Principles of Plant Genetics and Breeding

176 CHAPTER 10
Tubers of BC 2
generation
Tubers of somatic hybrids
from the cell fusion of S.
etuberosum with a S.
tuberosum haploid × S.
berthaultii hybrid
Tubers of four
BC 1 progeny
Figure 2 The progression of tuber type in somatic hybrids of S. etuberosum and their backcross progenies in
successive hybridizations with cultivated potato.
Analogous to observations in three of the BC 1 , all BC 2 (derived from a PVY-resistant BC 1 ) exhibited statistically significant
reduced PVY infection relative to the PVY-susceptible potato variety, “Russet Burbank”. BC 2 were found to segregate for resistance
to PLRV, with two of five displaying resistance to infection on the basis of field and cage evaluations. Progeny of a PLRVresistant
BC 2 clone also show high levels of resistance to PLRV in field evaluations in Idaho (author, unpublished data). S. etuberosum-derived
PLRV resistance is highly heritable on the basis of its expression in third generation progeny of the somatic hybrids.
Backcross progenies are being analyzed with molecular markers to identify chromosomal regions from S. etuberosum associated
with its observed PVY and PLRV resistances (Figure 3). Once identified, prospective regions will be further saturated with
additional markers to identify those that are tightly linked to the virus resistances. Such markers can then be used for markerassisted
selection (MAS) in our breeding program. These correlated DNA markers can be used to assess whether an individual
will express resistance to PLRV or PVY, thereby speeding the development of potato varieties with the virus resistances of
S. etuberosum.
Wireworm resistance of backcross progeny derived from somatic hybrids
Wireworm, a larval stage of a beetle, is the most damaging soil-dwelling pest of potato. The larvae spend 3–4 years in the soil and
their entry and feeding into potato tubers detrimentally impacts the marketability of the tuber for fresh consumption or processing.