTLs were identified in more than one storage period. The qSS3-1, qSS3-2, qSS12-1, and qSS12-2 were detected in SL-RILs. Similarly, qSS2-2, qSS2-3, qSS6-2, qSS6-3, qSS6-4, qSS9-1, and qSS9-2 were detected in SH-RILs. In addition, the maximum phenotypic variation was derived from the qSS6-1 and qSS9-2, explaining 53.58 and 29.09%, respectively, while qSS6-1 was a new stable QTL for seed storability. These results provide an opportunity for pyramiding and map-based cloning major QTLs for seed storability in rice.

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.