Figure 4. Abnormal conidial morphology, appressorial formation, and pathogenicity of the MgRac1 dominant mutants.

(A) Differential interference contrast (DIC) microscopy of conidia collected from WT (70-15), MgRac1-CA (constitutively active mutant), and MgRac1-DN (dominant negative mutant), as indicated. Bar = 20 µm. (B) Conidial suspensions of MgRac1-CA and MgRac1-DN were applied on the hydrophobic side of Gelbond film and examined with DIC microscopy. Bar = 20 µm. (C) Conidial suspensions (about 1,000 conidia in 20 µl) of 70-15 and MgRac1 mutants were inoculated on strips of onion epidermis. Infectious hyphae were photographed 2 days after inoculation with DIC microscopy. A = appressorium, C = conidium, H = hypha, IF = infectious hypha. Bar = 20 µm. (D) Leaves of rice cultivar CO39 were sprayed with conidial suspensions (1×10⁵ conidia/ml) from WT, MgRac1-CA, and MgRac1-DN. Typical leaves were photographed at 7 days after inoculation. (E) Disease symptoms on the wounded leaf tissues of rice inoculated with conidia (5×10⁴ conidia/ml) from WT and MgRac1 mutants, as indicated. And unwounded rice leaf tissue was inoculated with the mutant of MgRac1-OE. Typical leaves were photographed 5 days after inoculation.