Silício e indutores de resistência no controle da pinta bacteriana do tomateiro e na atividade de enzimas de defesa

Abstract

The bacterial speck caused by Pseudomonas syringae pv. tomato (Pst) (Okabe) Young, Dye & Wilkie has economic relevance to the tomato for industry in Brazil. The use of products that potentiate and/or induce plant defenses is an alternative that meets the requirements of integrated disease management. This study aimed to evaluate the effect of silicon (Si) and chemical inducers in some components of tomato resistance to bacterial speck and activity of enzymes involved in plant defense. In the first study, tomato plants were grown in: soil without calcium silicate (control) (T1), soil without calcium silicate and plants sprayed with Supa Silica® (SS) (2 mL/L SS) (T2) and soil with calcium silicate (0.38 g) (T3), being inoculated by spraying with a suspension of the pathogen. Our research evaluated the incubation period (IP), number of lesions (NL) per plant, severity estimated by the software QUANT 1.0 (SEQ) and leaf concentration of Si, as well as the activity of enzymes peroxidases (POX), polyphenoloxidases (PPO) β-1,3-glucanases (GLU), phenylalanine ammonia lyases (PAL), lipoxygenases (LOX) and concentration of malondialdehyde (MDA). It was assessed the effect of SS in the Pst growth in vitro. There was no significant difference between treatments for the IP and the foliar concentration of Si. No significant differences were found for the NL per plant and SEQ between T3 and control. T2 significantly reduced NL in 46.8 and 45.1% and SEQ in 61.5 and 56.2% when compared with control and T3, respectively. There was negative linear response of SS doses on the Pst growth in vitro. The activity of POX, PPO and GLU was significantly higher in T2 and T3. The activity of FAL and LOX was significantly higher in T3. The MDA concentration was significantly higher in T2 compared to control, in non-inoculated plants and at 7 days after inoculation (d.a.i.), being significantly lower at 10 d.a.i. In the second study, three experiments were conducted to evaluate the effect of jasmonic acid (JA; 0.1 mM), ethephon (ET, 0.5 mM) and acibenzolar-S-methyl (Bion®, ASM; 300 mg/L) sprayed 48 h before inoculation with Pst, evaluating the IP and NL per plant, and the activity of enzymes POX, PPO, GLU and LOX. It was also assessed the effect of JA and ET in the growth of Pst in vitro. Only in experiment 3 incubation period increased significantly by one day in the plants sprayed with ASM compared with control. In all experiments, NL per plant was significantly reduced by JA, ET e ASM in relation to the control reaching values of 38.9, 45.3 and 68.1%, respectively, in experiment 2. The growth of Pst in vitro was not significantly influenced. In some evaluation times JA has significantly raised the activity of POX, PPO and GLU; ASM has elevated the activity of PPO, GLU and LOX, while ET only significantly raised the activity of GLU and LOX compared to the control. The results of these studies suggest that spraying tomato plants with SS and the inducers JA, ET and ASM affected some components of tomato resistance to bacterial speck, and activated the enzymes POX, PPO, GLU, PAL and LOX, involved in defense responses of tomato plants to Pst.