HYDROXAMIC ACID CONTENT AND PLANT DEVELOPMENT OF MAIZE (ZEA-MAYS L) IN RELATION TO DAMAGE BY THE WESTERN CORN-ROOTWORM, DIABROTICA-VIRGIFERA-VIRGIFERA LECONTE

Recently identified resistance factors in two inbreds of maize (Zea ma ys L.) were investigated in relation to their concentrations over the course of maize root development. The purpose of this study was to det ermine the time of peak expression in relation to field resistance to larvae of the western corn rootworm (Diabrotica virgifera virgifera Le Conte). Bi-weekly variation in root hydroxamic acid content, as determ ined by high-pressure liquid chromatography, was compared with field r esistance of 4- to 16-wk-old maize plants. The phytochemical analysis showed that the major hydroxamic acids in corn roots were -dihydroxy-7 -methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA), and its main degradat ion product was 6-methoxy-benzoxazoline (MBOA). The highest concentrat ions of DIMBOA equivalents, 2-hydroxy-7-methoxy-1,4(2H)-benzoxazin-3-o ne (HMBOA) and total hydroxamic acids were found in 6-wk-old root extr acts for the inbred with low susceptibility, and 10-wk-old root extrac ts for the inbred with high susceptibility. In field trials, the inbre d with low susceptibility suffered maximal root damage 8 wk postinfest ation, followed by a rapid and pronounced recovery. Damage to the root system of the inbred with high susceptibility rose rapidly throughout the growing season, reaching a maximum 12 wk post-infestation, follow ed by minimal recovery. Plant morphological factors were unaffected an d are insensitive as measurements of plant damage. Based on the observ ations of this study, it would appear that the concentration of hydrox amic acids in the root systems of maize plants plays a role in resista nce to western corn rootworm larvae under field conditions.