Knowledge of the genetics of salt tolerance and mining of favorable alleles from germplasm should help develop rice varieties with high salt tolerance.QTLs affecting six salt-tolerance related traits including score of salt toxicity(SST),survival days of seedlings(SDS),shoot K+ concentration(SKC),shoot Na+ concentration(SNC),root K+ concentration(RKC),root Na+ concentration(RNC) were detected using 85 backcrossing introgression lines derived from a indica cultivar IR64 and a japonica upland cultivar Tarom Molaii from Iran under salt stress with the concentration of 140 mmol L-1 NaCl at the seedling stage.Continuous variation and transgression for all six traits were observed in the BIL population although there were only significant differences in SDS and SNC between the parents.Correlation analysis indicated that SDS had highly negative correlation with SNC and positive correlation with SKC but no correlations with RKC and RNC,suggesting that salt toxicity of leaves resulted from over-accumulation of Na+ in shoots.RKC highly positively correlated with RNC while both of them had no correlations with SKC and SNC,respectively,indicating different mechanisms in uptake of K+ and Na+ in roots and their transport from roots to shoots.Twenty-three QTLs for the six traits on the ten chromosomes except chromosomes 5 and 10 were identified by single-marker ANOVA using SAS PROC GLM,including 5 for SST,6 for SDS,4 for SKC,4 for SNC,1 for RKC,and 3 for RNC.Among them,the region of RM240-RM112 on chromosome 2 simultaneously affected SST,SDS,SKC,and SNC and the allele associated with improvement of salt tolerance was from Tarom Molaii.This QTL could be useful for improvement of salt tolerance through marker assisted selection.The QTLs affecting SKC and SNC didn't share the same genomic region with the QTLs for RKC and RNC,further confirming the view that different genetic mechanisms involved in uptake of K+ and Na+ between roots and shoots.By comparative mapping,12(52.2%) QTLs for the six related traits located in the same or near genome regions on chromosomes 1,2,3,7,and 9 with the QTLs previously identified in different mapping populations.The advantages of mapping QTLs using BILs and strategy of mining 'hidden' salt-tolerant main-effect QTL from rice germplasm were discussed.
The predatory capacities and functional responses of the mirid bug, Cyrtorhinus lividipennis Reuter, on the brown planthopper (BPH), Nilaparvata lugens Stl, on rice plants with different nitrogen contents and the effects of the rice sap and BPH honeydew on its predatory function were determined in the laboratory at International Rice Research Institute (IRRI), Philippines. The results showed that the predatory capacities of C. lividipennis on BPH eggs and young nymphs were negatively related to the nitrogen content of host plants, while no significant difference in predatory capacities was recorded between C. lividipennis populations successively fed on host plants applied with 0 kg N/ha and 200 kg N/ha nitrogen fertilizer for 2 generations. The functional responses of C. lividipennis populations on BPH eggs belonged to typical Holling II, and the instantaneous rate of discovery (a) and handling times (T_h) were strongly affected by nitrogen contents in host plants. The instantaneous rate of discovery reduced obviously resulted in the lower functional responses on the host plants applied with high nitrogen rate; however, the similar response shapes of different populations were found on the plants with the same nitrogen regime. Furthermore, the influences of rice sap from the plants and honeydew of the BPH females fed on the plants with high nitrogen regime on the extension of longevities of the adults of C. lividipennis were higher than those on the plants with low nitrogen regime. However, the honeydew of BPH on the plants with high nitrogen regime significantly decreased the predatory capacity of C. lividipennis on BPH eggs. These results implied that the reduction of C. lividipennis natural control function should be one of the crucial factors to induce the outbreak of BPH population in rice fields applied with excessive nitrogenous fertilizer.
Sanhuangzhan 2(SHZ-2) has been considered as a promising blast resistance source in rice breeding in South China because of its durable blast resistance and good agronomic traits.Three major genes responsible for qualitative resistance and five defense genes significantly associated with quantitative resistance to blast in SHZ-2 have been identified and mapped using the candidate resistance gene approach in our previous study.However,its edible quality of kernel is relatively poor because of high amylose content(AC),and most derived resistant cultivars have the similar shortcoming.To have an insight into the relationship between strong blast resistance and high AC in(SHZ-2),a RIL population derived from a cross between SHZ-2 and Lijiangxintuanheigu(LTH) was used to identify the blast resistance genes in SHZ-2 and QTL for AC in the study. Results revealed no significant(P0.05) correlation between blast resistance and AC in the RIL population(Table 2).t-test also indicated that there was no significant difference for average AC between highly blast-resistant RI lines and blast-susceptible RI lines(Table 3).Three QTLs for AC were identified when single-factor analysis of variance and interval mapping were performed.They were mapped on chromosome 5,6 and 7,respectively.All the three QTL were from LTH and contributed to the reduction of AC.Comparing the locations of QTL for AC identified in this study with the locations of previously identified genes(major genes and QTL) conferring blast resistance in SHZ-2,there was no close linkage among these genes for the two traits(Fig.2).These results suggested that the strong blast resistance are not linked with the higher AC in SHZ-2 and it is possible to combine the two traits and develop an elite cultivar with durable blast resistance and ideal AC by proper selection of parents and marker-assisted selection.
Phenotype,RT-PCR and real time PCR experiments were performed to reveal the resistance reaction of rice to Xanthomonas oryzae pv.oryzicola mediated by Rxo1 using a pair of transgenic and non-transgenic rice lines.Our results indicated that Rxo1 trigged a typical hypersensitive reaction(HR)based on the observation and expression analysis of 3 gene involved in HR.3 genes involved in coding pathogenesis-related proteins also specifically up-regulated in transgenic rice plants,suggesting that salicylic acid(SA)signal transduction pathway played a role in resistance reaction.
Two years field experiment(2001 ~ 2002) was conducted in Beijing to explore the effect of irrigation on yield,yield component,water use efficiency(WUE) and water consumption characteristics of two aerobic rice cultivars(HD297and HD502).When irrigation is 300 ~ 522 mm,yield of HD297and HD502 is 3 876 ~ 5 289 kg·hm-2 and 3 977 ~ 5 664 kg·hm-2 respectively and corresponding WUE is 1.01 ~ 1.29 g·kg-1 and 1.03 ~ 1.33 g·kg-1.Significant differences exist among irrigation treatments;however,yield and WUE of HD502 are always higher than those of HD297 for all treatments.Therefore,HD502 is more suitable for Beijing area than HD297.The analysis on aerobic rice yield shows that WUE increases by 1.9% ~ 27.7% with only 7.9% ~ 29.8% decrease in yield,especially in early and middle stages,the highest increase of WUE,3.6% ~ 23.1% increase with only 7.9% ~ 15.5% decrease in yield,is observed in limited irrigation treatment.Therefore limited irrigation in early stage and sufficient irrigation in later stage is the best water-saving irrigation model for aerobic rice in Beijing.Using historical weather data for Beijing,precipitation characteristics for the growing season of aerobic rice are analyzed.The period is divided into three phases based on precipitation in the growing season of aerobic rice and using the Person-III method.The relation between water requirement of aerobic rice and precipitation is discussed.It is necessary to irrigate at all growth stages of aerobic rice in mild and dry years.However,irrigation is only needed at flowering to maturity stage in humid years.
Some issues on identification of rice blast resistance were studied by using CO39 nearisogenic and pyramid lines and 4 original isolates and their mutants of Magnaporthe grisea. The results were very useful to blast resistance breeding: that spore number for inoculation was significantly positive correlated to score, lesion number and diseased leaf area, resistance of a line to mixed spore suspension depended on the compatible isolate and induced resistance by incompatible isolate was very limited, much nitrogen application made resistant line susceptible and residual resistance did not appear among the defeated major resistance genes.
The traditional mapping population with complicated genetic backbround is usually derived from a cross between two parents with a lot of unfavorable agronomic traits. The identified QTLs by traditional mapping can not be applied in genetic im-provement of crops due to complicated interactions between QTLs and genetic background. The advanced backcross method for QTL mapping with elite variety as recurrent parent could partially eliminate the background effects and integrate QTL mapping with genetic breeding. In present study,using Shuhui 527,an elite indica restorer in China as recurrent parent and Milagrosa from Philippines as donor,the BC2F2 advanced backcross population with 199 individuals was developed. A total of 85 polymorphic SSR markers evenly distributed on 12 chromosomes were applied to genotype the mapping population. The grain length,grain width,ratio of grain length to width and thousand grain weight of the parents and the BC2F2 population were evaluated after har-vesting. The QTL identification of the above traits was conducted by one-way ANOVA(for single QTL) and two-way ANOVA(for digenic epistatic interaction loci) . Among ten QTLs for grain length,grain width,ratio of grain length to width and thousand grain weight detected by one-way ANOVA(P0.01) ,there were three pleiotropic QTLs. QTLs for ratio of grain length to width could be identified in QTLs for grain length due to highly close relationship between them. The results in present study indicated that qgl3b on chromosome 3 was a major QTL controlling grain length,ratio of grain length to width and thousand grain weight,which explained 29.37%,26.15%,and 17.15% of phenotypic variation of the three traits and showed large additive effects(posi-tive allele from Shuhui 527) and negative overdominant effects,qgw8 was also a major QTL controlling grain width with 21.47% contribution to phenotypic variation and a minor QTL controlling thousand grain weight with 5.16% contribution to phenotypic variation. It had large additive effects(positive allele from Shuhui 527) and positive partial dominant effects in both traits. Two-way ANOVA(P0.005) showed 61 pairs of digenic epistatic interactions involved in 54 QTLs among which 23 loci had pleiotropism affecting two to four traits and eight loci were the same as those detected by one-way ANOVA. It was observed that eight of thirteen pairs of digenic epistatic interactions related to ratio of grain length to width could be found in grain length. The results above will lay a good foundation in fine mapping,cloning and designed molecular breeding of favorable genes related to rice grain size and shape.
To further inspect physiological mechanisms of salt tolerant ability between different rice genotypes,and reveal salt tolerant ability mechanisms of rice which was regulated by ABA content in root during early salt stress stage,a solution culture experiment was conducted at phytotron in International Rice Research Institute(IRRI) from Oct.2009 to Feb.2010,and strictly controlled the water supply,temperature,illumination and nutrients supplying.The results showed that biomass of the tolerant genotype(IR651) is higher than that of the sensitive genotype(IR29),and the Na+ content of the tolerant genotype is diluted by higher biomass,and is lower than that of the sensitive genotype.There is no significant difference of total Na+ absorption between the sensitive and tolerant genotypes.The root biomass of the tolerant genotype is higher than that of the sensitive genotype,and amount of Na+ in roots of the tolerant genotype is higher than that of the sensitive genotype,while the amount of Na+ in shoot of the tolerant genotype is lower than that of the sensitive genotype.Because of large amount of ABA in roots of the tolerant genotype during the early salt stress stage,the stomatal conductance and transpiration effective of the tolerant genotype are decreased significantly,the Na+ absorption is inhibited by decreasing of transpiration effective,and salt stress of rice plant is alleviated at a large scale.It can be concluded that compared with the sensitive genotype,the tolerant genotype has special root physiological characteristics,higher biomass and special ABA regulation mechanisms,that's why the tolerant ability of the tolerant genotype is higher than that of the sensitive genotype significantly under the saline condition.
In this study,the resistance of 212 rice varities,which were used in molecular breeding program,were screened at blast nursery in Liaoning Province.The results showed that 117 and 39 varieties were resistant to Magnaporthe grisea at the seedling stage and adult stage,respectively.There was significantly correlation between the resistance at the two stages,and among them,19 varieties exhibited mid-resistance to leaf blast and panicle blast.In addition,the resistance of 19 rice varieties was further evaluated by artificial inoculated in greenhouse at the seeding stage.13,17,6 and 2 rice varieties were resistant to the mixed strains derived from Donggang,Shenyang,other locations in Liaoning,and Heilongjiang,respectively.Pokhreli was resistant to the isolates of rice blast pathogen from Liaoning and Heilongjiang.Our results will provide useful information for rice breeding resistant to blast in Liaoning and Heilongjiang province.
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