333 Evaluation of New Elms from China for Stress Tolerance

Abstract

The high resistance of Chinese elms to Dutch elm disease and elm leaf beetles makes them excellent trees for the urban landscape. There are many new Chinese elms being developed through the tree breeding program at The Morton Arboretum. Many new elms are already on the market or will be available soon from nurseries. There is little known about the stress tolerance, e.g., cold, heat, drought, etc., of new elms from China. The objectives of this study were 1) to determine the midwinter cold hardiness of new Chinese elms and 2) to determine the leaf heat tolerance and stem cold hardiness of new elms from the nursery. The stem cold hardiness of nine new elms from China was evaluated in Feb. 1998 and 1999 from the elm breeding program at The Morton Arboretum by using an artificial freezing test. The LT50 (the temperature at which 50% of the tissues were killed) of the most to least hardy genuses for Feb. 1998 were Ulmus macrocarpa (> -36 °C), U. wilsoniana # 673 (-34 °C), U. parvifolia R-89-120 (-34 °C), U. wilsoniana # 669 (-34 °C), U. wilsoniana # 997 (-33.8 °C), U. szechuanica (-30 °C), U. gaussenii R-94-85D (-30.7 °C), U. bergmanniana var. lasiophylla R-9422SD (-27.7 °C), and U. castaneifolia #R-9411-11-SD (-25.9 °C). Four new elms from Schmidt Nursery, Boring, Ore., were also evaluated for leaf heat tolerance in August and cold hardiness in Dec. 1998 and Feb. 1999. The LT50 of cold hardiness of stem tissues of cultivars in December were U. parvifolia `Emer 1' P.P. 7551, Athena® elm (-23.5 °C), U. parvifolia `Emer 1' P.P. 7552 Allee® (-26.5 °C), U. Accolade™ (-33.5 °C), and U. Danada Charm™ elm (-31 °C). The LT50 of the most to least heat-tolerant cultivars were U. parvifolia `Emer 1' P.P. 7551, Athena® elm (53.8 °C), U. parvifolia `Emer 1' P.P. 7552 Allee® (52.1 °C), U. Accolade™ (50.8 °C), and U. Danada Charm™ elm (50.6 °C). Growth, dormancy development, spring budbreak, and performance of these cultivars will be compared.