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Breeding better dry bean varieties

Higher yields, increased disease resistance, enhanced seed quality.

May 20, 2024  By Carolyn King


Resistant (left) versus susceptible (right) bean lines in the common bacterial blight nursery at Morden. ALL Photos courtesy of Anfu Hou, AAFC.

“The Morden dry bean breeding program was established in 2004, so it is still a very young program. There are many traits associated with dry bean yield, quality, and disease resistance, and we have to consider all those traits. So, it takes a long time to build up elite breeding materials. We have been working hard on this, continually improving our breeding lines,” says Anfu Hou, who leads this program at the Morden Research and Development Centre (MRDC) of Agriculture and Agri-Food Canada (AAFC).

“The program’s primary goal is to develop dry bean varieties for the growers and the industry in Manitoba; these varieties can also be grown in neighbouring regions. We also try to generate new knowledge on the genetics of issues like disease resistance, seed quality, and all the other important characteristics of bean varieties.”

He adds, “We work on quite a few different market classes. My focus most recently is on the major beans grown in Manitoba. That includes navy and pinto beans, which are the largest acreage beans. I also work on black beans, a very popular market class in western Manitoba.”

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 Fighting bean diseases
Improving resistance to yield-limiting bean diseases is a significant part of Hou’s program. “I work very closely with our pulse pathologist here at MRDC. Until recently, it was Dr. Robert Conner, who retired about three years ago. Currently, I’m working with Dr. Ahmed Abdelmagid; he is an oilseed pathologist but is supervising the pulse pathology team for now,” says Hou.

 “Although quite a few different dry bean diseases occur in this region, I have really been focusing on resistance to common bacterial blight, the most common foliar disease in the area. And we spend quite a bit of time on anthracnose, which can cause significant yield losses and quality reduction when conditions favor the disease. Another focus in the last few years is root rot; it is always a serious concern for the growers, but it is very difficult to work with. White mould is another concern that is also difficult to work with.”

 Hou and the pulse pathologist lead a dry bean disease survey every year in Manitoba. Hou says, “We monitor the dynamic changes of diseases and make sure we don’t miss any emerging concerns.” Along with helping Hou to target his program’s disease resistance work, the survey results also help bean growers and crop advisors to keep up to date on disease issues. 

“Also, we work closely with the Manitoba Pulse and Soybean Growers [MPSG] on the different yield trials every year. I have been coordinating the variety registration trials in Manitoba. As part of that, we evaluate disease resistance.”

 The pulse pathologist manages the MRDC disease nurseries used to assess the resistance levels in these dry bean varieties and in elite breeding lines developed by Hou’s program and other dry bean breeding programs. Screening for bacterial blight, white mould and root rot is done in the field nurseries; anthracnose resistance screening takes place indoors in growth chambers.

 Their research also includes mapping genes involved in resistance to the different diseases and developing molecular markers for screening breeding materials for those resistance genes. Using such markers can really save time in the breeding process.

 The breeding program’s most recently registered variety is a cranberry bean named AAC Scotty by Canterra Seeds, which has been granted exclusive rights to the variety. Hou notes, “AAC Scotty is a very high yielding cranberry bean with resistance to anthracnose. Canterra Seeds is marketing this variety in Manitoba, North Dakota and other regions.”

An early maturing navy bean selection in Hou’s field plots.

Getting a grip on seed hardness
Another key objective of Hou’s program is to improve seed quality. “Years back, people didn’t really pay that much attention to the quality side, but we started working on it about 10 years ago and we are making progress,” he says.

 When Hou started at Morden in 2008, he heard some concerns about seed hardness in some varieties so he made improving this trait a priority.

 Seed hardness problems can occur in dry bean seeds, as well as most other legume seeds. “Normal beans soak up water uniformly and pretty quickly before we cook them. But there are beans that do not absorb water very well even when you soak them overnight. We refer to those beans as ‘stone seeds’ because they are stone hard,” he explains.

“We call this characteristic seed hardness. It is a bad trait for canning and other processing uses.” For example, it can impact processing costs, cooking time, canning quality and nutritional quality.

“We make sure our new breeding materials and new cultivars have much improved characteristics on this aspect.”

Hou and his research group are also investigating the genetic and environmental factors affecting seed hardness. “We have studied different genetic populations of dry beans over the years, and we have been able to identify a few candidate genes or gene loci [locations on the dry bean genome] that are associated with this trait,” he says.

“Seed hardness seems to be a very complex trait. There are many genes involved in different bean populations, different bean types, and different environmental conditions.” Hou and his group are continuing to study seed hardness to further increase understanding of this trait.

Tackling marsh spot
Marsh spot is another seed quality issue that the program is tackling through breeding and research. “Marsh spot is most commonly found in cranberry beans, but sometimes people also report it in kidney beans,” notes Hou. “If you crack open a normal, healthy cranberry bean seed, you’ll see that the center is pure white or cream-coloured. But with marsh spot, you see a dark spot right in the core of the seed, which really reduces seed quality.”

He explains that marsh spot is thought to be associated with a mineral deficiency, most likely a manganese deficiency. It can be considered an abiotic stress disorder connected with certain soil or growing conditions that limit manganese uptake by plants. But susceptibility to this disorder also has a genetic component.

“On the breeding side, we screen for the trait in our breeding materials to make sure we don’t get that bad trait in our new varieties,” he says.

On the research side, they have been investigating the disorder’s genetics. “Through extensive screening of germplasm, Bob Conner found a couple of cranberry bean lines that have better resistance to marsh spot. So, we created genetic populations [by crossing resistant and susceptible cranberry lines]. And we had a graduate student who examined these populations to look at the genetics of this trait.”

Their results show that resistance to this disorder is controlled by multiple genes. In particular, they determined marsh spot resistance is linked to two genes associated with manganese transport in the plant. Their findings are helping to increase understanding of this disorder as well as identifying candidate genes that could help in breeding for resistance to marsh spot.

“We are continuing to work on marsh spot to mine the germplasm for more potential resistance genes that we can stack to improve this trait,” Hou says.

“We are also trying to develop different protocols to speed up the evaluation of breeding materials for resistance to marsh spot because field screening for this trait takes multiple years. One of our goals is to develop molecular markers that we can use to quickly screen breeding materials for the resistance genes.”

Boosting nitrogen fixation
One of Hou’s newest projects aims to develop dry bean varieties with a greater capability for nitrogen fixation, which is the process by which a legume plant and its rhizobial bacteria convert atmospheric nitrogen into a form that the plant can use.

Greenhouse bean plants used for seed propagation in Hou’s breeding program.

 Improved nitrogen fixation would reduce input costs for growers and improve the sustainability of bean production. “Dry beans are considered poor fixers of nitrogen, compared to other legumes like soybean. For instance, the application of nitrogen isn’t usually recommended in soybean production [because soybeans can fix enough nitrogen to meet their own needs]. But people say dry beans usually fix no more than 50 per cent of their nitrogen, so the application of some nitrogen fertilizer is typically recommended for growing dry beans,” he explains.

Hou notes that previous research, for example, studies at Michigan State University and the University of Guelph have shown there is genetic variation in the nitrogen fixation capacity of dry beans, with certain lines being better than others at fixing nitrogen. However, there is little information about the range of variation in this trait in the early maturing germplasm suited to much of Manitoba’s dry bean growing area.

“We have a large collection of dry beans, and hopefully, we can identify materials with a higher capability for nitrogen fixation that we can use in the future to improve this trait in our dry bean cultivars,” he says.

“But we believe nitrogen fixation is a very complicated issue, and many different elements may be involved, including growing conditions such as night temperatures. So, in addition, we also want to try to understand the mechanisms involved and find the genes associated with nitrogen fixation.”

For Hou, one of the most rewarding aspects of his dry bean breeding and research program is the opportunity to work with growers. “I’ve been the AAFC representative to the board of directors of the Manitoba Pulse and Soybean Growers. I love to interact with the growers and listen to their concerns and suggestions for research, which help me tremendously in deciding my research directions and projects. And every year, I love to see the growers’ harvest, and every improved harvest makes me so happy.”

He also enjoys collaborating with other researchers across Canada, including both private and public breeders, pulse pathologists and molecular biologists. And he really appreciates the ongoing support from MPSG and AAFC for the Morden dry bean breeding and pathology programs, as well as the efforts of the technicians and others involved in these two programs. “Without this support, we wouldn’t be able to do this work to develop new knowledge and new dry bean varieties that can benefit the farmers and the industry in this region.” 

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