Quantitative trait loci detection of E dwardsiella tarda resistance in Japanese flounder Paralichthys olivaceus using bulked segregant analysis

In recent years, Edwardsiella tarda has become one of the most deadly pathogens of Japanese fl ounder( Paralichthys olivaceus), causing serious annual losses in commercial production. In contrast to the rapid advances in the aquaculture of P. o livaceus, the study of E. tarda resistance-related markers has lagged behind, hindering the development of a disease-resistant strain. Thus, a marker-trait association analysis was initiated, combining bulked segregant analysis(BSA) and quantitative trait loci(QTL) mapping. Based on 180 microsatellite loci across all chromosomes, 106 individuals from the F1333(♀: F0768 ×♂: F0915)(Nomenclature rule: F+year+family number) were used to detect simple sequence repeats(SSRs) and QTLs associated with E. tarda resistance. After a genomic scan, three markers(Scaffold 404-21589, Scaffold 404-21594 and Scaffold 270-13812) from the same linkage group(LG)-1 exhibited a signifi cant difference between DNA, pooled/bulked from the resistant and susceptible groups( P <0.001). Therefore, 106 individuals were genotyped using all the SSR markers in LG1 by single marker analysis. Two different analytical models were then employed to detect SSR markers with different levels of signifi cance in LG1, where 17 and 18 SSR markers were identifi ed, respectively. Each model found three resistance-related QTLs by composite interval mapping(CIM). These six QTLs, designated q E1–6, explained 16.0%–89.5% of the phenotypic variance. Two of the QTLs, q E-2 and q E-4, were located at the 66.7 c M region, which was considered a major candidate region for E. tarda resistance. This study will provide valuable data for further investigations of E. tarda resistance genes and facilitate the selective breeding of disease-resistant Japanese fl ounder in the future.

Genetic Analysis of Main Plant Type-related Traits in Bitter Gourd(Momordica charantia L.)

In this study,the cultivated bitter gourd inbred line‘Foli 112’and the wild bitter gourd accession THMC170 were used as female(P1)and male(P2)parent,respectively,to obtain 4 generations(P1,P2,F1 and F2)through self-crossing and hybridization.The mixed major gene plus polygene inheritance model of plant quantitative trait was used to perform genetic analysis for 5 plant type-related traits including the number of internode,leaf length,leaf width,stem width and internode length in bitter gourd.Results showed that the inheritance of internode number,leaf length and leaf width was in accordance with E-6 model which involved two pairs of equi-dominant major genes with additive-dominant polygene model;the stem width was controlled by additive-dominance-epistasis polygene inheritance model(C-0 model);the inheritance of internode length involved 2 pairs of equi-additive major genes with additive-dominant polygene model(E-4 model).Meanwhile,the heritability(h2)of stem width and internode number was 20.08%and 39.28%,respectively,indicating that they were vulnerable to environment impacts;leaf length,leaf width and internode length had a higher heritability of 51.50%,52.16%and 64.36%,respectively;the inheritance of leaf length was mainly controlled by major gene(the heritability of major gene was 40.75%),indicating that early-generation selection was better for leaf length,while the inheritance of leaf width and internode length was mainly controlled by mutiple minor genes,indicating that it was better to select these two parameters for late generation.