Salicylic acid and Piriformospora indica induced modulation of stress resistance mechanism in Tomato (Solanum lycopersicum L.)

Abstract

The study entitled “Salicylic acid and Piriformospora indica induced modulation of stress resistance mechanism in tomato (Solanum lycopersicum L.).” was conducted at College of Agriculture, Vellayani, Thiruvananthapuram, during 2020 – 2021. The primary objective of this study was to analyse the salicylic acid induced NPR1 gene expression as well as Piriformospora indica induced resistance modulation to stress and its persistence and transmission through seeds. The induced resistance in plants can be classified as Systemic Acquired Resistance (SAR), mediated by the signalling molecule salicylic acid and Induced Systemic Resistance (ISR) which was induced by the presence of non-pathogenic plant growth promoting fungi or bacteria. In the present study two treatments, plant growth promoting endophytic basidiomycete fungus Piriformospora indica (biological inducer) and salicylic acid (chemical inducer) were applied on bacterial wilt resistant (Vellayani Vijay, KAU) and susceptible (Pusa Ruby, IARI) varieties of tomato and the expression rate of Non-expresser of pathogenesisrelated genes1 (NPR1) gene was evaluated using q-RTPCR. In first generation, one set of seed were inoculated with P. indica (1%) by incorporating it into the potting mixture before filling the pot-tray cavities. After confirming endomycorhizal root colonization, leaf samples were collected for analyzing NPR1 expression. Seeds from these plants were collected and progeny seedlings were maintained for analysing transgenerational expression of NPR1 gene. Second set of seeds were sown in the nursery and two weeks old seedlings were transplanted in to pots. Salicylic acid(100ppm) was sprayed at flowering stage and NPR1 gene expression was analysed on 5th day and 7th day after treatment in leaves and compared to next generation (in two weeks old seedlings) for understanding transgenerational expression. The evaluation of stress tolerance of the treated (P. indica and S.A) plants was done on progeny seedlings of Vellayani Vijay by treating it with a low density inoculum of virulent Ralstonia solanacearum (106 cells/ ml). Similarly abiotic stress tolerance evaluation was carried out by subjecting the plants to a higher temperature in polyhouse. Physiological and biochemical observations showed that application of P. indica and salicylic acid can induce resistance by regulating the enzyme activities and other physiological parameters. The resistant variety (Vellayani Vijay) gave a relative change of 7 fold and 4 fold for NPR1 expression (on 5th day and 7th day respectively) on the application of salicylic acid. The susceptible variety (Pusa ruby) showed a relative change of 6 fold and 2 fold for NPR1 expression on the application of salicylic acid. A relative change of 7 fold and 5 fold was shown respectively for first generation and second generation on treatment with salicylic acid, which confirms a transgenerational expression of the defence related gene. Similarly P.indica also showed transgenerational expression with a relative change of 5 fold and 2 fold respectively for first and second generation. P. indica treatment and exogenous application of salicylic acid can induce resistance in plants and thus induced resistance can be transferred to progenies. Transgenerational induction might be vital to the long-term survivorship of plant species on novel environments or adapt to other forms of environmental change.