Construction Of SSR Linkage Map And Mapping Of QTLs Conferring Resistance To Bacterial Wilt In Tobacco

Tobacco (Nicotiana tabacum L.) is an important economic crop and one of themodel plant species. Tabacco bacterial wilt (TBW) caused by Ralationia solancenrumis one of the most serious tobacco diseases in the world. As a kind of bacterial diseasewith soil-spread nature, TBW is very prevalent in tobacco-growing areas in south ofChina in recent years and has spread to north, which caused severe economic losses.Making use of resistance genes of tobacco for desease resistance breeding programs isan effective way to control the prevalence of bacterial wilt and reduce productionlosses radically. Marker-assisted selection (MAS) may greatly increase the efficiencyin plant breeding, and the TBW resistant varieties may be selected quickly andeffectively. This paper mainly focuses on SSR linkage map construction and mappingof QTLs coferring resistance to bacterial wilt in tobacco, both of which are of greatsignificance for TBW molecular breeding programs. The main results are as follows:(1) A population consisting of237F2:3lines, derived from a TBW-mid-resistantcultivar Yanyan-97and a susceptible cultivar Honghuadajinyuan was used for geneticmapping.691pairs of SSR primers were employed to detect the polymorphismsbetween the parental cultivars. The355pairs of polymorphic primers were utilized toidentify the genotypes of parts of the population.173pairs of primers showing goodamplification effect with clear differentiation were obtained.58pairs of markers(33.5%) showed segregation distortion,42(72.5%) of which deviated toward one ofthe two parents, the other16pairs of markers deviated toward heterozygotes. All ofF2:3genotypes were analyzed with the173pairs of primers,157of which were used toconstruct the SSR genetic linkage map in tobacco. The total map length was1574.5cM; the lengths of linkage group were from10.4cM to192.9cM. The numbersof markers located at each linkage group were from2to14. The average distancebetween adjacent markers was10.03cM and the orders of markers on each linkagegroup are in agreement with those on the map published by Bindler.(2) F2:3families and their parents were planted in the TBW disease nursery inBeifeng test site of Fujian tobacco agriculture research institute in2011. According tothe TBW classification, the disease situation was independently investigated in the early, serious and last period of TBW. The results showed that the index of the diseasein three onset periods displayed mormal distribution, showing quantitativecharacteristics, supposing that the resistance of TBW was controlled by multiplegenes. QTLs of TBW were analyzed by QTL Network2.0software by means ofMixed-model base Composite Interval Mapping (MCIM). The mapping results ofanalysis of single environment and conjoint analysis of three disease index showedthat two QTLs were identified in all analyses, which were located on linkage group17a and17b respectively, and explained25.7%and13.28%of phenotypic variation.Two pairs of minor QTLs detected from conjoint analysis were involved in epistaticeffects with contribution rate4.73%and3.91%respectively.(3) Ten of the most resistant lines and ten of the most susceptible lines wereselected to construct resistant DNA pool and susceptible DNA pool, respectively.109pairs of SSR primers were used to detect the two DNA pools, including all of SSRprimers located on linkage group2,17a,17b,20and22with QTLs and two to fiveprimers selected from one of the remaining linkage groups respectively.14SSRprimers (11of which located on linkage group17) showed polymorphisms betweenthe two DNA pools in agreement with the two parents (resistant and susceptiblerespectively), indicating that these markers are possibly linked to genes of TBWresistance. The result also reflects the QTL mapping is reliable, and has importantvalue in tobacco molecular breeding.