SELECTING SORGHUM GENOTYPES EXPRESSING A QUANTITATIVE BIOSYNTHETIC TRAIT THAT CONFERS RESISTANCE TO STRIGA

One of the best characterized mechanisms of host resistance to witchweeds (Striga spp.) is exudation by host plant roots of relatively low amounts of compounds that Striga seeds require as stimulants for germination. We find that all sorghums tested, regardless of whether they are susceptible or resistant to Striga, produce equivalent amounts of sorgoleone, the alkylated hydroquinone we previously identified from sorghum root exudate as the first host-derived Striga germination stimulant to be characterized. In contrast, some highly resistant sorghums produce relatively tiny amounts of another germination stimulant, as yet unidentified but with properties quite different from sorgolcone, whereas all susceptible sorghums produce relatively large amounts. A simple, rapid and nondestructive agar gel assay which detects this second stimulant, but not sorgoleone, reliably distinguishes low (Striga resistant) and high (Striga susceptible) stimulating parental genotypes and progenies from crosses among them. Because the lack of a reliable and rapid method for screening germplasm and breeding progenies has hampered the development of crop varieties resistant to Striga, this gel assay is expected to greatly enhance the efficiency of sorghum breeding for Striga resistance.