Construction Of High-Density Genetic Map And QTL Mapping Of Main Agronomic Traits In Bitter Gourd(Momordica Charantia L.)

Agronomic traits such as first female flower node,female flower rate,fruit size and so on,are important indicators for assessing the early maturity and yield of bitter gourd.Therefore,genetic analysis and gene mapping of important agronomic traits of bitter melon are very important scientific issues.In this study,we first used bitter gourd high-generation inbred lines hai09-2 and hai09-1 to produce 6 populations of P₁,P₂,F₁,B₁,B₂,and F₂ as experimental materials,and used plant quantitative trait mix major gene plus polygene genetic model analysis method to analyze the genetic rules of the main agronomic traits of bitter gourd.Secondly,the chi-square test was used to analyze the biased segregation of the amplified band pattern of the F₂ population.At the same time,180 F₂individual plants were sequenced using whole-genome resequencing technology.Based on this technology,a large number of SNP polymorphism markers were developed to construct a high-density genetic map of bitter gourd,combining the phenotypes of the main agronomic traits of the F₂ population to complete the QTL preliminary positioning of the corresponding traits.The test results are as follows:1.Based on genetic analysis of agronomic traits in six generations:the length of the hypocotyl at the seedling stage,lateral branch number and lateral branch length of bitter gourd conform to two pairs of additive-dominant-epistasis major genes plus additive-dominant polygenes inheritance model,and the long hypocotyl was not completely dominant to the short hypocotyl,the two major genes that control the length of the hypocotyl both have a positive superdominant effect,and the heritabilities of major genes and polygenes in B₁,B₂ and F₂ were 63.56%,86.01%and 84.24%,respectively.The inheritance of the lateral branch number is dominated by additive effects,and the more lateral branches was not completely dominant to the less lateral branches,the heritabilities of major genes and polygenes in B₁,B₂ and F₂ generations were 65.72%,84.96%and 66.91%,respectively.The genetic of lateral branches length is mainly by dominantive effect,and the gene controlling long lateral branch is recessive relative to short lateral branch,the heritabilities of B₁,B₂ and F₂ were 88.66%,55.94%and 95.75%,respectively.Leaf chlorophyll content conforms to one major gene with additive-dominant plus additive-dominant-epistatic polygene inheritance model.And high chlorophyll content was not completely dominant to low chlorophyll content,the main gene additive-effect and dominantive-effect were 17.739 and 17.682,respectively.The main gene heritability and polygene heritability of B1,B₂,and F₂were 90.67%,75.35%,and 79.79%,respectively.2.Based on genetic analysis of agronomic traits in a single generation（F₂）:The internode length,first female flower node,fruit diameter,and longitudinal diameter all conform to 2 pairs of additive-dominant-epistatic major gene inheritance models,and the major gene heritability are 74.32%,83.01%,96.34%and 89.93%respectively.Single fruit weight,and seed number conform to a pair of additive-dominant major gene inheritance models,and the major gene heritability rates are 50.06%,and 75.08%,respectively.Female flower node rate and male flower node rate accorded with 2 pairs of additive-dominant major genes and 2 pairs of additive major genes respectively,and the major gene heritability rates were 85.82%and 87.12%,respectively.3.The 180 F₂ individual plant band patterns amplified by 4 pairs of SSR primers SSR1506,SSR3882,SSR2789 and SSR3721 were tested by the chi-square test,and the separation ratio was close to 1:2:1,and no serious segregation occurred,which conforms the requirements of genetic map construction.4.The effective data utilization rate of parents generated by whole-genome resequencing technology is as high as 99.88%,and the comparison rate is above 96.32%.The effective data utilization rate of the offspring is 99.91%,and the average comparison rate is 95.77%,both Q20 and Q30 in base are greater than 90%.At the same time,using the 10419 SNP markers obtained through screening,a high-density genetic map of bitter melon with a total length of 4953.11 c M,11 linkage groups,9432SNP markers distributed,and an average map distance of 0.53 c M was constructed,after the heat map and monomer source evaluation,the accuracy of the map is better.5.Use Map QTL software’s MQM mapping method to perform QTL analysis on the trait phenotype,and some traits are mapped to the corresponding QTL segment.Among them,a total of 31 QTLs were detected for 8 agronomic traits including internode length,femaleflower rate,male flower rate,single fruit weight,fruit tumor type,fruit tumor size,fruit tumor density and seed number.Among them,there are 4QTLs for internode length（q IL.5.1/LG5,98.664 c M;q IL.5.2-q IL.5.3/LG5,574.794-574.795c M;q IL.5.4/LG5,116.925c M）;3 QTLs for female flower rate（q FFR.5.1-q FFR.5.3/LG5,543.476-545.521c M）;5 QTLs for fruit weight（q FW.5.1-q FW.5.5/LG5,529.137-539.882c M）,and the QTLs of the 3 traits are all located in LG5,the corresponding contribution rates are 7.4%-7.9%,10%-10.3%and 22.5%-23.1%respectively;6 QTLs for male flower rate（q MFR.2.1-q MFR.2.3/LG2,145.428-145.802 c M;q MFR.5.1-q MFR.5.3/LG5,553.749-571.818 c M）,which are located in LG2 and LG5,respectively,with a phenotypic contribution rate of 9.3%-9.7%;4 for fruit tumor types（q FTT.10.1-q FTT.10.4/LG10,90.197-96.258 c M）,3 for fruit tumor size（q FTS.10.1-q FTS.10.3/LG10,90.197-97.358 c M）,2 for fruit tumor density（q FTD.10.1-q FTD.10.2/LG10,92.286-97.358 c M）,and 4 for seed number（q SN.10.1-q SN.10.4/LG10,37.947-58.361 c M）,the QTLs of the 4 traits are all located in LG10,and the corresponding contribution rates are 24.1%-25%,68.6%-69.7%,77.8%-78.4%and 7.4%-7.6%.In summary,the major gene plus polygene heritability rates of the four traits including hypocotyl length,lateral branch number,lateral branch length and leaf chlorophyll content are all higher,indicating that the phenotypic variation of these four traits is mainly controlled by genetic factors,suitable for early generation selection,the main gene that controls the lateral branch number and chlorophyll content through backcross transfer.The internode length,first female flower,fruit diameter,longitudinal diameter,seed number,female flower rate and male flower rate are higher in the major gene heritability in the F₂ generation,these traits are mainly controlled by genetic factors,and the environmental impact is small,the selection of genes should be carried out in the early generation,and fruit weight is greatly affected by environmental factors and should be selected in the high generation.A high-density genetic map with a total length of 4953.11 c M,11 linkage groups,9432 SNP markers and an average distance of 0.53 c M was constructed by whole genome resequencing,and according to F₂ phenotypes,the trait including internode length,male and female flower rate,fruit weight,fruit tumor type,fruit tumor size,fruit tumor density and seed number total 31QTL locus were located.