Disease Cycle
The disease cycle of loose smut begins when teliospores are blown to open flowers and infect the ovary either through the stigma or directly through the ovary wall. There are multiple mating types for Ustilago spp. so infection will only occur if two compatible mating types are present in the same flower.
After landing in an open floret, the teliospores give rise to basidiospores. Without dispersing to any alternate host plant, the basidiospores germinate right where they are. The hyphae of two compatible basidiospores then fuse to establish a dikarytic state.
After germination inside the ovary, the fungal mycelia invade the developing embryo in the seed. The fungus stays alive in the seed until the next growing season, when it is planted along with the seed. As the developing plant grows, the fungus grows with it. Once it's time for the flowers to form, teliospores are produced in place of the flowers and develop where the grain would be.
Plants which are infected with Ustilago spp. actually grow taller and flower earlier than their healthy counterparts. This gives the infected plants an advantage in that the flowers of uninfected plants are more physically and morphologically susceptible to infection. The teliospores in the smutted grain heads disperse to the open flowers of the healthy plants, and the cycle continues.
Read more about this topic: Ustilago Nuda F.sp. Hordei
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