Agriculture Reference
In-Depth Information
Moreover, due to lack of adequate screening be-
forehand, when new cultivars are released, in-
formation on whether any virus resistance
genes are present is rarely provided, only less
helpful descriptors, such as “moderate resist-
ance” to PVX, PVY, PLRV, or PVA, or “low resist-
ance” to one or other of these viruses.
3.
Quantification of virus-induced yield losses
needs to be revisited, as the data available for
common potato viruses present singly, or in mixed
infections, is mostly old, limited, and involves out-
moded potato cultivars (e.g. Broadbent
et al
.,
1957). Furthermore, such yield data tend to be
lacking for viruses found more recently. Compari-
sons between infected and healthy potted plants,
spaced plants, or single-row plots are inadequate
here. This is because, when virus spreads from in-
fected plants within the crop, plants become in-
fected at different growth stages, and the growth
of neighboring healthy plants compensates for the
growth of infected plants (e.g. Jones, 2006).
Therefore, what is needed to quantify the conse-
quences of infection is replicated field experiments
with large plots, sensitive and tolerant cultivars,
mild and severe virus strains, and introduced
virus infection foci consisting of infected trans-
plants or planted, secondarily infected tubers.
Tuber quality should also be assessed so that mar-
ketable yield data can be provided.
4.
The process of searching for and character-
izing additional potato viruses in the Andean
region recommenced on a small scale recently
(Adams
et al
., 2013; Kreuze
et al
., 2013; Sou-
za-Richards
et al
., 2014). With the aid of innov-
ations in molecular techniques, the time has
arrived to revitalize the effort to find new potato
viruses and to complete the characterization of
ones identified earlier. Such research will help in
identifying reasons why potato yields are not
achieving their full potential in the Andean re-
gion. It will also help to avoid the introduction
to other continents of potato viruses currently
restricted to the Andes. It should include studies
on virus transmission through true potato seed,
as this is an important route via which Andean
potato viruses might be introduced, when ger-
mplasm is being exchanged worldwide by plant
breeders. National and international plant
quarantine authorities need to remain vigilant
to ensure that the risk of such introductions is
minimized.
5.
Since potato is being grown increasingly in
warmer regions of the world, the possible emer-
gence of new tospoviruses, begomoviruses, and
other types of viruses via new encounter scen-
arios with native vegetation needs to be moni-
tored carefully. This is necessary as part of the
efforts to ensure food security and to avoid new
virus problems building to serious levels without
being noticed. The same applies to their possible
spread to potato from other Solanaceous crops
such as tomato, pepper, tobacco, or aubergine.
6.
Improved diagnostic techniques suitable for
mass virus detection in samples from seed po-
tato fields or stored dormant tubers are in-
creasingly likely to arise through medical re-
search in virus diagnostics (e.g. Boonham
et al
.,
2014; Jones, 2014). These need to be exploited
rapidly to benefit seed potato industries.
7.
High incidences of plants with mixed in-
fections with common potato viruses, espe-
cially PVY, PVX, PVS, and PLRV, are still com-
mon in potato fields in many countries
without sophisticated seed potato production
schemes. For example, in Kenya, mixed infec-
tions in seed potatoes ranged from
50
to
100% (Gildemacher
et al
., 2009), and in Iran
an extensive survey revealed an average 52%
of plants with mixed infections (Pourrahim
et al
., 2007). These mixed infections contrib-
uted to very low average potato yields in ware
crops. It is important to continue to develop
simple yet effective seed production systems
that control potato viruses effectively for
such countries.
8.
Finally, looking to the future, forewarned is
forearmed, so research is urgently needed to
understand better the likely consequences of cli-
mate change on the impacts of virus disease on
potato industries worldwide. This requires exam-
ining the effects of different climate change
parameters alone or in combination on potato
plants or stored tubers with single or mixed virus
infections. It also requires modeling studies that
establish where climate change is likely to result
in damaging potato virus epidemics in regions
where they were previously considered of minor
importance. Similarly, more climate change
scenario modeling is needed to establish when
potato viruses or vectors are likely to invade re-
gions where conditions were formerly unsuitable
for them.
