Relation between the mating type of fungus and mycorrhizal symbiosis

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A chlorophyll-less orchid, Erythrorchis ochobiensis, was co-cultured with different isolates of a fungus Pleurotus ostreatus, to clarity the influence of the fungus nuclear phase and mating type on their symbiosis. Four sib-monokaryons and two reconstituted dikaryons obtained from the progeny of a single strain of this tetra-polar fungus were used. These isolates induced seed germination of the orchid whereas germination was not induced without them. One monokaryotic isolate with compatible mating type, A1B1, induced 44% seed germination and moderate growth of the orchid, while the other, A2B2, induced only 6% and very slow growth. Reconstituted dikaryotic isolate, A1B1xA2B2, induced high germination rate, over 60%, with markedly better growth than A1B1. Different mating type monokaryon A1B2 induced remarkable germination, near to 90%, with satisfactory growth, whereas A2B1 induced below 2% germination. Contrary to A1B1xA2B2, another dikaryon A1B2xA2B1 induced markedly slower growth than A1B2. These results suggested that (1) factor A promotes seed germination and growth of the orchid, and factor A1 has higher promoting ability than A2, (2) factor B prohibits the germination and growth, and B1 has much prohibiting ability than B2, or (2) only B1 strongly prohibits the germination and growth, and B2 promotes the ability of A, and (3) A1B1 and A2B2 in dikaryon A1B1xA2B2 act positively and complementary for the germination and growth whereas A2B1 reduce the A1B2 effect in A1B2xA2B1. Two monokaryons of the same mating type showed difference in the germination rate, that is, 44% and 67%, and growth of the orchid, which might result from nucleic difference. Moreover, the two dikaryons with the same nuclei and different cytoplasm showed almost same in the germination but difference in the growth, which might result from cytoplasmic difference.