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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Publications at this Location » Publication #340628
Title: Screening almond rootstocks for sources of resistance to Armillaria root disease

Author
item Baumgartner, Kendra
item Fujiyoshi, Phillip
item Ledbetter, Craig
item DUNCAN, ROGER - University Of California - Cooperative Extension Service
item Kluepfel, Daniel

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2017
Publication Date: 2/7/2018
Citation: Baumgartner, K., Fujiyoshi, P.T., Ledbetter, C.A., Duncan, R., Kluepfel, D.A. 2018. Screening almond rootstocks for sources of resistance to Armillaria root disease. HortScience. 53(1):4-8. https://doi.org/10.21273/HORTSCI12038-17.
DOI: https://doi.org/10.21273/HORTSCI12038-17

Interpretive Summary: Peaches and almonds are among the most susceptible tree crops to Armillaria root disease. Resistance to the two aggressive fungi Armillaria mellea and A. tabescens has been evaluated in separate field trials where these species occur (Western US and southeastern US, respectively), but not in one comprehensive study. We evaluated the relative resistance to these two fungi of six clonally propagated almond rootstocks (Bright 5, Empyrean 1, Hansen 536, Krymsk 1, Krymsk 86, Lovell), in comparison to that of clonally propagated Marianna 2624 rootstock (resistant control) and clonally propagated Nemaguard rootstock (susceptible control). Replicate clonal plants used in the growth-chamber assay were micropropagated and rooted in vitro prior to inoculating the culture medium with Armillaria. At 2 months post-inoculation, the most resistant and susceptible rootstocks were Krymsk 86 and Hansen 536, respectively, with 27 versus 89% mortality, and this finding was consistent among two isolates of A. mellea and one isolate of A. tabescens, in all three replicate experiments. Our finding of the lowest mortality among Krymsk 86, Krymsk 1, and Marianna 2624, which all share P. cerasifera (Myrobalan plum) parentage, is consistent with past reports of resistance to A. mellea, but conflicts with reports of susceptibility to A. tabescens. Resistance to A. tabescens of rootstocks with Myrobalan plum parentage in our assay may reflect the simplified rooting environment of tissue culture medium, which does not perfectly mimic the soil, where biotic and abiotic factors may interact with host resistance.

Technical Abstract: Prunus is one of the most susceptible horticultural crops to Armillaria root disease. Resistance to the geographically isolated causal fungi Armillaria mellea and A. tabescens has been evaluated in separate field trials of almond and other Prunus rootstocks, but not in one comprehensive study. We evaluated the relative resistance to A. mellea and A. tabescens of six clonally propagated almond rootstocks (Bright 5, Empyrean 1, Hansen 536, Krymsk 1, Krymsk 86, Lovell), in comparison to that of clonally propagated Marianna 2624 rootstock (resistant control) and clonally propagated Nemaguard rootstock (susceptible control). Replicate clones used in the growth-chamber assay were micropropagated and rooted in vitro prior to inoculating the culture medium with Armillaria. At 2 months post-inoculation, the most resistant and susceptible rootstocks were Krymsk 86 and Hansen 536, respectively, with 27 versus 89% mortality, and this finding was consistent among two isolates of A. mellea and one isolate of A. tabescens, in all three replicate experiments. Our finding of the lowest mortality among Krymsk 86, Krymsk 1, and Marianna 2624, which all share P. cerasifera (Myrobalan plum) parentage, is consistent with past reports of resistance to A. mellea, but conflicts with reports of susceptibility to A. tabescens. Resistance to A. tabescens of genotypes with Myrobalan plum parentage in our assay may reflect the simplified rooting environment of tissue culture medium, which does not perfectly mimic the soil, where biotic and abiotic factors may interact with host resistance.