Utilizing a natural population of inter-specific barberry hybrids in New England to characterize the genetics of Puccinia graminis resistance in Berberis thunbergii

In the northeastern United States, outside the boundaries of the 20th century federal barberry eradication zone, both common barberry (Berberis vulgaris) and Japanese barberry (B. thunbergii) are found in great abundance, to the extent that both are considered invasive species. Much less common and relatively less studied is their interspecific hybrid, B. ×ottawensis, which has been produced in the ornamental horticultural industry but which also occurs naturally.  Since B. vulgaris is a competent host of Puccinia graminis and B. thunbergii is not, B. ×ottawensis presents a unique system for characterizing the genetic mechanism(s) underlying what appears to be non-host resistance to P. graminis in B. thunbergii. In this study, a natural population of about 1,000 individuals (mixed B. vulgaris, B. thunbergii, and B. ×ottawensis) in Sheffield, MA, was investigated. While wide morphological variation was observed among and within the populations of all three species at the site, the most pronounced variation was observed among B. ×ottawensis individuals. A subset of the population was selected for genotyping by sequencing (GBS) and evaluated for reaction to P. graminis via controlled inoculations. The response was found to segregate clearly among B. ×ottawensis individuals; and GBS was shown to be a viable means of generating molecular markers in these species, despite the lack of a reference genome. These results suggest that P. graminis resistance in B. thunbergii can be genetically mapped, and mapping populations are currently under development to accomplish this goal. The genomic resources developed in this work may facilitate both barberry surveillance efforts and ornamental barberry testing programs. Furthermore, knowledge of the genetics of response to P. graminis in the alternate host has the potential to inform efforts in breeding for stem rust resistance in wheat.

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Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, USA
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