TRANSMITTIBILITY OF EAR RESISTANCE TO EUROPEAN CORN-BORER IN SWEET CORN TESTCROSSES AND RESISTANCE STABILITY

Concern over insecticide usage for control of European corn borer (Ostrinia nubilalis Hubner) in sweet corn (Zea mays L.) in recent years has increased the need for genetic control. Our objectives were to determine the degree of ear feeding resistance transmitted by resistant breeding lines to testcrosses and to investigate the-relationship between resistance and both ear silk channel length, and infestation level. Testcrosses averaged 35% acceptable ears compared to 7% for two commercial control hybrids and 45% for the lines pei se when artificially infested at the ear tip at mid-silk at two locations. Generally, resistance in the testcrosses was closer to the resistance level of the resistant parent, indicating good combining ability for resistance. Heterosis above the resistant parent was found in 8 of 12 testcrosses. Across entries, ears having relatively longer silk channel length tended to have less damage but the relationship was not strong (r(2) = 0.24, P < 0.01). When silk channels were artificially shortened at infestation, resistance levels were lower, but five of seven lines had a higher proportion of acceptable ears than did the control hybrid. Across increasing levels of infestation from 50 to 200 neonate larvae her ear eight of nine lines had higher resistance (P < 0.05) than the control.