A culture comprising at least one set of the chromosomes of the Agaricus bisporus line J10102-s69, the culture of the line J10102-s69 having been deposited under the NRRL Accession Number 50893, wherein said chromosomes comprise all of the alleles of the line J10102-s69 at the sequence-characterized marker loci listed in Table I. Methods are provided for introducing a desired trait into a culture of Agaricus bisporus line J10102-s69, as well as methods and processes for producing hybrid mushroom cultures. A method of mushroom strain development is further provided.