Table 1. A summary of the nuclear and mitochondrial genotypes of the different compatible strains used in the vegetative fusion experiments.

Strain	Nuclear	Mitochondrial
L1	Hygromycin-resistant	cytb-i2(l)
L2	Phleomycin-resistant	cytb-i2(–)
L3	Phleomycin-resistant	cytb-i2(s)
L4	Hygromycin-resistant	cytb-i2(–)

These strains were constructed by nuclear transformation of the L isolate with plasmid pBC phleo or pBC hygro, which confer resistance to phleomycin and hygromycin, respectively. After transformation, protoplast fusions with incompatible strains of P.curvicolla A and L allowed us to introduce the different forms of the cytb-i2 intron into their mtDNA (see Materials and Methods). Cytb-i2(l) and cytb-i2(s) indicate that the mitochondrial genome contains the long or short form of the intron, respectively, and cytb-i2(–) that it lacks it.