No abstract

Pseudomonas fluorescens (two native strains, one collection strain and their strain mixtures in all possible combinations) when applied through seed, seedling dip, soil and on leaf significantly reduced the tomato spotted wilt virus (TSWV) disease. In P. fluorescens-treated plants, the peroxidase and phenylalanine ammonia-lyase activity increased. Accumulation of phenolic compounds and lignin were shown to be increased in the P. fluorescens-treated plants. Isoperoxidase native PAGE indicated that the peroxidase isoforms in tomato plants induced by fluorescent pseudomonads were different from the control plants; this suggests that the general phenylpropanoid pathway is probably stimulated in tomato plants treated which in turn led to significant reduction in TSWV.

To understand the suppression mechanisms against disease resistance in rice, we took advantage of the fact that suspension cultured cells exhibit many of the defence responses that are characteristic of intact tissues. In this study we constitutively measured the Rhizoctonia solani and Sarocladium oryzae toxins, induced and suppressed levels of phenylalanine ammonia lyase, peroxidase, superoxide dismutase, phenols, catalase, b-1,3-glucanase and chitinase in rice suspension cultured cells. The addition of Rhizoctonia solani and Sarocladium oryzae toxins separately in suspension cultured cells shows the suppression of defence enzymes and compounds at 24 h and 48 h respectively except SOD. The rice cultivar IR50 delays the disease suppression effect when compared to the other cultivars viz., Pusa Basmati and Co 43. The PR proteins (namely b-1,3-glucanase and chitinase) activities in rice suspension cultured cells were reduced during 48 h and 72 h after the addition of Rhizoctonia solani toxin, whereas the activities were suppressed only after 72 h when inoculated with Sarocladium oryzae toxin. Selective suppression of these defence enzymes and compounds by Rhizoctonia solani and Sarocladium oryzae toxin shows that toxins play a major role during pathogenesis in rice cells.