Histopathological Spikelet Changes Produced by Fusarium graminearum in Susceptible and Resistant Wheat Cultivars

Abstract

Scab is an important disease of wheat throughout the world. Fusarium graminearum is the species most frequently isolated in Argentina. Histopathological modifications observed in Pro INTA Oasis (a susceptible Argentine cultivar) and in Sumai 3 (a resistant Chinese cultivar) from the time of inoculation, at the spike emergence stage, until major disease expression (10.5 days postinoculation in the susceptible cultivar) are described. Both cultivars showed a horizontal progression of disease, from anthers to glumes, and a vertical progression, from anthers to rachis. Chlorenchyma was the most damaged tissue, with progressive chlorosis and necrosis. Walls of mesophyll, parenchyma, and epidermal cells around the lesions became thicker, particularly in the resistant cultivar. Vessels and sieve tubes were occluded, particularly the former in the susceptible cultivar and the latter in the resistant cultivar. Possible relationships between tissue changes generated during disease progression and known resistance mechanisms are discussed.

Secreted Fungal Effector Lipase Releases Free Fatty Acids to Inhibit Innate Immunity-Related Callose Formation during Wheat Head Infection

“…An increased callose deposition in the spikelet's transition zone in combination with type II resistance was also reported for the wheat cv Sumai 3 (Ribichich et al, 2000), where the spreading of F. graminearum was strongly reduced compared with a susceptible wheat cultivar. The deposition of callose in the phloem also occurred after bacterial infection of Citrus spp.…”

Autophagy provides nutrients for nonassimilating fungal structures and is necessary for plant colonization but not for infection in the necrotrophic plant pathogen Fusarium graminearum

“…In wheat, the fungus form infection cushions 13 and spread by systemic growth through the rachis from one spikelet to another when inoculated by point inoculation of one spikelet. 14,15 Autophagy could be important for both successful infection and spread between spikelets in wheat since the initial infection and the growth through the nutrientpoor rachis could need mobilization of recycled nutrients. The autophagy-associated lipase ATG15 from F. graminearum has been shown to be required for infection which support this hypothesis.…”

Evaluation of resistance and the role of some defense responses in wheat cultivars to Fusarium head blight

“…Callose deposition is typically triggered by conserved PAMPs (Gomez-Gomez et al 1999). Wheat cultivars, which were partially resistant to F. graminearum, showed increased callose deposition in the transition zone of the spikelet's rachilla and rachis (Ribichich et al 2000). Callose accumulation at sites of pathogen penetration is known as a physical barrier to slow pathogen invasion (Jones and Dangl 2006).…”