Genetics, Molecular Tagging Of QTLs For Lint Percentage Etc. Yield Traits In Cotton And Comparative Studies On Fiber Initiation Development Of Different Materials Varied In Lint Percentage

Improving cotton yield is still the main goal of present cotton breeding;it is meaningful for studying the genetics of cotton yield traits for yield breeding.Lint percentage is one of the important yield components,and plenty of data show that the raising of cotton yield has close relation with lint percentage improvement.At the same time,the different level correlation is existed between lint percentage and other yield traits,yield components and fiber quality characters.Therefore,the inheritance and related research of lint percentage is more important than other traits.In the present paper,the inheritance and QTL tagging of lint percentage and its related yield traits,as well as fiber initiation development of cottons varied in lint percentage were studied.The results are given as follows:1.Diallel crossing genetic analysis6×(6-1) crosses were made among 6 upland cotton varieties or lines varied in lint percentage including Banbanmian,Simian 3,Sumian 12,Guannong 1,Shiduan 5 and Qiannong 465.The parents and hybrids were planted in 3 replications with randomized plots.Genetic analysis for each of yield traits was conducted by Zhu's AD (additive-dominance) with MINQUE(â… ) approach.The results indicated that each yield trait of Upland cotton had always higher variance of genetic major effects,and yield traits were controlled by additive effects and dominant effects altogether.In which,lint percentage,lint index was mainly controlled by additive effects;seed yield,boll size and seed index were mainly controlled by dominant effects;lint yield and bolls per plant were mainly controlled by additive effects and dominant effects.Both common broad heredity and common narrow heredity of lint percentage and lint index were always the highest,whose additive variance percentages were 61.8%and 65.6%,respectively.Correlation analysis and path analysis of yield traits always indicated that among yield components,bolls per plant had the most contribution to lint yield,secondly by lint percentage,and the least by boll size.Heterosis prediction of F₁ and F₂ showed population mean heterosis values for seed yield,lint yield and boll size were always more positively significant;lint percentage and lint index had negative population mean heterosis,that of lint index was more significant;bolls per plant and seed index had not significant population mean heterosis.Population over-parent heterosis values of lint percentage,lint index and seed index were always more negative significant,for other traits,however,were not significant.2.Major gene-polygene genetic analysisJoint analyses of multiple generations of P₁,P₂,F₁,F₂,B₁ and B₂ was used to analyze the genetics of lint percentage and its related yield traits in two crosses Simian 3×Shiduan 5(corssâ… ) and Simian3×Qiannong 465(crossâ…¡),by using the method of major gene-polygene mixed inheritance model.It was found from the results that major genes controlling each of yield traits were always detected for at least in one cross although the optimum models for each trait were not completely consistent and the genetic effects,the heritability of major gene and polygene had also differences between two crosses, indicating that the major genes controlling yield traits were existed generally.The comparison of major gene and polygene heritability for all traits between two crosses showed,major gene heritability had comparatively stable tendency change than polygene heritability.Heritability proportion of each trait was also different between two crosses. seed yield and lint yield was mainly controlled by major gene in two crosses;lint index was mainly controlled by polygene in crossâ… and belonged to typical polygene inheritance in crossâ…¡;bolls per plant and boll size were controlled by major gene and polygene in two crosses,respectively;seed index was controlled by polygene and major gene in two crosses, respectively;lint percentage was controlled by major gene and polygene altogether in crossâ… and belonged to typical polygene inheritance in crossâ…¡.3.Tagging and mapping of QTLs for yield and its components in Upland cotton (Gossypium hirsutum L.) population with varied lint percentageQTLs for yield and its components were tagged and mapped in populations with varied lint percentage of Simian 3×Shiduan 5(Crossâ… ) F₂,F_2:3 and Simian 3×Qiannong 465(Crossâ…¡) F₂.123 and 107 polymorphism loci from 6111 pair SSR primers were obtained in crossâ… and crossâ…¡,respectively.18 QTLs for yield and its components were identified in Crossâ… including 2 QTLs for lint percentage,4 QTLs for seed yield,4 QTLs for lint yield,2 QTLs for lint index,3 QTLs for bolls per plant,2 QTLs for boll size and 1 QTL for seed index,which separately explained 6.9%～16.9%,5.6%～16.2%,4.8%～15.6%,7.7%～13.3%,8.2～11.6%,6.1%～7.0%and 6.6%of the phenotypic variance.In addition,8 molecular markers were detected linked with yield traits using the single-marker analysis.7 QTLs for yield and its components were identified in Crossâ…¡including 1 QTL for lint percentage,1 QTL for seed yield,1 QTL for lint yield,1 QTL for lint index,1 QTL for bolls per plant,2 QTLs for seed index.They separately explained 10.0%,41.9%,36.5%,12.6%,15.9%å’Œ6.8%～10.9%of the phenotypic variance,QTLs for boll size were not identified.In addition,11 molecular markers were detected linked with yield traits using the single-marker analysis.Different QTLs affecting yield traits were always detected within the same or closer chromosome region in two crosses,suggesting that genes controlling yield traits may be linked closely or the result of pleiotropy.The QTLs controlling yield and its components might mainly be dominant and over-dominant.The molecular markers linked closely to the major QTLs may be used in MAS(marker-assisted selection) to improve cotton yield.The conclusion was drawn from the comparison of QTL tagging among different crosses or different populations that Chr3(A3),Chr6(A6),Chr9(A9),Chr11(A11) and Chr12(A12)/Chr26(D12) might respectively contain the cluster of QTL for yield traits,in which the QTL for lint percentage identified in F_2:3 population of Crossâ… (qLP03, explained 16.9%of the phenotypic variance) might be same as or closely linked to the QTL identified in three environments simultaneity reported by Shen(2007),because they were always linked to the bridge marker BNL1190.The stability of this QTL would be tested in next experiments.4.Fiber initiation development in Upland cotton(Gossypium hirsutum L.) varieties varied in lint percentageFiber initiation was observed in five Upland cotton(Gossypium hirsutum L.) varieties that vary in lint percentage,from 28.53%to 43.10%,using scanning electron microscopy (SEM).The results indicated that at-1 days post-anthesis(dpa),fiber cell protrusions were found in all varieties,but these protrusions varied among the materials and the differences did not correlate with lint percentage.At 0 dpa,a large amount of fiber cell protrusions appeared on the ovular surface of all samples,and these protrusions had been elongated significantly by +1 dpa.Interestingly,fiber density at +1 dpa of almost all samples was always lower than that at 0 dpa except Simian 3,the variety with the highest lint percentage 43.10%.This observation suggested that with the expanding of the cotton ovular volume, fiber "diluting" degree on the ovular surfaces might be related to higher or lower lint percentage.The cultivar with the lowest lint percentage(28.53%),Quiannong 465,was found to exhibit the fewest fiber protrusions.Rather,many sunken,morphologically abnormal protrusions were observed on the ovular surface at 0 dpa,it was speculated that these protrusions might not yield mature cotton fibers ultimately.Correlation analysis suggested that either fiber protrusion density at 0 dpa or fiber elongation density at+1 dpa had a highest positive correlation with lint percentage(0.8642 and 0.8141,respectively), secondly with fiber index(0.8055 and 0.7968,respectively).The grey relational analysis suggested that fiber elongation density at+1 dpa correlated most with lint percentage (0.7029),secondly with fiber index(0.6820),and the least with seed index and boll weight;fiber protrusion density at 0 dpa correlated most with lint index was the highest (0.7111),followed by lint percentage(0.6571),and again the lowest were seed index and boll weight.A conclusion was drawn from two analyses that during fiber initiation stage, fiber density had closest relations with lint percentage and lint index,which could provide invaluable predictive information for cotton fiber yield breeding.5.Comparative studies on fiber initiation development of four cultivated cotton speciesThere are 4 cultivated species involved in cotton varied significantly in lint percentage. Here we observed the ovules before and after anthesis of 4 cultivated cotton species including Gossypium hirsutum cv.Simian 3,Gossypium barbadense cv.Hai 7124, Gossypium arboreum cv.Dingyuan xiaohua,and Gossypium herbaceum cv.A1-50 by utilizing SEM(scanning electron microscope),and explored the influence of delay pollination on fiber initiation development of each cultivar.The results showed that under the climate conditions in the field at Nanjing,fiber cells protruded on the ovular surface in all cultivars except G.arboreum at -1 dpa.At 0 and +1 day post-anthesis(dpa),fiber protrusion(or elongation) density of all materials was the highest at the funicular crest, higher at the chalazal cap and the middle part of ovule,and the least near the micropyle; moreover except Upland cotton cultivar Simian 3(lint percentage 43.10%),fiber density of the other three cultivars was always lower at+1 dpa than that at 0 dpa,suggesting that with the expanding of the cotton ovular volume,the fiber "diluting" degree on the ovular surfaces was greater in G.barbadense,G.arboreum and G.herbaceum than in G.hirsutum with high lint percentage.During cotton fiber initial stage,fiber density not only was affected by weather factors such as temperature but also related to the viability of stigma. Delay pollination exerted relatively significant influence on fiber initiation development of G.herbaceum,relatively less influence on G.barbadense,and the least influence on G. hirsutum and G.arboreum.Our studies might provide some theoretical references on understanding the mechanism of fiber differentiation and growth of 4 cultivated cotton species,and exploring their phylogenetic relationships of fiber development,as well as utilizing the heterosis of cotton fiber through artificial pollination.