Genetic Studies On Heterosis Of Flue-cured Tobacco Ms-hybrids

The heterosis utility of flue-cured tobacco,introduced earlier in China,develop slowly and lag much behind America and Brazil.At present,the varieties of flue-cured tobacco,spreading in most China,are all conventional varieties,and flue-cured tobacco hybrid never attains its rightful position in Chinese tobacco production.Therefore it is necessary to strengthen the studies on heterosis utility of flue-cured tobacco.In the experiment,12 hybrids crossed among 3 cytoplasmic male sterile lines,bred in Central-South Agricultural Experiment station,CNTC,and 4 varieties of flue-cured tobacco popularized in China were used to determine the heterosis and its genetic effect in economic,agronomic and quality traits;RAPD markers were used to classify heterotic group of 48 genetic resources of tobacco,and the possibility of heterosis prediction,by RAPD genetic distance and physiological means,was discussed.Results were as following:1.The heterosis for economic,agronomic and quality traits,was found in most crosses,which indicated that improvement of economic,agronomic and quality traits by heterosis utility was possible.Perfect Crosses of MsYZ206-9×Yunyan87 and MsYZ216-Yunyan87 showed big potentiality in tobacco production.2.Flue-cured tobacco's different characters are controlled by several genetic effects.Yield,top-class tobacco and high-class tobacco;plant height,leaf length, width and length-width ratio;TS,TN,Cl,and K₂O/Cl in upper leaves,Nic,TN,Cl, TS/Nic,TN/Nic and K₂O/Cl in cutters,TS,Nic,TN,Cl,and TS/Nic in lower leaves are mainly controlled by dominance effects,which has more potency on the utilization of heterosis.Average price,production value and class index;leaf harvested,stem girth,pitch and single leaf weight;Nic and TS/Nic in upper leaves of quality characters are highly controlled by dominance effects and additive effects at the same time.Not only can these traits' dominant effects' potency be exhumed with the utilization of hybrid superior,but also they can be accumulated and fixed by selection in routine cross-breeding.TN/Nic and K₂O in upper leaves;TS in cutters and K₂O in lower leaves are controlled mainly by additive effects,which has less potency on the utilization of heterosis.Dom.*Evn.effects of some characters,such as economic and agronomic traits,showed significantly different at 0.05 or 0.01 levels, and the environments,the Mshybrids of flue-cured tobacco growing in,might have great influence on hybrids heterosis.In order to give a comprehensive evaluation on crosses and their value of utilization,it is necessary to make an on-the-spot investigation on the crosses under different environment.3.Genetic correlation with significant difference at 0.05 or 0.01 levels, between Some agronomic traits and economic,quality traits of flue-cured tobacco, was found.So it is possible for economic characters and quality traits to be synchronously improved by indirect selection based on agronomic traits during the growth season.Dom.* Env.Cor significantly different at 0.05 or 0.01 levels,exist in some pair-traits,and environment has great effects on the synchronous improvement by indirect selection for some pair-traits.Therefore,the results of synchronous improvement may be better by indirect selection in different environments.4.About 3 to 17 bands were amplified among 16 RAPD primers.Each primer produced average 10.4 bands in total,8.2 polymorphic fragments,and the frequency of polymorphism was 78.9%.48 tobacco varieties were classified into six clusters by using RAPD markers,which radically revealed the genetic relationship and source region of these germplasms.The genetic background of the varieties involved,whose genetic distance mainly varies from 0.2 to 0.4,is narrow.5.The negative genetic correlation between the genetic distance,based on RAPD markers,and Heterosis apart from mid-parent,heterosis over high-parent,and dominant effect of F₁ yield was significantly different at 0.05 or 0.01 levels,which indicated that flue-cured tobacco parents with less genetic distance could get F₁ hybrids with stronger heterosis in yield.Chla/b and SOD activity in seedling stage might be favorable reference index in the improvement of agronomic,economic and quality traits of flue-cured tobacco hybrids.