NOVELTY - A hybrid mushroom strain culture having a strain belonging to derived lineage group which includes initial strain BP-1 as a first parent, and a strain chosen from OW-type strains, SW-type strains, HW-type hybrid strains, experimental BW-type hybrid strains as a second parent, is new.    USE - The hybrid mushroom strain culture is useful for preparing product chosen from mycelium, spawn, inoculum, casing inoculum, fresh mushrooms, processed mushrooms, mushroom extracts and fractions, mushroom pieces, and colonized substrates including grain, compost, and friable particulate matter (all claimed).    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) part of the hybrid mushroom strain culture chosen from hyphae, mushrooms, spores, cells, nuclei, mitochondria, protoplasts, cytoplasm, DNA, RNA, proteins, cell membranes and cell walls;    (2) method for obtaining offspring of hybrid mushroom strain culture involves obtaining a mushroom from hybrid mushroom strain culture, obtaining spores from mushroom, germinating spores, transferring cultures from germinating spores to new growth media;    (3) offspring including heterokaryons and homokaryons obtained by the method; and    (4) method for producing hybrid mushroom strain culture having a strain belonging to the derived lineage group which includes initial strain BP-1 as a first parent and a strain chosen from strain types comprising OW-type strains, SW-type strains, HW-type hybrid strains, experimental BW-type hybrid strains as a second parent involves (a) mating a culture from first parent, including homokaryotic offspring line cultures, with a culture from the second parent, including homokaryotic offspring line cultures, to obtain a hybrid culture, isolating the hybrid culture in pure form by transferring it to fresh nutrient growth medium or (b) mating a culture from strain B 12998 derived lineage group first strain parent, including homokaryotic offspring line cultures, with a culture, including homokaryotic offspring line cultures, from a second parent, to obtain a hybrid culture, isolating the hybrid culture in pure form by transferring it to fresh nutrient growth medium.