Identification and characterization of genetic variants in sorghum for specific mechanisms of Striga resistance
Several sorghum [Sorghum bicolor (L) Moench] genotypes with varying degrees of Striga (Striga spp) resistance have been identified. However, the specific mechanisms of these resistance sources have not been properly characterized, mainly because of the lack of adequate laboratory techniques that uncover critical host-parasite interactions, which naturally occur beneath the soil. In this study we have developed two screening techniques, Paper Roll Assay and Extended Agar Gel Assay, which we have used to evaluate a selected set of sorghum lines and wild sorghum accessions for specific Striga resistance mechanisms. We have observed several distinct defense responses to Striga parasitism. These responses indicate the potential existence of the following four separate mechanisms of Striga resistance in sorghum: (1) little or no Striga seed germination and evidence of germination inhibitors; (2) low haustorial initiation factor that is needed for haustoria initiation; (3) a hypersensitive reaction (characterized by a distinct necrotic area on the host root at the attachment site that discourages parasitic establishment); (4) an incompatible response (the parasite development arrested with no apparent necrosis on the host root). Our analysis indicated that, low production of the haustoria initiation factor in a wild sorghum genotype, P78, is inherited as a single dominant gene. Hypersensitive response to Striga infection is conditioned by two dominant genes. SSR marker, TXP358, at a distance of 19.3 cM was identified to be linked to the low haustoria initiation factor gene. SSR marker combinations, TXP96 and SBKAFGK1, were identified to be linked to the hypersensitive response at a distance of 7.5 cM and 12.5 cM from the gene respectively.
Ejeta, Purdue University.
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