Breeding and Evolution

There is an intimate connection between what we do as plant breeders and the evolutionary processes. Plant breeding is about selecting the “fittest” plants that show the best traits on a long list of breeding objectives. Whether these are traits associated with yield, disease and insect resistance or quality traits they are all subjected to selection pressure in one form or another. Like evolution this selection process is very slow for some traits or dramatically quick for others. The difference between evolution and plant breeding is that the plant breeder can “create” diversity through a number of techniques including

• Intra-species wide crosses between populations that would not come into contact in nature

• Inter species crosses where species barriers can be overcome by biotechnology or through “helper” techniques that allows fertilization to occur.

• Mutation breeding to create new traits – usually the removal or silencing of a function.

• Transformation and genetic transfer of genes from any species/genera – GMO route.

• Genomic techniques where by specific genes are switched off or up regulated

There are two major issues, that we face as plant breeders, which we need to overcome before we can make significant progress above what we are making at the moment.

1. Plant breeding is a slow process, especially for quantitatively controlled traits like yield. Evolution is based around selection of the fittest under specific or general pressure to survive. As plant breeders we have done an excellent job in creating selection pressures for certain traits like disease resistance. We now have glasshouse, and/or field tests for selecting plants under high levels of disease. This is an “active” process that involves delivering high levels of disease to a diversity of plants and then we select the survivors. This works especially well where one gene or a small number of genes are involved in the resistance process. We also have the capacity to pyramid genes together under these conditions and even to develop molecular markers that then allow us to select the genotypes rather than the phenotypes. This assumes of course that the genes for resistance exist in the gene pool or closely related species. Consequently these techniques have allowed breeders to integrate these genes into new varieties with the resultant positive outcome for the food/feed industries.

On the other hand there are traits which are controlled by quantitative genes which are very difficult to make significant progress on. Yield is such a trait where a great result is 1 – 2% genetic gain each year. The major reason for slow progress is that the selection process is a “passive” process not an “active” process as in the above. It is passive because we plant out the progeny then leave them to their own resources to produce or not to produce. The only “pressure” we put on is in selecting the top 20% yielders, and then we start the process again. The plants are not forced to survive or show their fitness “during” the testing process only after. If you are selecting for salt tolerance for instance you can grow the plants in a salty environment then select the highest yielding survivors from that “active” environment. In normal yield testing the environment we put the plants into is not a “testing” environment so survival is not paramount.

How can we change the way we test for higher yield? How can we change the process from a “passive” to an “active” testing arena?

2. The crops that we deal with have evolved over a long period of time and have developed their biological factories to cope with life in the wild. Life in the wild is about survival and generating enough seed to make sure that the species can produce another generation. Sometimes this involves risk management in that plants need to produce enough seed so that there is a seed bank for seasons when rainfall or frost etc can prevent any new seed production. Modern man however requires vastly different things from their crop plants – they require maximum production of seed not survival levels. They require maximum production under all circumstances. The only upside is that risk management is handled by the farmer, for instance, by saving seed for next year just in case the crop fails.

Plant breeders have come along and now want to modify this ancient factory that has evolved over millennia. Man is quite capable of “evolving” machines over a short period of time and one only has to look at the evolution of the internal combustion engine and the development of jet engines to see that we are masterly engineers. However, these are things that we have control over – plants have a factory that we know very little about and we certainly do not know enough about the controls and switches that operate the biochemical pathways. Evolution has tweaked these controls and switches to make the plant what it is today but those processes still remain somewhat a mystery. Certainly we know that Transcription Factors (TF) play a major role in the controlling and switching process. What process will allow plant breeders to manipulate these TFs or what “active” selection pressure can we use to identify superior forms of the factory?

Plant breeders have made considerable progress in genetic gain over time and there are many papers published on sets of historical varieties that confirm these outcomes. Is this the key to the breeder’s evolutionary process – can we investigate the changes within the Transcription Factors within historical varieties to identify changes that we have made through “passive” selection? Will this give us an insight into where we can go in the future?

The photo below shows what great progress breeders have made in changing pod set on the main stem in lupins over a 40 year period of breeding. Phenotypically this looks fantastic and it represents about a 80% increase in yield over that period but we have no idea what is happening at the genome level nor what is happening at the expression level which allows for different uses of sink and source.