Intensive study site: INRAE chestnut germplasm collection (Domaine de la Grande Ferrade, Villenave d'Ornon)

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).