| Tobacco(Nicotiana tabacum L.)is an important economic crop in China,which is widely cultivated throughout the country.Cigar is a type of tobacco.In recent years,the global cigar industry has shown a trend of vigorous development.With the continuous improvement of consumption quality and the promotion of cigar culture in China,cigar has become a new growth point in the development of Chinese tobacco.The quality of cigar leaves determines the quality of cigar products.The integrity and maturity of tobacco leaves are important prerequisites for the production of high-quality cigar leaves,especially cigar-wrapped tobacco leaves.Identifying and cultivating cigar varieties with consistent overall maturity suitable for mechanized whole plant harvesting is a new direction for cigar breeding.At present,the cigar germplasm resources suitable for whole plant harvesting in China are not clear,which hinders the development of the whole plant harvesting process of tobacco leaves in the producing areas,and also causes great difficulties in the classification,variety identification and new variety breeding of cigar germplasm resources.Therefore,constructing a method for identifying the overall maturity of cigar,clarifying the overall maturity of the existing cigar germplasm resources in China,systematically construct the method of the overall maturity of the cigar germplasm resources in China,and analyzing the genetic law of the overall maturity of the cigar,which is of great significance for the breeding of new varieties and the production of high-quality cigar leaves.This study constructed an identification method for the overall maturity of cigar tobacco,which identified the overall maturity of 183 cigar germplasm resources.And the genetic law of the overall maturity of cigar was studied by using four generations.The main findings are as follows:Construction of a method for identifying the overall maturity of cigar.The SPAD-502 Plus chlorophyll meter was used to measure the SPAD values of the upper,middle and lower leaves of the tobacco plant at the mature stage of the cigar leaves,and the number of leaves of each germplasm resource was counted.In DPS,the measured data were input in turn according to the type of cigar,and the average,standard deviation,average number of leaves and coefficient of variation of SPAD values of upper,middle and lower leaves of each germplasm were calculated.The coefficient of variation can be used to objectively compare the overall maturity of the varieties.If the coefficient of variation is less than 15 %,it indicates that the overall maturity of the germplasm is consistent,which can provide a basis for the subsequent harvesting of the whole cigar.The yield of germplasm with less than 17 leaves is limited,and it is not easy to popularize in production.Therefore,the number of leaves is greater than or equal to 17 as a limiting condition for the whole plant harvesting and semi-whole plant harvesting.The coefficient of variation of the middle and upper leaves was less than 11.7 % as the condition for harvesting the semi-whole plant.The overall maturity of 183 cigar germplasm resources was identified.The whole plant maturity of 183 germplasm resources in three periods of the two places was comprehensively analyzed by using the constructed cigar overall maturity identification method.The coefficient of variation of the maturity of Willow leaves is the smallest,which belongs to the eggplant core material,and the number of leaves is only 13.Burley21 had the largest coefficient of variation in maturity,belonging to the eggplant material,with 22 leaves.These two materials were stable in three periods.The average coefficient of variation of 183 germplasm maturity was 18.78 %,of which less than 15 % accounted for 11.35 %.At the same time,considering the yield demand of production,when the number of leaves is greater than or equal to 17 as a limiting condition,106 germplasms are eligible.The coefficient of variation of maturity of Xiangtan fine-leaf loquat is the smallest,which belongs to eggplant core material;burley 21 maturity coefficient of variation is the largest.The average coefficient of variation of 106 germplasm maturity was 18.96 %.There were 8 germplasms with consistent maturity and less than 15 %coefficient of variation,which were Xiangtan fine leaf loquat,Friedrichstaier,unknown cigar,Connecticut-s98,Tangpeng,Liubamaoliu,Havana2000 and Habano.The genetic law of the overall maturity of cigars was studied.The F2 generation genetic population was constructed by using the cigar parents Habano and Burley21 with significant differences in the overall maturity of cigar leaves,and the genetic analysis of the overall maturity was carried out by using the quantitative trait separation analysis system.The results showed that the overall maturity of cigar was mainly controlled by two pairs of additive-dominance-epistatic major genes additive-dominance polygenes.The additive effect of the first pair of major genes was 0.1090,and the dominant effect was-0.0516.The additive effect of the second pair of major genes reached 0.1050,and the dominant effect was-0.0225.There was a strong interaction between the two pairs of major genes regulating the maturity of cigar.The dominant effect of the major gene was smaller than the additive effect |h/d| < 1,that is,the dominant effect was smaller than the additive effect,indicating that the main gene controlling the overall maturity of cigar was mainly additive effect.The epistatic effect of the two pairs of major genes was also significant,and the polygenes also showed a strong additive effect.The genetic efficiency of the major genes of this trait was high,reaching 70.82 %.BSA-seq analysis revealed that three SNPs were associated with overall maturity traits.This study can lay a theoretical foundation for the gene mapping of the overall maturity of cigars and the search for major QTL loci,and then provide a theoretical basis for cigar breeding suitable for whole plant harvesting. |
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