Evaluation of Two Procedures to Select for Resistance to the European Corn Borer in a Synthetic Cultivar of Maize

A recurrent selection breeding procedure was used to reduce leaf-feeding damage by lst-generatlon European corn borer (ECB), Ostrinia nubilalis Hübner, and to increase 2,4-dihydroxy- 7-methoxy-(2H)-l,4-benzoxazin-3(4H)-one (D1MBOA) content in a synthetic maize, Zea mays L., cultivar (BS1); chemical analysis was for 6-methoxybenzoxazolinone (MBOA). Thin-layer chromatography (TLC) plate ratings (intensity of MBOA on plates) also were determined. Cycle populations, population crosses, and check crosses were evaluated. Plants from the ClI, C2I, and C3I populations were selected on the basis of insect damage, whereas the CID, C2D, and C3D populations were selected by chemical analysis for DIMBOA. Leaf-feeding damage caused by the insect, MBOA concentration in whorl leaf tissue, and TLC plate ratings of MBOA intensity on TLC plates were all improved with recurrent selection procedures when selection was made on the basis of insect damage and also when selection was made by chemical analysis for MBOA in leaf tissue. Each method of selection accumulated about the same level of resistance. Gene actioin for these traits was found to be primarily additive. One hundred S₁ lines from each of the CO, C31, and C3D populations were evaluated for leaf-feeding resistance by first-generation ECBₛ. Mean leaf-feeding ratings of the S₁ lines from CO, C3I, and C3D populations were 4.3, 2.8, and 2.5, respectively. Means of CO S₁'s were significantly greater (higher susceptibility) than were the means of the C3I and C3D S₁'s. The mean of the C3I S₁'s was greater than the mean of the C3D S₁'s. These results were consistent with the results of the C3 population per se. Plants from cycle populations and population crosses were susceptible to sheath-collar feeding and stalk feeding by second-generation ECBs.