S02 - Session O2 - Conservative selection of a population variety under various agroecological conditions, zucchini as a model species

Authors: Laura Gautier *, Louis-Marie Broucqsault, Rémi Kahane, Lise Malicet-Chebbah, Jacques David, Cyriaque Crosnier-Mangeat

The management of Cucurbita population varieties is complex because of their genetic and phenotypic heterogeneity. In organic agriculture, this heterogeneity is sought for adaptation to various stresses. This question is central for the multiplication of quality farmer seeds as well as for materials adapted to a tropical context such as in West Africa. A research program was initiated by the seed company AGROSEMENS, supported by the Institut Agro of Montpellier and CIRAD, to characterize the criteria to consider in maintenance breeding. For this purpose, an experimental protocol was set up with the zucchini variety 'Black Beauty' chosen as a control, propagated for four years at AGROSEMENS, with two contrasting watering regimes. The study of these four generations intends to identify the impact of certain practices of the various farmers involved in the propagation of this variety. Five seed batches from different origins were used. A field trial was set up to analyze phenotypic diversity within and between seed lots and to analyze genetic diversity from the DNA of sampled individuals. Of the 23 recorded phenotypic traits, 13 were retained after the estimation of correlations. The seed lots were then grouped into clusters according to the genotyping study. The analysis of eight SSR markers allowed to complete the analysis of the intra and inter-lot diversity thanks to F-statistics and confirmed, thanks to this population genetics approach, the relevance of the typology in the previously identified clusters. Large genetic and phenotypic differences were observed between the lots. The effect of agronomic practices, including the number of multiplications, genetic diversity and trait conservation, was significant. In contrast, the two watering regimes did not generate significant differences between the seed batches on the observed criteria. This study has laid the foundation for a maintenance breeding strategy for Cucurbita population varieties and will be continued.