Planting back-to-back lentil crops can place high
pressure on genetic resistance in lentil varieties,
according to pathologists and plant breeders.
Pathologists and plant breeders are advising growers planning to grow back-to-back lentil crops this season that the practice can cause a high disease risk and that a disease management strategy is needed throughout the growing season.
Both of the main foliar diseases affecting lentils, ascochyta blight and botrytis grey mould (BGM), can carry over on previous lentil stubble, meaning planting lentils on lentils or planting them in a two year rotation carries a higher risk than a typical three-year rotation.
Planting lentils in a paddock neighbouring the previous year’s stubble carries the same high risk as fungal spores can blow onto the new crop.
Leader of the lentil breeding program at Pulse Breeding Australia Dr Matthew Rodda says placing lentils under high pressure by planting them back-to-back means disease pathogens can overcome resistance genes.
This means resistance genes in the plant will be ineffective. This is not only detrimental to individual growers but their whole district and the wider lentil industry.
“From a breeding point of view, we have seen a fairly rapid breakdown on the Yorke Peninsula of resistance genes,” Dr Rodda says. “For example, Nipper was released in 2005 and has gone from resistant to ascochyta blight to only moderately resistant/moderately susceptible.
“It has gone half way down the disease resistance scale in only a few years. If we identify a new source of resistance it’s going to be at least 10 years to get a new variety to growers.”
Pulse pathologist Dr Jenny Davidson from the South Australian Research and Development Institute, a division of Primary Industries and Regions SA, says growers need to make their own decisions about planting lentils in tight rotations but need to be aware of the risks in breaking down genetic resistance and the implications for the industry.
She says if growers do choose to plant back-to-back lentils, in a two year rotation, or lentils close to the previous year’s stubble then they need to assume a high disease risk and have a sound disease management strategy in place throughout the growing season, starting with variety selection.
“What growers should be looking at is varieties with good resistance to both ascochyta blight and BGM,” she says. “PBA Jumbo2 fits into that category well, but PBA Hurricane XT, which will be widely grown again because of its herbicide tolerance, has resistance to ascochyta blight but is moderately susceptible to BGM.”
She says coating seed in a thiram-based seed dressing will prevent infection at the seedling stage and should last for approximately eight weeks.
The next step for growers is to monitor crops very closely and implement their foliar fungicide program.
“Normally we would say to spray for BGM on susceptible varieties as the crop approaches canopy closure, even varieties with resistance should also get that canopy closure spray against BGM, especially in high disease risk situations,” Dr Davidson says.
“For any crops susceptible to ascochyta blight, growers should be out scouting during the vegetative phase in August and getting an idea as to whether the disease is present and, if it is, then they need to do a spray for it.”
Dr Davidson says the key for growers is to be vigilant and monitor crops carefully.
“Intensive lentil cropping puts a lot of pressure on genetic resistance in varieties and, in the longer term, there is a much higher chance we could lose resistance in those varieties,” she says.
“I understand farmers have to make an economic decision and lentil prices are high, but they must also be aware of the long-term ramifications.”
Dr Jenny Davidson,
08 8303 9389,
Dr Matthew Rodda,
03 5362 2111,
GRDC Ground Cover supplement: Foliar fungal diseases of pulses and oilseeds
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