Effect of Bacillus Bacteria on Hydrogen Peroxide Content and Gene Expression of Hydrolase Inhibitors in Potato Plants Infected with Phytophthora infestans (Mont.) de Bary

Late blight of potato (Solanum tuberosum L.) caused by the oomycete Phytophthora infestans (Mont.) de Bary was studied in respect to the disease resistance induced by Bacillussubtilis Cohn (strains 26D and 11VM) and B. thuringiensis Berliner (strains B-5351 and B-6066) bacteria. The content of hydrogen peroxide, activities of antioxidant (catalases and peroxidases) and hydrolytic (proteases and amylases) enzymes, together with the gene expression of inhibitors of hydrolases, as the parameters related to the resistance, were assessed. The 15-day-old plants of a cv. Rannyaya Rosa susceptible to late blight were derived from microtubers. The plants were sprayed with bacterial suspension (10(8) cells/mL) of one of the mentioned strains of B. subtilis or B. thuringiensis. After 5 days, part of the plants was inoculated with P. infestans zoospores (10(5) spores/mL). After 6, 24, or 48 h postinoculation, the plants were fixed for biochemical analyses. It was found that either B.subtilis or B. thuringiensis reduced the late blight severity on the potato leaves; the effect depended on the particular bacterial strain applied. This was apparently a consequence of H2O2 accumulation and increased expression of the genes encoding protease and amylase inhibitors. The transcriptional activity of the genes of hydrolase inhibitors was stimulated by B.subtilis and B. thuringiensis to different extents. This suggests the existence of different strain-dependent pathways of establishment of bacteria-induced potato resistance to P. infestans.