Chestnut reproductive biology and orchard design

Without reliable pollination services, it is not possible to have high-yielding orchards. In chestnut, results obtained in recent years call into question traditional orchard conception. To design well-pollinated orchards, it is important to include enough genetic diversity to ensure effective cross-fertilization. Traditional use of as few cultivars as possible in chestnut orchards has been counterproductive. We found a strong positive effect on cultivar diversity on pollination success. However, not only the number and proportion of cultivars used and their spatial distribution in the orchard matter but also their identities. In European chestnut (Castanea sativa) and in its hybrids, many trees are male-sterile: they have aborted stamens, allowing them to escape the negative consequences of self-pollination. In male-fertile trees, on the contrary, many female flowers are wasted due to ovule usurpation following self-pollination, thus reducing orchard yield. To illustrate the effect of pollen donor diversity, spatial distribution of the trees in the orchard and self-pollen interference, we are currently developing a predictive Bayesian model to evaluate pollination success as a function of various orchard designs, with a focus on the proportion of male-sterile cultivars deployed. Here we give some first indications of the main conclusions and propose a few rules for designing well-pollinated orchards. In particular, we strongly encourage the use of male-sterile cultivars to increase yield.