Synthesis and screening of 5-carbethoxy-N-aryl-4, 6-dimethyl-1,2-dihydropyrid-2- ones as chemical hybridising agents for wheat (Triticum aestivum L.)

In the absence of alternative technology of hybrid development, chemical induction of male sterility-mediated technology based on chemical hybridising agents (CHAs) holds immense potential. 5-Carbethoxy-N-aryl-4,6-dimethyl-1,2dihydropyrid-2-ones have been synthesized by the condensation between substituted anilines with ethyl isodehydracetate and evaluated as chemical hybridising agents on wheat genotypes PBW 343, HW 2046 and HD 2733 at 1000 and 1500 ppm concentration in a field trial during November 2001-April 2002. Maximum male sterility has been induced by 5-carbethoxyN-(4-chlorophenyl)-4,6-dimethyl-1,2-dihyropyrid-2-one 10 followed closely by N-(4-fluoro phenyl)-2-pyridone 5 and N-(4bromophenyl)-2-pyridone 6 causing > 98 per cent induction of spikelet sterility at 1500 ppm on PBW 343. Except CF3containing analogues, in all cases the influence of aromatic substituents on the induction of male sterility is in the order: para > ortho > meta. The substituents at para position have a positive effect on induction of male sterility in the order: Cl (10) > Br (6) >F (5) > CF3 (25) > CN (22) > OMe (13) > NO2 (17) > ethyl (26). QSAR analysis reveals a positive contribution of field effect exemplified by Swain-Lupton constant Fp and molecular weight for the aromatic substitution, but negative contributions of molar refractivity MR for the side chain in influencing the bioactivity in the CHAs. These leads explain the CHA binding fit in macromolecular receptor site. The CHAs act by creating an imbalance in acid-base equilibrium in pollen mother cells resulting in dissolution of callose wall by premature callase secretion.