Indian Phytopath.gfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 54 (3) : 284-287 (200 I) Influence of salicylic acid on protein content and catalase activity in relation to systemic acquired resistance in cowpea against root rot AMARESH CHANDRA, ANJALI ANAND, PRANAB KUMAR MANDAL and PRADEEP SAXENA Crop Improvement Division, Indian Grass/and and Fodder Research Institute, Jhansi 284 (J(J3 ABSTRACT: Salicylic acid treatment as foliar spray caused a reduction in the root rot disease caused by Rhizoctonia so/ani to control as revealed by disease progress curve. Total soluble proteins and catalase activity in leaves were measured in seven genotypes of cowpea differing in their reaction to the disease sprayed with 0.02% salicylic acid. Soluble proteins declined in response to salicylic acid treatment in all genotypes except UPC 4200. Though maximum decline in catalase activity was observed initially in IGFRI 450, a significant drop in it was noticed in UPC 4200 until four days after treatment. Key words: Cowpea, root rot, SAR, salicylic acid The systemic acquired resistance (SAR) is an im- portant component of plant's defense against diseases where initial infection provides systemic resistance to subsequent infection by a variety of bacterial, fungal and viral pathogens (Gaffney et al., 1993). In recent years a large number of chemicals which mimic the function of pathogen in inducing the SAR have been reported (Ryals et al., 1996). Salicylic acid (SA) which is known to be present in plants has been found to induce resistance to viral infection when applied to tobacco (Antoniw and White, 1980; White, 1979). Maximum level of SA (19-37mg/g fr.wt.) has been reported to be present in rice seedlings (Silverman et aI., 1995). The interest in this simple phenolic com- pound become prominent when it was demonstrated that SA is produced by plants during the resistance responses, suggesting that SA may be a natural signal in the induction of resistance (Malamy et aI., 1990; Metraux et al., 1990; Malamy and Klessig, 1992). Chen et al. (1993) have cloned and sequenced the salicylic acid binding protein which exhibited catalase activity. They have also reported that the action of SA in SAR is mediated by elevated amounts of HP2 by inhibiting the catalase activity. Apart from this, it has also been reported that SA induces many proteins simi- lar to the nature of pathogenesis related proteins (Linthorst, 1991). This study reports the catalase activ- ity and total leaf soluble proteins in seven different genotypes of cowpea in response to salicylic acid treat- ment and its effect on root rot disease caused by Rhizoc- Ionia solani. MATERIALS AND METHODS Surface sterilized seeds of seven cowpea genotypes namely IFC 901, 902, 8401, 8402, Bundel 2-8503, IGFRI 450 and UPC 4200 were grown in 12- inch clay pots containing steam sterilized farm soil in six repli- cations at the Indian Grassland and Fodder Research Institute, Jhansi during 1996. Thinning was done to keep ten plants per pots after seven days of sowing. One - month - old plants were sprayed twice at a week interval with 0.02% solution of SA (pH 6.5). Simulta- neously, half of the plants (i.e. 3 replications) were inoculated with R. solani @ 10gm (10 gm mycelial mat with media)/kg sterilized soil, grown on Potato- Dextrose-.Agar for fifteen days, to make the soil sick. Rest three replications were used as control. After in- oculation, plants were observed fortnightly for mortal- ity. The disease first appeared in the form of yellowing of leaves which later droop. The plants showed wilting within a week time. In some cases dark lesions were produced on bark at ground level. The disease inci- dence was recorded on 0-9 point. At the end of the experiment, on the basis of disease incidence, area under disease progress curve (AUDPC) was estimated by using following formula: K AUDPC (A - Value) L~(Si +Si_l)xd i-3