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

Knowledge of the molecular changes in resistant and susceptible cultivars during nematode attack is essential for developing plant resistance. Increased expression of genes related to the synthesis and signaling of salicylic acid, jasmonic acid, and ethylene is known to induce expression of genes related to defense against plant parasitic nematodes. Here, we inoculated approximately 3000 s-stage juveniles (J2s) of Meloidogyne javanica to moderately resistant and highly susceptible tomato cultivars (ALYSTE F-1 and Dutch Mobil, respectively) to compare the developmental disease stages. The roots of each cultivar were collected daily until 30 days after inoculation (DAI). The roots were stained with acid-fuchsin and dissected under a microscope. The results showed that a few parasitic J2s were converted to J3s in the moderately resistant cultivar at 14 DAI, at which time, the highly susceptible cultivar had the highest number of J3s. Comparison of hormonal pathways in the two cultivars revealed that the expression of genes related to the ethylene pathway in ALYSTE F-1 was more strongly upregulated than in Dutch Mobil at 14 DAI. Moreover, the jasmonic acid pathway in the roots of both cultivars decreased at 14 DAI. The expression of genes related to salicylic acid synthesis and signaling was not significantly different between the two cultivars with regard to their non-inoculated controls, respectively, but ALYSTE F-1 in general showed constitutively higher levels of these genes compared to Dutch Mobil at 14 DAI. These results suggest that constitutive and induced expression of genes related to the salicylic acid pathway and ethylene pathway, respectively, delay the development of M. javanica J2s in ALYSTE F-1.