Agriculture Reference
In-Depth Information
regions. Relying on visual inspections alone
during seed certification will not be sufficient to
identify all infected plants. This requires
large-scale testing of samples from growing
seed crops and tubers after harvest (e.g. Loeben-
stein
et al
., 2001; Mortimer-Jones
et al
., 2009;
Cox and Jones, 2012). Commencing the flush-
through system by starting the first generation
with virus-tested minitubers should be adopted
universally. Effective hygiene should be empha-
sized, involving timely roguing of symptomatic
potato plants within crops, and prompt removal
of volunteer potatoes, alternative virus or aphid
weed hosts (especially Solanaceous weeds), and
nearby finished crops of other cultivated plants
that harbor aphids. Non-host border crops that
act as virus-cleansing barriers and straw
mulches that diminish aphid landing rates be-
fore foliage closes across rows can be deployed.
Early foliage destruction to avoid PVY spread
during late aphid flights can be practiced (e.g. de
Bokx and van der Want, 1987; Saucke and Dor-
ing, 2004; Jones
et al
., 2009; Gray
et al
., 2010;
MacKenzie
et al
., 2014).
The development of predictive models
that forecast the timing of aphid flights should
be encouraged (e.g. Sigvald, 1986; Jones
et al
.,
2010), as they can help with decisions over
deploying cultural control measures against
PVY spread at planting time. They can also
help with decisions over when to deploy foliar
applications of mineral oils supplemented
with insecticide to help suppress PVY spread
within seed potato crops (MacKenzie
et al
.,
2014). Although insecticide applications used
alone as seed tuber dressings or foliar sprays
can be effective against PLRV, such treatments
are generally ineffective at controlling non-
persistently aphid-borne viruses like PVY.
If timed to coincide with aphid flights from
external sources, targeted insecticide applica-
tion suppressed
Myzus persicae
numbers arriv-
ing at crop margins in large seed potato fields,
thereby diminishing their movement deeper
into the crop (Carroll
et al
., 2009). This is
likely to help diminish PLRV spread and might
provide some benefits with PVY where other
species are minor components of the migrant
aphid population and large-sized seed fields
with small perimeter:area ratios are planted
with seed potatoes.
12.5
Future Research Needs
Although potato viruses have been the subject of
much research, they still cause substantial losses
in seed and ware potato production in many
parts of the world. There are still many research
areas where questions need to be answered and
additional investigations undertaken. Some of
the most important of these are:
1.
Over the past
20
or so years, PVY has become
an increasingly major concern for potato seed
and ware production in many countries, yet the
disagreement between its biological and phylo-
genetic strain group nomenclature systems re-
mains unresolved. The relationship between
these two classification systems needs to be un-
raveled. It would help to resolve this if (i) use of
identical names for strain groupings within the
two systems, and (ii) phylogenetic group names
based on tuber symptoms or geographical re-
gions were avoided. Moreover, further studies to
reveal the full biological and phylogenetic diver-
sity of PVY strains are required, as more are
likely to be found, especially in the Andean do-
mestication center where the greatest potato
virus diversity exists, and little research of this
kind has been done. Such research should in-
clude a search for biological strain groups that
overcome more than one PVY resistance gene, as
with PVX group
4
(Cockerham, 1955), and for
additional strain-specific PVY resistance genes.
Understanding of the key factors driving the
rapid evolution of new PVY variants at the mo-
lecular level also needs to be improved (e.g. Visser
et al
., 2013).
2.
Breeding for virus resistance is likely to be
highly beneficial, especially incorporation of re-
sistance gene
Ry
against PVY in new cultivars
destined for regions with temperate or Mediter-
ranean climates, and for resistance to PVX,
PVY, and PLRV in cultivars produced for
food-insecure subtropical or tropical regions.
There is therefore a need for potato breeding
programs to refocus on releasing new cultivars
with resistance to common potato viruses. Cur-
rently, breeding for virus resistance is rarely
considered a priority for potato breeding pro-
grams, and knowledge of whether the parental
lines they use in crosses possess virus resistance
is often lacking (e.g. Nyalugwe
et al
., 2012).
