Joop van Leur (00:00): Thanks very much [Zorica 00:00:03] the short
presentation ... short story about the pulse viruses in Northern New South Wales. Just
a few key points. Most of you would ... will know this already but just to repeat it again.
There is ... in pulse crops, pulse crops can be affected by a very large, relatively large
number of viruses particularly compared to winter cereals. And there are already, there
are over 20 pulse viruses or 20 viruses that affect pulse crops, different types of pulse
crops of economic importance worldwide. Fortunately, a large number of ... a fair number of these
viruses have never entered the country so far. And also with the ones that we have here,
some of them at this moment, we would not consider them to be really important, but
there are nine viruses on pulse crops, and that can be faba bean, chickpea, lupins, field
peas, lentils, that have caused in the recent past significant losses in one or more locations.
And what the nine important viruses have one thing in common is that they're all aphid
transmitted. Now, there are two ways that depending on the virus species, how they can
be transmitted. The non persistent way means that the virus only has to ... an aphid ... sorry.
An aphid only has to probe an infected plant in order to be able to transmit that virus
to a healthy plant. On the other hand, the non persistently transmitted viruses are lost
after one or two probes on the healthy plants, which they will infect then. But then after
that, the aphid is not [inaudible 00:02:03] anymore. The persistently transmitted viruses
are ... actually need to feed on the plant. They need to put their stylet into the [inaudible
00:02:13] of an infested plant in order to acquire the virus, and on the moment that
they have acquired the virus that aphid remains [inaudible 00:02:22] the rest of his life.
Now, because they require a longer time to acquire the virus, and a longer time to transmit
the virus, there are more control options in terms of aphicides possible with the persistently
transmitted viruses than with the non persistently transmitted.
Also, the persistently transmitted viruses, because again, because they require feeding
are often very specific in the aphid species that can transmit them. So, it often the specialised
aphids that colonise the host plants can only transmit the virus, while the non persistently
ones, even pulse viruses can be transmitted by non colonisers even by serial aphids because
serial aphids might come into a pulse crops and they might still probe it. They might
still put the stylet quickly in the leaves before they realise that is not a suitable
host, but even that quick probing is enough to transmit non persistently transmitted viruses.
Another very important thing, of course, for the viruses and the vectors is that they require
living plants to survive between cropping seasons.
So, it makes the whole epidemiology or virology of viruses far more complicated than with
fungal diseases, because you do not only have to look at the current weather during the
season in order to get an idea whether or not we have a virus favourable year. You also
have to look at the preceding summer season. If there are no crops over summer, the reservoir
for viruses and their vectors is limited, and you will rarely see a major virus epidemic
occurring. So, and that's what's happened in the 2018, 2019 seasons. I mean, there were
... the summer rains in the Northern region were minor. And because of that, we did not
see much viruses in the winter season, the following winter season. Of course, the last
year was a horrible season altogether. There was hardly any crop around so, also that affects
of course, development of the viruses. Now we have very important thing to remember
is that once a virus ... once a plant get infected by a virus, that's it. The far ... there
is no way that you can cure the plant after infection. So, there is no ... all control
strategies have to be based in avoiding the infection. So, quick overview on the viruses
that, that we consider important in the Northern region. I did not put [inaudible 00:05:27]
mosaic virus there because in field peas [inaudible 00:05:29] not a many field peas grown, but
these are eight viruses that we have observed in the last 10, 15 years, in that they can
be either in large areas or in localised area cause problems. The two most important ones
are bean leafroll virus, particularly for fava bean. It's a persistent transmitted virus,
pea aphid is the most important vector there. And in case ... for the chickpeas, it is turnip
yellows virus, which was earlier known on the beet western yellow virus.
It's more of a group of viruses, it's not just a single species and their main vector
is green peach aphid but we are looking at the moment, particularly in chickpeas, whether
there is any other aphid species can also transmit turnip yellows virus, or one of the
variants of turnip yellows virus. Because we do know that green peach aphids do not
visit or don't ... rather avoid chickpeas. And the impact of pulse viruses, I mean, one
of the things occur is what makes the pulse ... what makes viruses dangerous is that they
are generally not restricted to one single host species. They jump from one pulse species
to the other, including the pasture legumes. And even some of them can go into non pulse
hosts, particularly the turnip yellows virus, which is also very important in canola crops.
And we are looking at a moment into what effect, to what extent the early sown canola crops
that get infected by turnip yellow virus have an effect on the later sown chickpea crops,
whether or not canola act as a reservoir for turnip yellow virus in chickpeas later.
Again, the [inaudible 00:07:43] can go on different hosts species not necessarily, they
all have the same effect. Alfalfa mosaic virus for instance, has little impact on fava bean,
but it can definitely kill chickpeas and bean leafroll virus does not show symptoms in lucerne,
but lucerne is the main over summer hosts for bean leafroll virus, and on the moment
it gets into fava beans, particularly early infection, it can be a lot of damage. The
thing with these viruses also is that they can cause symptoms in the field that are indistinguishable.
And that's why, that's why we need to do the, do the testing using proper diagnostic tools.
And we have developed an diagnostic laboratory here at Tamworth, and you're all free to submit
samples on the moment that you think that you got virus in a crop. And remember that
virus symptoms can often look or herbicide symptoms can often look like virus symptoms.
So, proper diagnostic is pretty important. Here just an example on what, even though
that these are completely different viruses on fava bean, different hosts, that the symptoms
look very much the same. So three different viruses, symptoms the same, and you need only
be proper diagnostically can be the diff ... can ... you can distinguish them. The same even
more so with chickpeas. Chickpeas, you can have not only related virus look the same
symptoms, but viruses like turnip yellow virus, alfalfa mosaic virus and cucumber mosaic virus
all give the same symptoms. Chickpeas are particularly sensitive to viruses, even though
that aphids don't like chickpeas. And then you often ... the incidences might be a bit
lower, but if chickpea plant get infected early on, particularly of course it dies.
The last slide just for the outlook 2020 in the first slide I said already, the only way
to avoid viruses is to, to prevent infection. And for a lot of the early sound crops this
year, the virus is already there because we did have the preceding summer season, particularly
the end of the summer and the start of the autumn. We had some regular ... we had some
good rains in quite a large, a large area. So, there were ... the summer rains resulted
in, in volunteers in plants that could harbour the viruses and the vectors. And we have seen
already, and it's already mentioned by both you and Zorica that we've seen already quite
a lot of activity of aphids going around. Also, there's been quite a bit of early fava
bean sown, very early fava bean that were particularly vulnerable to the virus infection.
So for the ... some of these crops, might've been infected already. I say might because
we haven't tested many samples as yet. The aphid activity will now slow down on the
moment it gets cold weather, but particularly in fava bean crops, if you do have some virus
foci in your crop already, then it might ... you might want to consider to be particularly,
particularly careful about aphid movements again in autumn, because then if you have
already some virus in your crop, it can easily spread in springtime. Very last, last point
and that is, most of the growers are very much aware, very much aware of that the best
way actually on preventing losses caused by viruses is to practise good agronomy in your
pulse crops. Good growing crops, particularly if they're sown in stubble, have the ability
to resist virus, and they're also less attractive to aphid. So, at this stage, that is the best
way of preventing losses by viruses. Thank you.