Dikaryotization of mycelium in fungi
The process by which primary haploid mycelium is converted into secondary dikaryotic mycelium is called dikaryotization. Dikaryotization may take place by various methods. Some important ones are described below:
i) By fusion between primary hyphae:
This type of dikaryotization occurs in U. maydis. The basidiospore, on germination, forms primary mycelium on the host surface. This mycelium enters the inter cellular spaces by penetrating the host epidermis. Somatogamy takes place between the hyphae of two opposite strains, resulting in the establishment of dikaryotic phase. The dikaryotic cell divides several times by the process of clamp connections and forms secondary mycelium.
ii) By fusion between germ tubes of two basidiospores:
In some species of Ustilago the germ tubes of two different strains come in contact during basidiospore germination, their walls are dissolved at the contact point and the nucleus of one germ tube migrates into the other. This act establishes dikaryophase. The germ tube develops into secondary mycelium.
iii) By conjugation between the basidiospores:
In some species like U. violacea propagation of basidiospore takes place by budding, and a number of secondary spores, known as sporidia, are formed. A dikaryotic spore is formed by the fusion of two sporidia of different strains. The dikaryotic spore germinates to form secondary mycelium.
iv) By union of infection threads:
In U. tritici the basidium is septate and it does not produce sporidia. Each haploid cell of the basidium produces a minute tubular filament, known as infection thread. Two adjacent infection threads of different strains fuse to forms dikaryotic(secondary) mycelium.