Striga Control: Mechanisms and Strategies for Promoting Sustainable Sorghum Production in Africa with Special Emphasis on Host Plant Resistance

摘要

Striga species constitute a major biotic constraint to sorghum production in sub-Saharan Africa. About two-thirds of fields planted to cereal in 17 sub-Saharan African countries are estimated to be seriously infested by these parasitic weeds. Successful Striga management depends on the development and regular application of integrated control systems. Adapted, productive Sfriga-resistant sorghum varieties could be a highly efficient management component as they require no additional inputs other thanimproved seed. However, known resistance sources in sorghum are frequently low-yielding with poor agronomic background. Insufficient information on the genetics of resistance to Striga and the difficulty of evaluating resistance in the field have seriously limited research progress. The agar-gel assay is the first inexpensive, rapid and reliable laboratory screening tool permitting the characterization of cereal genotypes for a well-defined resistance mechanism, i.e., low stimulation of Striga seed germination. Efforts are underway to develop other assays screening for individual resistance mechanisms. Strategies in Striga resistance breeding should include: characterization of crop germplasm and improvement of available resistance sources for agronomic characters; transfer and pyramiding of resistance genes into adapted genotypes; development of Sfnga-resistant parent lines for use in hybrids or open-pollinated synthetic varieties; and development of random-mating populations with multiple sources of resistance. Due to parasite variability and significant genotype x environment interactions, multi-locational testing is recommended. The development of marker-assisted selection techniques for broad-based Striga resistance is underway. The approach ispromising, since most Striga resistance tests are difficult, expensive and unreliable; the parasite is quarantined; and resistance genes are partly recessive. In the short to medium term, selection of adapted sorghum genotypes for use in integrated Striga control packages could contribute to sustained sorghum production in Striga-infested areas of sub-Saharan Africa.