Pre-breeding:

Bridging Genebanks and Breeders (and Farmers)

Plant breeders need as wide a range of diversity as possible to use in their breeding programs to develop new crop varieties that are resilient to the changes being caused by runaway climate change.

Working closely with genebanks, and building on the decade-long Crop Wild Relatives Project, the BOLD pre-breeding partners identify the plants that have traits that are of interest to them, and to farmers. This involves growing out the seeds in the field and observing the resulting crop, often over several years. This is costly and labor-intensive work.

The next step is to cross plants with the desired characteristics–such as disease resistance or drought tolerance–with other varieties that already have key characteristics such as high yield and ease of harvesting.

But working with crop wild relatives is challenging and time-consuming. Most crop wild relatives have characteristics that farmers really don’t want. For example, their seeds or fruits don’t all mature at the same time, the plants are different heights, and their seeds are usually much smaller than their domesticated relatives. So pre-breeders cross the wild relatives with elite varieties or landraces and select the resulting plants that are closest to the ideal they are looking for. Sometimes, crosses have difficulty producing viable seed, so they need extra help through a process called embryo rescue.

And they then have to go through this crossing process again and again, until they have a product that has most of the characteristics of the elite variety–high yield, for example–plus the desirable characteristic of the wild relative–disease resistance, say.

Once the initial screening has been done and promising materials have been identified, the next step is to turn these into “varieties” that can be released to farmers.

In most countries, “varieties” must be stable (i.e. they don’t change from one generation to the next) and uniform (all the plants look alike and have the same characteristics before they can be released to farmers). And, of course, they must perform well in farmers’ fields under a range of conditions.

Getting here from the initial crosses takes many rounds of crossing, planting and harvesting the best plants and discarding any that don’t come up to scratch. In Vietnam, for example, farmer “seed clubs” test new varieties in their fields and promote the best through “farmer field days”, where local farmers are invited to come and see the plants growing under their own conditions.

Conserving and using crop diversity takes a wide range of knowledge, expertise and skills.

The BOLD Project is working with national genebanks, breeders, researchers, students and farmers to ensure that they have all they need, including:

• Genebank management protocols and equipment.
• The skills needed to perform crosses and backcrosses and use up-to-date research tools such as molecular markers.
• Experimental designs for evaluating crop diversity.
• Tools for data collection, analysis and visualization, such as GRIDScore from the James Hutton Institute.
• Communication skills needed to promote awareness of the value of their work.

Breeders carefully choose parents that have the characteristics they want in their future elite variety – high yield, disease resistance, drought tolerance or nutritional value. They then transfer pollen – the male reproductive cells – from the male parent to the female parent, a manual process that might involve using a small paintbrush.

This can be especially challenging as the different parent plants might not flower at the same time. Or the pollen might not want to germinate on the female parent. Or, if it goes that far, the resulting embryo might not survive to maturity, and the only way to get a viable plant is through in vitro culture – sort of “IVF for plants.”