Figure 6

Illustration of the response of roots on wild-type and composite cowpea plants to attempted parasitism by  Striga gesnerioides  race SG3. Shown are photographs of representative cowpea root-Striga interactions. Pre-germinated S. gesnerioides race SG3 seedlings were placed in contact with cowpea roots and the interactions were analyzed at 8 days post inoculation. A. Light microscopic photograph and (E) associated fluorescence microscopic image of the hypersensitive response (HR) observed on the roots of resistant cowpea cultivar B301 when attached by S. gesnerioides race SG3. Note the browning and associated cell death in the cowpea root at the site of parasite infection, and browning of the attached parasite. B. Light microscopic photograph and (F) associated fluorescence microscopic image of showing the lack of an observed HR on the roots of susceptible cowpea cultivar Blackeye when attached by S. gesnerioides race SG3. Note that the parasite has formed xylem-xylem connections as evidenced by the presence of a tubercle. C. Light microscopic photograph and (G) associated fluorescence microscopic image showing tubercle growth of S. gesnerioides races SG3 on the transgenic roots of Blackeye cowpea transformed with the pK7WG2D empty vector construct. D. Light microscopic photograph and (G) associated fluorescence microscopic image of the hypersensitive response (HR) observed on the roots of Blackeye cowpea transformed with the pKMG-RSG3-301 resistance gene construct. Note the visible HR at the site of SG3 attachment similar to that observed in the interaction with the resistant cowpea cultivar B301. Arrows indicate host-parasite interaction.