Irregular segregation at the Pr locus controlling plastid inheritance in Pelargonium: gametophytic lethal or incompatibility system?

Two distinct segregation patterns are recognized after G X W plastid crosses in Pelargonium. Type I parents produce offspring in which maternal zygotes are frequent, biparental intermediate, and paternal zygotes rare (MZ>BPZ>PZ), as defined by the presence or absence of green or white plastids in the young embryos into which the zygotes develop. Type II parents produce offspring in which maternal and paternal zygotes are frequent with biparental zygotes the least frequent class (MZ>BPZ