Hypersensitive response to Striga infection in Sorghum

Availability of appropriate laboratory procedures that reveal the specific interactions between the parasitic striga (Striga spp.) and host genotypes in the early stages of infection facilitates characterization of the specific mechanisms of resistance. Our objective was to use an in vitro extended agar gel assay (EAGA) to characterize hypersensitive response (HR) to parasitic invasion of sorghum [Sorghum bicolor (L.) Moench] genotypes. The HR was characterized by expression of necrotic lesions at the haustorial attachment sites which discouraged further penetration of the parasite into host roots. We examined the HR reaction of seven cultivated, five wild, and 95 BC3F4 genotypes derived from a wild resistant (P47121) and two susceptible male sterile based populations (CK60 and KP9). The susceptible genotypes showed no necrosis. In contrast, resistant cultivars Framida and Dobbs, and a wild accession, P47121, showed necrosis in >67% of attached striga. In each of these lines, attached striga were discouraged from penetration and further development. P47121 had the highest level of necrosis (89.9%) and discouraged haustoria penetration (83.1%), followed by Framida (71.4,56.7%) and Dobbs (67.8,49.4%). However, resistant genotypes SRN-39, IS9830, and 555 with low striga germination distance did not exhibit any HR. Only Framida possessed both a low germination distance and high HR. Nine BC3F4 genotypes had a moderate to high HR. These results suggest that use of P47121 and other resistant genotypes would further enhance development of striga-resistant sorghum cultivars through directed introgression.