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CCDM researchers have been working on sclerotinia for a while now – on both host resistance and management strategies.
More recently, we’ve had some success in investigating this disease in lupins. CCDM researchers Sarita Bennett and Pippa Michael have been working on sclerotinia in lupins for the past three years within a GRDC project in collaboration with DPIRD.
They were able to confirm that lupin varieties commonly grown in WA were highly susceptible to sclerotinia stem rot.
“We also tested fungicides on mycelium growth, looking at if there’s basal infection, will the fungicides control the mycelium growth, and we found that they will. However, trying to get that fungicide onto the mycelium is tricky with the canopy closure,” Pippa said.
“For disease management, recommendations are similar to strategies for canola, monitor environmental conditions and spray prophylactically if you need to, and particularly in years where there are dense crops, be aware of sclerotinia occurring.
“But I think it was most interesting, and a pity, to find that all lupin varieties are still very, very susceptible to sclerotinia.”
CCDM researchers Sarita Bennett and Pippa Michael, with sclerotinia stem rot on a lupin plant in the middle
The unfortunate yield drag when breeding for resistance
Peter Bostock is a technical support manager for WA and SA with Pioneer Seeds, with an extensive history of working with growers and agronomists, with a major focus on canola.
Over the years he’s seen this crop go from strength to strength to a point where it has dominated as a break crop in rotations across Australia.
He said he thought by now there would have been a canola variety with resistance to sclerotinia stem rot, but understands the challenges breeders experience with breeding for disease resistance over yield.
“With protective traits, and particularly with, say, disease resistance, there’s often a level of yield drag, and if the yield drag is at a point where it’s not giving real benefit over just using chemicals, then it just doesn’t work out,” Peter said.
“And I guess over the years we’ve seen a lot of that in cereals, we’ve seen varieties being released where they’ve had very high levels of disease resistance, but they just don’t yield as well.
“So I think researchers are going to have to continue searching for novel traits potentially, to find something that’s commercially good enough. When you look at how fast technology is moving, I suspect at some point we will see resistance, but right at the moment there’s no proper resistance included in any of the Australian material.”
Peter Bostock of Pioneer Seeds, in a canola crop in WA’s Great Southern in 2022
So why is there this trade-off between yield and disease resistance?
CCDM researcher Mark Derbyshire
CCDM sclerotinia researcher Mark Derbyshire recently published a paper on this very problem – the complexity of breeding for resistance and yield in crops.
In a nutshell, he found that plant growth and defence is controlled by many molecular pathways that are incompatible with each other.
“So we’re seeing this growth/defence trade-off where plants will reduce their growth in response to pests or diseases,” Mark said.
“On the bright side, the genetic pathways behind this antagonism don’t always mean choosing between disease resistance and yield.
“While trade-offs may occur in some cases, both traits are complex and influenced by many factors. With new tools like genomic prediction, breeders now have better ways to manage these trade-offs and achieve stronger, less disease-suscebtible crops.”
This research review was published in collaboration with UWA and can be found here.
How to manage sclerotinia this season
From her many years of working on sclerotinia stem rot, Sarita said there was definitely a better understanding of the disease, however strategies for management have not changed that much.
She said using DPIRD’s Sclerotinia CM app can help with decisions around if or when to spray crops based on environmental conditions, especially as sclerotinia needs to be managed with prophylactically applied fungicides.
“Unfortunately prevention is the way to manage it, so you have to use prophylactic spraying, as once you see the disease, it’s too late,” Sarita said.
“But it’s so hard to tell, as we’ve seen some years when it seems like it’s going to be really bad, but nothing comes of it, and other years like this year where it has started off dry, but now looking like it could be quite severe, so it’s really important to consider a prophylactic spray now if needed on those crops.”
Her team also recently conducted a simulated yield loss experiment with sclerotinia stem rot to determine what level of infection economically justifies a fungicide application.
“We found that it was about 15%, so if you’ve just got a small amount of sclerotinia then, economically, it’s actually not worth applying the fungicide,” she said.
Peter said unless a paddock has not had sclerotinia in the past, and if the rotation is 1 in 2 or 1 in 3 with canola, he’d strongly recommend that growers talk to their preferred agriculture retailer, and ensure they have some product put aside in preparing for a portion of the crop to be sprayed with products for sclerotinia.
“And often those same products can be used for the earlier treatment of blackleg infection as well as for cereal diseases. So they’re often used widely in the farming system, but at least be prepared and have some product available.”