APS Homepage

Poster: Molecular & Cellular Plant-Microbe Interactions: Biochemistry & Cell Biology


Differential effects of Fusarium thapsinum on host nitric oxide (NO) synthesis among stalk rot resistant and susceptible sorghum lines
A. BANDARA (1), C. Little (1) (1) Kansas State University, U.S.A.

Fusarium thapsinum (FT) is a hemibiotrophic fungus causing stalk rot in sorghum (Sorghum bicolor (L.) Moench). NO is a powerful oxidant involved in programed cell death and FT-mediated NO synthesis was investigated in host stalk tissues. Two greenhouse-grown stalk rot resistant (SC599, SC35) and susceptible (Tx7000, BTx3042) sorghum lines were inoculated with FT and phosphate-buffered saline (control). At 7 and 30 d post-inoculation (d.p.i.), FT- and mock-inoculated stem cross sections were treated with 4-amino-5-methylamino-2?,7?-difluorofluorescein diacetate, and observed under a confocal microscope (excitation 488; emission 515 nm). The fluorescence generated by controls was used as the baseline. At 7 d.p.i, strong green fluorescence was observed in FT-inoculated resistant lines, confirming the presence of NO, while no (or weak) signal was evident at 30 d.p.i. The susceptible lines revealed the opposite phenomenon, except for the signal detected in BTx3042 at 7 d.p.i. These patterns suggested that FT switches from biotrophy to necrotrophy by 30 d.p.i. While the presence of NO in SC599 and SC35 at 7 d.p.i contributes to resistance against the biotrophic phase, its absence at 30 d.p.i may decrease vulnerability to the necrotrophic phase. Tx7000 showed the opposite response and is susceptible to both phases of the pathogen's lifestyle. Based on NO response, BTx3042 appeared to be moderately resistant to the biotrophic phase but prone to the necrotrophic phase of FT.