Chemical hybridizing agents for chickpea (Cicer arietinum L.): leads from QSAR analysis of ethyl oxanilates and pyridones.

In the self-pollinated crops such as chickpea, induction of male sterility by deployment of chemical hybridizing agents (CHAs) facilitating "two-line" approach holds immense potential in heterosis breeding. A total of 40 test CHAs comprising 20 ethyl oxanilates and 20 pyridones were screened as potential CHAs on chickpea (variety BG 1088) at 500, 800, and 1000 ppm. Three test compounds mostly having either F (4)/Br (5)/CF(3) (19) at the para position of the aryl ring from a pool of 20 ethyl oxanilates were identified as the most potent CHAs causing >or=99% induction of pollen sterility and >90% total flower sterility at 1000-ppm test concentration. Among pyridone derivatives, N-(4-chlorophenyl)-5-carbethoxy-4,6-dimethyl, 1,2-dihydropyrid-2-one (26) was found to be the most active. Quantitative structure activity relationship (QSAR) analysis has revealed a direct involvement of Swain-Lupton field constant, F(p), with the target bioactivity which implied that field rather than resonance effect (R) had a positive effect on the activity. The real guiding principle for selectivity was found out to be the hydrophobic parameter pi value. The QSAR models indicated that increased steric bulk at the 4-position on the phenyl ring is associated with enhanced activity. The CHAs appeared to act by mimicking UDP-glucose, the key substrate in the synthesis of callose, or lead to an imbalance in acid-base equilibrium in pollen mother cells resulting in dissolution of callose wall by premature callase secretion.