GCTV Ep#9 Crown Rot
Narrator: Seeing is believing and in this case what
you’re seeing is the impact root lesion nematodes have had on two popular wheat varieties.
Same population levels of Pratylenchus thornei in both plots, but on the right the moderately
nematode-tolerant EGA Wylie, on the left, the intolerant Strzelecki.
Richard Daniel: CEO Northern Grower Alliance That’s the sort of result you’re going
to get by choosing the wrong variety where you’ve got root lesion nematode at any sort
of concerning level of density.
Narrator: This trial at Yallaroi in northwestern NSW
is one of a number being run by the Northern Grower Alliance in collaboration with NSW
DPI, and with GRDC’s support.
At the various sites the impact of either Pratylenchus thornei or Pratylenchus neglectus
on rotation crops is being assessed.
This research follows on from earlier trials that focused on the northern region’s other
major cereal diseases.
Richard Daniel: Three of four years ago we did a series of
22 trials looking at the impact of crown rot on a range of bread wheat, durum and barley
varieties.
Narrator: That earlier research revealed the impact
of crown rot on yield was more severe where root lesion nematodes were present.
Richard Daniel: They’re totally independent but it appears
that when you’ve got nematodes present, if you’ve got crown rot, the crown rot effects
that you’re seeing are going to be much more dramatic.
Narrator: And that’s because of the way the two diseases
attack the plant.
Darryl Anderson: Reporter Root lesion nematodes burrow into the root
system damaging the plants capacity to take up moisture and nutrients.
While the crown rot fungus sends mycelium up into the vascular system, which further
inhibits the flow of moisture.
Narrator: Without moisture and nutrients seed heads
don’t fill and dry off, leaving a tell tale white head.
EGA Wylie is a variety that not only has moderate resistance to nematodes; it also has a similar
level of resistance to crown rot.
However in particular season’s moderate resistance is not enough.
Steven Simpfendorfer: Senior Plant Pathologist NSW DPI Tamworth
You put it under high crown rot pressure, get a hot dry finish that really exacerbates
the expression of those white heads you’ll still get 50% yield loss to crown rot in EGA
Wylie, a moderately resistant variety.
Rob Long: B&W Rural, Moree NSW If people get it wrong they can lose 20 to
50% of their yield I mean it can be absolutely catastrophic.
Narrator: Rob Long is a local agronomist whose work
also involves assessing cereal varieties for crown rot.
This past season no variety was spared from infection.
Rob Long: The last two years have been wet springs and
we haven’t noticed any yield implication at all but in those years the infections rates
haven’t dropped.
The inoculum is still there but where you get the perfect storm like this year where
you get a wet start and a really dry spring those white heads and yield losses are dramatic.
Narrator: Crown rot lives in retained stubble, which
is why it’s become such a serious problem for the northern grains region.
When new crops emerge the fungus will be waiting to spread.
Steven Simpfendorfer: The way that does that is you get a basal
infection in the base of the plant here, get the characteristic browning, and given moisture
stress the fungus proliferates in the base and clogs up that vascular system and you
can’t get water up to the heads and that’s where you get these classic white heads.
Narrator: While crown rot is expressed as white heads,
not all white heads are necessarily caused by this fungal infection.
Mice damage or the disease Take-all will also produce white heads although Take-all as the
name suggests will take the entire plant rather than random tillers.
However a lack of white heads in a crop doesn’t mean crown rot isn’t present.
The real indicator of the true level of infection is the presence of basal browning.
Steven Simpfendorfer: Yeah so this one here is unaffected at this
stage no basal browning so that’s the normal colour you’d expect this sort of whitey,
light green and here’s one infected with crown rot.
You’ve got this characteristic; they call it honey brown colour produced by the fungus.
Narrator: All cereals are susceptible to crown rot but
Durum wheats are the hardest hit.
Rob Long: Well the Northern Alliance did some really
good work in 2007/2008 and in the 2008 year which was similar to this year where it had
a wet start and a dry finish the average loss in bread wheat, average yield loss where the
only difference was either the presence or absence of the crown rot inoculum, was about
27%, whereas for Durum it was 58%.
Narrator: The key to managing crown rot is to break
the cycle of cereal sown on a cereal stubble.
Rotation crops such as chickpeas, faba beans and canola are recommended and crop canopy
plays a significance role.
Steven Simpfendorfer: Canola closes over the ground quite early,
produces a big bulky crop, get all that leaf drop, and that leaf is high in nitrogen, you
actually then drive decomposition of the cereal stubble underneath a lot more and you’ll
break down more stubble and therefore get rid of a lot more crown rot.
Whereas the chickpeas, slow early on, generally don’t get the cover till late; certainly
don’t give you as good a decomposition of cereal stubble underneath a chickpea crop
as you get with some of those other breaks but still is very useful in our system.
Narrator: And chickpea will leave more soil water at
depth for a following cereal crop than canola will.
Another way to break the disease cycle is to make use of GPS technology.
Steven Simpfendorfer: In a no-till system stubble retained you actually
confine your inoculum to that old row so sowing back with guidance in between the rows you
remove contact between your new crop and this stubble which has got the crown rot in it
and we know we need intimate contact between an infected piece of residue and the new crop
to initiative an infection so roughly we’re finding that inter-row sowing reduces our
crown rot levels by about 50% just by that simple action of where we put our next row.
Narrator: And while there is some discussion about the
use of strategic tillage in this no-till age, for weed control reasons, where crown rot
is present, Stephen Simpendorfer doesn’t recommend it’s use.
Steven Simpfendorfer: Some of these aggressive strategies growers
use like Kelly chains and things to try and break that stubble up can actually make their
crown rot problem worse in that they have spread their inoculum more evenly across the
paddock and they have taken a lot of moisture out of the system which might have allowed
them to compensate and deal with that infection a bit better.
Narrator: Steven Simpfendorfer also says growers can’t
rely on breeding programs alone to find a solution for managing crown rot.
Steven Simpfendorfer: Varieties are not a key tool for crown rot,
they’re certainly a useful tool you get about a 15% difference in yield loss from
swapping from something that’s very susceptible to moderate resistance and I guess the key
one is really getting out of Durums if you are in a high risk, they suffer a lot more
yield loss but you need an integrated approach with inter-row sowing, break crops.
Narrator: The northern growers alliance’s trial is
also studying the impact root lesion nematodes have on rotation crops and ultimately the
research will produce recommendations that will have application for the management of
nematodes and crown rot.
Richard Daniel: Brassica, a broad leaf crop helps to break
down the wheat stubble so it helps to reduce the crown rot issue.
Cotton, sorghum, sunflower, all fall into that same camp.
So in general the things from a good rotation point of view that are going to help reduce
the impact and threat from root lesion nematode, in general are also going to be things that
are advantageous in terms of crown rot management.
Narrator: But going back to those first images we saw
when it comes to root lesion nematode management varietal selection is important.
Richard Daniel: Growers have a lot of ammunition, a lot of
power to improve their management by their variety choice.
We don’t get that with crown rot.
With Crown rot it’s really the rotation and our stubble management, which is our key
tool to reduce the problem, variety choice is really a very small part of it.
With root lesion nematode it’s a critical part of it.
ENDS
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