Current status and spatial analysis of Guinea yam (Dioscorea cayenensis Lam. -D. rotundata Poir. complex) diversity in Benin

Abstract

Guinea yam (Dioscorea cayenensis - Dioscorea rotundata complex) is one of the most important root and tuber crops contributing to food security and poverty alleviation in West Africa. To assess the diversity and analyse its spatial distribution in the production zones of Benin, 136 villages were randomly selected from four predefined diversity zones and surveyed using participatory rural appraisal. Altogether, and subject to synonymy, 668 yam cultivars were recorded. The number of cultivars accessed varied from 3 to 66 per village (23 on average) and from 1 to 19 (5 on average) per household. Highly significant differences (P< 0.001) were found between diversity zones for the mean values of the number of cultivars maintained at both community and household level and for the relative proportion of the two types (single-harvest and double harvest) of cultivars. A principal component analysis grouped villages surveyed into four clusters that correctly match with the diversity zones initially defined. The distribution and extent analysis revealed some worrying rates of cultivar loss in the range of 0.0 - 65.8% (30.8% on average) per village. The spatial analysis and the prediction indicated that in absence of appropriate actions, Benin will experience, in the next coming five years, a strong degradation of cultivar diversity in all zones with probably severe consequences on the food security of the population. Among the reasons of cultivars abandonment documented across diversity zones, the environmental factors (mostly pests, diseases, soil poverty, climate variability and drought) were, on average, the most important (31.9 - 57.9% of responses). The study revealed that farmers have no strategy to avoid cultivar losses but use domestication of wild yams and introduction from other villages to strengthen existing diversity. The resulting evolutionary dynamic of cultivar diversity at community level integrating domestication, genes flow, loss of cultivars and new introduction was schematized and discussed, and the development of a dynamic in-situ conservation program incorporating both cultivated and wild yams was proposed. For sustainable use, the constitution of a pool of elite cultivars through participatory evaluation coupled with molecular analysis to identify duplicate accessions was recommended