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Ozark chinkapin demonstrates compatibility as a scion grafted to Chinese chestnut rootstocks: implications for ex situ conservation

The Ozark chinkapin (Castanea ozarkensis Ashe [Fagaceae]) is a true chestnut that is native to the Ozark Highlands of Missouri, Arkansas, and Oklahoma and to the Ouachita Mountains of Arkansas. It has been decimated by chestnut blight, and the species’ long-term survival is precarious. Few seed-producing trees can now be found in the wild, and the species requires very specific soil and site conditions, making it difficult to cultivate. We studied grafting Ozark chinkapin scions to its readily grown congener, Chinese chestnut (Castanea mollissima Blume) in controlled orchard settings at 2 Missouri sites, with orchard establishment in 2007 and grafting conducted in 2008. Our grafting success was 56% over all experimental parameters, but up to 83% with optimal combination of site, grafting technique, and scionwood type. Whip-and-tongue grafts were slightly (but not significantly) more successful than chip-bud grafts; however, a more vigorous scionwood type yielded significantly greater graft success (75%) compared with a second scionwood source (38%). By 2014, no indications of interspecific graft incompatibility were evident, and grafted trees were producing abundant nut yields. The successful demonstration that Chinese chestnut can be used as a rootstock for Ozark chinkapin has profound implications for the rapid propagation of Ozark chinkapin germplasm in ex situ orchards and as an important tool in a larger conservation context. In such settings, research, breeding, and mass propagation efforts with the threatened Ozark chinkapin can become much more simple, successful, and cost-efficient.