| This research was conducted to analyze heterosis, combining ability and heritability for main agronomic traits, economic traits and some quality characters of burley tobacco. The following is the research results.1. The research results of combining ability and heritability for burley tobacco traits(1) The significant variances of the general combining ability (GCA) and specific combining ability (SCA) for four agronomic traits and three economic traits of burley tobacco, such as plant height, leaf number, the length of middle leaves, the width of middle leaves, yield, output value as well as the first class ratio, suggested that genetic variations of these quantitative traits was mainly controlled by additive effect, for example plant height, or dominance effect, or both additive and dominance effects. The extreme significant variances of GCA and SCA which is smaller than GCA for three burley tobacco quality characters of middle leaves indicated that the genetic variations of these traits were both controlled by additive effect and dominance effect. The non-significant variance of SCA of nitrogen/nicotine ratio (NNR) indicated that the genetic variation was mainly influenced by additive effect.(2) Except the width of middle leaves, three agronomic traits and all three economic traits had greater general heritability in the broad sense (HB) with 33.4% to 46.24%. The quantitative traits including plant height, the first class ratio and output value had greater general heritability in the narrow sense (HN) with 6.55% to 17.48%. The rank of HN was listed, plant height> output value> the first calss ratio> yield> leaf number> the width of middle leaves> the length of middle leaves. HB of nicotine content was more than 50%, which was higher than total nitrogen content and nitrogen/nicotine ratio. Compared to total nitrogen content and NNR of middle leaves, the ratio of HN of nicotine content and NNR of upper leaves took major part in HB with 59.2% to 70%. In middle leaves, nicotine content had greater HN, followed by NNR and total nitrogen content. In upper leaves, nicotine content had geater HN than NNR. 2. Results of heterosis and traits'genetic analysis for burley tobacco(1) The heterosis analysis for agronomic traits suggested that the heterosis varied in different agronomic traits and different crossing combinations. Plant height had greater population heterosis over parent mean (Hpm), followed by node length, leaf number, angle of leaf and inflorescence, stalk circumference, the width of middle leaves as well as the length of middle leaves with negative Hpm. Only plant height and node length had a little positive Hpb. The heterosis analysis for main economic traits and quality characters showed that the heterosis was varied in different economic traits and quality characters as well as different crossing combinations. Hpm results indicated that five quantitative traits including rate of first class with greater Hpm, yield, output value, average price and nicotine content had positive heterosis. Total nitrogen content had a greater negative heterosis. Rate of first class had significant positive Hpb, while total nitrogen content had significant negative Hpb. Output value and average price had a little positive Hpb, while yield and nicotine content have a little negative Hpb.(2) HB of all seven agronomic traits was 18% to 58%, which implied that phenotypic variations were mainly controlled by environmental effects and random errors. Leaf number had higher general heritability in the narrow sense (HN), followed by node length, the width of middle leaves, plant height, angle of leaf and inflorescence, stalk circumference and the length of middle leaves, respectively. The unbiased estimate results of genetic random effect variance components showed that only dominance effect controlled the genetic variation of the length of middle leaves, and additive effect and dominance effect did the genetic variation of other six agronomic traits. The genetic variation of plant height, angle of leaf and inflorescence and stalk circumference, was mainly controlled by dominance effect with little additive effect. Dominance effect took the larger part of genetic variation for Node length, which also could be influenced significantly by additive effect. HB analysis for four economic traits and two quality characters with 21% to 66% indicated that phenotypic variations were significantly influenced by environmental effects and random errors. Nicotine content had higher HN, followed by yield, average price, output value, rate of first class and total nitrogen content respectively. The unbiased estimate results of genetic random effect variance components showed that only dominance effect controlled the genetic variation of output value, rate of first class as well as total nitrogen content. The genetic variation of quantitative traits including yield, average price and nicotine content were both controlled by additive effect and dominance effect.
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