CORNGRASS1 OF MAIZE (ZEA-MAYS L) DELAYS DEVELOPMENT OF ADULT-PLANT RESISTANCE TO COMMON RUST (PUCCINIA-SORGHI SCHW) AND EUROPEAN CORN-BORER(OSTRINIA-NUBILALIS HUBNER)

Based on morphological evidence, researchers have proposed that Corngr ass1 (Cg1) of maize (Zea mays L.) is a heterochronic mutation that pro longs the juvenile-vegetative phase because distal tissues display juv enile traits that normally occur only basally, Physiological or bioche mical evidence in support of this hypothesis is lacking, Disease and i nsect resistance often depends on physiological, biochemical, and morp hological factors and can vary during ontogeny, We evaluated resistanc e to common rust (Puccinia sorghi Schw,) and European corn borer (Ostr inia nubilalis Hubner) in cg1 and wild-type segregating families in or der to test the hypothesis that Cg1 is a heterochronic mutation that e xtends the juvenile-vegetative phase, In backgrounds with high express ion, Cg1 mid-whorl leaves had similar resistance as Cg1 and wild-type seedling leaves, whereas wild-type mid-whorl leaves differed in resist ance from the other three leaf types, In the Mo17 background, which ha s reduced Cg1 expression, Cg1 mid-whorl leaves had resistance levels i ntermediate between wild-type seedling and mid-whorl levels, These res ults support the hypothesis that Cg1 prolongs the juvenile-vegetative phase and suggest that heterochrony may be among the factors responsib le for disease and insect resistance in normal populations of maize.