Characterization of Cylindrocarpon populations associated with replant disease of almond and peach
L. S. SCHMIDT (1), R. G. Bhat (2), G. T. Browne (1)
(1) USDA ARS, Davis, CA, U.S.A.; (2) University of California, Davis, CA, U.S.A.
Growth and cumulative yield of replanted almond and peach orchards are often seriously compromised by Prunus replant disease (PRD), a poorly understood soilborne complex affecting successive plantings of Prunus. Previously, our culture-based (CB) and culture-independent (CI) examinations of fungal, bacterial, and stramenopile communities revealed that the fungus Cylindrocarpon (Cyl) was among organisms commonly associated with PRD, yet little is known of Cyl on Prunus. We examined these Cyl species using CB and CI methods. Eighty-eight cultured isolates, each from roots of a different tree, were obtained from six California (CA) almond and peach orchards affected by PRD. The isolates were identified based on BLASTn searches of sequences of three loci (rDNA ITS, beta-tubulin, mtSSU rDNA). Also, from a subset of 17 of the trees among three of the six orchards, Cyl populations were examined using CI amplification and sequencing of ITS 2 rDNA fragments. Neighbor-joining cluster analysis and BLAST searches identified 87 of the cultured isolates as C. macrodidymum; one was C. liriodendri. Similarly, 117 of the 121 CI Cyl clones were C. macrodidymum; four were C. destructans. Our results indicate that C. macrodidymum is the most prevalent species of Cyl associated with PRD in CA. We are testing pathogenicity and aggressiveness of Cyl on Nemaguard rootstock for almond and peach; preliminary results indicate that at least some isolates of C. macrodidymum are pathogenic.
© 2011 by The American
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