Why Test for Disease Resistance?

- Raquel Salati

When planted in a production environment, plants — no matter the species — must be able to fend against a number of stressors, including insects, pathogens and weeds. As a trained molecular virologist, my specialty is disease and pathogens, mainly viruses. As plant breeders work to introgress resistance genes into their elite lines, my staff and I put those genes to the test. The ability for plants to resist pathogens is becoming more and more important as plant breeders try to address the global nature of the seed business.

At Eurofins BioDiagnostics, we’ve recently increased one of our services: disease resistance screening for cucurbits, leafy greens and solanaceous varieties. For example, there’s a continuous effort to breed squash varieties that are more resistant to Cucumber mosaic virus (CMV) or lettuce to downy mildew. Now companies who might not have their own laboratories or the resources to conduct these tests can still verify if a plant is or is not resistant to a specific pathogen. Our program is set up to use our laboratory, greenhouse and staff to provide them the data they need so that they do not have to make the same investment in those resources.

As pathologists, we challenge inbred lines or varieties by exposing them to different pathogens, including fungi, bacteria, viruses and nematodes. Then we provide the data generated to the breeders to help them make better selection decisions within their breeding programs.

How It Works

We typically ask the seed company for 18 seeds per line, and we’ll evaluate three repetitions of six plants. We plant the lines and begin inoculations at the cotyledon stage (before true leaf) and at true leaf. The plants are then allowed to grow in our greenhouse for two to three weeks, depending on the species. After that, we visually evaluate the plants on a disease scale and record resistance levels. We’ll do a weighted average for the three replications. The accumulated data is tabulated and sent to the breeder to be used to advance their program.

Disease resistance screening is also helpful in verifying markers for marker-assisted selection. Even though a marker might push very high numbers, or be tightly linked to a disease resistance gene, it’s always good to confirm with disease resistance screening to make sure the marker performs as expected. It can happen that if a marker is linked to a gene that is close to the disease resistance (DR) gene, that DR gene can be lost but the test using molecular markers still indicates that the line is resistant. Using a bioassay such as our resistance screening program will uncover this issue.

For more on this, you can read seedworld.com/success-molecular-markers-hinges-precise-phenotyping/.