Developmental Genetics Analysis for Plant Height in indica Hybrid Rice Across Environments

The developmental genetics of plant height was analyzed from two groups of three-line indica hybrid rice at two environmental conditions based on the NCII design,using the additive-dominant developmental genetics models and the statistic methods.The results showed that the rice genotypes and environmental conditions could both affect plant height,and the effects of environment on plant height decreased gradually with plant development.Additive and dominant effects both governed the performance of plant height at all developmental stages.However,the degrees of effect varied among the rice genotypes.Moreover,the interaction between environments and genotypes also affected plant height.The genetic effects differed at most developmental stages.Furthermore,the expression of additive effect was more active than that of dominant effect.Conditional interaction effects with environment also influenced plant height during genetic development,especially at the early stage.Mid-parent heterosis(HMP) increased gradually with the developmental stage of plant height,and maximized at the latest stage,whereas the heterosis over the better parent(HBP) showed small differences among the genotypes,and kept stable at the later stage,with positive numeric value.At most developmental stages,conditional HMP was positively significant,while conditional HBP was negatively significant.All above results suggest that HMP and HBP have some new expressions in all developmental periods and the levels and directions are quite different.

Suitable growing zone and yield potential for late-maturity type of Yongyou japonica/indica hybrid rice in the lower reaches of Yangtze River, China

Late-maturity type of Yongyou japonica/indica hybrids series(LMYS) have shown great yield potential, and are being widely planted in the lower reaches of Yangtze River, China. Knowledge about suitable growing zone and evaluation of yield advantage is of practical importance for LMYS in this region. Fifteen LMYS, two high-yielding inbred japonica check varieties(CK-J) and two high-yielding hybrid indica check varieties(CK-I) were grown at Xinghua(119.57°E, 33.05°N) of Lixiahe region, Yangzhou(119.25°E, 32.30°N) of Yanjiang region, Changshu(120.46°E, 31.41°N) of Taihu Lake region, and Ningbo(121.31°E, 29.45°N) of Ningshao Plain in 2013 and 2014. The results showed that maturity dates of the 15 were later than the secure maturity date at Xinghua and 6, 14 and 15 LMYS were mature before the secure maturity date at Yangzhou, Changshu and Ningbo, respectively. One variety was identified as high-yielding variety among LMYS(HYYS) at Yangzhou, 8 HYYS in 2013 and 9 HYYS in 2014 at Changshu, 9 HYYS at Ningbo. HYYS here referred to the variety among LMYS that was mature before the secure maturity date and had at least 8% higher grain yield than both CK-J and CK-I at each experimental site. Grain yield of HYYS at each experimental site was about 12.0 t ha–1 or higher, and was significantly higher than CK varieties. High yield of HYYS was mainly attributed to larger sink size due to more spikelets per panicle. Plant height of HYYS was about 140 cm, and was significantly higher than check varieties. Significant positive correlations were recorded between duration from heading to maturity stage and grain yield, and also between whole growth periods and grain yield. HYYS had obvious advantage over check varieties in biomass accumulation and leaf area duration from heading to maturity stage. Comprehensive consideration about safe maturity and yield performance of LMYS at each experimental site, Taihu Lake region(representative site Changshu) and Ningshao Plain(representative site Ningbo) were thought suitable growing zones for LMYS in the lower reaches of Yangtze River. The main factors underlying high yield ofHYYS were larger sink size, higher plant height, longer duration from heading to maturity stage and whole growth periods, and higher biomass accumulation and leaf area duration during grain filling stage.

Breeding of New Japonica-indica Hybrid Rice Combination Chunyou 59

Chunyou 59 is a japonica-indica hybrid rice combination developed from Chunjiang 16A(a late japonica CMS line with dwarfness and early anthesis time)and CH59(an indicaclinous wide compatibility restorer line).It has the characteristics of strong heterosis,strong stem,good lodging resistance,large panicles,good cold tolerance,high yield and wide adaptability.It was registered and released by Jiangxi Provincial Crop Variety Appraisal Committee in March 2009.The breeding procedure,characteristics,major techniques of cultivation and seed production of Chunyou 59 were introduced in the paper.

Studies on the Developmental Genetics of Tiller Number in Three-line Indica Hybrid Rice

Following NC Ⅱ design, the developmental genetic behavior of tiller number (TN) in three-line indica hybrid rice was studied using additive-dominance developmental genetic models and the corresponding statistical methods. The results showed that dominance effects were predominant for TN. The expression of those additive effects were affected by environment and genotype interaction, but the expression of dominance effects were not affected. Heterosis was the strongest in the middle developmental periods of TN. Additive effects and dominance effects were selectively expressed throughout in the entire tillering developmental stage.Analysis of genetic correlation between TN at different stages and the productive panicles indicated that a close correlation appeared earlier in the populations with higher heterosis than in those with less heterosis. Utilization of heterosis at the middle tillering stage might enhance the final biomass but reduce the percentage of productive panicles.

Breeding of New Japonica-indica Hybrid Rice Combination Chunyou 284

Chunyou 284 is a medium- japonica hybrid combination,as well as an indica-japonica subspecific hyrbid with super-high yield,which was developed from Chunjiang 23A,a thermo-sensitive CMS line with very early anthesis time,and C84,an indica-japonica intermediate type restorer line with wide compatibility.This combination has the advantages of high yield potential,early maturity,excellent comprehensive agronomic traits and wide adaptability.It was approved by Jiangsu Provincial Crop Variety Approval Committee in June,2018.The breeding process,main characteristics,cultivation techniques and seed production points of the combination were introduced.

Grain yield,nitrogen use efficiency and physiological performance of indica/japonica hybrid rice in response to various nitrogen rates

Utilizing the heterosis of indica/japonica hybrid rice(IJHR)is an effective way to further increase rice grain yield.Rational application of nitrogen(N)fertilizer plays a very important role in using the heterosis of IJHR to achieve its great yield potential.However,the responses of the grain yield and N utilization of IJHR to N application rates and the underlying physiological mechanism remain elusive.The purpose of this study was to clarify these issues.Three rice cultivars currently used in rice production,an IJHR cultivar Yongyou 2640(YY2640),a japonica cultivar Lianjing 7(LJ-7)and an indica cultivar Yangdao 6(YD-6),were grown in the field with six N rates(0,100,200,300,400,and 500 kg ha^(-1))in 2018 and 2019.The results showed that with the increase in N application rates,the grain yield of each test cultivar increased at first and then decreased,and the highest grain yield was at the N rate of 400 kg ha^(-1)for YY2640,with a grain yield of 13.4 t ha^(-1),and at 300 kg ha^(-1)for LJ-7 and YD-6,with grain yields of 9.4–10.6 t ha^(-1).The grain yield and N use efficiency(NUE)of YY2640 were higher than those of LJ-7 or YD-6 at the same N rate,especially at the higher N rates.When compared with LJ-7 or YD-6,YY2640 exhibited better physiological traits,including greater root oxidation activity and leaf photosynthetic rate,higher cytokinin content in the roots and leaves,and more remobilization of assimilates from the stem to the grain during grain filling.The results suggest that IJHR could attain both higher grain yield and higher NUE than inbred rice at either low or high N application rates.Improved shoot and root traits of the IJHR contribute to its higher grain yield and NUE,and a higher content of cytokinins in the IJHR plants plays a vital role in their responses to N application rates and also benefits other physiological processes.

Yield characteristics of japonicalindica hybrids rice in the middle and lower reaches of the Yangtze River in China

Although a lot of researches have been done on yield characteristics of japonica/indica hybrid rice,there is itte information on differences of yield characteristics between different types of hybrid.To determine common characteristics of japonical indica hybrid rice(JIHR)and identify the differences between different types of JIHR,the present study assessed yield characteristics,such as panicle trait,leaf area index(LAI),above-ground biomass accumulation,and nitrogen absorption and uilization,among three types of cultivar of JIHR.In our field experiments,three types of JIHR,e.g.,Yongyou,Chunyou and Jiayouzhongke,were divided,and each of them has two cultivars,which were used as materials,meanwhile,using conventional japonica rice(CJR)Wuyingjing 31 and Sujing 9 were as controls.The results showed that the mean yield of those JIHR was above 12 t ha^-1 in 2017 and 2018,and was 31.9 and 32.2%,respectively higher than that of CJR in the two years.Spikelet number per panicle of JIHR resulted in high yield.Higher yield of JIHR was likely contributed to greater panicle number and more spikelets per panicle.Higher yielding JIHR showed stronger tllering capacity,larger LAI and above-ground biomass accumulation from jointing to heading stages,which likely contributed to the higher number of spikelets per panicle.The long duration from heading to maturity stages allowed more nitrogen accumulation of higher yielding JIHR.

Solar radiation-use characteristics of indica/japonica hybrid rice (Oryza sativa L.) in the late season in southeast China

New indica and japonica hybrid rice cultivars,such as the Yongyou series,provide farmers with very high yield potential.However,information on their canopy light capture and solar radiation use efficiency in the late season is limited.Field experiments were performed to compare the radiation-use parameters of four rice types:indica rice(IR),inbred japonica rice(IJR),hybrid japonica rice(HJR),and hybrid indica/japonica rice(HIJR),from 2016 to 2018 during the late season in Hangzhou,China.The grain yield,aboveground biomass,intercepted solar radiation(SI),and radiation-use efficiency(RUE)of the HIJR were on average respectively 13.4%–53.4%,14.3%–30.6%,7.6%–21.4%,and 8.2%–14.9%higher than those of the HJR,IJR,and IR.The leaf area index(LAI)of the HIJR was 18.2%–57.0%greater than that of the IJR and HJR at four growth stages,resulting in respectively 17.8%–38.5%and 10.7%–42.8%greater canopy light interception rates(LIR)and amount of intercepted solar radiation during the vegetative stage.The prolonged grain-filling stage also led to respectively 33.9%–52.6%and 30.5%–51.4%increases in amounts of incident and intercepted radiation for the HIJR relative to the IR during grain filling.These results indicate that the SI superiority of the HIJR was caused by canopy closure as rapid as that of the IR during the vegetative stage(greater LAI and canopy LIR during the growing season)and a grain-filling stage as long as that of the HJR.For grain-filling stage,differences in leaf Pn between HIJR,IR,and IJR were not significant,suggesting that the greater RUE of the HIJR(12.7%–52.8%higher)than that of the other rice types resulted from improved canopy architecture after flowering(FL).Principal components analysis(PCA)revealed that the superiority of the HIJR in terms of solar radiation use resulted from the greater canopy light capture capability of IR and the prolonged growth period(especially during grain filling)of japonica rice in the late growing season.

Effects of chilling tolerance induced by spermidine pretreatment on antioxidative activity,endogenous hormones and ultrastructure of indica-japonica hybrid rice seedlings

Spermidine(Spd) is known to be involved in the regulation of plant responses to chilling stress and counteract the adverse effect of stress conditions.Antioxidant activities,endogenous hormones and ultrastructure change under chilling stress were investigated in indica-japonica hybrid rice seedlings.12-d-old seedlings were subjected to exogenous Spd(1 mmol L^(-1)) and then a chilling stress(6℃,4 d) was induced,followed by a subsequent recovery(25℃,4 d).Results showed that malondialdehyde(MDA) and proline content were enhanced significantly,whereas shoot fresh and dry weights decreased during chilling stress and after recovery;chlorophyll content of chilling-stressed seedlings increased slightly but declined after recovery;additionally,total soluble sugar,sucrose,fructose and starch contents increased significantly during chilling stress,and only soluble sugar and fructose contents were observed in increase after recovery;chilling stress-induced increases in superoxide dismutase(SOD),peroxidase(POD) and catalase(CAT) activities,but declined after recovery,and the level of ascorbate peroxidase was lower during chilling stress and after recovery;however,endogenous indole-3-acetic acid(IAA),zeatin riboside(ZR),gibberellic acid(GA_3),and abscisic acid(ABA) levels were induced decreased compared with Spd pretreatment.The microscopic analysis revealed that chilling stress-induced destruction of the chloroplast envelope during chilling stress and increased the number of plastoglobuli along with aberrations in thylakoid membranes after recovery.In contrast,exogenous Spd protected rice seedlings from chilling-induced injuries in terms of lower malondialdehyde,proline and carbohydrates accumulation coupled with increased endogenous hormones metabolism.After recovery,Spd pretreatment chilling-exposed seedlings showed higher activities of antioxidant enzymes and normal physiological function of chloroplasts.These results suggest that Spd could promote effectively chilling tolerance which might be largely attributable to the integrity of cell structure and normal metabolism of endogenous hormones in indica-japonica hybrid rice seedlings.

A Preliminary Study on the Relationship Between the Indica-Japonica RAPD Differentiation of Parents and Heterosisin Dian Type Hybrid Rice

The relationship between the indica-japonica differentiation of parents and heterosis of hybridin rice was studied with 10 sterile lines, 10 maintainer lines of the sterile lines, 38 restorer lines of Dian typehybrid rice and 40 hybrids derived from the sterile lines and restorer lines. The results indicated that there wasa parabolic correlation between the indica-japonica differentiation of parents detected by RAPD markers andheterosis of hybrid rice. When certain indica-japonica differentiation of parents exists, the percentage of com-binations with positve heterosis and the mean heterosis of hybrids were high. But that didn't mean too muchdifference of parents could lead to stronger hetesosis, that meant overdiffernt parents seldom bring positve het-erotic hybrids. Suitable difference of percent of indica alleles of parents of stronger heterotic hybrid was 12 -16%.

Different Aluminum Tolerance among Indica, Japonica and Hybrid Rice Varieties

Hydroponic cultures were conducted to compare the aluminum(Al) tolerance among different rice(Oryza sativa L.) varieties, including indica, japonica and their hybrids. The results showed that the root growth of rice plant was inhibited in different degrees among Al treated varieties. The Al tolerance observed through relative root elongation indicated that five japonica varieties including Longjing 9, Dharial, LGC 1, Ribenyou and Koshihikari were relatively more tolerant than indica varieties. Most indica varieties in this study, such as Aus 373 and 9311(awnless), were sensitive to Al toxicity. The Al tolerance of most progenies from japonica × indica or indica × japonica crosses was constantly consistent with indica parents. The differences of Al tolerance among Longjing 9(japonica), Yangdao 6(indica) and Wuyunjing 7(japonica) were studied. Biomass and the malondial-dehyde content of Yangdao 6 under Al exposure decreased and increased, respectively, while there was no significant effect on those of Longjing 9 and Wuyunjing 7. Remarkable reduction of root activities was observed in all these three rice varieties. Significantly higher Al content in roots was found in Yangdao 6 compared to Longjing 9 or Wuyunjing 7.

Relationship of Parental Indica-Japonica Indexes with Yield and Grain Quality Traits of Japonica Hybrid Rice in Northern China

Taking the main parents (10 male sterile lines and 10 restorer lines) and their 100 combinations of japonica hybrid rice in northern China as materials, the relationships of parental indica-japonica indexes determined by the methods of the Cheng's index as well as simple sequence repeat (SSR) markers with yield and grain quality traits of hybrid rice were studied. For the parents, the Cheng's index (Chi) ranged from 13.5 to 19.3 and the indica index in SSR markers (ADi) were from 0.12 to 0.38. The classification of parents by Chi was not completely consistent with that by ADi. The Chi of male parent was more closely related to hybrid traits than that of female parent, as contrasted to ADi. At the same time, the difference between parents (PD) in Chi was more closely related to hybrid traits than that in ADi. The indica-japonica indexes of parents and their difference between parents appeared quadratic relationship to hybrid traits with the critical extremum. The directions of the correlation of indica-japonica indexes of parents and their differences with hybrid yield traits were on the opposition to those with hybrid grain quality traits. Therefore, the female parent should match the male parent moderately in indica-japonica index to obtain the optimum of hybrid traits, high yield as well as good quality.

Development and Characterization of Elite Doubled Haploid Lines from Two Indica Rice Hybrids

Despite significant yield advantage over inbred rice, the adoption rate of hybrid rice in India is very low due to the high seed cost and poor quality of the produce. To alleviate the problem, we initiated a doubled haploid(DH) breeding approach to develop new lines from two elite indica rice hybrids(CRHR5 and CRHR7) through rapid fixation of homozygosity in the recombinants. In vitro culture of the rice anthers resulted in 243 and 186 fertile DH lines of CRHR5 and CRHR7, respectively. Flow cytometric and pollen fertility analyses confirmed the DH ploidy status of the regenerations. Morpho-agronomic evaluation revealed 100% uniformity and stability for all the characters in the DH lines of both hybrids. Nineteen promising DH lines of each hybrid were advanced to A2 generation for yield evaluation. The yield levels of the DH lines ranged from 5 097–6 965 kg/hm2 for CRHR5 and 5 141–7 235 kg/hm2 for CRHR7, which were at par or higher than the parental hybrids. Physico-chemical characterization and cooking quality analyses revealed significant and acceptable values for grain length and width, alkali spreading value, amylose content and water uptake ratio of the selected DH lines. Three DH lines, CR5-10, CR5-49, CR5-61 from CRHR5, and four DH lines, CR7-5, CR7-7, CR7-12 and CR7-52 from CRHR7, showed significant grain yield and quality characteristics and have been recommended for multi-location trials for subsequent release as new indica doubled haploid rice varieties.

Developmental Analysis of Genetic Behavior of Brown Rice Width in indica-japonica Hybrids

The developmental genetic behaviors of brown rice width (BRW) have been studied in indica-japonica hybrid rice (Oryza sativa L.), in which seven indica male sterile lines and five japonica restorer lines were applied, by using the developmental genetic models and corresponding statistical approaches for quantitative traits of triploid in cereal crops. The BRW of indica-japonica hybrid rice was co-determined by gene expression of triploid endosperm, cytoplasm, diploid maternal plant and their genotype × environmental interaction effects. Unconditional analysis showed that the endosperm additive and maternal additive effects were predominant for the development of BRW from early- to late-stage of the grain development, but the endosperm dominant effect together with maternal effect and cytoplasmic effect became the major factor determing the BRW at the ripening stage. Moreover, conditional analysis found that there were new onset and offset of gene expression at different developmental stages of BRW in indica-japonica hybrid rice. Maternal and cytoplasm general heritabilities and their interaction heritabilities were more important compared to other components of heritability for BRW at all the five developmental stages.

Genetic Analysis of Leucine Content in Indica-Japonica Hybrid Rice (Oryza sativa L.)

Genetic control of leucine content in indica-japonica hybrid rice (Oryza sativa L.) was studied in 35 crosses of F1 and F2 generations, which were derived from crossing 7 male sterile indica rice lines with 5 restorer japonica rice lines along with their parents. Two genetic models and their corresponding statistical methods for quantitative traits of triploid seeds in cereal crops were used for the analysis. The first was the unconditional genetic model, which refers to the analysis of cumulative measurements (from flowering to a specific time) along the developmental stages, while the second was the conditional genetic model, which relates to analysis from one developmental stage to another stage (t - 1→t). The results showed that leucine content of indica-japonica hybrid rice was controlled by the expression of triploid endosperm effect (endosperm additive effect and endosperm dominant effect), cytoplasm effect, diploid maternal plant effect (maternal additive effect and maternal dominant effect) and their environmental interaction effects. Of these effects, endosperm dominant effect and maternal dominant effect were more important at the earlier stages, while endosperm additive effect and maternal additive effect were more important at the later stages of rice grain development under both unconditional and conditional genetic analyses. Due to the high heritabilities, which came from endosperm, maternal and cytoplasm effects for leucine content at different developmental stages, selection for leucine content of indica-japonica hybrid rice would be more efficient at early generations in breeding programs.

Resistance Evaluation of Some Hybrid Rice, Conventional Early Indica and Late Japonica Rice to Magnaporthe grisea

Thirty isolates of Magnaporthe grisea collected from 18 provinces/cities representing 21 pathotypes and 9 different lineages were inoculated to rice varieties with known resistance genes and some hybrid rices, conventional early indica and late japonica varieties cultivated recently in China. Virulence spectrum of the 30 isolates was very different, showing that they recognize numerous different resistance genes. Varieties also revealed very different resistance patterns showing that they carry different resistance genes or combinations of resistance genes. On the basis of comparisons with international differential varieties with known resistance genes, resistance genes in certain Chinese varieties could be speculated. The results indicated that some of them were resistant to most of the isolates tested and that they could be of interest as resistance sources for hybrid parents or to be planted in the field directly.

Indica rice restorer lines with large sink potential exhibit improved nutrient transportation to the panicle,which enhances both yield and nitrogen-use efficiency

The yield and nitrogen use efficiency(NUE)of hybrid rice combinations are closely related to restorer line.Therefore,it is essential to evaluate the agronomic characteristics of restorer lines with high yield and high NUE(HYHN).However,it is unclear which restorer lines are HYHN,and neither have the common agronomic traits of the HYHN restorer lines been identified.Aiming to address this issue,we conducted two filed experiments using three nitrogen applications,which screened five HYHN restorer lines from 15 indica restorer lines.Yield,NUE and nutrient transportation of restorer lines with different yields and NUE types were examined.Yield and total nitrogen absorption in aboveground biomass(TNA)increased,whereas NUE for grain production decreased with increasing nitrogen application levels.The HYHN restorer lines had large spikelets and high weight per panicle that were significantly positively correlated with yield and NUE.Therefore,large sink potential may be beneficial for both yield and NUE.We further studied the differences in nutrient transportation to panicles between the HYHN and low yield and low NUE(LYLN)restorer lines and found that the former had a higher nitrogen absorption level and dry matter weight ratios of panicle in maturity.Moreover,the HYHN lines also had a higher root and neck-panicle node bleeding intensity per stem after heading and more developed vascular bundles of neck-panicle nodes and leaves than the LYLN lines,which could contribute to the transportation of nutrients from root to ground and from stem and leaf to spike.Therefore,the advantages of large sink potential of the HYHN restorer lines include large nutrient accumulation in and distribution to the panicles and smooth flow of nutrients along the transportation channels.

Morpho-physiological traits contributing to better yield performance of japonica/indica hybrids over indica hybrids under input-reduced practices

It is widely reported that japonica/indica hybrids(JIH)have superior grain yield over other main varietal groups such as indica hybrids(IH)under sufficient resource inputs.To date,little attention has been paid to yield performance of JIH under input-reduced practices,and whether JIH could have better grain yield performance over IH under input-reduced practices.In this study,three JIH varieties and three IH varieties were compared in grain yield and their related morpho-physiological traits under two cultivation modes,i.e.,conventional high-yielding method(CHYM)and double reductions in nitrogen rate and planting density(DRNP).Our results showed that JIH had 8.3 and 13.3%higher grain yield over IH under CHYM and DRNP,respectively.The superior grain yield of JIH over IH under DRNP was mainly attributed to larger sink size and improved sink filling efficiency.Three main morpho-physiological traits were concluded for better yield performance of JIH over IH under DRNP.Firstly,JIH had the reduced unproductive tillers growth,indicated by a higher percentage of productive tillers and the percentage of effective leaf area index(LAI)to total LAI at heading stage.Secondly,a synergistic increase in biomass accumulation and harvest index were achieved of JIH,supported by higher biomass accumulation and leaf area duration during the main growth periods,and improved non-structural carbohydrate(NSC)remobilization after heading.Thirdly,JIH had an improved canopy structure,showing as higher leaf area of upper three leaves and lower light extinction coefficient.Our results suggested that improved morpho-physiological traits of JIH could lead to better grain yield performance over IH under input-reduced practices.

Numerical Simulation of Root Growth Dynamics of CO_2-Enriched Hybrid Rice Cultivar Shanyou 63 Under Fully Open-Air Field Conditions

Hybrid indica rice(Oryza sativa L.) cultivars play an important role in rice production system due to its heterosis,resistance to environmental stress,large panicle,and high yield potential.However,no attention has been given to its root growth dynamic responses to rising atmospheric CO2 concentration([CO2 ]) in conjunction with nitrogen(N) availability.Free air CO2 enrichment(FACE) and N have significant effects on rice root growth.In this experiment,a hybrid cultivar Shanyou 63(Oryza sativa L.) was used to study the effects of FACE and N levels on roots growth of rice.The results showed a significant increase in both adventitious root volume(ARV) and adventitious root dry weight(ARD) under the FACE treatment.The application of nitrogen also increased ARV and ARD,but the increase was smaller than that under FACE treatment.On the basis of the FACE experiment,numerical models for rice adventitious root volume and dry weight were built with the time as the driving factor.The models illustrated the dynamic development of rice adventitious root volume and dry weight after transplanting,regulated either by the influence factor of atmospheric [CO2 ] or by N application.The models were successfully used to predict ARV and ARD under FACE treatment in a different year with the predicted data being closely related to the actual experimental data.The model had guiding significance to growth regulation of rice root under the condition of atmospheric [CO2 ] rising in the future.

Analysis of Indica-Japonica Differentiation in Rice Parents and Derived Lines Using ILP Markers

Revealing the indica-japonica differentiation in parents of hybridization between indica and japonica rice and their derived lines can provide theoretical and practical bases for the breeding of practical inter-subspecific hybrid rice.Using subspeciesspecific molecular markers ILP (intron length polymorphism) and Cheng's index,the indica-japonica differentiation was analyzed with special materials including 18 indica-japonica hybrid parents and 39 derived lines,which accumulated different wide compatibility and restoring genes by convergent cross method in 21 years spanning four breeding phases.The indica-japonica differentiation was detected on all tested loci in 57 materials.Among the 18 parental lines,4 were japonica type,5 japonicaclinous type,8 indicaclinous type and one indica type.The japonica proportion indexes in indica restorer lines Minghui 63 and 9308 were 12.50 and 33.33%,respectively,while that in japonica restorer line C418 was only 31.25%.Among the 39 derived lines from indica-japonica hybridization,one was japonica type,11 japonicaclinous type,20 indicaclinous type and 7 indica type.The japonica proportion index in Minghui 502 was only 10.42%.The results of indica and japonica classification by ILP molecular markers and Cheng's index were relatively consistent.The correlation coefficient between the japonica proportion index and morphology index was 0.794,while that between the indica proportion index and morphology index was-0.7662.ILP markers could be used to accurately detect the proportion of indica/japonica content in the genome of a rice variety.The results of indica-japonica differentiation analysis could make reasonable explanation for that the hybrids obtained from indica-japonica type restorer lines had obvious heterosis.This conclusion would provide important guidance in efficient use of beneficial genes of inter-subspecific hybrid rice.