Role of 6-Methoxybenzoxazolinone in Inbred Resistance of Host Plant (Maize) to First-Brood Larvae of European Corn Borer123

Abstract

Eleven maize inbreds were used in a quantitative analysis for 6-methoxybenzoxazolinone (6MBOA) by the technique of isotopic dilution. Carbon¹⁴-labeled 6MBOA was synthesized, and isolation and purification of 6MBOA from plant tissues were accomplished by thin layer chromatography. A correlation exists between the amount of 6MBOA produecd by 11 inbred strains of maize at the whorl stage of plant development and the field rating of resistance of the inbred strains to 1st-brood larvae of the European corn borer, Ostrinia nubilalis (Hübner). The correlation can he expressed by the general equation: Log₁₀(concentration of 6MBOA) = K (resistance rating) + B, where K and B are constants. Lighly resistant inbred lines yielded about 10 times more 6MBOA than the highly susceptible inbred strains. The yield of 6MBOA or the content of the glucoside precursor of inbred strains of maize may serve as an indicator of the degree of resistance a given inbred strain may express in the field. Bioassay tests of 6MBOA showed the compound to be an inhibitor of the rate of borer pupation when it was incorporated into an artificial diet at a concentration of 0.5 mg/g diet. No significant difference of mortality or average pupal weight was detected. Addition of vitamin supplement to the diet of the borer grossly attenuated the effect of 6MBOA. If 1 g of diet is assumed to be equivalent to 1 g of tissue from fresh corn plants, the concentration of 0.5 mg per g diet is twice the concentration found in any inbred strain analyzed for content of 6MBOA. Evidence indicates that 6MBOA is of little consequence in the phenomenon of resistance. However, precursors of 6MBOA may play an active role.