Management of maize insect and disease pests using host plant resistance - successes and prospects.

Maize insect and disease pests are estimated to cause annual world production losses of 9 to 12 and 9.4 percent, respectively. Losses in the tropics and subtropics are conceded to be higher than an estimated 30 percent from insect damage alone. A major research objective of the maize program at CIMMYT [International Maize and Wheat Improvement Center, Mexico] is to develop host plant resistance (HPR) to the most important maize insect and disease pests. An attempt was made to incorporate polygenic (non-specific) resistance into various cultivars. Most materials are developed or improved for resistance by following a family structured recurrent selection scheme. High levels of host plant resistance, when found, may serve as the sole or chief means of control; lower, even moderate levels, are useful and compatible with other methods used in integrated pest management and contribute to its effectiveness. Research is directed at developing both specific and multiple resistance (to several insect and disease species, separately or combined) in an array of genetic materials. Resistance to fall armyworm, corn earworm, seven species of stem borers, and two species of stored grain weevils, as well as prevalent stalk and ear rots, foliar diseases, corn stunt, maize streak and the downy mildew disease complex is under development. Results from the multiple-borer and downy mildew breeding efforts provide case studies. The deployment of downy mildew resistant cultivars has resulted in the control of this important group of diseases worldwide. Good progress has been made for multiple insect resistance; as it is a recent achievement, improved cultivars with the highest resistance levels have yet to be deployed to help reduce production and storage losses.