Agrobacterium vitis-Induced Electrolyte Leakage in Crown Gall-Susceptible and -Resistant Grape Genotypes

Abstract

Plant tissue disruption caused by strains of <i>Agrobacterium</i> spp. was evaluated by measuring electrolyte leakage from inoculated tissues. Compared to <i>Agrobacterium tumefaciens</i> (AT) strains, all <i>A. vitis</i> (AV) strains (which are the principal pathogens in grape crown gall) produced significantly greater cell disruption in grape shoot and root tissue. AT did not induce significantly greater electrolyte leakage than water control inocula- tions. AV strain K1059 consistently induced greater electrolyte leakage than the other AV strains. AV strain CG50, a polygalacturonase-minus mutant, induced significantly lower electrolyte leakage than the wild-type parental strain, CG49. However, CG50 produced significantly greater leakage than AT in the <i>V. vinifera</i> cultivar Cabernet Sauvignon and the hybrid rootstock C3309. Incubation with cell homogenate from an <i>E. coli</i> strain constitutively producing AV polygalacturonase (DH5pCPP2608) did not induce electrolyte leakage in grape shoot tissue even though it degraded polygalacturonic acid in agarose plates. Shoot tissue of crown gall-resistant grape genotypes <i>V. amurensis</i> (42.7% of Cabernet Sauvignon leakage) and C3309 (60.6% of Cabernet Sauvignon leakage) had significantly less AV-induced electrolyte leakage than crown gall-suscep- tible Cabernet Sauvignon. In inoculated shoots, initial necrosis occurred in the cambium of <i>Vitis</i> stem sections incubated with AV but not with other <i>Agrobacterium</i> strains. Effect of shoot anthocyanin and vigor on AV- induced cell disruption were evaluated to determine if these factors were sources of variation in experiments. Anthocyanin in <i>V. amurensis</i> and C3309 had no significant effect, but slightly chlorotic shoots of C3309 were much more susceptible to AV-induced electrolyte leakage. Stem tissues of tomato, strawberry, black rasp- berry, and apple also displayed electrolyte leakage when incubated with AV.