Timing of Fusarium Head Blight Infection in Rice by Heading Stage

Abstract

Fusarium graminearum causes the devastating plant disease Fusarium head blight and produces mycotoxins on small cultivated grains. To investigate the timeframe of F. graminearum infection during rice cultivation, a spore suspension of F. graminearum was applied to the rice cultivars Dongjin 1 and Nampyeongbyeo before and after the heading stage. The disease incidence rate was the highest (50%) directly after heading, when the greatest number of flowers were present, while only 10% of the rice infected 30 days after heading showed symptoms. To understand the mechanism of infection, an F. graminearum strain expressing green fluorescent protein (GFP) was inoculated, and the resulting infections were visually examined. Spores were found in all areas between the glume and inner seed, with the largest amount of GFP detected in the aleurone layer. When the inner part of the rice seed was infected, the pathogen was mainly observed in the embryo. These results suggest that F. graminearum migrates from the anthers to the ovaries and into the seeds during the flowering stage of rice. This study will contribute to uncovering the infection process of this pathogen in rice.

Keywords: Fusarium graminearum; Fusarium head blight; infection; rice.

Figure 1.

Symptoms of FHB on rice after artificial inoculation with F. graminearum isolate Z39G418 expressing GFP in the z3639 background. Spore suspension was adjusted to 10⁴ spores/mL.

Figure 2.

Comparison of pathogen detection rates between the F. graminearum wild-type strain z3639 and the GFP-expressing strain Z39G418. The strains were tested on two rice cultivars (Dongjin 1 and Nampyeongbyeo) and inoculated at different rice developmental stages before and after heading, over three replicates. Duncan’s test was used to determine significance at the 95% probability level. The same letters indicate no significant difference between results.

Figure 3.

Detection rates of the FHB pathogen in seeds following inoculation with the GFP-expressing strain Z39G418 at different rice developmental stages before and after heading, over three replicates. Duncan’s test was used to determine significance at the 95% probability level. The same letters indicate no significant difference between results.

Figure 4.

Microscopy images of the interior of infected rice seeds inoculated with the GFP-expressing F. graminearum strain Z39G418 were captured with the Leica TCS SP2 microscope. (A) inner glume, (B) inner seed coat, (C) surface of endosperm cells, (D) embryo bud. Arrows indicate the presence of the pathogen.