Mapping Genes For Fruit Bitterness In Luffa

The utilization of heterosis is one of the common breeding methods.However,the fruits of hybrids between Luffa acutangula?L.?Roxb.and Luffa cylindrica?L.?Roem.show bitterness,resulting in the loss of edible value.The bitterness trait needs to be removed through breeding method.To establis the molecular marker-assisted selection and improve the breeding efficiency,two backcross populations derived from‘4-0-0-0'?L.acutangula?and‘48-1-0-0'?L.cylindrica?were used to map the genes for fruit bitterness in this study.The main results are as follow.1.The segregation ratios of bitterness traits in the backcross populations?‘48-1-0-0'ב4-0-0-0'?ב48-1-0-0'and?‘4-0-0-0'ב48-1-0-0'?ב4-0-0-0'were consistent with the Mendel's law with the theoretical ratio of 1:1,suggesting that the character of fruit bitterness is controlled by two dominant complementary genes.2.A genetic linkage map was constructed using?‘48-1-0-0'ב4-0-0-0'?ב48-1-0-0'BC₁ population,which covered 835.6 CentiMorgans?cM?with an average distance of 7.96cM between markers,consisted of 13 linkage groups with an average length of 64.3 cM and contained 105 SSR markers.Labt,a gene for fruit bitterness from L.acutangula,was located between the marker SGC196 and SGE292 on LG7,with a distance of 4.0 cM and6.2 cM,respectively.Another genetic linkage map,constructed using?‘4-0-0-0'ב48-1-0-0'?ב4-0-0-0'BC₁ population,had a total coverage of 856.8 cM and possessed 11linkage groups including 100 SSR markers.The average length of each linkage group was77.8 cM and the average distance between markers was 8.6 cM.The bitterness gene Lcbt from L.cylindrica was mapped onto LG5,and the nearest SSR marker was SGJ789 with a distance of 6.3 cM.3.Through the bioinformatical analysis,SSR markers SGC196 and SGE292 were anchored to chromosome 1 of cucumber genome.Based on the e-mapped luffa sequences between above two markers,20 pairs of primers were designed and 8 among them showed frangment length polymorphism.Further mapping allocated Labt gene to the region spaned by markers LuBt1-2 and LuBt1A,with the genetic distances of 1.9 cM and 1.2 cM repectively.These two markers could be used for molecular marker assisted selection for Labt gene.4.LuBt1-2 and LuBt1A were e-mapped to cucumber chromsome 1.A bitterness gene Csa1G044 of cucumber was found to exist within the spaning region,to which the Labt could be homologous.Based on the conserved sequence between cucumber and watermelon,marker LaBt was developed to amplify the full length of Labt genes.Sequence alignment showed that a deletion/insertion of one base existed between 48-1-0-0 and4-0-0-0,which may lead to the premature termination of translation of the gene Labt in L.cylindrica and results in the loss of protein function.