Bridging conventional and molecular genetics of sorghum insect resistance

Abstract

Sustainable production of sorghum, Sorghum bicolor (L.) Moench, depends on effective control of insect pests as they continue to compete with humans for the sorghum crop. Insect pests are a major constraint in sorghum production, and nearly 150 insect species are serious pests of this crop worldwide and cause more than 9% loss annually. Annual losses due to insect pests in sorghum have been estimated to be $1,089 million in the semiarid tropics (ICRISAT Annual report 1991. International Crop Research Institute for Semi-arid Tropics. Patancheru, Andhra Pradesh, India, 1992), but differing in magnitude on a regional basis. Key insect pests in the USA include the greenbug, Schizaphis graminum (Rondani); sorghum midge, Stenodiplosis sorghicola (Coquillett); and various caterpillars in the Southern areas. For example, damage by greenbug to sorghum is estimated to cost US producers $248 million annually. The major insect pests of sorghum on a global basis are the greenbug, sorghum midge, sorghum shoot fly (Atherigona soccata Rond.), stem borers (Chilo partellus Swin. and Busseola fusca Fuller), and armyworms (Mythimna separata Walk and Spodoptera frugiperda J.E. Smith). Recent advances in sorghum genetics, genomics, and breeding have led to development of some cutting-edge molecular technologies that are complementary to genetic improvement of this crop for insect pest management. Genome sequencing and genome mapping have accelerated the pace of gene discovery in sorghum. Other genomic technologies, such as QTL (quantitative trait loci) mapping, gene expression profiling, functional genomics, and gene transfer are powerful tools for efficient identification of novel insect-resistance genes, and characterization of the key pathways that regulate the interactions between crop plants and insect pests leading to successful expression of the host plant defense. Traditional breeding methods, such as germplasm evaluation and enhancement, backcrossing, pedigree selection, and recurrent selection continue to play important roles in developing insect-resistant cultivars with major resistance genes; and new cultivars with enhanced resistance to several important insect pests are released continuously. Future research efforts should focus on identification of new sources of resistance, characterization of resistance genes, and dissecting the network of resistance gene regulation. Collaboration between research institutions and the sorghum industry as well as international cooperation in utilization of emerging knowledge and technologies will enhance the global efforts in insect pest management in sorghum.