Developing Blight-Resistant Boxwood Germplasm
Floral and Nursery Plants Research Unit
2013 Annual Report
1a.Objectives (from AD-416):
The primary objective of this work is to develop boxwood cultivars that are tolerant of boxwood blight by collecting, evaluating, and breeding boxwood and characterizing host pathogen interactions.
1b.Approach (from AD-416):
Germplasm collection will be done through cooperation with existing national and international contacts. Germplasm will be maintained at the USNA as part of the permanent collection. Genetic diversity and relatedness of accessions will be characterized using SSR markers developed by ARS. Screening for resistance to boxwood blight will be based on previously established protocols. Basic breeding behavior of boxwood will be assessed by making controlled crosses, screening for ploidy level, and determining technical aspects such as pollen viability and seed germination parameters.
We have acquired approximately 60 new boxwood accessions, either as rooted or unrooted cuttings or living plants, and have identified several additional valuable taxa from the US or Europe that we will pursue. Early work on ploidy analysis revealed that most of the taxa in using plants at the U.S. National Arboretum’s boxwood collection, controlled hybridizations were made in order to determine basic flowering, breeding, and seed set behavior of accessions, as well as to develop a first set of hybrids to screen for resistance. Notes on flowering (number of flowers, male vs female flowers) and seed set for self pollinations, open pollinations, and inter- and intraspecific pollinations were made. Ploidy analysis of a subset of plants used in hybridizations revealed that the plants were diploid. A postdoc began work in the spring to develop a rapid and reliable resistance screening assay that can be done in the laboratory on detached leaves or stems. This will allow us to efficiently screen the parental taxa and the thousands of hybrids that will be created in the breeding program.