AAFC research proving diploid breeding is more than just small potatoes

Diploid potatoes are quickly becoming the stud spuds for breeding new commercial potato varieties. Wild diploid potatoes have 2 copies of each chromosome in their DNA, unlike more traditional tetraploid potatoes, like Russet Burbank, which have 4 copies of each chromosome. Fewer chromosomes make diploid genetics easier to work with for breeders. First domesticated in the Andes of South America, diploid potatoes are often a little smaller in size than their tetraploid cousins. Their untapped genetic potential is being harnessed by geneticists and breeders to develop new diploid potato varieties for farmers.

Agriculture and Agri-Food Canada (AAFC) research scientist Dr. Bourlaye Fofana is leading the pre-breeding charge for diploid potatoes. After successfully pinpointing drought resistant and early maturing genes in diploid potatoes, he’s moved onto to his next foe — common scab disease. Common scab is a widespread issue that can lead to major economic losses for producers across Canada. Lost profits from waste occur when more than 5% of a potato is affected by unsightly common scab, which means they cannot be sold to the fresh vegetable market. Also, the lesions make potatoes difficult to peel, resulting in waste and lost profits in the chip and fry markets. Common scab resistant potato varieties are scarce, so developing potato varieties with resistance is vital for the industry.

Comparing traits for common scab

Dr. Fofana has been studying common scab for many years at the AAFC Charlottetown Research and Development Centre on Prince Edward Island. As recently as 2021, he compared the genes of tetraploid potato varieties: Green Mountain (more prone to common scab) and Hindenburg (develops fewer symptoms of common scab). This research discovered genes that may be responsible for common scab resistance. Now, he wanted to find the same for diploid potatoes.

“There is more natural genetic diversity in wild diploid potatoes compared to tetraploids that make them interesting for breeding. First, we created more diversity on top of what they have naturally by inducing a change in their genetic make-up. Those changes are random, however, and we don’t know the full picture until further research is done.”

- Dr. Bourlaye Fofana, Research Scientist, Agriculture and Agri-Food Canada

In order to find common scab resistance for diploid potatoes, Dr. Fofana dipped into his vast collection of diploid germplasm — the seeds, plants, or plant parts used in crop breeding — research, and conservation efforts. The seeds were planted at the AAFC Harrington Research Farm and, once harvested, were evaluated for various common scab resistant traits including the percentage of the surface area of the potato covered by common scab, the severity of common scab (number and depth of lesions on potato skin), and the incidence of common scab (how many harvested potatoes have any lesions versus no lesion at all). The diploid potato clones that have the least of these 3 traits are good candidates to go to the next stage of the breeding process.

Narrowing down varieties

Dr. Fofana, along with AAFC researchers in Charlottetown, Prince Edward Island, and Kentville, Nova Scotia, as well as former AAFC student Dr. Braulio Soto-Cerda, now at the Universidad Católica de Temuco in Chile, evaluated 384 diploid potato clones for common scab resistance traits. The team found genetic markers on the diploid chromosomes for common scab resistance. Of the 384 diploid clones, the group identified 61 that are tolerant or resistant to common scab disease and have genes that help the potato plants to defend and protect themselves against diseases. These 61 varieties will now be evaluated for yield and quality in larger commercial field plots which have greater numbers of plants (minimum of 25), compared to the research field plots (maximum of 6 plants) that have been used until now.

“The commercial plots are more comparable to what a commercial farmer might see on their fields. We want to see how the common scab resistance of the diploid varieties translates from the research field plots to commercial field plots. This gets us another step closer to commercial diploid potato varieties.”

- Dr. Bourlaye Fofana, Research Scientist, Agriculture and Agri-Food Canada

So far, Dr. Fofana’s research is an important first step. It shows that varieties associated with common scab disease resistance can be developed, and that the markers, gene sequences, and the 61 selected clones are key resources for breeders to make future potato varieties more resilient to climate change.

Key discoveries and benefits

• Wild diploid potatoes have 2 copies of each chromosome in their DNA make-up (genome), unlike more traditional tetraploid potatoes, like Russet Burbank, which have 4 copies of each chromosome. Fewer chromosomes make diploid genetics easier to work with and their untapped genetic potential is being harnessed by geneticists and breeders to develop new diploid potato varieties for farmers.
• Dr. Bourlaye Fofana, along with other AAFC researchers in Charlottetown, Prince Edward Island, and Kentville, Nova Scotia, as well as former AAFC student Dr. Braulio Soto-Cerda, now at the Universidad Católica de Temuco in Chile, evaluated 384 diploid potato clones for resistance to common scab disease.
• Of the 384 diploid clones, the group found 61 that are tolerant or resistant to common scab disease based on the percentage of the surface area of the potato covered by common scab, the severity of common scab, and the incidence of common scab.
• The 61 varieties will now be evaluated further for yield and quality as well as tested in larger commercial field plots to see how they perform in settings similar to farms.

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Related information

• AAFC profile – Dr. Bourlaye Fofana
• Charlottetown Research and Development Centre