Variation in the Growth Traits and Wood Properties of Chinese Fir from Six Provinces of Southern China

Bipolaris fujianensis sp. nov., an Emerging Pathogen of Sapling Shoot Blight on Chinese Fir, and Its Sensitivity to Fungicides

Chinese fir is an extremely important economic tree species in southern China. In recent years, 74.5% of Chinese fir saplings suffered from shoot blight in Shunchang County, Nanping City, Fujian Province, China. Seventeen isolates were collected from rotten shoots, and their pathogenicity was confirmed following Koch's postulates. The five pathogenic isolates were identified as belonging to the genus Bipolaris based on morphological characteristics, including septate and geniculate conidiophores, smooth to slightly verruculose conidiogenous nodes, dematiaceous phragmospore conidia, oblong or fusiform conidia, and slightly protruding or truncate hilum on conidia, but the number of pseudosepta (3 to 11, mostly 5 to 8) and the size of conidia ([22.81 to 116.13] × [9.16 to 26.58] μm) are different from those of the known species of Bipolaris. A phylogenetic analysis based on ITS, GAPDH, and Tef1-α sequences determined that the five strains belong to a new species of Bipolaris, and the name Bipolaris fujianensis sp. nov. is proposed. The fungicide sensitivity of the pathogen strain Cfsb3 was further evaluated using eight fungicides. Flusilazole, difenoconazole, tebuconazole, and propiconazole exhibited high toxicity to Cfsb3, and the effective concentration inhibiting 50% (EC50) of mycelial growth was 0.08, 0.20, 0.34, and 0.36 μg/ml, respectively, for these four fungicides. Flusilazole, difenoconazole, and iprodione inhibited B. fujianensis by 100% on detached Chinese fir shoots at their recommended concentrations, but azoxystrobin and thiram were ineffective. In conclusion, this study reported an emerging pathogen of Chinese fir sapling shoot blight and proposed triazole and dicarboximide fungicides for disease control.

Genome-Wide Association Study With Growth-Related Traits and Secondary Metabolite Contents in Red- and White-Heart Chinese Fir

Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] is an important evergreen coniferous tree species that is widely distributed in many southern provinces of China and has important economic value. The Chinese fir accounts for 1/4 and 1/3 of the total artificial forest area and stock volume, respectively. Red-heart Chinese fir is popular in the market because of its high density and red heartwood. The long-growth cycle hindered the breeding process of Chinese fir, while molecular marker-assisted breeding could accelerate it. However, Chinese fir, a perennial conifer species, has a large genome, which has not yet been published. In this study, the growth-related traits and secondary metabolite contents of red- and white-heart Chinese fir were measured and found to be different between them. There are extremely significant differences among growth-related traits (p < 0.001), but secondary metabolite contents have different correlations due to differences in chemical structure. Moreover, genotype effect analysis of the substantially correlated single nucleotide polymorphisms (SNPs) revealed that most of the loci related to each growth-related traits were different from each other, indicating a type specificity of the genes regulated different growth-related traits. Furthermore, among the loci related to secondary metabolite contents, nine loci associated with multiple metabolite phenotypes such as Marker21022_4, Marker21022_172, Marker24559_31, Marker27425_37, Marker20748_85, Marker18841_115, Marker18841_198, Marker65846_146, and Marker21486_163, suggesting the presence of pleiotropic genes. This study identified the potential SNP markers associated with secondary metabolites in Chinese fir, thus setting the basis for molecular marker-assisted selection.

Geographical Variation in the Growth and Nutritional Traits of Leaf Powder from Broussonetia papyrifera (L.) L’Hér. ex Vent. from Different Provenances

Broussonetia papyrifera (L.) L’Hér. ex Vent, a perennial deciduous tree, is used in feed, medicine, papermaking, environmental protection, and ecological restoration. This paper ttook 33 provenances from the natural distribution as the research objects, observes their growth and nutritional traits, and analyzes the laws of geographical variation. The repeatability was 0.80–0.88 and 0.48–0.91, respectively. The correlation was significant (the correlation coefficient was 0.764). The variation is greatly affected by the latitudinal direction. Through clustering, the 33 provenances were clustered into 4 groups and most provenances with relatively close geographical origins were clustered together, showing differences between different geographical regions. Using leaf biomass (0.4662 g) and crude protein content (14.39%) as the selection index, the Sichuan Mianyang (SCMY), Chongqing Kaizhou (CQKZ), Shanghai (SH), and Fujian Nanping (FJNP) provenances were selected as fast-growing, high-yield, and high-quality paper mulberry provenances. This study provides the basis for the selection of excellent paper mulberry trees.

Phenotypic Diversity Analysis and Superior Family Selection of Industrial Raw Material Forest Species-Pinus yunnanensis Franch

Pinus yunnanensis Franch is a major forest species in southwest China as a source of timber and industrial raw materials. The genetic quality of the species is declining and the differentiation of offspring is strong as affected by environmental change and improper management measures. To assess the phenotypic diversity of natural populations, the evaluation of twelve phenotypic traits in nine populations from its whole distribution was performed. Studies revealed plentiful phenotypic variations within and among populations. The phenotypic variation within the population was 4.03%, and was lower than that among populations (21.04%), indicating that the phenotypic variation among populations was the main source. The mean differentiation coefficient was 91.23%, and the mean coefficient of variation of twelve traits was 28.27%, ranging from 14.18% (length of needles) to 70.11% (height under the branches). No significant correlation between plant height and environmental factors was found. Mean annual temperature, mean temperature of the driest quarter, mean temperature of the wettest quarter, and latitude were significantly correlated to diameter breast height, respectively. Temperature is the most important factor affecting the diameter of breast height. Three principal components that represent plant shape, needle, and lateral branch trait, respectively, were obtained while the cumulative contribution rate reached 74.40%. According to the unweighted pair-group method with arithmetic means (UPGMA) cluster analysis, nine populations were divided into three clusters. However, populations were not clustered strictly according to geographic distance, implying that there is a discontinuity in the variation of phenotypic traits. Compared with other populations, the Lufeng population contains obvious advantages in plant height, diameter breast height, crown diameter, and needle length and width, whereas the Yongren population has the worst performance in plant height, crown diameter, and the number of lateral branches. Moreover, for selecting superior families, both the comprehensive scoring method and principal component analysis were combined. By comparing trait values from 258 families, eleven superior families with an actual gain of each trait ranging from 0.02% to 32.23% were successfully screened out. This study provides a certain reference significance for the breeding of improved varieties and plantation management of P. yunnanensis.

Comprehensive Transcriptome Analysis of Stem-Differentiating Xylem Upon Compression Stress in Cunninghamia Lanceolata

Compression wood (CW) in gymnosperm brings great difficulties to wood industry using wood as raw materials since CW presents special wood structure and have different physical and chemical properties from those of normal wood (NW). Chinese fir (Cunninghamia lanceolata) is widely distributed in China. However, global transcriptome profiling of coding and long non-coding RNA in response to compression stress has not been reported in the gymnosperm species. In this study, we revealed that CW in Chinese fir exhibited distinct morphology and cytology properties compared with those of NW, including high lignin content, thick and round tracheid cells. Furthermore, we combined both PacBio long-read SMRT sequencing (Iso-Seq) and Illumina short-read RNA-Seq to reveal the transcriptome in stem-differentiating xylem (SDX) under different time points (2, 26, and 74 h) upon compression stress in NW, CW, and OW (opposite wood), respectively. Iso-Seq was successfully assembled into 41,253 de-novo full-length transcriptome reference (average length 2,245 bp). Moreover, there were striking differences in expression upon compression stress, which were involved 13 and 7 key enzyme genes in the lignin and cellulose synthesis, respectively. Especially, we revealed 11 secondary growth-related transcription factors show differential expression under compression stress, which was further validated by qRT-PCR. Finally, the correlation between 6,533 differentially expressed coding genes and 372 differentially expressed long non-coding RNAs (lncRNAs) indicates that these lncRNAs may affect cell wall biogenesis and xyloglucan metabolism. In conclusion, our results provided comprehensive cytology properties and full-length transcriptome profiling of wood species upon compression stress. Especially we explored candidate genes, including both coding and long non-coding genes, and provided a theoretical basis for further research on the formation mechanism of CW in gymnosperm Chinese fir.

Seed rain and soil seed bank in Chinese fir plantations and an adjacent natural forest in southern China: Implications for the regeneration of native species

The natural regeneration of native broadleaved species underneath forest monoculture plantations is important to recover ecosystem functions and to mitigate adverse environmental effects. To understand how seed rain and soil seed bank facilitate natural regeneration, we surveyed their density and composition in a monoculture Chinese fir plantation, a mixed Chinese fir-broadleaf plantation, and an adjacent natural broadleaved forest for two years in southern China. Twenty-eight species (16 families) were in seed rain, and 45 species (27 families) were in soil seed bank. Seed rain density did not differ significantly across stands; however, the number of taxa in seed rain was highest in the mixed plantation and lowest in the natural forest. Seed bank density was significantly higher in the mixed plantation than in the other stands (p < .05). The Sørensen similarity index of species composition between seed sources and aboveground vegetation were relatively low (<.50). The seeds of various native tree species were common in the seed bank of the plantations, indicating that seed rain and seed bank played an important role in native forest regeneration. We recommend that managers interested in sustainable forestry should take into consideration the presence of existing soil seed bank when developing their management strategies. In addition, with regard to forest regeneration process, we also recommend supplementation of the species composition by direct seeding or planting of desired species.

Variation in wood physical properties and effects of climate for different geographic sources of Chinese fir in subtropical area of China

Chinese fir is one of the most important commercial timber species in China, with many geographic sources. However, little is known of the variation in wood physical properties among them. To explore the differences in wood physical properties and their influencing factors, five geographic sources of Chinese fir were selected. The variance inflation factor, stepwise regression, and principle component analysis were used to reduce multicollinearity and dimensions of the 19 wood physical properties (including density, shrinkage, and mechanical properties). The results showed that the wood density differed significantly among five geographic sources. The tangential shrinkage rate and radial shrinkage rate reached maximum values in black-heart Chinese fir (HNYX-T) but accompanied by the lowest value for difference dry shrinkage. The wood density and mechanical properties of HNYX-T was exceeded to that of others geographic sources. Fast-growth Chinese fir (FJYK-P) had the lowest value for all mechanical properties. The precipitation and temperature had significant correlations with the wood physical properties of this five geographic sources. The temperature in summer was mainly positive correlated with physical properties, while precipitation was negatively correlated with them. HNYX-T had the highest comprehensive score of PCA, followed by JXCS-R, emerged as higher-quality geographic source, which is important for selecting and utilizing geographic sources in forest management.

Single-nucleotide polymorphisms(SNPs) in a sucrose synthase gene are associated with wood properties in Catalpa fargesii bur

BACKGROUND

Association study is a powerful means for identifying molecular markers, such as single-nucleotide polymorphisms (SNPs) associated with important traits in forest trees. Catalpa fargesii Bur is a valuable commercial tree in China and identifying SNPs that associate with wood property would make a foundation of the marker-assisted breeding in the future. However, related work has not been reported yet.

RESULTS

We cloned a 2887 bp long sucrose synthase (SUS) gene from the genome of C. fargesii, which is a key enzyme in sucrose metabolism and also associated to wood formation in trees, coding 806 amino acids that expressed mainly in young branches, xylem, and leaves according to real-time quantitative PCR. Then we identified allelic variations of CfSUS associated with nine wood quality associated traits in Catalpa fargesii Bur. Totally, 135 SNPs were identified through cloning and sequencing the CfSUS locus from a mapping population (including 93 unrelated individuals) and 47 of which were genotyped as common SNPs (minor allele frequency > 5%) in the association population that comprised of 125 unrelated individuals collected from main distribution area. Nucleotide diversity and linkage disequilibrium (LD) analysis showed CfSUS has a relative low SNP diversity (πT = 0.0034) and low LD (r2 dropped below 0.1 within 1600 bp). Using the association analysis, we found 11 common SNPs and 14 haplotypes were significantly associated with the traits (false discovery rate, Q<0.1), explaining 3.21-12.41% of the phenotypic variance. These results provide molecular markers above associated with wood basic density, pore rate, and six other traits of wood, which have potential applications in breeding of Catalpa fargesii Bur.

CONCLUSION

We first cloned a SUS gene in C. fargesii, then identified several SNPs and haplotypes that associated with wood properties within this gene, suggesting CfSUS participates in the wood formation of C. fargesii. Moreover, molecular markers we identified in this study may be applied into marker-assisted breeding of C. fargesii in the future.

Effects of sulfuric, nitric, and mixed acid rain on Chinese fir sapling growth in Southern China

The influence of acid rain on plant growth includes direct effects on foliage as well as indirect soil-mediated effects that cause a reduction in root growth. In addition, the concentration of NO₃^- in acid rain increases along with the rapid growth of nitrogen deposition. In this study, we investigated the impact of simulated acid rain with different SO₄^2-/NO₃^- (S/N) ratios, which were 1:0, 5:1, 1:1, 1:5 and 0:1, on Chinese fir sapling growth from March 2015 to April 2016. Results showed that Chinese fir sapling height growth rate (HGR) and basal diameter growth rate (DGR) decreased as acid rain pH decreased, and also decreased as the percentage of NO₃^- increased in acid rain. Acid rain pH significantly decreased the Chlorophyll a (Chla) and Chlorophyll b (Chlb) content, and Chla and Chlb contents with acid rain S/N 1:5 were significantly lower than those with S/N 1:0 at pH 2.5. The chlorophyll fluorescence parameters, maximal efficiency of Photosystem II photochemistry (Fv/Fm) and non-photochemical quenching coefficient (NPQ), with most acid rain treatments were significantly lower than those with CK treatments. Root activities first increased and then decreased as acid rain pH decreased, when acid rain S/N ratios were 1:1, 1:5 and 0:1. Redundancy discriminant analysis (RDA) showed that the Chinese fir DGR and HGR had positive correlations with Chla, Chlb, Fv/Fm ratio, root activity, catalase and superoxide dismutase activities in roots under the stress of acid rain with different pH and S/N ratios. The structural equation modelling (SEM) results showed that acid rain NO₃^- concentration and pH had stronger direct effects on Chinese fir sapling HGR and DGR, and the direct effects of acid rain NO₃^- concentration and pH on HGR were lower than those on DGR. Our results suggest that the ratio of SO₄^2- to NO₃^- in acid rain is an important factor which could affect the sustainable development of monoculture Chinese fir plantations in southern China.

Genetic Characterization of Chinese fir from Six Provinces in Southern China and Construction of a Core Collection

Large ex situ germplasm collections of plants generally contain significant diversity. A set of 700 well-conserved Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) clones from six provinces in southern China in the ex situ gene bank of Longshan State Forest, was analyzed using 21 simple sequence repeat markers, with the aim of assessing the genetic diversity of these germplasm resources. Genetic analysis revealed extensive genetic variation among the accessions, with an average of 8.31 alleles per locus and a mean Shannon index of 1.331. Excluding loci with null alleles, we obtained a low level of genetic differentiation among provinces, consistent with the interpopulation genetic variation (1%). Three clusters were identified by STRUCTURE, which did not match the individuals’ geographical provenances. Ten traits related to growth and wood properties were quantified in these individuals, and there was substantial variation in all traits across individuals, these provide a potential source of variation for genetic improvement of the Chinese fir. Screening large collections for multiple-trait selective breeding programs is laborious and expensive; a core collection of 300 accessions, representative of the germplasm, was established, based on genotypic and phenotypic data. The identified small, but diverse, collections will be useful for further genome-wide association studies.