Incorporating an herbicide resistance gene into tropical maize with inherent polygenic resistance to control Striga hermonthica (Del.) Benth

P>Striga hermonthica is a widespread parasitic weed species that can cause considerable yield loss in susceptible maize cultivars in West and Central Africa. To use low doses of imidazolinone herbicides for controlling this parasite, maize cultivars should possess resistance to this group of herbicides as they kill both maize and S. hermonthica. An imidazolinone resistance (IR) gene was incorporated into maize inbred lines with known field resistance to S. hermonthica for developing IR-maize lines with genetic resistance to the parasite. Three field trials were conducted to determine the reaction of newly developed IR-maize inbred lines to S. hermonthica and to assess performance of selected IR inbred lines in hybrids combinations with and without S. hermonthica infestation as well as with and without imazapyr seed coating at two locations. Results of the inbred trial revealed the presence of IR-maize inbred lines with distinct resistance or tolerance reactions to S. hermonthica. The hybrids formed from selected IR-maize inbred lines with field resistance to S. hermonthica sustained less damage symptoms and yield loss under S. hermonthica infestation and supported fewer emerged parasites than the susceptible hybrid check. Also, imazapyr-coated seeds of these hybrids planted under S. hermonthica infestation sustained either no or less than 20% yield loss and supported very few emerged parasites. The IR hybrids may be planted without imazapyr seed coating in infested fields at certain intervals to delay the development of high levels of resistance to imazapyr.