The construction of a molecular linkage map, mapping of quantitative trait loci, characterization of polyphenols, and screening of genotypes for Striga resistance in sorghum

Sorghum ranks fifth in importance among the world\u27s cereals. Despite its economic importance and decades of genetic breeding and research, sorghum is still poorly characterized genetically. A molecular linkage map of sorghum was constructed with the use of a recombinant inbred (RI) population derived from a cross between SRN 39 and Shanqui Red. This population was mapped using 137 RAPD loci, 12 I-SSR loci, 42 RFLP loci, and 5 morphological markers. Of the 196 loci, 167 loci were placed on 19 linkage groups spanning a map distance of 1173 cM. The genes for low production of Striga germination stimulant, adult plant color, seedling color, and testa were also placed on this map. In addition, quantitative trait loci for plant height, peduncle length, panicle length and width, leaf length and width, awns, maturity, leaf apigenin, 3-deoxyanthocyanidins, flavan-4-ols, pro-3-deoxyanthocyanidins, and seed apigenin, 3-deoxyanthocyanidins, flavan-4-ols, tannins, total phenols, and resistance to rust and anthracnose were also placed on this map. Analysis of the distribution of polyphenols between red and tan lines indicated that plant color was correlated with all leaf polyphenols as well as with seed apigenin and 3-deoxyanthocyanidins. Breeding for host resistance is the most practical and effective method of Striga control. Although resistant sorghums have been identified, little information exists about their mechanisms of resistance. One hundred and seventy lines with field resistance to Striga were assayed for two possible mechanisms of host resistance: production of low amounts of germination stimulant and haustorial inducer. Of these lines, 97 lines were low stimulant producers whereas none of these lines produced low amounts of haustorial inducer. Whereas production of low amounts of germination stimulant is a prevalent mechanism of host resistance, production of low amounts of haustorial inducer was not a prevalent mechanism of host resistance. Identification of host genotypes which inhibit Striga development at different stages of its life cycle would enable the pyramiding of these genes into a host genotype