This intensive study plot is located in Villenave d’Ornon, near Bordeaux in southwestern France (44.788319 N, -0.577062 E). It includes the INRAE chestnut germplasm collection and all isolated trees located in the immediate surroundings (<1 km from the INRAE research site). The germplasm collection is distributed in two nearby orchards. The first orchard was planted in 1970 and comprises 29 widely spaced trees on 2.3 ha while the second orchard was planted in 1990 and includes 211 trees on 3.5 ha. In contrast to the Asiatic chestnut species, the European chestnut is very vulnerable to blight and ink diseases originating from Asia (Gonthier and Robin 2019). Cross-breeding between Asiatic species and European chestnut has been carried out to select new tolerant hybrid cultivars (Barreneche et al. 2019), some of which have been massively planted for fruit production. Hence, the two orchards include different taxa: 117 C. sativa (European chestnut), 22 C. crenata (Japanese chestnut), 20 C. mollissima (Chinese chestnut) and 81 interspecific hybrids, including 56 C. sativa x C. crenata. In some cases, both parental trees and their offspring are found in the orchards. Most trees are grafted on both rootstocks: Marsol (CA07) or Maraval (CA74).
Pollination and hence pollen limitation are still poorly understood in chestnuts (Larue et al. 2021a). To investigate these topics, the site described above, which is fairly isolated from other chestnut pollen sources, seemed appropriate. Our ultimate goal is to develop a spatially explicit individual-based mating model to investigate intra- and interspecific mating events with pollen coming from inside and outside of the INRAE germplasm collection. This model will allow a simultaneous estimation of all parameters influencing not only male but also female fecundity and pollen dispersal using a Bayesian approach for random effect mating model (Klein et al. 2008, 2011; Chybicki et al. 2021).
Many efforts were made to gather a comprehensive data set as input for this model and for other studies. All trees of the intensive study plot were genotyped and their phenotypes were precisely described, including floral characters. We scored their phenology with a newly developed BBCH scale adapted for chestnut (Larue et al. 2021b), and we estimated seed-set during two consecutive years.
