Breeding for quantitative resistance to potato cyst nematode (Globodera pallida) in tetraploid potatoes using dihaploids and unreduced gametes

Summary Dihaploids were produced from tetraploids resistant to potato cyst nematode (Globodera pallida (Stone)). High levels of resistance were found in the dihaploids and three were used to produce tetraploid progenies by crossing them with susceptible tetraploid cultivars. One dihaploid, PDH505, produced more highly resistant offspring than the other two, PDHs 417 and 418. The latter gave progenies whose levels of resistance were similar to those obtained from susceptible dihaploids crossed with resistant tetraploids.The differences between the progenies of the resistant dihaploids were probably due to different modes of unreduced gamete formation (PDH505 producing gametes by first division restitution (FDR) and PDHs 417 and 418 by second division restitution (SDR)) although cytological studies would be necessary to confirm this. The methods by which dihaploids could be utilised in a tetraploid potato breeding programme are discussed in relation to the mode of unreduced gamete formation.