Genetic variation in ectomycorrhiza formation byPisolithus arhizusonPinus pinasterandPinus banksiana

summary The ability of 28 monokaryons and 78 reconstituted dikaryons ofPisolithus arhizus(Scop, pers Pers.) Rauchert [Syn.:Pisolithus tinctorius(Pers.) Coker & Couch] to form ectomycorrhizas onPinus pinaster(Ait.) Sol. andPinus banksiana(Lamb.) was studied using the growth pouch method. The ability to form mycorrhiza and promote growth ofP. pinasterdiffered both between and within monkaryons and dikaryons. Some monokaryons and dikaryons failed to form ectomycorrhizas. Monokaryons formed fewer ectomycorrhizas onP. pinasterthan dikaryons. The heterokaryotic state was necessary for the full expression of ectomycorrhiza‐forming ability. Growth ofP. pinasterwas more strongly correlated with ectomycorrhiza formation by dikaryons than by monokaryons.