The use of chloroplast gene sequences to confirm maternal backgrounds of powdery mildew resistant, putatively interspecific hybrid dogwood (Cornus kousa × C. florida) seedlings
Powdery mildew (PM), caused by both Erysiphe pulchra Cook and Peck and Phyllactinia guttata (Wall.:Fr) Lev., is a major fungal disease of flowering dogwood (Cornus florida L.) and genetic resistance to the pathogen is rare in the species. At Rutgers we have identified a population of 11 resistant seedling trees which phenotypically appear to be pure C. florida, but their pedigree records indicate that they are advanced generation backcross hybrids with C. kousa F. Buerger ex Hence. Several chloroplast genes including matK, rbcL and ycf1 have been used in phylogenetic analysis of the Cornaceae family. They have also been used to determine maternal species backgrounds of interspecific hybrid progeny of higher plants. In this study we utilize chloroplast genes to examine the maternal species of our powdery mildew resistant seedlings with the expectation of confirming C. kousa as the maternal source. Chloroplast genes were sequenced in the 11 seedlings along with three reference cultivars of C. kousa and four of C. florida. The recorded mother of the PM-resistant seedlings, breeding selection KF95-1 (a BC1 hybrid between C. kousa × C. florida crossed back to C. florida), was also included in the study. Further, two offspring from one of the PM-resistant seedlings crossed again to C. florida were included to trace the maternal line into the BC3 generation. We were able to successfully sequence the chloroplast genes for all genotypes included in the study, but had confounding sequencing results for the C. kousa controls. Nonetheless, results showed that while our pedigree records indicate that our PM-resistant seedlings trace their maternal lines to C. kousa LSQUOK2RSQUO, this is most likely in error. Gene sequences indicate that the seedlings were derived from C. florida maternal lines. While the results are humbling, they reinforce the value of supporting breeding records with molecular tools. Regardless of the origin of disease resistance, the presence of heritable PM resistance in C. florida holds significant potential for breeding.
Muehlbauer, M., Honig, J. and Molnar, T. (2018). The use of chloroplast gene sequences to confirm maternal backgrounds of powdery mildew resistant, putatively interspecific hybrid dogwood (Cornus kousa × C. florida) seedlings. Acta Hortic. 1191, 17-26
matK, rbcL, ycf1, Erysiphe pulchra, Phyllactinia guttata