Salicylic acid induced defence responses in Curcuma longa (L.) against Pythium aphanidermatum infection

The soilborne Oomycete, Pythium aphanidermatum is the causal agent of rhizome rot disease, one of the most serious threats to turmeric crops in India. At present, effective fungicides are not available. Here we report the enhanced resistance response induced by salicylic acid (SA) in susceptible turmeric plants. The enzymatic activities of pathogenesis related (PR) proteins in control and SA treated turmeric plants were measured. SA pretreatment elicited marked increases in the activity levels of protease, trypsin and chymotrypsin inhibitors, soluble and ionically bound peroxidase activity. Such an increase in enzyme activities and protease inhibitors was enhanced and occurred much more rapidly in P. aphanidermatum infected rhizomes than those that were previously treated with SA (0.5 mM) suggesting that increased activities of peroxidases and protease inhibitors may play a role in restricting the development of disease symptoms in the rhizomes infected with P. aphanidermatum as evidenced by reduction in cell death. SA also induced new polypeptides in turmeric rhizomes corresponding to 19.0 and 41.0 kDa. The results demonstrated that SA is an effective resistance activator in turmeric, and a potentially useful agent for the control of rhizome rot disease.