A gene controlling biosynthesis of isoorientin, a compound in corn silks antibiotic to the corn earworm

The corn earworm (Helicoverpa zea Boddie) is an important pest of corn (Zea mays L.), and its larvae sometimes cause severe ear damage to hybrids grow n in the southeastern United States. The antibiotic compound isoorientin is present in silks of some corn inbreds at a concentration that is harmful t o corn earworm larvae. The inbred T21X, which produces biologically active levels of this compound (>2.0% dry weight), was evaluated in hybrid combina tion with two other non-isoorientin producing inbreds to determine the mode of isoorientin inheritance in corn silks. Silk masses from individual ears of each parent, the F-1, F-2, first backcrosses, F-3 families and selfed B C1 families were evaluated in 1994 and 1995 for isoorientin concentration. Reversed-phase high performance liquid chromatography (HPLC) was used to ma ke chemical determinations. Segregation ratios in the F-2, first backcross to T218, F3 families and selfed BC1 families were tested. The rests were co nclusive in the identification of a single recessive gene controlling high isoorientin concentration in the silks of inbred T218. Some evidence for mo difiers exists, in that there was a statistically nonsignificant trend for more plants than expected to occur in the low isoorientin concentration cla sses. Development of inbreds with a high concentration of the simply inheri ted isoorientin in their silks will add to the arsenal of compounds availab le in corn silks to combat damage to corn by corn earworm larvae.