Interaction between silicon amendment, bacterial wilt development and phenotype of Ralstonia solanacearum in tomato genotypes

Silicon amendment significantly reduced bacterial wilt incidence expressed as area under disease progress curve for tomato genotypes I.390 (susceptible) by 26.8% and King Kong2 (moderately resistant) by 56.1% compared to non-treated plants grown in hydroponic culture. However. wilt incidence in silicon-treated plants of genotype L390 reached 100% at 13 days post-inoculation (dpi), while in genotype King Kong2, plant death was retarded by 6 days, with 20% reduction of final wilt incidence. Bacterial numbers were significantly lower in silicon-treated compared to non-treated plants in King Kong2 at 2 dpi in midstems and in all organs at 5 dpi, and in Hawaii 7998 (resistant) in all organs at 2 dpi. Differences between genotypes were obvious on midstem level (5 dpi), where bacterial populations were generally significantly lower compared to roots. Increased tolerance was observed in genotypes L390 and King Kong2 with silicon treatment. Silicon accumulated in roots and was low in stems and leaves. Inoculation with Ralstonia solanacearum did not significantly affect silicon uptake and distribution. Negative correlations between root silicon content and bacterial numbers of midstems in genotypes Hawaii 7998 and King Kong2 suggested an induced resistance. Indications for an influence of host genotype and silicon treatment on the phenotypic conversion of R. solanacearum strain To-udk2-sb from fluidal to non-fluidal colonies in planta were observed. This is the first report on the effect of silicon on a bacterial disease and in a silicon-non-accumulator plant. (C) 2004 Elsevier Ltd. All rights reserved.