Competition and Distribution Studies of Genetically Marked Strains of Ustilago violacea in the Same Host Plant

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Abstract
Four plants of Silene alba were inoculated with a suspension of cells of the anther smut fungus, U. violacea, containing 6 genetically marked strains, 3 of each mating type; 9 possible dikaryons could form and compete within the plant. On average, 44 infected flower buds from each plant were sampled and analyzed for genotype of the infecting dikaryon using rapid screening techniques capable of identifying the 9 possible dikaryons. Different dikaryons could penetrate and infect the same flower shoot, lateral branch, pedicel or, even rarely, the same anther. Of 177 infected flower buds, 90 were infected by a wild-type + wild-type dikaryon, 86 with 1 of 3 wild-type + mutant dikaryons and only 2 anthers of 9 analyzed from 1 flower were infected with a mutant + mutant dikaryon. Only 2 flowers of the 177 contained 2 different dikaryons, both of which could penetrate the same anther, sporulating together within it. Usually only 1 dikaryon comes to predominate in 1 area of the host.