Elicitation of SAR in muskmelon lines against downy mildew caused by Pseudoperonospora cubensis

Exogenous foliar SAR elicitors like Jasmonic acid (JA), Salicylic acid (SA) and Benzothiadiazole (BTH) @ 500μM and Beta Amino butyric acid (BABA) @ 50 mM were tested to induce systemic acquired resistance (SAR) in muskmelon against downy mildew caused by Pseudoperonospora cubensis. Thirty-three germplasm lines/varieties of muskmelon were evaluated for three years and the results revealed that: eleven muskmelon varieties were moderately resistant and showed better response to SAR elicitors against P. cubensis. These elicitors were sprayed on three-week-old plants and effect on induction of defence related proteins and downy mildew severity was studied. Leaf samples were collected upto 7 days post treatment for estimation of total proteins. Sporangial solution (4.0 x 10⁴ sporangia per ml) was sprayed after one week of elicitors spray and per cent disease severity was recorded at 14 days interval. SA, JA, BTH and BABA caused statistically significant increase in total soluble protein in sprayed as well new unsprayed leaves indicating systemic induction of defense related proteins. Mean maximum protein i.e. 11.4 mg/g FW was highest in SA treated, three muskmelon varieties i.e. Punjab Sunehri, MC 2012-9 and MM105-Kajri followed by 11.2 mg/g FW in Hemed and 11.1 mg/g FW in MM4305, respectively. Maximum per cent disease control of 93.48 was observed in SA treated Rough skin variety followed by MM3843 and MM4305 with disease control of 92.07 and 91.27%, respectively. Minimum disease control was observed in BTH treated Kajri plants. Foliar application of SA was most effective followed by JA, BABA and BTH. The response was higher in moderately resistant variety but susceptible variety also showed better response as evident by decreased disease severity. Therefore application of elicitors followed by inoculation with P. cubensis help in eliciting the levels of defense related proteins which play an important role in protecting muskmelon against downy mildew disease.