Biological control for grapevine crown gall using nonpathogenic <i>Rhizobium vitis</i> strain ARK-1

Abstract

Crown gall of grapevine, which is caused by tumorigenic Rhizobium vitis, is the most important bacterial disease of grapevine throughout the world. Screening tests of biological control agents resulted in the discovery of a nonpathogenic R. vitis strain ARK-1. By soaking grapevine roots with a cell suspension of strain ARK-1 prior to planting in the field, ARK-1 treatment significantly reduced the number of plants with crown gall symptoms. Several field trials result indicated that ARK-1 was very useful in the field, not only for grapevine but also for various other plant species. In experiments where a mixture of ARK-1 and a tumorigenic strain at a 1 : 1 cell ratio was examined in vitro and in planta, expression levels of the virulence genes virD2 and virE2 of the tumorigenic strain were significantly lower. The suppression of virulence genes, which can result in a reduction of gall formation and the pathogen population, seems to be a unique mechanism of ARK-1. These results indicated that ARK-1 is a promising new agent to control grapevine crown gall.

Biological control agent Rhizobium (=Agrobacterium) vitis strain ARK-1 suppresses expression of the essential and non-essential vir genes of tumorigenic R. vitis

“…Previously, we have reported that a nonpathogenic R. vitis strain VAR03-1, which was isolated from grapevine in Japan and strongly inhibited tumor formation in tomato, grapevine, rose, sunflower, and apple [8–11]. Moreover, we isolated and identified nonpathogenic R. vitis strain ARK-1, which performed much better than VAR03-1 at inhibiting tumor formation in grapevine in greenhouse and field trials, as a new antagonistic strain [12–16]. ARK-1 is also endophytic in grapevine [12].…”

“…Two different mechanisms (antibiotic compounds or quorum-sensing) of biological control of plant crown gall disease using antagonistic bacteria have been reported [8–10, 17–23], but disease suppression mechanism of ARK-1 is different from these two mechanisms [13, 14, 16]. The biological control activity of ARK-1 is likely based on the suppression of some essential virulence genes [14, 16]. Two Rhizobium proteins, VirD2 and VirE2 expressed by virD and virE , respectively, are directly associated with the T-strand [4–6].…”

“…Two Rhizobium proteins, VirD2 and VirE2 expressed by virD and virE , respectively, are directly associated with the T-strand [4–6]. Co-inoculation of grapevine shoots with ARK-1 and Ti strain at a 1:1 cell ratio resulted in significantly lower expression of the virulence genes virD2 and virE2 of Ti strain at 1 dai than expression levels of these genes by a Ti strain inoculated by itself [14, 16]. When a non-pathogenic R. vitis strain VAR06-30, which is neither antagonistic against R. vitis (Ti) nor limit the development of crown gall of grapevine, was co-inoculated with a Ti strain, expression levels of virD2 and virE2 were not affected (Additional file 1: Table S1), [14].…”

Characterization of Migration and Induced Resistance of Rhizobium Vitis Strain ARK-1, a Biological Control Agent Against Grapevine Crown Gall Disease

“…The culture ltrate (CF) of ARK-1 (without cells) or heat-killed culture was not able to inhibit tumor formation on grapevine 16 . These results indicate that ARK-1 must be alive to effectively antagonize gall formation by Ti 27 . ARK-1 has antibiotic activity against Ti strains of Rhizobium spp.…”

“…In other words, even small numbers of ARK-1 could work to a certain extent. We previously demonstrated that ARK-1 was effective in preventing gall formation on grapevine shoots when it was co-inoculated with Ti strains at a 1:1 cell ratio 16,27 . Although the effective concentration of ARK-1 is now being investigated, in the case of R. vitis VAR03-1 gall formation was suppressed when it was inoculated with the pathogen at a 1:1 ratio, but its control activity was decreased at 1:3 or 1:9 ratios 15 .…”