Evidence has been documented in Europe of introgression, the transfer of genetic material, between Asian chestnut species (Castanea crenata and C. mollissima) and the native C. sativa through spontaneous hybridization and subsequent backcrossing. However, the extent of this introgression has not been monitored in a particular forest stand or in adult and juvenile trees simultaneously. We assessed introgression in a natural C. sativa forest in northwest Spain and developed a reliable method to detect the presence of Asian germplasm of Castanea spp. A total of 34 adult trees and 42 saplings were genotyped at 13 SSRs in a forest where ink-disease-resistant C. crenata and C. mollissima seedlings had been planted in the 1940s. The 13 SSR loci selected were highly polymorphic and 115 different alleles were detected for the individuals sampled. Bayesian clustering identified two groups for C. sativa and one group each for C. mollissima and C. crenata. Within the forest, 70.6 per cent of adults and 28.6 per cent of juveniles were classified as pure C. sativa. Most juveniles were C. sativa × C. crenata (>40 per cent) and ca. 10 per cent were C. crenata × C. mollissima hybrids. Six new alleles private to C. crenata are reported here. The study quantifies, for the first time in Europe, introgression of Asian germplasm into a natural C. sativa forest. It also examines the extent of introgression in offspring and provides a method to detect exotic germplasm in C. sativa forests. We discuss why the forest studied may benefit from transfer of alleles involved in ink-disease resistance and why introgression will be detrimental to drought tolerance in offspring.

中文翻译：

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亚洲种质渗入西班牙天然板栗林的分子证据

在欧洲，有证据表明通过自发杂交和随后的回交，在亚洲板栗物种（Castanea crenata 和 C. mollissima）和本地 C. sativa 之间进行基因渗入，遗传物质的转移。然而，这种基因渗入的程度尚未在特定林分或成年树和幼树中同时监测。我们评估了西班牙西北部天然 C. sativa 森林的基因渗入，并开发了一种可靠的方法来检测亚洲栗属种质的存在。在 1940 年代种植了抗墨病 C. crenata 和 C. mollissima 幼苗的森林中，共有 34 棵成年树和 42 棵树苗在 13 个 SSR 上进行了基因分型。选择的 13 个 SSR 基因座具有高度多态性，并为样本个体检测到 115 个不同的等位基因。贝叶斯聚类确定了 C. sativa 的两组，C. mollissima 和 C. crenata 各一组。在森林中，70.6% 的成年人和 28.6% 的青少年被归类为纯苜蓿。大多数少年是 C. sativa × C. crenata (>40%) 和 ca. 10% 是 C. crenata × C. mollissima 杂交种。这里报告了 C. crenata 的六个新等位基因。该研究首次在欧洲量化了亚洲种质渗入天然 C. sativa 森林的情况。它还检查了后代的基因渗入程度，并提供了一种检测 C. sativa 森林中外来种质的方法。我们讨论了为什么研究的森林可能受益于与墨病抗性有关的等位基因的转移，以及为什么基因渗入会损害后代的耐旱性。