Could you be a little more specific? Are you simply looking for a gene to amplify by PCR to show that your genomic DNA isolation from fungi was successful? Or are you looking for a specific gene to amplify?
Agree with Aniko but i suspect mushroom genomic DNA is much larger than 10 kb. You need a PFGE ladder since everything above 8 kb usually difficult to resolve under the average agarose electrophoresis condition