Harnessing Plant Reproduction for Crop Improvement

The world’s population is booming and food security is one of the key issues facing us, as land suitable for agriculture is impacted by climate change and soil degradation. Genetic modification of crops can help, but the risk of cross-contamination is holding back uptake.

We need a sustainable, efficient way to feed a burgeoning population: in 2017, the United Nations Population Division anticipates that there will be 10 billion mouths to feed by 2055. At the same time, land is being eroded by sea and desert and soil is increasingly degraded. Genetic modification of crops could offer a solution, but currently traits that are useful are typically polygenic, involving plants which reproduce by pollination. Most arable crops reproduce this way, and it is the risk of cross-pollination between modified and unmodified plants that is proving challenging.

“If the plant can reproduce without the need for pollen, you can have transgenic-apomictic, male-sterile plants that do not produce pollen and therefore cannot spread the transgenic pollen to organic fields,” explains Professor Emidio Albertini, based at the University of Perugia and principal researcher on the EU-supported PROCROP project. "Introgression of apomixis from wild relatives into crop species, and the transformation of sexual genotypes into apomictically reproducing genotypes, are long-held goals of plant breeding," he explains.

In traditional breeding, some genotypes are selected and following phenotypic selection. These are then tested for their specific combining ability in order to be used as parental lines for the constitution of heterotic F1 hybrid seeds (those offering an improved or increased function of any biological quality in a hybrid offspring).

The best-performing inbred lines are selected, multiplied in isolated fields and crossed in pair-wise combinations to obtain uniform, vigorous and high-yield F1 hybrids. This scheme, however, requires a series of actions: the two inbred lines must be kept pure and multiplied in separate fields. Then, to obtain the hybrid seed, it is necessary to establish a dedicated field where about one quarter of the plants is used as pollinator (i.e. pollen donor inbred), the hybrid F1 seeds being harvested from the remaining plants.

Farmers cannot reuse seeds collected from F1 hybrids as these seeds will give rise to highly variable populations because of genetic segregation and recombination.

“Using apomictic lines, those which reproduce asexually, without fertilisation, makes the situation much simpler. Once superior inbred lines to be used as the seed parent are selected, they can be crossed with clonal lines as pollen donors carrying the gene for apomixis, in order to obtain F1 hybrid seeds sharing a highly heterozygous genotype. From this moment on, each F1 hybrid variety can be maintained for several generations with permanently fixed traits,” says Prof. Albertini.

Breeders, he explains, believe that the introduction of apomixis into agronomically important crops will have revolutionary implications for agriculture. The fixation of hybrid vigour through apomixis is a desirable objective for breeders and farmers alike and is expected to have a revolutionary impact on food and agriculture production.

“The impact of apomictic crops in agriculture would be comparable to, or even greater than, the impact of the Green Revolution, especially in Third World countries. In fact, it has been estimated that the use of apomixis technology in the production of hybrid rice alone could provide benefits exceeding EUR 1 800 million per year.”

Apomixis technology could also provide benefits for clonally propagated crops, such as mangos. Clonal crop yields are limited by pathogens (mainly viral and endophytic), which accumulate over successive rounds of vegetative propagation and seriously limit the yield and exchange of germplasms between countries. “The use of apomixis technology in these crops would provide the additional option and benefit of propagation via clonal seeds, thus generating disease-free material that can be more easily stored and transported,” says Prof. Albertini.

This research was undertaken with the support of the Marie Skłodowska-Curie programme. The team is still collaborating on trying to shed light on the genetic control of apomixis and has presented a follow-up project to build on the promising ground work of PROCROP.

Reference source: Harnessing Plant Reproduction for Crop Improvement