Genetics and breeding of white button mushroom, Agaricus bisporus (Lange.) Imbach. - A comprehensive review

Breeding of white button mushroom ( Agaricus bisporus ) is a complex proposition due to its unusual secondary homothallic sexual behavior. The percentages of bi-, tri- and tetrasporic basidia found in A. bisporus are on an average 81 %, 18 %, and 1 %, respectively. Moreover, contrary to other basidiomycetous fungi, A. bisporus mycelium is multinucleate and lacks clamp connections. Hence, it is not easy to identify non-fertile isolates for hybrid breeding. The only method to identify non-fertile isolates is the fruiting trial.  Despite its economic relevance, the breeding effort in white button mushroom was low due to its complicated life cycle and lack of knowledge. The strains of white button mushroom available in the world show high similarity with the strain U-3 and seem that almost all the available strains are derived from one strain U3. During last few decades, serious efforts were made to investigate the life cycle and breeding pattern. In 2007, the Joint Genome Institute, US Department of Energy (DOE), sequenced the whole genome of A. bisporus . The size of the genome sequence was found to be 31 Mb and number of chromosomes was 13 in A. bisporus variety Horst U1. Complete sequence of the mtDNA of A. bisporus was observed to be 135,005 bp and is available with its complete nuclear genome. Recently, authors have developed and released two browning resistant hybrids in this mushroom (NBS-1 and NBS-5) and identified WRKY transcription factors associated with abiotic stress tolerance and nucleotide binding site of disease resistance gene. Present communication reviews the studies undertaken on problems in breeding, life cycle patterns, mating systems, genetic diversity assessment, genome sequencing, classical and molecular breeding, and  other genetic improvement approaches in this important crop all through the world along with authors own contribution in this field. This communication also put forward author’s view on the way forward to develop new high yielding, disease resistant and high quality strains.