Agriculture Reference
In-Depth Information
RKNs are the two major nematological problems
in potato, and for both, breeders have been de-
veloping resistant varieties. Resistant cultivars
carrying the gene
H1
, derived from
Solanum tu-
berosum
L. ssp.
andigena
(CPC 1673), have been
extremely effective at reducing populations of
G. rostochiensis
throughout Europe, providing
resistance to pathotypes Ro
1
and Ro
4
(Dale
et al
., 2010). Additional resistance genes against
G. rostochiensis
have been detected in other gen-
etic sources (Gebhardt and Valkonen, 2001).
However, it has become apparent that these cul-
tivars are primarily useful when
G. pallida
is
absent or present at very low levels, though in
the latter situation gradual increases in
G. pallida
populations are probable. Fewer cultivars are
available with high levels of resistance for
G. pallida
,
though in the Netherlands, and to a lesser extent
in Germany, there are some specialized cultivars
for starch production with resistance (Hockland
et al
., 2012). For fresh consumption, a few culti-
vars have also been registered, i.e. cultivar
Amanda in Germany in 2006 and cultivar Iled-
her in 2009 in France (Hockland
et al
., 2012).
No cultivars with very high levels of resistance
to all
G. pallida
Pa1, 2/
3
pathotypes are cur-
rently listed in the European Potato Database
(
www.europotato.org)
. Producent and Sante are
reported to have very high levels of resistance to
Pa2; Cyprian, Innovator, Pallidia, Seresta, Ska-
wa, Zagloba, and Zeus with high levels of resist-
ance to Pa3; and Arela, Benol, Morag and Vales
Everest with high to very high levels of resist-
ance to Pa1. On the UK Potato Database (
http://
www.varieties.potato.org.uk/
)
, Ambassador,
Crisps4all, and Vales Everest are classified as
resistant to
G. pallida
pathotypes Pa2/
3,
1.
In the
future, combining resistances to both species
and to different pathotypes should provide an
improved spectrum of cultivars. Cultivars with
partial resistance, such as Nadine, Valor, Rocket,
and Sante, allow only a proportion of juveniles
to reach maturity, and they could be used in PCN
management programs, but their use requires
careful monitoring for the selection of new
nematode genotypes that are more virulent
(Hockland
et al
., 2012).
Several resistance loci have been mapped
that confer resistance to
G. pallida
pathotypes
Pa2 and Pa3. These loci are derived from the dip-
loid relatives of cultivated potato, including
Sola-
num vernei
Bitter & Wittm.,
Solanum sparsipilum
(Bitter) Juz. & Bukasov,
Solanum spegazinii
Bitter,
Solanum tarijense
Hawkes and the tetraploid
S. tuberosum
ssp.
andigena
CPC1673 (only patho-
type Pa2) and CPC 2802 (pathotypes Pa2 and
Pa3) (Moloney
et al
., 2009), and no single resist-
ance gene has yet been identified that gives com-
plete resistance to
G. pallida
. The higher diversity
of the
G. pallida
populations compared to
G. ros-
tochiensis
populations also makes it more diffi-
cult to incorporate effective broad-spectrum re-
sistance (Schnick
et al
., 1990; Folkertsma
et al
.,
1994). However, the diversity of both species
found in Europe represents only a small amount
of the diversity in comparison to their center of
origin in South America (Andes) (Hockland
et al
., 2012). The resistance sources used in
European breeding programs are directed to the
particular populations introduced into Europe,
and for this reason it is important to avoid the
introduction of more virulent pathotypes from
their center of origin (Hockland
et al
., 2012).
Efficient potato breeding strategies against
PCNs have been developed (Bradshaw
et al
.,
2003), with the emphasis placed on a progeny
test to assess and select or discard whole progen-
ies before starting conventional within-progeny
selection at the unreplicated small-plot stage
(Dale
et al
., 2010). However, the use of molecu-
lar markers will assist in the selection for important
disease resistance and quality traits, allowing
the development of lines with multiple resist-
ance sources (Dale
et al
., 2010). In some cases,
the combination of different resistance loci can
result in apparent additive effects on resistance
levels (for example in pathotypes Pa5 and Pa6 in
G. pallida
) (Rouppe van der Voort
et al
., 2000).
The use of parental material which is triplex or
quadruplex for a single resistance gene will also
help to ensure that the progeny have the resist-
ance gene, eliminating the need to test for resist-
ance. New methods using pyrosequencing or
single-nucleotide polymorphism markers have
been developed in order to determine the dosage
of the resistance gene (in this case
H1
) (Dale
et al
.,
2010), and recently
Av r
genes have been used as
probes to screen for resistance in progeny.
Several
Solanum
wild species have resist-
ance against
Meloidogyne
spp. The introgression
of several genes against RKNs has been devel-
oped from some wild parentals. Resistance intro-
gression into cultivated potato for
M. chitwoodi
has been achieved using
Solanum bulbocastanum
