July NUI Galway research reveals how social factors can spread pandemic crop viruses in Africa

Scientists show that different marriage systems within traditional farming communities in Africa affect the spread of variants of pandemic crop viruses

Scientists from the Ryan Institute at NUI Galway have analysed the social factors that influence the spread of viruses responsible for Cassava Mosaic Disease, one of the most important virus crop diseases in Africa.

Their results revealed contrasting dynamics of viral diversity due to different marriage systems across traditional farming communities in Gabon, Central Africa, directly related to cultural differences in the way villages exchange cassava varieties through matrimonial networks. The study has been published today (23 July 2021) in the leading journal Nature Communications.

The ongoing Covid-19 pandemic has made all of humanity acutely aware of how social interactions contribute to the spread of viral diseases. The research by Dr Marc Delêtre, Professor Charles Spillane and Dr Ronan Sulpice from NUI Galway, in collaboration with Dr Jean-Michel Lett from Cirad (France), has now shown that social factors that govern interactions between communities of farmers also influence the spread of pandemic crop viruses that threaten food security in Africa.

The research combined anthropological field research by Dr Delêtre in Gabon with molecular plant virus epidemiology in the lab to analyse factors that influence the spread of viruses responsible for the Cassava Mosaic Disease, one of the most important virus crop diseases in Africa.

Dr Marc Delêtre conducted the interdisciplinary research as a member of Professor Charles Spillane’s Genetics and Biotechnology lab in the Ryan Institute at NUI Galway during his EU Marie Curie funded postdoctoral research project. Dr Delêtre analysed the DNA sequence of plant viruses in infected cassava plants collected from different villages across Africa and found that the diversity of the viral variants causing Cassava Mosaic Disease was much higher in matrilineal communities (where membership to the social group is inherited from the mother) compared to patrilineal communities (where descent is traced through the father).

Dr Delêtre said: “I have been working in Gabon since 2004, interviewing farmers, recording varieties and collecting samples. I discovered that there is a strong relationship between rules that control exchanges of cassava landraces between smallholder farming communities and rules that govern the transmission of the clan (kinship), with a direct impact on the dynamics of crop genetic diversity.”

In matrilineal societies, farmers readily import new cassava varieties through matrimonial networks, and as a result varietal diversity increases in the community. In patrilineal villages, farmers rely mainly on small sets of heirloom crop varieties. On average, cassava varietal diversity is five times higher in matrilineal villages than it is in patrilineal ones. However, communities who exchange germplasm are also more exposed to new viral variants.

Dr Delêtre added: “Seed exchange networks play an active role in the dynamics of agrobiodiversity and can make smallholder farming systems more robust to pathogens where they favour the adoption of disease-resistant varieties. However, they can also make these systems more vulnerable if they facilitate the dissemination of seedborne plant pathogens. What we found is that there is also a cultural component to crop plant epidemiology.”

Cassava mosaic disease is one of the most important virus crop diseases in Africa, causing losses of 20% to 95% of cassava harvests and economic losses estimated at US$1.2 to 2.3 billion each year in Africa. With the threat of other crop pandemics spreading across Africa, such as the Cassava Brown Streak Disease, an emerging threat to regional food security, understanding how social systems can drive transmission of crop viruses is key to designing and promoting local strategies for preventing or curbing the spread of crop pandemics.

Professor Charles Spillane, Director of the Ryan Institute at NUI Galway, commented: “Understanding different social systems is critical for understanding the transmission and evolution of pandemic viruses, whether they are viruses infecting humans, livestock or crops. Genetic epidemiology combined with an understanding of social interaction systems can generate the knowledge necessary for reducing the transmission of viral diseases that are catastrophic for the poorest or most marginalised in society. The findings of this interdisciplinary research will inform new approaches for reducing the burden of viral disease on staple crops of smallholders in Africa.”

Read the full study in Nature Communications here: https://doi.org/10.1038/s41467-021-24720-6.

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