| Although common buckwheat belongs to the minor corps, it has many characteristics, such as short growth period, adaptable, tolerance of drought and barrenness, nutritious value, medicinal value and so on, making it a traditional food and important economic crop in China. But lodging is a very important problem in the production of common buckwheat, which limiting common buckwheat reduction of output, even extremely. So it is a great significance to study lodging resistance in common buckwheat.Both external factors such as wind, rain, soil and genotype differences in the internal factors are affecting lodging resistance capacity in common buckwheat. To improve lodging resistance capacity of crop varieties, we have to find out the genetic rule of lodging resistance in order to guide breeding programs. Besides, we have found that lignin content of culm can be used as an important indicator to evaluate lodging resistance of common buckwheat. Whilst lignin biosynthesis has not been reported in common buckwheat.In this paper, the joint segregation analysis method of a mixed genetic model of major gene plus polygene was used to analyze the inheritance of lodging resistance trait in common buckwheat. Further more, quantitative real-time polymerase chain reaction(qRT-PCR) and pyrolysis-gas chromatography-mass spectrometry(GC-MS) were used to analyze the characteristics of lignin biosynthesis gene expression level and the synthesis of lignin monomer. Our results will provide important theoretical basis and key gene resources for breeding lodging resistance common buckwheat variety. 1 Genetie analysis of lodging resistance in common buckwheatInheritance of lodging resistance was analyzed applying the joint segregation analysis of a mixed genetic model of major gene plus polygene in six generations(Pl, P2, Fl, Bl, B2 and F2) derived from reciprocal crosses of Youqiao2(YQ2) is a lodging-resistance cultivar and Ukraine daliqiao(UD) is a lodging-susceptible cultivar in common buckwheat. Plant height, stem diameter, culm gravity height and culm snapping resistance were measured at milky ripe stage, which were used to assess the ability of lodging resistance. The results are as follows:(1) Genetic model examination showed: 1) The trait of plant height: the combination of reciprocal crosses materials were fitted to two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance effects(E-1 model); 2) The trait of stem diameter: the combination of reciprocal crosses materials were fitted to two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance effects(E-1 model); 3) The trait of culm gravity height: orthogonal combination was fitted to one major genes with additive-dominance effects plus polygenes with additive-dominance-epistatic effects(D-0 model), the combination of back-cross was fitted to two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance effects(E-1 model); 4) The trait of culm snapping resistance: orthogonal combination was fitted to two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance-epistatic effects(E-1 model), the combination of back-cross was fitted to two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance effects(E-1 model).(2) Genetic parameter analysis showed: Heritability of major genes plus polygenes for plant height was above 80%, and it indicated that the trait was mainly determined by genetic factors which guide us should select in early generation to improve breeding efficiency in common buckwheat. Heritability of major genes plus polygenes for plant height, stem diameter, culm gravity height and culm snapping resistance was under 80%, indicating that the environmental factors have a great effect for these traits, especially for culm gravity height. 2 The synthetic characteristic of lignin relating to the lodging of common buckwheatLignin content, the characteristics of lignin biosynthesis related gene(PAL, 4CL, C4 H, C3 H, CAD, CCR, F5 H, COMT and CCOAOMT) expression and lignin monomer synthesis were investigated during branching stage, bloom stage and milky ripe stage by qRT-PCR and GC-MS in three kind of common buckwheat with different lodging resistance. The results are as follows:(1) The lignin content progressively increased from branching to milky ripe stage. The cultivar YQ2 with strong lodging-resistance has a significantly higher lignin content compared with XN1 with moderate lodging resistance cultivar and UD with lodging-susceptible cultivar at branching stage, bloom stage and milky ripe stage.(2) The trends that the expression of lignin biosynthesis genes in common buckwheat was divided into three classes: 1) The expression level of PAL, 4CL, C4 H, CAD, CCR, F5 H and CCOAOMT offered upgrade firstly then descending latter tendency, and the maximum appeared in bloom stage. The expression level of CCOAOMT and CAD increased rapidly at bloom stage, and lodging-tolerant cultivar was significantly higher than that of lodging-susceptible cultivar; 2) The expression level of C3 H remains constant and there is no obvious regularity between different lodging resistance cultivar; 3) The expression level of COMT decreased, and the maximum appeared in branching stage. Besides, thehe expression level of COMT decreased rapidly at bloom stage, and lodging-susceptible cultivar was significantly higher than that of lodging-tolerant cultivar.(3) The relationship between lignin content and gene expression level in the common buckwheat lignin biosynthetic pathway. The lignin content was positive correlated significantly with the expression of genes CAD, F5 H and CCR, negative correlated significantly with the expression of gene COMT, not significant positive correlation with the expression of genes PAL, 4CL, C4 H and CCOAOMT, and not significant negative correlation with the expression of gene C3 H.(4) The relationship between gene expression level in the common buckwheat lignin biosynthetic pathway. The expression of gene PAL was significantly correlated with that of most other genes. The expression of gene COMT was negative correlated with all other genes. And the expression of gene C3 H was negative correlated with PAL, COMT and F5 H. There was a positive correlation between the other genes.(5) Change of lignin monomer in common buckwheat:Total monomer yields, G and S types monomer increased gradually, and H type monomer and the ratio of S/G decreased gradually from branching stage to milky ripe stage, which showed H type is deposited first, followed by S ype and then G type in common buckwheat. G and S types monomer are main pathway of lignin synthesis and the amount of S type monomer in common buckwheat is the largest. The cultivar YQ2 with strong lodging-resistance has a higher S, G and H types monomer content compared with XN1 with moderate lodging resistance cultivar and UD with lodging-susceptible cultivar. |
