Inheritance Analysis and Marker Development of White Rust Resistance in Chrysanthemum

Abstract

The main aims of this study were to understand the inheritance mode of hexaploid chrysanthemum (random or preferential chromosome pairing) and to develope molecular markers to enhance breeding efficiency for the white rust resistance in chrysanthemum. A segregation analysis using simple sequence repeat (SSR) markers was carried out to clarify the inheritance mode of chrysanthemum. Through genotyping the pseudo-F1 testcross population derived from a cross between Dancer and Puma White using 49 polymorphic SSRs, 65 informative SSR marker alleles were analyzed. Of them, 33 marker alleles showed a good fit to the expected segregation ratio for the hexasomic inheritance, whereas 24 marker alleles showed for the disomic inheritance supporting the autopolyploid segregation mode in chrysanthemum. The observed ratio of non-simplex to simplex markers, 25 versus 99, indicated the hexasomic inheritance mode. In addition, random marker allele assortment showed in the six markers gave a conclusive evidence for the hexasomic inheritance mode of these loci. After revealing the inheritance mode of chrysanthemum, genetic analysis of white rust resistance was carried out. A total of 188 pseudo-F1 testcross progenies were inoculated with Puccinia horiana isolates, then 161 progenies were identified as the resistant and 27 as the susceptible. This result gave a good fit to a ratio of 4:1 (P = 0.05327,  = 0.05) for resistance and susceptibility, suggesting that a single dominant gene controls resistance and Dancer carries two dominant alleles coding the resistance gene. To improve breeding efficiency for white rust resistance in chrysanthemum, molecular markers were developed through the bulked segregant analysis. A total of 280 random amplified polymorphic DNA (RAPD) and 256 amplified fragment length polymorphism primers were screened. Then, OPI-13520 RAPD marker was presumed as the linked marker to the white rust disease resistance. The OPI-13520 marker was verified in 188 pseudo-F1 testcross progenies and just six off-springs were found as the recombinants. Based on the expected phenotypic segregation ratios in a pseudo-F1 testcross population, a duplex type of white rust resistance alleles and a duplex type of OPI-13520 markers in Dancer were on the same chromosome and hence linked in coupling phase. The genetic distance between white rust resistance gene and OPI-13520 marker was determined to be 4.0 cM. The OPI-13520 marker was successfully converted into sequence characterized amplified region (SCAR) marker.