Physiological Characters And Genetic Basis Of Super-high-yield Rice

The realization of super-high-yielding of rice has a great significance for food security of China.The physiology characteristics and genetics basis of super-high-yield rice is its theoretical basis.Shennong 265 and Shennong 6014,developed by Rice Research Institute of Shenyang Agricultural University,are erect panicle type Japonica super-high-yield rice varieties.These two rice varieties promoted the in-depth research in breeding of Japonica super-high-yield rice and the expansion of cultivated area of Japonica super-high-yield rice. The physiology characteristics of Shennong 265 and Shennong 6014 and the genetics basis of Shennong 265 were studied from various aspects in this PhD thesis.The research contents were as follows:1)The characteristics of yield,photosynthetic,vascular bundle and grain-filling of Shennong 265 and Shennong 6014 were studied by using Liaojing 294 and Laojing 371 as check varieties;2)The lodging resistance of erect panicle type rice(EPT)and curved panicle type rice(CPT)were studied by using 12 japonica rice cultivars as materials, Shennong 265 and Shennong 6014 were used as samples of erect panicle type among them;3) QTLs controlling yield traits,panicle characteristics,panicle base vascular bundle traits and lodging resistance traits were detected in 176 F2 population derived from a cross between super japonica rice Shennong265 and japonica rice Lijiangxintuanheigu.The major results were as follows:1 The yield of Shennong 265 was 7.96%and 14.16%higher than that of Liaojing 294 and Liaojing 371 respectively.The yield of Shennong 6014 was 9.50%and 15.80%higher than that of Liaojing 294 and Liaojing 371 respectively.Yield components analysis demonstrated that Shennong 265 and Shennong 6014 achieving high yield through increasing spikelet number per panicles and seed setting rate,but decreasing effective panicle number and 1000-grain weight moderately.The panicle characteristics of Shennong 265and Shennong 6014 can be summarized as follows:medium panicle length,higher spikelets density,a larger number of primary(PB)and secondary branches(SB)and grains on primary and secondary branches,higher seed setting rate of PB and SB,less 1000-grain weight of PB and SB,and bigger panicle trait index.The correlation coefficient between panicle traits,yield and its components showed that the important factor of these two varieties in high-yield can be summarized as:higher spikelets density of PB and SB,a larger number of PB and SB and grains on PB and SB,and higher seed setting rate of PB.The high-yield characters of Shennong 265 and Shennong 6014 can be used as an important reference for Northern rice breeding. 2 The photosynthetic capacity and photosynthate transport capacity of Shennong 265 and Shennong 6014 were better than those of Liaojing 294 and Liaojing 371.These characters were the physiological basis for these two varieties to achieve high yield.Compared with Liaojing 294 and Liaojing 371,the photosynthetic capacity and photosynthate transport capacity of Shennong 265 and Shennong 6014 can be summed up as follows,1)they had a little lower in the leaf area index(LAI),but much higher percentage of efficient LAI,and they had moderate length and larger width and specific leaf weight of top 3 leaves.2)The chlorophyll content and the Ch1 a/b value in flag leaves of Shennong 265 and Shennong 6014 were higher and decreased slowly after heading,and its had stronger ability to adapt to the environment;Shennong 265 and Shennong 6014 had an ability of keeping high level photosynthesis and Pn under high or low light intensity,high temperature and low CO₂ concentration,and its also had stronger light oxidation ability.3)Percentage of productive panicle of Shennong 265 and Shennong 6014 was higher,so that it's had less photosynthate waste;Shennong 265 and Shennong 6014 had higher photosynthetic productivity and dry matter accumulation superiority and harvest index,and it also had high export amount and transformation of the mater in stems and sheathes.3 The vascular bundles traits and grain-filling characteristics of Shennong 265 and Shennong 6014 were investigated and summarized as follow,their vascular bundles trait of flag leaf and neck-panicle and primary and secondary branches on the lower panicle were better than that of check varieties,which indicated that these two super-high-yield rice had efficient transporting system in photosynthetic products;Although Shennong 265 and Shennong 6014 had stronger photosynthetic capacity and photosynthate transport capacity, but its also had more spikelets per panicles,so that they did not have advantage in grain-filling characteristics,but they still had higher seed setting rate and filled-grain percentage on different panicle part eventually.Correlation analysis showed that improving on vascular bundle traits of flag leaf,panicle neck and branches was not only beneficial to got an increase in the number of spikelets per spike but also beneficial to got an improving on seed setting rate and filled-grain percentage on different parts of panicle.Correlation analysis also indicated that improvement of the ratio of total phloem area of small vascular bundle (SVB)to total area of SVB of branches was beneficial to ameliorate grain-filling characteristics.Besides,there is a positive correlation between flag leaf,panicle neck and branches on vascular bundle traits.Improving on vascular bundle traits of flag leaf and panicle neck was beneficial to improving on vascular bundle traits of branches on panicle,the positive correlation was in order of lower panicle＞middle panicle＞upper panicle.Improving on the ratio of total phloem area of small vascular bundle(SVB)to total area of SVB of panicle neck will help to improve the ratio of branches.4 There was no significant difference in bending moment of the 1st,2nd,3rd and 4th internodes between erect panicle type rice and curved panicle type rice(CPT).But EPT had greater breaking resistance of the 1st,2nd and 3rd internode than CPT.So that the lodging index of the 1st,2nd and 3rd internode of EPT was lower than that of CPT.The correlations between the breaking resistance of culm and its morphological traits,anatomical features, chemical components were further studied.There were many reasons for the breaking resistance of 1st,2nd and 3rd internode of EPT increased.Firstly,EPT had thicker culm wall and larger culm wall area than CPT.Secondly,the mummer of vascular bundles,the area of vascular bundles,the area of phloem and the area of xylem of EPT were lager than those of CPT.Thirdly,EPT had higher cellulose content in comparison with CPT.TO select lodging resistant cultivars,one should consider these characterized includeing thicker culm wall, larger culm wall area and better vascular bundle characters with high cellulose content in their stems.In northern of China,breeding erect-panicle cultivars would be an effective way to improve lodging resistance of japonica rice5 QTLs for yield,panicle and panicle base vascular bundle characteristics and lodging resistance related characteristics were identified by using a population of an F₂ population derived from a cross between japonica rice Shennong265 and Lijiangxintuanheigu.1)A total of 17 QTLs for yield traits which distributed on 6 chromosomes.The variances explained by each QTL from 12%⁶5%.There were 4 QTL explaining more than 25%of total phenotypic variation individually,which were qPL9 conferring PL,SPP4-1 conferring SPP,qSD9 conferring SD and qRG12 conferring RG.2)A total of 37 QTLs controlling 24 panicle and panicle base vascular bundle characteristics were detected,which distributed on chromosome 1,2,3,4,5,6,7,8,9 and 12.The phenotypic variations explained by individual QTL were ranged from 11.0%to 65.0%,among which 15 QTLs explained VE by more than 20%.These QTLs showed cluster forms on chromosome 3,4,6,9 and 12.All the information suggests that the closed linkage between genes and phenotypes and clusters of QTLs in genome highlight the correlation of panicle and panicle vascular bundle characteristics,as the important genetic basis.3)A total of 18 QTLs for 14 traits were detected for basal second internodes' culm mechanical strength and related traits,including 4 for the breaking resistance of the basal second internode on chromosome 4,7,9,and 10.The variances explained by each QTL from 12%²3%.For all loci,the Shennong265 alleles increased Culm's breaking resistance.The QTLs controlled Stem diameter,Wall thickness,Area of large vascular bundle,Xylem areas of large vascular bundle,Area of small vascular bundle and Xylem areas of small vascular bundle characteristics were detected on the same area on chromosome 4.The phenotypic variations explained by individual QTL were ranged from 12%～21%.The QTLs controlled Stem diameter and QTLs controlled the breaking resistance of the basal second internode were detected on the same area on chromosome 7.The qSD7 explained about 13%of the total phenotypic variation in the F₂ population.All the information suggests that these QTLs are important for the breaking resistance of the basal second internode,and as the important genetic basis of the positive correlation of culm,vascular bundle and stem strength characteristics.