The Chinese chestnut (Castanea mollissima) carries resistance to Cryphonectria parasitica, the fungal pathogen inciting chestnut blight. The pathogen, introduced from Asia, devastated the American chestnut (Castanea dentata) through- out its native range early in the twentieth century. A highly informative genetic map of Chinese chestnut was constructed to extend genomic studies in the Fagaceae and to aid the intro- gression of Chinese chestnut blight resistance genes into Amer- ican chestnut. Two mapping populations were established with three Chinese chestnut parents, 'Mahogany', 'Nanking' ,a nd 'Vanuxem', totaling 337 progeny. The transcriptome-based ge- netic map was created with 329 simple sequence repeat and 1,064 single nucleotide polymorphism markers all derived from expressed sequence tag sequences. Genetic maps for each parent were developed and combined to establish 12 consensus linkage groups spanning 742 cM, providing the the most com- prehensive genetic map for a Fagaceae species to date. Over 75 % of the mapped markers from the Chinese chestnut con- sensus genetic map were placed on the physical map using overgo hybridization, providing a fully integrated genetic and physical map resource for Castanea spp. About half (57 %) of the Chinese chestnut genetic map could be assigned to regions of segmental homology with 58 % of the peach (Prunus per- sica) genome assembly. A three quantitative trait loci (QTL) model for blight resistance was verified using the new genetic markers and an existing interspecies (C. mollissima × C. den- tata)F2mapping population. Two of the blight resistance QTLs in chestnut shared synteny with two QTLs for powdery mildew resistance in peach, indicating the potential conservation of disease resistance genes at these loci.

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A transcriptome-based genetic map of Chinese chestnut (Castanea mollissima) and identification of regions of segmental homology with peach (Prunus persica)

Despite the well-known effects that Quaternary climate oscillations had on shaping intraspecific diversity, their role in driving homoploid hybrid speciation is less clear. Here, we examine their importance in the putative homoploid hybrid origin and evolution of Ostryopsis intermedia, a diploid species occurring in the Qinghai-Tibet Plateau (QTP), a biodiversity hotspot. We investigated interspecific relationships between this species and its only other congeners, O. davidiana and O. nobilis, based on four sets of nuclear and chloroplast population genetic data and tested alternative speciation hypotheses. All nuclear data distinguished the three species clearly and supported a close relationship between O. intermedia and the disjunctly distributed O. davidiana. Chloroplast DNA sequence variation identified two tentative lineages, which distinguished O. intermedia from O. davidiana; however, both were present in O. nobilis. Admixture analyses of genetic polymorphisms at 20 SSR loci and sequence variation at 11 nuclear loci and approximate Bayesian computation (ABC) tests supported the hypothesis that O. intermedia originated by homoploid hybrid speciation from O. davidiana and O. nobilis. We further estimated that O. davidiana and O. nobilis diverged 6–11 Ma, while O. intermedia originated 0.5–1.2 Ma when O. davidiana is believed to have migrated southward, contacted and hybridized with O. nobilis possibly during the largest Quaternary glaciation that occurred in this region. Our findings highlight the importance of Quaternary climate change in the QTP in causing hybrid speciation in this important biodiversity hotspot.

Diploid hybrid origin of Ostryopsis intermedia (Betulaceae) in the Qinghai‐Tibet Plateau triggered by Quaternary climate change

Corylus mandshurica, also known as pilose hazelnut, is an economically and ecologically important species in China. In this study, ten polymorphic simple sequence repeat (SSR) markers were applied to evaluate the genetic diversity and population structure of 348 C. mandshurica individuals among 12 populations in China. The SSR markers expressed a relatively high level of genetic diversity (Na = 15.3, Ne = 5.6604, I = 1.8853, Ho = 0.6668, and He = 0.7777). According to the coefficient of genetic differentiation (Fst = 0.1215), genetic variation within the populations (87.85%) were remarkably higher than among populations (12.15%). The average gene flow (Nm = 1.8080) significantly impacts the genetic structure of C. mandshurica populations. The relatively high gene flow (Nm = 1.8080) among wild C. mandshurica may be caused by wind-pollinated flowers, highly nutritious seeds and self-incompatible mating system. The UPGMA (unweighted pair group method of arithmetic averages) dendrogram was divided into two main clusters. Moreover, the results of STRUCTURE analysis suggested that C. mandshurica populations fell into two main clusters. Comparison of the UPGMA dendrogram and the Bayesian STRUCTURE analysis showed general agreement between the population subdivisions and the genetic relationships among populations of C. mandshurica. Group I accessions were located in Northeast China, while Group II accessions were in North China. It is worth noting that a number of genetically similar populations were located in the same geographic region. The results further showed that there was obvious genetic differentiation among populations from Northeast China to North China. Results from the Mantel test showed a weak but still significant positive correlation between Nei’s genetic distance and geographic distance (km) among populations (r = 0.419, P = 0.005), suggesting that genetic differentiation in the 12 C. mandshurica populations might be related to geographic distance. These data provide comprehensive information for the development of conservation strategies of these valuable hazelnut resources.

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Assessment of Genetic Diversity and Population Genetic Structure of Corylus mandshurica in China Using SSR Markers.

Corylus was renowned for its production of hazelnut and taxol. To understand the local adaptation of Chinese species and speed up breeding efforts in China, we analyzed the leaf transcriptome of Corylus mandshurica, which had a high tolerance to fungal infections and cold. A total of 12,255,030 clean pair-end reads were generated and then assembled into 37,846 Expressed Sequence Tag (EST) sequences. During functional annotation, 26,565 ESTs were annotated with Gene Ontology (GO) terms using Blast2go and 11,056 ESTs were grouped into the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways using KEGG Automatic Annotation Server (KAAS). We identified 45 ESTs that were homologous to enzymes and transcription factors responsible for taxol synthesis. The most differentiated orthologs between C. mandshurica and a European congener, C. avellana, were enriched in stress tolerance to fungal resistance and cold. In this study, we detected a set of genes related to taxol synthesis in a taxol-producing angiosperm species for the first time and found a close relationship between most differentiated genes and different adaptations to fungal infection and cold in C. mandshurica and C. avellana. These findings provided tools to improve our understanding of local adaptation, genetic breeding and taxol production in hazelnut.

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Transcriptome analyses of a Chinese hazelnut species Corylus mandshurica

Mountainous forest areas are vitally important for water supply in dryland regions which suffer from high erosion risk and severe water shortage. Massive afforestation, mainly for erosion control, may reduce the water yield and threaten local water supply security. Moreover, many over-dense forests due to a strict logging ban policy have produced remarkably negative impacts for both forests (e.g., low timber quality, restricted natural regeneration, and high stand instability) and water yield. To satisfy the rapidly increasing demands on water supply and other services, a practical approach for managing forest stands in a multifunctional way, which particularly addresses water yielding, is urgently required. For this purpose, we integrated the existing knowledge and experience, designed an “ideal” stand structure to represent multifunctional forest (MFF) and determined its key parameters (a ground coverage of >0.7, a canopy density around 0.7, and an H/DBH ratio (tree height [m] to the diameter at breast height [cm]) of <0.7). Moreover, a decision process for MFF stand management was recommended as: (1) investigating the site quality; (2) identifying the site-specific main forest functions; (3) quantifying the stand structure; (4) diagnosing the stand structure by comparing with the “ideal” one; and (5) arranging the functions/structure-oriented management measures. In this way, the water-yielding function can be improved and meanwhile other forest functions can be promoted.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/1752-1688.12314

A Water Yield-Oriented Practical Approach for Multifunctional Forest Management and its Application in Dryland Regions of China†

Vegetation carrying capacity based on soil water on typical slopes in the Diediegou small watershed of Liupan Mountains, northwestern China.

Ten SSR primer pairs of Castanea mollissima amplified good PCR products from 60 genotypes of wild chestnut (C. mollissima) that were collected from four mountainous regions of China. With an average level of 7.9, ten loci showed a total of 79 alleles, ranging from 4-11 per locus. High values of PIC and H e in wild populations of C. mollissima were up to 0.74 and 0.78, respectively. In comparison with low values of PIC and He (0.601 and 0.522) in a wild population of the Da Bie Shan mountains, high genetic diversity levels were found in other populations obtained from three mountainous regions (Da Bie Shan, Qin Ling and Lian Hua Feng). The geographic relationship among these four populations is discussed.

Cheng Lili

Papers

Vegetation carrying capacity based on soil water on typical slopes in the Diediegou small watershed of Liupan Mountains, northwestern China.

Analysis of genetic diversity among wild Chinese chestnut populations using SSR markers.

Genetic diversity of six Corylus species in China detected with microsatellite isolated from Corylus avellana.

Influencing factors of water consumption from tree transpiration.

Diversity of chloroplast DNA SSRs in the wild and cultivated chestnuts (Castanea mollissima).