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United States Department of Agriculture

Agricultural Research Service

Title: Desiccation sensitivity of white and black (red) oak embryonic axes

Authors
item Chmielarz, Pawel - POLISH ACADEMY OF SCIENCE
item Walters, Christina

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 6, 2006
Publication Date: January 14, 2007
Citation: Chmielarz, P., C. Walters. 2007. Desiccation sensitivity of white and black (red) oak embryonic axes. Symposium Proceedings for the 5th Workshop on Desiccation of Plants. January 14-24, 2007, Durban, South Africa. pp. 38.

Interpretive Summary: The genus Quercus is the most important aggregation of hardwoods found on the North American and European continents. Quercus is generally divided into two categories black (red) and white oak groups though a third category of live oaks is sometimes recognized as well. Natural populations of oaks are at risk because of pollution, disease or loss of habitat. Populations of Q. robur (white) have been of particular concern in Europe since the 1970s (Liese and Siwecki 1991, Oleksyn and Przyby' 1987) and populations of Q. kelloggii (black) along the California coast were reported at risk in 1995 (McPherson et al., 2005, Davidson et al., 2005). This study was undertaken to determine the feasibility of preserving genetic resources of Quercus ex situ. Seeds of all Quercus species are considered recalcitrant. Viability decreases after seeds are stored for about 4-5 months under moist conditions and immediately if seeds are dried to water contents less than 20 to 50% (fresh weight basis). We wished to compare desiccation sensitivity of embryonic axes isolated from acorns of white (Q. macrocarpa, Q. robur) and black (Q. shumardii, Q. velutina) and live (Q. kelloggii) oak species. To do this, we isolated embryonic axes, dried them for different time intervals, and assessed viability using in vitro germination techniques. Axes from black oaks dried relatively quickly compared to white oaks. Black oak axes and Q. virginiana survived drying to water contents of 0.20-0.25 g water/ g dry mass and slight drying stimulated root and/or shoot growth. Axes of white oaks only survived drying to water contents of about 0.40 g water/g dry mass and recovery time increased progressively with drying. Drying and in vitro culture affected the timing of organ development in germinating seeds of different species. For example, root and shoot development was concurrent in Q. shumardii axes, but shoots formed before roots in Q. robur axes, and roots formed before shoots in undried Q. kelloggii axes. When Q. kelloggii axes were partially dried shoots formed before the roots. Combined with cryopreservation studies, our results demonstrate the feasibility of genebanking Quercus germplasm. Literature: Davidson J.M., Wickland A.C., Patterson H.A., Falk K.R., Rizzo D.M., 2005. Transmission of Phytophtora ramorum in mixed-evergreen forest in California. Phytopathology 95: 587-596. Liese W., Siwecki R., 1991. Oak decline in Europe. Proceedings of an International Symposium Kórnik, Poland, May 15-18, 1990. McPherson B.A., Mori S.R., Wood D.L., Storer A.J., Svihra P., Kelly N.M., Standiford R.B., 2005. Sudden oak death in California: Disease progression in oaks and tanoaks. Forest Ecol. Manag. 213: 71-89. Oleksyn J., Przyby'., 1987. Oak decline in the Soviet Union - Scale and hypotheses. Eur. J. For. Path 17: 321-336.

Technical Abstract: The genus Quercus is the most important aggregation of hardwoods found on the North American and European continents. Quercus is generally divided into two categories black (red) and white oak groups though a third category of live oaks is sometimes recognized as well. Natural populations of oaks are at risk because of pollution, disease or loss of habitat. Populations of Q. robur (white) have been of particular concern in Europe since the 1970s (Liese and Siwecki 1991, Oleksyn and Przyby' 1987) and populations of Q. kelloggii (black) along the California coast were reported at risk in 1995 (McPherson et al., 2005, Davidson et al., 2005). This study was undertaken to determine the feasibility of preserving genetic resources of Quercus ex situ. Seeds of all Quercus species are considered recalcitrant. Viability decreases after seeds are stored for about 4-5 months under moist conditions and immediately if seeds are dried to water contents less than 20 to 50% (fresh weight basis). We wished to compare desiccation sensitivity of embryonic axes isolated from acorns of white (Q. macrocarpa, Q. robur) and black (Q. shumardii, Q. velutina) and live (Q. kelloggii) oak species. To do this, we isolated embryonic axes, dried them for different time intervals, and assessed viability using in vitro germination techniques. Axes from black oaks dried relatively quickly compared to white oaks. Black oak axes and Q. virginiana survived drying to water contents of 0.20-0.25 g water/ g dry mass and slight drying stimulated root and/or shoot growth. Axes of white oaks only survived drying to water contents of about 0.40 g water/g dry mass and recovery time increased progressively with drying. Drying and in vitro culture affected the timing of organ development in germinating seeds of different species. For example, root and shoot development was concurrent in Q. shumardii axes, but shoots formed before roots in Q. robur axes, and roots formed before shoots in undried Q. kelloggii axes. When Q. kelloggii axes were partially dried shoots formed before the roots. Combined with cryopreservation studies, our results demonstrate the feasibility of genebanking Quercus germplasm. Literature: Davidson J.M., Wickland A.C., Patterson H.A., Falk K.R., Rizzo D.M., 2005. Transmission of Phytophtora ramorum in mixed-evergreen forest in California. Phytopathology 95: 587-596. Liese W., Siwecki R., 1991. Oak decline in Europe. Proceedings of an International Symposium Kórnik, Poland, May 15-18, 1990. McPherson B.A., Mori S.R., Wood D.L., Storer A.J., Svihra P., Kelly N.M., Standiford R.B., 2005. Sudden oak death in California: Disease progression in oaks and tanoaks. Forest Ecol. Manag. 213: 71-89. Oleksyn J., Przyby'., 1987. Oak decline in the Soviet Union - Scale and hypotheses. Eur. J. For. Path 17: 321-336.

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