Cold and heat tolerances of hybrids for restoration of the endangered Juglans cinerea L

Abstract

• Key message Hybrids had overall intermediate cold and heat tolerances compared to their progenitors, Juglans cinerea and Juglans ailantifolia . Differences in hybrids were small compared to J. cinerea though, indicating that when considering extreme temperature tolerances, hybrids might be usesd in some restoration circumstances. However, hybrids might exceed their cold tolerance in especially cold areas, such as J. cinerea’s northern range limits. • Context Hybridization could incorporate traits for surviving detrimental global changes. Juglans cinerea, an endangered North American tree species, can hybridize with non-native Juglans ailantifolia Carr. Evidence indicates their hybrids could hold resistance to the fungal disease threatening J. cinerea. Consequently, the hybrids are being evaluated for restoration use, but to be effective, they must survive in J. cinerea’s distribution. An ecophysiological evaluation could contribute to predicting potential hybrid utilization areas. • Aims To provide a relative comparison of the cold and heat tolerances among J. cinerea provenances and between J. cinerea, J. ailantifolia, and their hybrids. • Methods In the cold test, twigs were subjected to five freeze treatments and resulting damage was estimated using electrolyte leakage. In the heat test, leaflets were subjected to six hot water bath treatments and damage was estimated using chlorophyll fluorescence. • Results Within J. cinerea, trees from colder areas exhibited less cold damage than those from warmer areas. Differences in heat damage did not occur among hardiness zones. Juglans cinerea exhibited greatest cold tolerance, J. ailantifolia exhibited greatest heat tolerance, and hybrids were intermediate. • Conclusion Differences in the cold and heat tolerances of J. cinerea and its hybrids were overall minimal, although greater in cold tolerance.