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Abstract Key message In arboriculture, the number and diversity of pollen donors can have a major impact on fruit production. We studied pollination insurance in hybrid chestnut orchards (C. sativa × C. crenata) provided by nearby wild European chestnuts (C. sativa) in southwestern France. Most fruits were sired by hybrid pollenizers rather than by wild chestnuts. When these hybrid pollenizers were too scarce, a frequent situation, pollen produced by wild chestnut trees did not compensate for the lack of compatible pollen and fertilization rates and fruit production collapsed. Context The demand for chestnuts has been increasing in recent years in many European countries, but fruit production is not sufficient to meet this demand. Improving pollination service in chestnut orchards could increase fruit production. Aims Investigate pollination service in chestnut orchards. Evaluate the contribution to pollination of trees growing in chestnut woods and forests. Methods We investigated five orchards planted with hybrid chestnuts (C. sativa × C. crenata) cultivars in southwestern France. We combined fruit set data, which provide information about pollination rate, with genetic data, which provide information about pollen origin. We used this information to estimate the contribution of nearby C. sativa forest stands to the pollination of each orchard. Results Pollination rates vary considerably, being fivefold higher in orchards comprising numerous pollen donors than in monovarietal orchards. Because of asymmetric hybridization barriers between hybrid and purebred cultivars, the surrounding chestnut forests provide very limited pollination insurance: less than 14% of the flowers in these monovarietal orchards had been pollinated by forest trees. Conclusion Because chestnut orchards are now increasingly relying on hybrid cultivars, surrounding wild European chestnut trees are no longer a reliable pollen source. To achieve maximal fruit set, efforts must therefore concentrate on orchard design, which should include enough cultivar diversity.

Abstract Key message Appropriate silvicultural practices combined with the use of resistant Central European provenances can reduce the prevalence of larch canker caused by Lachnellula willkommii (R. Hartig) Dennis, a major disease affecting larch plantations in France. However, cascading translocations have resulted in frequent admixture in European larch (Larix decidua Mill.) and subsequent certification errors regarding the origin of plant material. Our study highlights the urgent need to improve the certification process of seed orchards. Context The recent history of European larch has been marked by translocations of plant stock within and beyond its native range. In order to increase stand resistance to larch canker disease, it is strongly recommended by French authorities to plant Central European provenances. However, a recent disease outbreak questioned the resistance of Central European provenances and the origin of the forest material used in these plantations. Aims Our goal was to assess the effects of cascading translocations and mixing between larch gene pools on genetic composition of plantations and on their vulnerability to the disease. Methods In the outbreak area, we checked the genetic origin of the trees and we estimated the percentage of Central European trees, disease prevalence and severity. Results Intra-site genetic diversity was high. Genetic composition did not match with geographic origin certificates. A high proportion of trees could not be assigned to either the Alpine or Central European gene pools. These admixed trees were as resistant as Central European trees. Geographic origin turned out to be one of the main drivers of canker prevalence, along with abiotic factors. Conclusion We need a precise knowledge of the origin of material used in seed orchards to mitigate canker disease and adapt forests through assisted migration.

Premise: Gynodioecy is a rare sexual system in which two genders (sensu Lloyd, 1980), cosexuals and females, coexist. To survive, female plants must compensate for their lack of siring capacity and male attractiveness. In European chestnut (Castanea sativa), an outcrossing tree, self‐pollination reduces fruit set in cosexual individuals because of late‐acting self‐incompatibility and early inbreeding depression. Could this negative sexual interaction explain the presence of females in this species? Methods: We studied gender variation in wild populations of European chestnut. In addition, we compared fruit set (the proportion of flowers giving fruits) and other key female fitness components as well as reproductive allocation between genders. We then performed emasculation experiments in cosexual trees, by removing nectar‐producing fertile male inflorescences. We also removed sterile but nectar‐producing male inflorescences from female trees, as a control. Results: We found a highly variable proportion of male‐sterile individuals in the wild in European chestnut. In the experimental plot, trees from each gender had similar size, flower density, and burr set, but different fruit set. Removing nectar‐producing male inflorescences from branches or entire trees increased fruit set in cosexual but not in female trees. Conclusions: These results show that self‐pollination impairs fruit set in cosexual trees. Female trees avoid these problems as they do not produce pollen but continue to attract pollinators thanks to their rewarding male‐sterile inflorescences, resulting in a much higher fruit set than in cosexuals. This demonstrates that even outcrossed plants can benefit from the cessation of self‐pollination, to the point that unisexuality can evolve. [ABSTRACT FROM AUTHOR]