The ability of Meloidogyne javanica to suppress salicylic acid-induced plant defence responses

Abstract

Summary Suppression of the defence system of plants by some plant pathogens is an important mechanism of their parasitism, and plant-parasitic nematodes use several mechanisms to affect different parts of the plant defence system. This study was designed to investigate the ability of a root-knot nematode, Meloidogyne javanica, to reduce or suppress the plant (tomato) immune system, before or after activation by a strong inducer, salicylic acid (SA). The experimental treatments were tomato plants inoculated with nematodes alone, plants pre-treated with SA and then nematodes (‘SA then nematode’), plants treated with SA after nematode inoculation (‘nematode then SA’), plants treated with SA alone, and plants treated with sterile distilled water. The results showed that treatment of the plants with SA before or after nematode infection reduced nematode disease indices compared to the control (nematode alone). The number of eggs per individual egg mass, in ‘nematode then SA’ treatment was significantly greater than the control, which shows the effect of nematodes on reducing the plant defence mechanism in this treatment. Evaluation of the activity of some defence enzymes such as chitinase, protease, phenylalanine ammonia lyase, catalase and density of hydrogen peroxide also showed that M. javanica is able to suppress these compounds in the ‘SA then nematode’ treatment, and to a greater extent in the ‘nematode then SA’ treatment. Suppression of plant defence responses by phytonematodes is of great importance in their synergistic relationship with secondary pathogens and plants.

Constitutive and Inducible Expression of Genes Related to Salicylic Acid and Ethylene Pathways in a Moderately Resistant Tomato Cultivar Leads to Delayed Development of Meloidogyne javanica

“…Based on these results, it is likely that the expression levels of other SA-responsive genes are also constitutively higher in ALYSTE F-1 at 14 DAI, which ultimately delays the development of M. javanica and reduces the nematode reproduction rate (Table 2). Several studies have shown that the application of SA, or chemicals with a similar action, can reduce nematode infection [23,[37][38][39]41,42]. Qtu et al (1997) [90] described an important role of chitinases in a resistant soybean cultivar during the M. incognita infection, and concluded that JA and SA pathways are likely involved in soybean resistance response.…”

“…Salicylic acid is a major defense hormone against biotrophic and hemibiotrophic pathogens [36]. The application of SA, or chemicals with similar actions, can reduce nematode infection, and in many cases, nematodes are able to suppress the SA pathway [5,15,35,[37][38][39][40][41][42]. Previous studies have shown that mutants or transgenics with lower SA levels or signaling are more sensitive to nematode attack [37,38], whereas increased SA levels or signaling reduces nematode infestation [43][44][45][46].…”