A culture of the Agaricus bisporus strain B12998 is provided, the culture of the strain B12998 having been deposited under the NRRL Accession Number 50902. Other embodiments include a hybrid strain of Agaricus bisporus having BP-1 as one parent and an OW, SW, HW or experimental BW strain as a second parent. Still other embodiments include a hybrid strain of Agaricus bisporus having strain B12998 as at least one parent. Methods are provided for obtaining offspring including homokaryotic lines from select hybrid strain cultures of Agaricus bisporus, as well as methods and processes for producing hybrid mushroom cultures. A method of mushroom strain development is further provided.
