MAIZE SILK-BROWNING, MAYSIN CONTENT, AND ANTIBIOSIS TO THE CORN-EARWORM, HELICOVERPA-ZEA (BODDIE)

Silks of some maize (Zea mays L.) genotypes turn brown after wounding, while those of other genotypes do not change color. The browning resp onse involves the oxidation of flavones to quinones, and is believed t o be controlled by the p1 locus. A flavone glycoside known as maysin o ccurs in silks of many genotypes, is a growth retardant to the corn ea rworm (CEW) Helicoverpa ten (Boddie), and is among the compounds that undergo a browning reaction. Our study sought to determine whether sel ection for browning and nonbrowning silks would result in correlated c hanges in levels of antibiosis to CEW and in concentrations of maysin. The population '10LDD Sel. Rec. Cycle 0' underwent five cycles of div ergent recurrent selection based solely on the browning reaction to fo rm two populations with nearly all browning or all nonbrowning silks ( '10LDD-BR' and '10LDD-NBR', respectively). A three-location evaluation showed highly significant differences (P < 0.001) between 10LDD-BR an d 10LDD-NBR, respectively, for concentrations of silk maysin (0.185 vs . 0.000% silk fresh weight) and the related compounds 3'-methoxymaysin (0.029 vs. 0.000% silk fresh weight) and chlorogenic acid (0.046 vs. 0.012% silk fresh weight). In a dried silk bioassay based on CEW growt h and development, silks of 10LDD-BR resulted in smaller 8-d larval we ights (63 vs. 335 g) and longer time to pupation (18.6 vs. 13.3 d) tha n those of 10LDD-NBR (P < 0.001 for both traits). Selection for browni ng silks was an easily implemented and effective method for increasing silk maysin concentration and CEW resistance (antibiosis) in 10LDD, b ut would not necessarily be as effective in all populations segregatin g for that trait.