MITOCHONDRIAL HAPLOTYPE INFLUENCES MYCELIAL GROWTH OF AGARICUS-BISPORUS HETEROKARYONS

We evaluated the influence of mitochondrial haplotype on growth of the common button mushroom Agaricus bisporus. Ten pairs of heterokaryon s trains, each pair having the same nuclear genome but different mitocho ndrial genomes, were produced by controlled crosses among a group of h omokaryons of both wild and commercial origins. Seven genetically dist inct mitochondrial DNA (mtDNA) haplotypes were evaluated in different nuclear backgrounds. The growth of heterokaryon pairs differing only i n their mtDNA haplotypes was compared by measuring mycelial radial gro wth rat on solid complete yeast medium (CYM) and compost extract mediu m and by measuring mycelial dry weight accumulation in liquid CYM. All A. bisporus strains were incubated at temperatures similar to those u tilized in commercial production facilities (18, 22, and 26 degrees C) . Statistically significant differences were detected in 8 of the 10 h eterokaryon pairs evaluated for one or two of the three growth paramet ers measured. Some heterokaryon pairs showed differences in a single g rowth parameter at all three temperatures of incubation, suggesting a temperature-independent difference. Others showed differences at only a single temperature, suggesting a temperature-dependent difference. T he influence of some mtDNA haplotypes on growth was dependent on the n uclear genetic background. Our results show that mtDNA haplotype can i nfluence growth of A. bisporus heterokaryons in some nuclear backgroun ds. These observations demonstrate the importance of including a numbe r of mitochondrial genotypes and evaluating different nuclear-mitochon drial combinations of A. bisporus in strain improvement programs.