Biochemical characterization of fenugreek (Trigonella foenum-graecum L.) genotypes for downy mildew resistance

Downy mildew (Peronospora trigonella Gaumann) of fenugreek is the most serious disease all over the country.The leaves of fenugreek genotypes AM-232, AM-251, AM-85, AM-256 and AM-286AM-660, AM-661, AM-663, AM-651 AM-665 and AFg-1 were taken after 5 days of visual symptoms from the field for biochemical characterization. Biochemical data were correlated with percent disease index (PDI) score. Maximum PPO activity was observed in AM-85 (10.5 unit min-1g -1 protein) and AM-256 (8.5 unit min-1g -1 protein). Genotypes AM-85 and AM-256 had PDI score of 26.3 and 16.3, respectively for downy mildew disease. Catalase activity was observed maximum in AM-660 (17.5µmol H2O2 min-1 g-1 protein) followed by AM-660 and AM-232 with a PDI score of 21.3, 23.8 and 8.8 respectively. Peroxidase activity was found maximum in AM-651 (1102.6 µmol guaiacol min-1 g-1 protein) with a maximum PDI score (32) while minimum activity was observed in AM-256 (517µmol guaiacol min-1 g-1 protein). Total phenol concentration in fenugreek genotypes was observed from 1.1 to 4.0 mg-1 g FW . Genotypes with higher phenol content scored less PDI than those with lower phenol content. PCA-biplot and correlation analysis revealed a significant positive correlation between PDI score and peroxidase activity while a significant negative correlation of PDI score was observed with catalase(-0.769**), PPO activity (-0.754**) and phenol content (0.570*). Biochemical and PDI score data were further used to obtain hierarchial clustering of genotypes which clustered fenugreek genotypes into three groups. The first group consisted of AM-232 and AM-256 with a PDI score of 8.8 and 16.3, respectively and identified as resistant sources for downy mildew disease of fenugreek. Thus, the present study demonstrated that PPO, peroxidase and catalase activity along with phenol content can distinguish the resistant germplasm.