Some single spore isolates of V. volvacea are self-fertile while others are self-sterile (Chiu and Moore, 1999), which raises the possibility of crossing self-sterile isolates to create strains with desirable traits. However, morphological differentiation between self-fertile (heterokaryotic) and self-sterile (homokaryotic) isolateshas been problematic due to the absence of clamp connections in heterokaryotic hyphae (Chang, 1965; Chang and Ling, 1970)