del Toro, F.J., Choi, K.S.,
Rakhshandehroo, F., Aguilar, E.,
Tenllado, F. and Canto, T.
2019
Ambient conditions of
elevated temperature
and CO2 levels are
detrimental to the
probabilities of transmission
by insects of a Potato Virus
Y isolate and to its stimulated
prevalence in the environment
Virology 530: 1-10
NOTE:
Plant viruses cause
extensive damage
to crops every year.
Most such viruses
are transmitted via insects,
who feed on infected plants
and then pass viruses
on to uninfected ones.
SUMMARY:
del Toro et al. (2019) recently
examined the probability
of transmission of potato virus Y
by the peach aphid (Myzus persicae)
to Nicotiana benthamiana plants
subjected to either:
(1)
present-day
temperatures (25°C)
and atmospheric
CO2 levels (405 ppm),
referred to as the
standard treatment (ST), or
(2)
future-projected
temperatures (30°C)
and CO2 levels (970 ppm),
referred to as the
climate change (CC)
treatment.
The authors conclude that
"conditions of elevated
ambient temperature
and CO2 levels
decreased probabilities
of transmission of viral
infection by aphids,"
which suggests that
"extended warm episodes
and permanent elevated
levels of CO2 associated
[with] climate change
could challenge the
prevalence of infections
by some populations
of non-persistently
transmitted potyviruses."
When the experimental
environment included
3 virus-infected aphids,
transmission frequencies
were 88% lower
in the CC treatment
(6.3% transmission rate)
compared to the ST treatment
(52.5% transmission rate).
Similar findings were observed
using fewer (1 or 2) or more (4)
aphids per recipient plantlet,
where virus transmission rates
in the ST treatment were always
significantly higher than those
in the CC treatment.
del Toro et al. next sought to
"calculate transmission probabilities
from either ST or CC donor [infected]
leaves for different numbers
of aphids probing on [uninfected]
recipient plantlets."
The resultant probabilities
are shown in the first chart below.
The probability of a single aphid
transmitting the virus
after feeding on an infected plant
in the ST treatment is 26% (0.260),
whereas in the CC treatment
it is a much lower 2.9% (0.029).
These probabilities rise
as more aphids are introduced
into the equation, such that
when there are five aphids
having the potato virus Y
probing on a plant,
the probability of virus
transmission to the
uninfected plant
reaches 100%
in the ST treatment.
However,
in the CC treatment,
100% infection probability
is not reached until
the number of
infected aphid events
on a given plant
reaches a whopping 34,
a value far off the graph!
DETAILS:
The second graph shows
the average number
of first-time probings
by aphids on recipient plants
after having fed on leaves
of infected plants
in the two temperature and
CO2 treatments that are
required to contaminate
the uninfected plant,
relative to the number
of aphids that reach
each recipient plant.
del Toro et al. determined
that in the ST treatment
a visitation rate of 1.10 aphids
per plant in a week was
"sufficient to maintain
potato virus Y
in a simulated
environment,"
whereas a visit of 4 aphids
per plant per week
was enough to ensure
maximum transmission/plant
infection.
In contrast, the researchers
determined that
"the virus disappeared
from the environment
when less than 10 aphids (9.881)
visited each plant in a week"
in the CC treatment,
and they note that
"only with values equal to
or greater than 10
visiting aphids/plant/week
infection became endemic,
although with percentages
of infection much lower
than under ST conditions."
