Genetic Analysis Of Bolting And Cultivar Fingerprinting In Radish (Rapanus Sativus L.)

Radish (Raphanus sativus L.), belonging to the Cruciferae family, is a biennial root vegetable that usually grows vegetatively in the first season and initiates bolting after exposure to a period of low temperature and subsequent long days. However, some cultivars with easy bolting trait will bolt in autumn and winter. The premature bolting is a destructive problem which causes lots of yield loss and low quality especially in the spring planting. Selection and breeding cultivars with late bolting would be a critical step in radish genetics and breeding and would be an essensial measure to solve premature bolting.To ensure reaction system veracity and stability, the SRAP-PCR system was optimized with the concentration of primer at 0.3μmol·L^-1, dNTPs at 0.2 mmol·L^-1, Mg²⁺ at 3.0 mmol·L^-1 and annealing temperature at 50℃, which prepared an important technical basis for further molecular marker analysis and cultivar identification of bolting trait in radish. Three molecular marker systems, RAPD, ISSR and SRAP, were employed for identification and genetic diversity analysis of 35 elite late-bolting cultivars. With 35 RAPD primers, 22 ISSR primers and 17 SRAP primer combinations, the proportions of polymorphic bands were 85.44%, 85.2% and 85.41%, respectively, and the mean genetic similarity coefficients between pairs of genotypes were 0.781, 0.787 and 0.764, respectively. Each of the three molecular marker system can identify all the cultivars. Five combinations of three RAPD primers, three combinations of three ISSR primers and sixteen combinations of three SRAP primer pairs were able to distinguish all the cultivars. A linear relationship was observed between Resolving Power (Rp) of a primer and its ability to distinguish genotypes. The 35 cultivars were clustered into three major groups with UPGMA and Principal Coordinate Analysis (PCoA) based on the RAPD, ISSR and marker combination data, which are in high accordance with their own origins and main characteristics.Segregation populations from two parents with defferent bolting traits were used in this study. The segregation analysis methods for major genes plus polygene mixed inheritance model were used to identify the genetic system of bolting trait. The results from joint analyses showed that two major gene plus polygene mixed inheritance model were the most fitted genetic model for bolting traits in populations(E-0, E-1). In E-1 model, Additive effects of two major genes were estimated as -7.818 and -5.084, respectively; The heritability values of major gene and polygene were 70.97 % and 1.86 %, respectively, and total heritability value was 72.83 %. Additive effect and dominance effect of polygene were negative effect and positive effect. In E-0 model, additive effects of two major genes were estimated as -12.344 and -8.600, respectively. The heritability values of major gene and polygene were 75.50 % and 0.22 %, respectively, and total heritability value was 75.72 %. However the heritabilities of major gene and polygene, the additive and dominance effects of bolting character were fluctuated based on different model.Multiple genetic segregant populations were developed with the elite advanced inbred lines of lately and early bolting; Using parental lines 'Nau-Wh' and 'Nau-Lhz', 'Nau-Wh'and 'Nau-Dyl3' and their corresponding F₁ and F₂ population as materials, Strategy of BSA and GRA were employed to tag the late bolting locus, and six RAPD, one ISSR and SRAP marker tightly linked to bolting locus were obtained. The results revealed that F₂ population was significantly distorted. Among these markers, 8 markers (66.67%) showed the genetics distortion (P＜0.05). The RAPD marker LBRp10-557 tightly linked to bolting locus was sequenced and the sequence length was 557bp. RAPD marker was converted into SCAR marker, however, polymorphism from converted SCAR marker was missed.The results would provide valuable information for exploring molecular mechanism of radish late bolting, molecular breeding and new elite late-bolting cultivar development.