Key points
- An ACIAR project aims to both improve production outcomes for Ethiopian faba bean growers and future-proof Australia’s young industry
- Already it has discovered the previously unknown cause of the devastating faba bean gall disease
- Identified in Ethiopia in 2012, faba bean gall disease can lead to complete crop failure
- A better understanding of it and other pathosystems in Ethiopia, where this pulse has been grown for millennia, will also help guide breeding and management decisions in Australia
- Australia produces up to 500,000 tonnes of faba beans annually and supplies one-third of the beans traded internationally
In the course of ‘future proofing’ Australia’s faba bean industry and improving production outcomes for Ethiopian growers, researchers have unlocked a decade-old mystery. They have discovered the previously unknown cause of the devastating faba bean gall disease.
In research funded by the Australian Centre for International Agricultural Research (ACIAR), Professor Martin Barbetti and research fellow Dr Mingpei You, both from the University of Western Australia (UWA) School of Agriculture and Environment and the UWA Institute of Agriculture, together with colleagues from the Ethiopian Institute of Agricultural Research, proved that the pathogen Physoderma viciae caused the disease, not Olpidium.
The work is part of a broader project, which includes collaborators from the New South Wales Department of Primary Industries (DPI) at Tamworth and the International Center for Agricultural Research in the Dry Areas (ICARDA), to improve the reliability, productivity and profitability of faba bean production in Ethiopia.
Wrong target
Until now, strategies to control and manage faba bean gall disease were based on a pathogen incorrectly identified as Olpidium viciae. This is a totally different pathogen in terms of its biology, infection, spread and management strategies.
Professor Barbetti says the wrongly identified pathogen is a genus generally restricted to underground parts of the plant. It does not show above-ground symptoms and is not spread by rain splash.
This contrasts with the correctly identified pathogen Physoderma, an above-ground pathogen primarily spread by rain splash.
This image shows clear gall formations on the bottom of leaves. On the top side, the depression can contain water. Photo: Martin Barbetti
The pathogen was identified using both classical mycology and advanced molecular tools and Professor Barbetti says management strategies can now be aligned with the pathogen’s nature and behaviour.
“Armed with the knowledge that the disease is caused by a pathogen that spreads by rain splash, we can now predict when the zoospores will be released and best timings for chemical spray applications to reduce reinfection cycles.”
Additionally, Physoderma resting spores can easily be spread by movement of infested stubble, machinery, contaminated soil, people or animals. The spores also survive in the manure of cows that have fed on faba bean-infested stubble. Growers’ practice of applying manure to growing paddocks likely contributes to both further disease spread and increased disease severity.
The first faba bean gall disease symptoms occur when upper leaf surface areas produce masses of water-splashed zoospores. These swimming spores are released into specialised sunken-well structures on the leaves that retain water – structures that the pathogen cleverly tricks the plant into producing for its benefit.
Ethiopian experience
When a faba bean gall disease was identified in Ethiopia in 2012, surveys showed that 50 to 100 per cent of crops quickly became infected. What followed was complete crop failure in many instances.
This pulse is of critical importance for food security in Ethiopia, where it has been cultivated for millennia. However, finding out more about the disease is also important to Australia – the world’s leading faba bean exporter – and particularly the northern region of NSW.
Collaborator NSW DPI plant pathologist and faba bean expert Joop van Leur says there are many similarities between the environmental conditions of the Ethiopian highlands, where faba beans are cultivated, and the northern region: “That is unreliable rainfall, heavy clays, droughts in some years and floods and waterlogging in other years,” he says.
When a former research colleague, ICARDA’s Dr Seid Kemal, originally told Mr van Leur about this new faba bean disease in Ethiopia, he took it with a grain of salt. “Plant pathologists all talk about the one disease that will absolutely kill everything and they tend to exaggerate a little.”
However, on an ACIAR-funded reconnaissance trip to Ethiopia with Professor Barbetti, he was taken aback.
“It was an eye-opener,” Mr van Leur says. “I have not seen such an incredible disease impact before. It is an absolute killer. With a disease like that, it is really important for the Australian industry to know more.
There is direct importance to Australian agriculture not only for faba bean production, but potentially for other crops and pasture legumes where it is now also found in Ethiopia.
Compared with Ethiopia, the Australian industry is very young and its pathosystems are still developing. “In northern NSW we have been growing pulses for perhaps 30 years compared to 2000 years in the Ethiopian highlands. That means we can learn a lot from Ethiopia, where both the crop, host and diseases have co-existed for millennia.”
One of the most exciting outcomes so far has been identifying the cause of faba bean gall disease. However, the project team is also looking to better understand other diseases and viruses.
Root rots are also being investigated. “Faba bean root rot is starting to become important in Australia but is considered to be one of the main faba bean diseases in Ethiopia,” he says.
Mr van Leur says most root rots start to become an issue when crop rotations shorten, as inoculum builds up during each growing season. “It is quite common for there to be a honeymoon period after a crop is introduced to a new environment as it takes time for inoculum to build up. That is particularly the case for root rot diseases.”
Root rot
As part of the project, soil and root samples from the main Ethiopian growing environments were analysed by SARDI using PREDICTA® B, a DNA-based soil testing service, and other molecular-based tests.
Mr van Leur says first results show there are numerous pathogens associated with faba bean root rot in Ethiopia.
“Most of these are already present in Australia and further research is needed to identify which pathogens are the most pathogenic. Knowing which pathogens are associated with severe root rot in Ethiopia will help prioritise our research.”
Before this analysis, the team had also looked into Aphanomyces euteiches, a water mould and one of the most aggressive faba bean root rots. It is the causal agent of Aphanomyces root rot (ARR).
Differences among faba bean genotypes in resistance to Aphanomyces root rot (ARR) at Tamworth Agricultural Institute’s field trials in naturally infested soil. From left to right is Nuraa, which is ARR susceptible; Ac1241, which is also ARR susceptible; and Ac1231#15009, an ARR resistant line. Photo: Joop van Leur
The pathogen was identified more than a decade ago as the cause of severe root rot in northern NSW. It has not been previously recorded in Ethiopia, but the PREDICTA® B testing showed it is widespread in the Ethiopian faba bean growing regions.
“ARR is a wet weather pathogen. In the north, we haven’t seen much in the past decade as we’ve had a prolonged drought. But in the past few years, it is becoming a major problem in parts of South Australia too,” Mr van Leur says.
Additionally, faba bean germplasm accessions from the Australian Grains Genebank were tested against A. euteiches strains isolated from faba beans in northern NSW.
“We found a wide range in host plant reactions from highly susceptible to near-immune, particularly in germplasm from Ethiopian origin.
“The lines with the highest level of ARR resistance identified so far are of Chinese and Ethiopian origin and have been made available to the Australian faba bean breeding program to be used in its crossing program.”
Mr van Leur says the Chinese lines were collected in Yunnan province as a part of an earlier ACIAR-funded project. “They were found to have outstanding resistance to bean leafroll virus and have been used extensively in the faba bean breeding program.”
The project will continue to test Australian breeding material in Ethiopia against a range of pathogens that are of importance to the Australian faba bean industry, such as chocolate spot, Ascochyta blight and rust. The local Ethiopian strains are expected to be completely different to those in Australia. “This will allow the detection of resistances that are broad-based and likely to be durable.”
Future-proofing against potential diseases is important to Australia’s industry, which produces up to 500,000 tonnes annually and supplies one-third of faba beans traded internationally.
The research is supported by ACIAR and other collaborating institutions, including the Ethiopian Institute for Agricultural Research in Ethiopia, Debre Birhan Agricultural Research Centre in Ethiopia, and the International Center for Agricultural Research in the Dry Areas (ICARDA) in Morocco.
A planning meeting will be held in Ethiopia in October. The project is scheduled to run until mid-2023.
More information: Martin Barbetti,