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The penetration of a susceptible lettuce variety by the downy mildew fungus Bremia lactucae Regel

1973; Academic Press; Volume: 3; Issue: 2 Linguagem: Inglês

10.1016/0048-4059(73)90085-4

1876-7974

John Sargent, I.C. Tommerup, David S. Ingram,

Plant Pathogens and Resistance

Within 1 h of inoculating leaves of the susceptible lettuce variety Trocadero Improved with conidia of Bremia lactucae race W5, germination had commenced. By 3 h a germ-tube and appressorium had been produced, and during the 1 h following penetration of an epidermal cell a primary vesicle was formed. A secondary vesicle arose from this, and 9 h later divided nuclei became visible and mycelial growth of the fungus started. Prior to penetration the following changes occurred in the host immediately below the appressorium: the cuticle became swollen and changes occurred in the staining properties of the wall; the plasmalemma separated from the wall and densely staining material occupied the resulting space; cytoplasm became aggregated with an increase in the number of cytoplasmic vesicles and the formation of crystal-containing microbodies. Within the fungus, cytoplasmic vesicles became concentrated at the tip of the appressorium where it is thought that they were involved in an enzymic penetration of the host cuticle and wall. The host plasmalemma proliferated markedly during expansion of the primary vesicle, which invaginated this membrane. The primary vesicle did not possess an encapsulation.