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

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.