Histopathology of Seed-Borne Infections - Applied Research Center ...

Location of Fungal Hyphae in Seeds 123TABLE 5.4Estimates of Loose Smut Infection in Wheat Varieties of Different Adult PlantReaction as Determined by Scutellum, Plumular Bud, and Adult Plant TestsPercentage InfectionEmbryosPlumular BudVarietal ReactionScutellumAdult PlantsArtificially inoculatedHighly susceptible 85 85 86Moderately susceptible 68 48 49Moderately resistant 83 8 7Highly resistant 68 0 0Immune 0 0 0Naturally infectedHighly susceptible 8 5 5Highly resistant 5 5 5From Popp, W. 1959. Phytopathology 49: 75–77. With permission.teliospores germinate at the time of seed germination and directly cause seedlingcoleoptile infection. The plant infection is systemic and latent in the vegetative phase.Microscopic examination prior to ear emergence from the boot leaf shows that thepistil in affected ears is larger and deep green and the ovary is double the length ofthe normal ovary. The stamens are reduced in length and breadth. The anthers arepale yellow instead of green, and they possess defective pollen grains. The buntedgrains are full of black spore mass (teliospores) covered with pericarp. The numberof teliospores in affected grains varies even in a susceptible cultivar (Griffith,Zscheile, and Oswald, 1955; Zscheile and Anken, 1956). Infected grains with alimited number of teliospores contain normal-appearing tissue surrounding the sorus.The spore-bearing region decreases toward the stigmatic side and increases towardthe base. The spores mature first at the center of the sorus and proceed centrifugallyto the periphery. The development of teliospores at more than one place may takeplace in a kernel, but these sori usually fuse in the mature kernel.Several other smuts, namely covered smut of barley caused by Ustilago hordei(externally seed-borne), loose smut of oats caused by U. avenae (grain infectionconfined to the pericarp and external seed contamination), covered smut of oatscaused by U. kolleri (externally seed-borne), loose smut of sorghum caused bySphacelotheca cruenta (externally seed-borne), and grain smut of sorghum causedby S. sorghi (externally seed-borne), have disease cycles broadly similar to those ofT. tritici (T. caries) and T. laevis (T. foetida). The teliospores fill the kernels and areenclosed in the pericarp membrane. No anatomical details are available.5.5.3.1.3 Type 3 Disease CycleT. penicillariae is the causal organism of smut of pearl millet and the smutted grainsare scattered in earheads. The primary inoculum consists of spore balls that adhere