Traditional Breeding and Cultivar Development - The Potato: Botany, Production and Uses - page 276

non-tuber-bearing species that cannot be hybrid-
ized with tetraploid or diploid forms of cultivated
potato. Sexual incompatibilities were overcome
by the use of somatic hybridization with the gen-
eration of somatic hybrids between S. etuberosum
and a Gp. Tuberosum dihaploid × S. berthaultii
hybrid clone (Novy and Helgeson, 1994a). The
tri-species somatic hybrids had very vigorous
foliar growth in the field, with low yields of tubers
having very poor type (Fig. 16.1 )— not totally un-
expected, with approximately 75% of the gen-
ome originating from wild species.
However, following two generations of hy-
bridization of the somatic hybrids to cultivated
potato, breeding clones having round, white-
skinned tubers with the appearance desired for
use by the chipping industry were obtained (Fig
16.1 ) . Following an additional two generations
of crossing to cultivated potato (four generations
removed from the somatic hybrid progenitors),
breeding clones with the long tuber type and
russeted skin desired by the western US potato
industry also were obtained ( Fig. 16.1 )—indicative
of how species can be used successfully in a
breeding program. The breeding clone with the
long, russeted tubers referenced in Fig. 16.1 has
potato leaf roll (PLRV) resistance derived from
S. etuberosum and the necessary processing

attributes for its continued evaluation and ad-
vancement for possible release as a potato culti-
var. In addition to PLRV resistance, the somatic
hybrids and their progenies have been shown to
have resistances to Potato virus Y , green peach
aphid, pink rot, Pythium leak, and potato psyllid
(Novy and Helgeson, 1994b; Novy et al ., 2002a,
2007; Thompson et al ., 2007; Butler et al ., 2011),
with unpublished data suggesting resistance to
wireworm and Colorado potato beetle as well.
A major gene for PLRV resistance derived from
S. etuberosum , Rlretb , has also been mapped (Gillen
and Novy, 2007; Kelley et al ., 2009). The numer-
ous resistances identified in the progenies of
S. etuberosum and S. berthaultii highlight the
contributions that wild species can make to the
genetic improvement of potato.

16.3 Emerging Issues of Importance

in Potato Breeding

Potato has a myriad of diseases, pests, and
physiological disorders that are problematic for
its production, the extent of which are detailed
in this volume (see Waters and Jensen, Chapter 9;
Palomares-Rius et al ., Chapter 10; Kirk and

Somatic hybrids

1st generation

4th generation 2nd generation

Fig. 16.1. Tubers of somatic hybrids of Solanum etuberosum and a Gp. Tuberosum dihaploid × Solanum
berthaultii hybrid and the improvement in tuber type over generations with successive hybridizations to
cultivated potato.