Incidence of Agrobacterium tumefaciens biovar 1 in and on ‘Paradox’ (Juglans hindsii x Juglans regia) walnut seed collected from commercial nurseries

Authors: YAKABE, L. - US Department Of Agriculture (USDA); PARKER, S. - US Department Of Agriculture (USDA); Kluepfel, Daniel

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2014
Publication Date: 6/15/2014
Publication URL: http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-07-13-0742-RE
Citation: Yakabe, L.E., Parker, S.R., Kluepfel, D.A. 2014. Incidence of Agrobacterium tumefaciens biovar 1 in and on ‘Paradox’ (Juglans hindsii x Juglans regia) walnut seed collected from commercial nurseries. Plant Disease. 98:766-770.

Interpretive Summary:

Technical Abstract: The walnut rootstock Paradox (Juglans hindsii (Jeps) Rehder x J. regia L.) is susceptible to Agrobacterium tumefaciens (7) which often results in a high incidence of crown gall in nursery or walnut production orchards. Though A. tumefaciens is susceptible to the commonly used preplant soil fumigants, crown gall incidence can rise above acceptable levels. We examined the ability of Paradox seeds to acquire A. tumefaciens as a function of harvest method used prior to planting. Over a two year period at two participating commercial nurseries, Paradox seeds were collected directly from the mother tree without contacting the soil or gathered after sitting on the orchard floor for up to 28 days. A. tumefaciens was never detected in/on the 2,650 seeds collected directly from the mother tree. Both virulent and avirulent A. tumefaciens strains were detected in and on the husk of nuts incubated on the orchard floor at a frequency directly proportional to the time spent on the orchard floor. Regardless of A. tumefaciens contamination in/on the husk, A. tumefaciens was never detected in the seeds interior. Avoiding soil-borne populations of A. tumefaciens at the time of seed collection will play an important role in managing crown gall.