Crop vulnerability: Carya

Authors: Grauke, Larry; Wood, Bruce; HARRIS, MARVIN - Texas A&M University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2016
Publication Date: 6/1/2016
Citation: Grauke, L.J., Wood, B.W., Harris, M. 2016. Crop vulnerability: Carya. HortScience. 51(6):653-663.

Interpretive Summary: Crop Vulnerability Reports are mandated by the National Plant Germplasm System as a means to communicate between those who maintain repository collections and those who use them. The U.S. pecan industry is at a critical turning point in its history, addressing issues that could further fragment an already regionally diverse commodity, yet needing the cohesiveness of community based research to coordinate strategies for development. This is a comprehensive report of the crop, the industry, and some of the emerging issues, along with itemization of assets for use in addressing those issues through breeding.

Technical Abstract: Long established native tree populations reflect local adaptations. Representation of diverse populations in accessible ex situ collections that link information on phenotypic expression to information on spatial and temporal origination is the most efficient means of preserving and exploring genetic diversity, which is the foundation of breeding and crop improvement. Throughout North America, sympatric Carya species sharing the same ploidy level tend to hybridize frequently, permitting gene flow that contributes to regional diversity and adaptation. The topographic isolation of many fragmented populations places native Carya populations in the US, Mexico and Asia in a vulnerable position and justifies their systematic collection and characterization. The characterization of indigenous Mexican pecan and other Carya populations will facilitate their appropriate utilization as rootstocks and for scion breeding and will contribute to pecan culture. The Asian species, as a group, are isolated not only from North American populations, but apparently occur in disjunct, fragmented populations that are also isolated from other Asian species. Recent characterizations have revealed nucellar polyembryony, a potentially valuable reproductive mechanism capable of exploitation in breeding. Section SinoCarya includes the members of the genus most vulnerable to genetic loss. Global genetic resources should be cooperatively collected, maintained, characterized and developed. The integration of crop wild relatives into characterization and breeding efforts represents a challenging opportunity for international cooperation. Genomic tools used on the accessible collections of the NCGR-Carya offer great potential to elucidate genetic adaptation in relation to geographic distribution, which has been impacted by hybridization between recognized species. The greatest progress will be made by integrating the disciplines of genetics, botany, pathology, entomology, ecology and horticulture into internationally cooperative efforts. International germplasm exchange is becoming increasingly complicated by a combination of protectionist policies and legitimate phytosanitary concerns. Cooperative international evaluation of in situ autochthonous germplasm provides a valuable safeguard to unintended pathogen exchange associated with some forms of germplasm distribution, while permitting the benefit of communal exploration and directed exchange. Proprietary focus on intellectual property threatens this. The greatest risk to the productive development of the pecan industry is myopic focus on pecan production through the lens of past practice. The greatest limitation to the culture of the crop in the west is reduced water quantity and quality; in the east the challenge is disease susceptibility; and in the north -lack of cold hardiness. The greatest benefit for the entire industry might be achieved by tree size reduction through both rootstock and scion selection, which will translate into improved management and production in all areas of culture. This will necessitate incorporation of crop wild relatives in breeding, will necessitate broad cooperation in the testing leading to selection, and will necessitate the development of improved methods linking phenotypic expression to genomic characterization. The development of a database to appropriately house that growing body of information, which is available to a diverse research community, will facilitate cooperative research. The acquisition of funds to pursue development of those tools will require the support of the pecan industry, which is currently regionally fragmented and focused on marketing rather than development.