Australian researchers have discovered a gene in the fungal pathogen causing ascochyta blight that triggers disease resistance in lentils, helping researchers to advise growers on lentil varieties with strong genetic resistance.

Recently published in scientific journal Molecular Plant Pathology, researchers from the Centre for Crop and Disease Management (CCDM), in collaboration with the South Australian Research and Development Institute (SARDI), were able to flip their thinking on the pathogen.

CCDM is a national centre co-supported by the Grains Research and Development Corporation (GRDC) and Curtin University.

Researchers found that some lentil varieties carried a gene that was able to recognise a key fungal protein normally responsible for disease development, which instead triggered a defence response, leaving certain lentil varieties asymptomatic.

CCDM researcher and co-author Dr Bernadette Henares says this was quite different to their usual approach to genetic improvement of crops where they try to breed out the genes involved in response to toxic proteins from the pathogen.  Furthermore, in Australia the pathogen population can be one of two forms, and the form type will determine whether it triggers the defence response or not.

“This is exciting news as it has led to the development of a laboratory test – similar to the PCR-based COVID-19 test – that has potential to inform growers which variety of lentil to grow for maximum resistance, based on the fungal gene that is present in the paddock,” Dr Henares says.

“The laboratory test has potential, with a little further work, to be deployed as an in-field test, and is showing promise in becoming an essential decision-support tool for growers to use when selecting their lentil varieties.”

Dr Henares says from this research, they now know there are two types of the ascochyta pathogen – pathotype 1 which doesn’t cause disease on PBA Hurricane XT, PBA Hallmark XT, PBA Bolt and other varieties that carry the same resistance, but does cause disease on Nipper. The other type, pathotype 2, is damaging to PBA Hurricane XT, PBA Hallmark XT and PBA Bolt, but not Nipper.

“If we can diagnose which pathotype of ascochyta is in the grower’s paddock or stubble, then we can let them know, for example, if PBA Hurricane XT might be susceptible to the ascochyta pathotype that is present in their paddock, and suggest they choose a different variety.”

SARDI pulse pathologist and co-author Sara Blake says knowing which pathotype was present in the paddock would be useful, but would need to be added to other tools in the toolkit.

“If used in conjunction with disease resistance ratings, along with rotation history, knowing about the presence of volunteer inoculum, along with knowing more about neighbouring properties as spores can travel up to 100m, this test could be quite helpful,” she says.

“Growers could use it to determine their disease risk and work out how proactive they need to be with monitoring and it could also help them plan their fungicide strategy.”

CCDM researcher and co-author Dr Lars Kamphuis says this discovery has helped to explain, in part, why certain lentil varieties have come and gone.

“We’ve been collecting samples of lentil ascochyta from across Australia since 2013. Analysis has shown that pathotype 1 was the predominant one at a time when the variety Nipper was popular,” Dr Kamphuis says.

“Then other varieties were introduced, with varieties such as PBA Bolt, PBA Hallmark XT and PBA Hurricane XT gaining a lot of popularity from 2016 onwards, which resulted in pathotype 2 becoming the more dominant pathotype.

“Both pathotypes have been found across the lentil cropping regions of southern Australia, but one will dominate over the other when a certain lentil variety is grown.”

Dr Kamphuis says once the test has been developed for the field, it will undergo some road testing amongst partnering pathologists, before it will be ready for the wider industry.

“Once the in-field test is ready, I imagine an agronomist could quickly carry out the test in the back of a ute,” he says.

“But in the meantime, lentil growers can send us diseased leaf samples now, or stubble samples later, and we can tell them if they have ascochyta blight and the pathotype present too. It may not be an immediate response at this stage, but it could help them for next season.”

CCDM Director Professor Mark Gibberd says this discovery was another example of CCDM researchers working collaboratively to find solutions to managing diseases.

“Discovering how lentil ascochyta causes infection and progressing towards a paddock-level tool for managing the different pathotypes ensures we are not only providing a solution for growers now, but also setting ourselves up for the next disease problem faced by growers.

“Pathogens are always changing, but thanks to a long-term investment between GRDC and Curtin, CCDM is well-placed to rapidly respond to industry needs and commit to research problems until we find solutions.”

To send CCDM a sample, Australian lentil growers are recommended to contact their local state pathologists for sampling kit instructions: Sara Blake from SARDI, Andrea Hills from the Department of Primary Industries and Regional Development (DPIRD) or Josh Fanning from Agriculture Victoria.

Alternatively, contact CCDM for more information at ccdm@curtin.edu.au.

Read the paper, The novel avirulence effector AlAvr1 from Ascochyta lentis mediates host cultivar specificity of ascochyta blight in lentil.