Biochemical and Physiological Factors Imparting Tolerance in Safflower against Aphid, Uroleucon compositae (Theobald)

Development of aphid tolerant cultivars is needed in pest management in safflower, where the crop is often grown with least plant protection measures. Sixteen recombination inbred lines (RILs) of F₇ generation of the cross, CO-1 (susceptible) X EC-523368-2 (tolerant) along with parents were studied to understand the biochemical and physiological factors operating in tolerant RILs. Eight RILs were confirmed tolerant (A.I.I., 1.1 - 1.5) and 8 RILs were found highly susceptible (A.I.I., 4.5- 5.0) to aphid. Susceptible RILs underwent more oxidative stress through more H₂O₂ (4908.0 ± 1287 nmols g^-1 fresh weight) production due to aphid infestation compared to tolerant RILs. Activity reactive oxygen species (ROS) enzymes, superoxide dismutase (53.63 ± 0.29 (nmols g^-1 fresh weight) and catalase (33.73 ± 3.3 nmols g^-1 fresh weight) and amount of metabolites like total phenols (169.60 ± 16.49 μg g^-1 gallic acid equivalent) were more intolerant RILs than susceptible ones. The tolerant RILs were physiologically more efficient with higher chlorophyll (8.45 ± 0.91 mgL^-1), net photosynthesis (28.9 ± 3.31 μmole CO₂ m^-2 sec^-1), net assimilation rate (0.289 ± 0.033 μmole CO₂ cm^-2 leaf area) and intrinsic water use efficiency (0.35 ± 0.05 μmole CO₂ mole^-1 H₂O) than the susceptible RILs.