Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2015
Publication Date: 3/30/2015
Citation: Rogers, E.E., Ledbetter, C.A. 2015. Susceptibility to Xylella fastidiosa in a first generation hybrid from a non-traditional peach-almond cross. HortScience. 50:337-340. 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 disease (ALSD) that reduces tree vigor and almond yields. ALSD has been a re-occurring problem throughout California's 850,000+ almond acres for more than sixty years. Use of an ALSD-susceptible rootstock allows the possible entry of ALSD into an orchard through rootstock infected prior to grafting. Because clonal peach-almond hybrids are becoming popular rootstock choices for commercial almond plantings in California, it is necessary to examine their reaction to bacteria causing ALSD. One particular peach-almond hybrid is not susceptible to bacteria that cause ALSD; however, this study reports on a different peach-almond hybrid that is susceptible to ALSD. Results demonstrate that any peach-almond hybrid being considered as a rootstock should be tested for susceptibility to ALSD on an individual basis.
Technical Abstract: To facilitate development of Prunus rootstocks with desirable agronomic traits, domesticated peach (Prunus persica) and almond (P. dulcis) were crossed with wild almond relatives. This work reports that a hybrid from a P. webbii x P. persica cv Harrow Blood cross is susceptible to almond leaf scorch disease (ALSD). ALSD is caused by the fastidious, xylem-limited bacterium Xylella fastidiosa. The P. webbii x ‘Harrow Blood’ hybrid, along with its parents, were inoculated with two ALSD-inducing strains (X. fastidiosa subsp. fastidiosa strain M23 and subsp. multiplex strain Dixon). Both X. fastidiosa strains grew to high titer in the susceptible P. webbii parent and in the interspecific hybrid; defoliation was also observed. As expected, ‘Harrow Blood’ did not exhibit defoliation symptoms or support growth of X. fastidiosa. This result contrasts with earlier work demonstrating that a P. persica x P. dulcis hybrid is not a suitable host for X. fastidiosa subsp. fastidiosa M23. It appears that the genetic basis of resistance/susceptibility differs between a P. persica x P. dulcis cross and the P. webbii x P. persica cross reported here. Understanding the degree of susceptibility to X. fastidiosa in complex hybrids of subgenus Amygdalus should be an important part of rootstock development.