Induced resistance in tomato by SAR activators during predisposing salinity stress

Abstract

Plant activators are chemicals that induce disease resistance. The phytohormone salicylic acid (SA) is a crucial signal for systemic acquired resistance (SAR), and SA-mediated resistance is a target of several commercial plant activators, including Actigard (1,2,3-benzothiadiazole-7-thiocarboxylic acid-S-methyl-ester, BTH) and Tiadinil [N-(3-chloro-4-methylphenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide, TDL]. BTH and TDL were examined for their impact on abscisic acid (ABA)-mediated, salt-induced disease predisposition in tomato seedlings. A brief episode of salt stress to roots significantly increased the severity of disease caused by Pseudomonas syringae pv. tomato (Pst) and Phytophthora capsici relative to non-stressed plants. Root treatment with TDL induced resistance to Pst in leaves and provided protection in both non-stressed and salt-stressed seedlings in wild-type and highly susceptible NahG plants. Non-stressed and salt-stressed ABA-deficient sitiens mutants were highly resistant to Pst. Neither TDL nor BTH induced resistance to root infection by Phytophthora capsici, nor did they moderate the salt-induced increment in disease severity. Root treatment with these plant activators increased the levels of ABA in roots and shoots similar to levels observed in salt-stressed plants. The results indicate that SAR activators can protect tomato plants from bacterial speck disease under predisposing salt stress, and suggest that some SA-mediated defense responses function sufficiently in plants with elevated levels of ABA.

Predisposition in Plant Disease: Exploiting the Nexus in Abiotic and Biotic Stress Perception and Response

“…The efficacy of plant activators depends on the environmental context, and abiotic stresses are expected to influence JA and SA network dynamics during pathogen attack (24). Encouraging are results acquired when using the SA mimic tiadinil, albeit conducted under highly controlled experimental conditions, which induces disease protection in tomato under salinity stress (152). This and other studies suggest that plant activators may offset or at least function adequately under conditions of predisposing stress, but further assessment under the environmental rigors of the field is needed.…”

“…In both diseases, nahG plants were more susceptible than the wild type, with salt stress causing the expected additional increase in disease severity in both host backgrounds (152). However, the impact of predisposing stress in the nahG lines was proportionally the same as in the wild type.…”

“…ABA induction precedes or temporally parallels the onset of the predisposed state, which is evident within 4-6 hours of salt exposure and persists for up to 24 h after salt removal, well after the decline in ABA levels to near prestress levels. Salinity stress in roots and its systemic impact are evident in various interactions, with similar effect in leaves challenged with the bacterial speck pathogen Pst (152,183) stress episode, these mutants show a significantly diminished predisposition to P. capsici relative to wild-type plants (50). The difference is most dramatic in the sitiens mutant, having the most depressed phenotype, with less than 10% of the ABA levels of wild-type seedlings.…”

Effects of Some Exogenous Applications on Some Agricultural Crops under Salt Stress

“…Due to these facts, researchers are trying to develop some effective treatments such as exogenous proline [15], [16,] [17], glycine betaine [14], paclobutrazol [7], triacontanol [18], selenium, silicone [19], salicylic acid [1], plant activator [20] and nitrogen [21] applications to reduce the detrimental effects of salinity.…”

Induced plant responses to microbes and insects

“…In recent years, many candidate molecules that function as systemically transported signals have been characterized (reviewed by Shah and Zeier, 2013). Other aspects of SAR, such as detailed insight in transcriptional reprogramming during SAR (Gruner et al, 2013), the role of the NPR1 regulatory NIMIN proteins in SAR (Hermann et al, 2013), and the effect of abiotic stress on the expression of SAR (Pye et al, 2013) are discussed in this Research Topic and provide interesting new insights into the field of SAR research. Plant hormones emerged as important regulators of local and systemic induced defense responses.…”