This article was originally published on GM Watch on November 1st, 2023

Findings are another nail in the coffin for genetic engineering approaches to disease resistance

Planting different varieties or cultivars of any given crop together in the form of seed mixtures has long been a key strategy of agroecology. The genetic diversity in these mixed “seed populations” avoids the vulnerability of a genetically uniform crop, helping to protect the crop from stresses such as fungal diseases, pest attacks, and bad weather.

There is renewed interest in the practice of mixing crop cultivars, and in France today more than 10 percent of the area under wheat cultivation is reported to use the method. However, mixtures have variable success in controlling disease. This may be caused by as yet unknown interactions between cultivars.

A new study sheds light on this phenomenon. The study found that certain mixtures can affect plants’ susceptibility to fungal disease, providing a form of social immunity in wheat and rice. The study found that disease susceptibility in wheat and rice is affected not only by genetic resistance traits, but also by interactions with neighbouring plants of the same species.

The findings, published in PLOS Biology, show that inter-plant cooperation can reduce disease susceptibility by nearly 90 percent in certain cases, as much as is conferred by a plant’s own resistance genes. The researchers also found that certain plant pairings can increase disease susceptibility.

Reducing pesticides

The French research institute INRAE, where many of the researchers on the new study are based, states in a press release that the findings create new possibilities for improving plant resistance to disease and reducing the use of pesticides.

In GMWatch’s view, they also represent another nail in the coffin for genetic engineering approaches to disease resistance (including via gene editing). These are narrowly obtained, by manipulating one or a few genes, and narrowly targeted, leading to a failure to provide resistance to multiple pathogens. Broadly based disease resistance is necessary for resilience in the field.

In addition, and crucially, the new study confirms that farming systems are equally as important as genetics – if not more so – in providing resistance to diseases and other stresses.

Insofar as genetics do play a role in disease resistance, conventional breeding continues to outstrip GM, as our Non-GM Successes database shows.

How the study was done

In the new study, to understand the effects of inter-cultivar interactions, the researchers studied the interactions between more than 200 pairs of rice or wheat cultivars in controlled conditions. They inoculated each pair with a foliar fungal pathogen, and then analysed plant susceptibility to the disease when grown in association with another plant of the same cultivar or with a different cultivar.

The findings demonstrate that in 10 percent of pairs studied, the presence of a neighbouring plant had an effect on disease susceptibility. With the use of genetic modelling, researchers were able to quantify the effect and demonstrate that certain pairings reduce disease susceptibility in the infected plant by almost 90 percent.

This means that disease susceptibility in two major crops, rice and wheat, is modulated not only by the resistance genes of each cultivar, but also by the interactions each plant establishes with its neighbours. In these two crops, there is a population-level type of cooperation. This may be akin to herd immunity responses found in animal species.

In certain circumstances, inter-plant cooperation can reduce disease susceptibility by as much as is conferred by a plant’s own genes. Consequently, there is considerable potential to strengthen resistance by means other than varietal improvement.

The study:
Pélissier R., Ballini E., Temple C. et al. (2023). The genetic identity of neighboring plants of neighboring plants in intraspecific mixtures modulates disease susceptibility of both wheat and rice. PLOS Biology, 21 (9), DOI: