Postinfection development of Polymyxa graminis in roots of Triticum aestivum

Abstract

Differential interference contrast, laser confocal, scanning electron and transmission electron microscopy were used to study developmental anatomy of sporangial and sporogenic plasmodia, zoosporangia, sporosori and resting spores of Polymyxa graminis in roots of Triticum aestivum grown in infested field soil. Anatomical properties of each stage were described, including the transition from wall-less plasmodia to zoosporangial initials, development of mature zoosporangia with multi-lobed compartments separated by septa and accompanied by exit tubes, and the formation of zoospores within zoosporangia, for the zoosporangial stage. Sporogenic plasmodia, which were larger than sporangial plasmodia, underwent rapid, total cleavage to form resting spores aggregated into sporosori of discoid or other flattened shapes. The cell walls of mature resting spores in sporosori contained up to five distinct layers. Numerous electron opaque storage bodies were present in resting spores; many of them migrated to just beneath the plasma membrane and cell wall during spore maturation.