Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2010
Publication Date: 4/30/2010
Publication URL: http://www.actahort.org/books/861/861_70.htm
Citation: Kluepfel, D.A., Yakabe, L., Parker, S., Mcclean, A.E., Maccree, M.M. 2010. DETECTION AND IMPLICATIONS OF EARLY AGROBACTERIUM TUMEFACIENS INFECTION OF PARADOX SEEDS AND SEEDLINGS. Acta Horticulturae. 861:497-500. Interpretive Summary:
Technical Abstract: Paradox (Juglans hindsii x J. regia), the dominant rootstock used in California, USA walnut production, has many desirable horticultural characteristics, but is highly susceptible to crown gall. Crown gall, caused by the soil-borne bacterium Agrobacterium tumefaciens, can not be consistently controlled with soil fumigation. This observation, in conjunction with observations of galls at above ground grafting wounds, led to the hypothesis that A. tumefaciens inoculum could also be endophytic in walnut seeds or seedlings. Preliminary investigations examining Paradox seeds collected from commercial mother trees indicate that A. tumefaciens can reside in/on Paradox seeds. Since sampling was conducted at multiple times during seed production, it was ascertained that seed populations of A. tumefaciens did not originate from the mother tree, but from orchard soil underneath the mother trees that came into contact with the seeds. In greenhouse experiments, seeds surface inoculated with A. tumefaciens produce seedlings with galls at the crown and/or roots. Endophytic populations of A. tumefaciens was also found in shoot and root tissues. These data suggest that A. tumefaciens inoculum can reside inside plant tissue and that timely Paradox seed collection which limits seed contact with the orchard floor could be an important first step in preventing crown gall on walnut.