Submitted to: Euphytica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/26/2009
Publication Date: 5/23/2009
Citation: Ledbetter, C.A., Chen, J., Livingston, S., Groves, R.L. 2009. Wintercuring of Prunus dulcis cv ‘Butte,’ P. webbii and their interspecific hybrid in response to Xylella fastidiosa infections. Euphytica. Available: http://www/springerlink.com/content/80775k3135586p81/fulltext.html Interpretive Summary: Almond is a widely grown tree nut in California’s central valley and is consistently among the top California exports in terms of tonnage and product value. Almond trees are affected by a bacterial disease called Almond Leaf Scorch that reduce tree vigor and almond yields. Some almond varieties are more severely affected by Almond Leaf Scorch, however, the variety Butte seems to tolerate the disease much better than most. Through conventional plant breeding with a wild almond relative, we developed a Butte-P. webbii hybrid that was better at overcoming Almond Leaf Scorch as compared with Butte. The Butte-P. webbii hybrid has edible almonds that are similar to Butte in color and kernel shape. This hybrid is significant because it demonstrates that through breeding efforts, an Almond Leaf Scorch resistant almond variety can be achieved. Almond Leaf Scorch has been a re-occurring problem throughout California for at least the last 50 years. The development of almond varieties resistant to this vascular disease will be an economic benefit for the California almond industry.
Technical Abstract: Clonal replicates of Prunus dulcis cv ‘Butte,’ P. webbii and their interspecific hybrid P 63-61 were inoculated with Xylella fastidiosa strain M23 and evaluated for Almond Leaf Scorch Disease and subsequent wintercuring of infections during three growing seasons. Initial inoculations established greater than 90 % infection in each of the accessions, based on PCR diagnoses from petiole tissues sampled near the inoculation site. Classic leaf scorch symptoms were evident in each population during the first growing season in a controlled greenhouse environment. Trees were removed from the greenhouse during the winters to accumulate chill hours and to provide the possibility of wintercuring X. fastidiosa infections. Both PCR diagnostics and in vitro cultivation were used during the second and third growing seasons to determine the persistence of X. fastidiosa in clones among the three populations. Tree survival and the degree of wintercured infections differed among the three populations, with P. webbii and P 63-61 demonstrating enhanced levels of survivorship over ‘Butte.’ After two cycles of ambient winter temperatures and subsequent growth, ‘Butte’ averaged 21.2% wintercured trees with 73.1% mean survival. Tree survival and wintercured infections were nearly 100% for both P. webbii and P 63-61, demonstrating the utility of P. webbii in almond breeding efforts aimed at reducing tree vulnerability to X. fastidiosa infections.