A new integrative indicator to assess crop genetic diversity

Various international initiatives have emerged to develop new sets of biodiversity indicators for wild biodiversity but little progress has been made for crop diversity. This study proposes a new methodology to assess the diversity of cultivated species. We developed a new integrative indicator HT* that takes account of varietal richness, spatial evenness, between-variety genetic diversity, and within-variety genetic diversity. This index is compared to existing indexes using a comprehensive historical dataset from a French territory. The study reveals that more varieties (the varietal richness factor) can mean less diversity when (i) their genetic structure is more similar (the effect of between-variety genetic diversity), or (ii) when more diverse landraces are replaced by many homogeneous lines (the effect of within-variety genetic diversity) or (iii) when one or a few varieties become hegemonic in the landscape (the spatial evenness effect). Furthermore, an increased evenness in variety distribution (varietal evenness) can also mean less diversity when varieties are genetically related. This is why indicators which do not take into account the full range of factors (varietal richness, between-variety genetic diversity, spatial evenness and within-variety genetic diversity) may provide a misleading assessment of the state and trend of crop biodiversity. New integrative indicators such as HT* are critically needed. We discuss potential further development such as the use of this indicator for monitoring and the perspective of a broader indicator to assess genetic diversity at the multi-species scale and landscape level. In the future, this indicator could be used to guide managerial decisions to prevent the erosion of crop genetic diversity in agricultural landscapes.