Genetic variation of Heterobasidion abietinum in Southern Europe and the Mediterranean Basin

Heterobasidion abietinum causes root and butt rot on Abies species occurring in central Europe and the Mediterranean Basin in a distribution extending from Spain in the west to Turkey and Caucasia in the east. To investigate the genetic diversity within H. abietinum, 95 isolates from different regions were analysed with 61 polymorphic molecular markers. The markers showed genetic differentiation amongst the H. abietinum populations. The most diversified population is that on A. pinsapo in southern Spain, which is isolated from gene flow with other populations. Lower but still significant differences were found amongst other European populations. Isolates from Turkey showed little diversification compared with the south European isolates from east of the Alps. The genetic structure of the H. abietinum populations in relation to postglacial recolonization of Abies is discussed.     

Heterobasidion abietinum on Abies species in western Turkey

Forty‐five basidiocarp specimens of Heterobasidion were collected from native Abies species in three locations in western Turkey: A. nordmanniana ssp. bornmülleriana in Bolu province, A. nordmanniana ssp. equi‐trojani in Balikesir province and A. cilicica in Antalya province. Pure cultures were isolated from the basidiocarps and identified to the species level with the aid of mating tests. All the specimens proved to belong to the species Heterobasidion abietinum. This root rot fungus is common in the forests investigated and appears to be relatively virulent on Abies in Turkey. This is the first report of H. abietinum outside Europe.     

An isolated population of Heterobasidion abietinum on Abies pinsapo in Spain

Abies pinsapo, a fir endemic to a small area in southernmost Spain, is frequently attacked in natural stands by Heterobasidion root rot. To identify the Heterobasidion species causing the disease, pure cultures of the fungus were isolated from symptomatic trees in five localities in Sierra de las Nieves Natural Park and identified by pairing tests. In addition, genets of the fungus were identified in two pure stands of A. pinsapo. All the Heterobasidion specimens collected belonged to the species Heterobasidion abietinum. The largest genet found was 57 m long, and had colonized 10 trees. The large size of the main genets implied that H. abietinum had spread via root contacts from old infections generated before the establishment of the Sierra de las Nieves National Park in 1989. Exceptionally dry summers in the last 20 years may have weakened A. pinsapo and favoured spread of the disease.     

Gene flow and inter‐sterility between allopatric and sympatric populations of Heterobasidion abietinum and H. parviporum in Europe

The tree pathogenic fungi Heterobasidion parviporum and H. abietinum are recently described sibling species that show marked host preference for Picea abies and Abies alba, respectively. H. parviporum shows a higher reproductive character displacement (i.e. higher inter‐sterility) towards H. abietinum in sympatry than in allopatry. We inspected whether this pattern was also present in H. abietinum by studying the inter‐sterility and gene flow amongst sympatric central European populations of H. abietinum and H. parviporum, and two isolated allopatric populations, Pyrenean H. abietinum and Scandinavian H. parviporum. Inter‐ and intra‐specific fixation index values were calculated from DNA sequence data of the GST‐1 locus and four microsatellite loci. Present allopatric and sympatric populations of H. abietinum were equally inter‐sterile towards H. parviporum, not suggestive of relaxed reinforcement. Several hypotheses explaining the observed pattern are presented. Genetic differentiation was observed between H. abietinum in the Pyrenees and in the Alps, suggesting geographical structure of H. abietinum in Europe.     

Genetic variation ofAlnus trabeculosa populations in Japan

Alnus trabeculosa Hand.-Mazz. is classed as “near threatened,” and efforts should be made to conserve the species, but effective action would require understanding of its genetic variation and structure. Therefore, the genetic variation at 12 isozyme loci was examined in seven populations of the species in Japan. The expected heterozygosity within species (H _es=0.222) and the expected heterozygosity within populations (H _ep=0.199) were found to be slightly higher than in most other woody species. The coefficient of genetic differentiation (G _ST=0.146) was also high. The northernmost population had the lowest values for almost all measures of genetic variation, and populations in southern Japan tended to show greater within-population variation than those in northern Japan. The level and distribution of genetic variation in this species might be related to its life history and ecological traits, and distribution history.     

Variation in Heterobasidion annosum detected by Random Amplified Polymorphic DNAs

The production of Random Amplified Polymorphic DNAs (RAPDs) by Polymerase Chain Reaction (PCR) was used to detect variation in the isolates of Heterobasidion annosum with various geographical origins. Specific RAPD products were detected for each of the intersterility groups: the European S, F, P and the North American S group. There was considerably more polymorphism found among European S than P isolates. The analysis of RAPDs was shown to be a simple and a fast way to generate DNA markers specific to the previously established intersterility groups and thus useful for diagnostic purposes.     

Epidemiology of Heterobasidion abietinum and Viscum album on silver fir (Abies alba) stands of the Pyrenees

In the last two decades, stand decline and increased mortality has affected silver fir (Abies alba) forests in the Spanish Pyrenees. Simultaneously severe occurrences of the root rot fungus Heterobasidion annosum s.l. and of the mistletoe Viscum album have been reported. We aimed to improve the understanding of the epidemiology of both pathogens in our region. All H. annosum isolates found on silver fir were typed as H. abietinum. H. abietinum was more frequently observed where cuttings had targeted fir trees rather than other species. H. abietinum fruiting bodies were observed in the most recently cut stumps. V. album was more abundant on more dominant fir trees, and in southern aspect stands. The number of V. album colonies in the stand correlated (R² = 0.40) with silver fir mortality. Stands with a high level of V. album infection tended to have a smaller percentage of basal area in species other than silver fir, and they tended to be located on more south‐facing slopes. H. abietinum was widespread in silver fir forests of the Pyrenees. Our data suggest that, in the Pyrenees, the observed H. abietinum incidence may represent a combination of both primary and secondary spread of the pathogen. Favouring mixed forests should be tested as a potential control method for V. album. The correlation between silver fir mortality and V. album infection warrants further study, as the observed tree mortality could have occurred due to other factors than V. album, such as drought damage.     

Genetic variation in natural populations of Abies nephrolepis Max. in South Korea

Abies nephrolepis Max. is a fir species occurring in Northeast China, the extreme southeast of Russia and Korea. In Korea, A. nephrolepis is one of only three native fir species growing in high, mountainous areas with a disjunct distribution. We investigated genetic variation in A. nephrolepis by examining 24 ISSR polymorphic loci in 248 individuals representing eight natural populations in Korea. The level of intra-population genetic diversity (H _e = 0.240) was similar to or slightly lower than that of plants with similar ecological traits and life history. Most of the genetic diversity was allocated among individuals within populations (G _ST = 0.082, Φ_ST = 0.041) and the number of migrants per generation (N _m ) was 5.56. Nei’s genetic distances were small (D = 0.027) and unrelated to geographic distances between populations. Implications for the conservation of genetic variation in A. nephrolepis in South Korea were discussed.     

Genetic variation of isolated Picea balfouriana populations from the southeast of the Qinghai-Tibet Plateau

? The objective of this work is to estimate the level of genetic variation and pattern of genetic structure of isolated Picea balfouriana populations.

? Nine SSR markers and six STS markers were assayed in ten natural populations of P. balfouriana, which is a regionally distributed conifer species in the southeast of the Qinghai-Tibet Plateau.

? Expected heterozygosity ranged from 0.592 to 0.710 based on SSRs, and from 0.489 to 0.635 based on STS markers. The SSR and STS markers revealed that 11% and 12% of variation, respectively, was present among populations. However, the SSRs showed no deviation from the Hardy-Weinberg equilibrium (F _IS = ?0.030), unlike the STS markers (F _IS = 0.249). In addition, assignment methods showed that individuals from the same sampling site usually cluster together.

? Our results indicated that the distribution of genetic variation and population genetic structure of P. balfouriana may be attributed to habitat fragmentation and heterogeneous environments caused by the complex topographic environment in the Qinghai-Tibet Plateau. The population genetic information obtained in our study will benefit the development and utilization of appropriate conservation and breeding strategies for P. balfouriana.

     

Genetic variation of Taxus baccata L. populations in the Eastern Alps and its implications for conservation management

Abstract

The English yew (Taxus baccata L.) is an endangered rare tree species in Austria. More than 600 bud samples were collected from seven populations in three regions of the Eastern Alpine mountains for estimating their genetic structures by using isozyme gene markers. Nine gene loci encoding for seven enzyme systems were investigated. The revealed 32 alleles indicate a higher multiplicity of the east alpine gene pool compared with other European regions. English yew showed a high level of genetic variation, with a mean number of alleles per locus (A/L) of 2.7. A total of 76.4% of the loci were polymorphic, the average expected heterozygosity was (H _e) 0.274 and the mean observed heterozygosity (H _o) was 0.238. The relative proportion of genetic differentiation among the regions was found to be 6.2%, the level of gene flow was high (Nm=3.78) and the level of inbreeding (0.130) among the regions was medium. The obligatory out crossing (dioecious plant), the long generation time, the ability to regenerate from stump and the seed dispersal by birds and rodents might contribute to the high level of genetic variation found within the population. The conservation propositions are discussed with respect to the genetic structure and the poor recruitment of this species.     

Genetic variation in architectural seedling traits of Patagonian cypress natural populations from the extremes of a precipitation range

? Species distributed along wide environmental ranges are expected to be either plastic or adapted to local optima. The elucidation of which of these alternatives prevails, is crucial in planning breeding and conservation strategies for not yet domesticated species. Austrocedrus chilensis (Cupressaceae) is the most commercially important conifer of the temperate forests of Argentina and the target of a domestication program. A steep precipitation gradient characterizes its Argentinean range.

? Variation within and differentiation among four natural populations of this Patagonian cypress representative of two contrasting precipitation regimes (>1 300 and 330 mm per y) were assessed by analyzing several morpho/architectural traits in one-year-old seedlings grown in a greenhouse.

? Progenies from one of the two xeric populations did not differ from those corresponding to both humid-site populations. The two most variable populations in terms of additive genetic variance belonged to contrasting precipitation regimes. Differentiation among populations was low as measured by each and every variable (average Q _st = 0.088). Morphological traits related to the main axis size would have a dubious adaptive meaning.

? The results suggest that the Patagonian cypress would have not evolved genetic pools adapted to local optima, and thus it appears to be a phenotypically plastic species, at least regarding growth at juvenile age.

     

Intraspecific variation in Heterobasidion annosum for growth in sapwood of Picea abies and Pinus sylvestris

Two greenhouse experiments were conducted to study intraspecific variation in growth of the root rot fungus Heterobasidion annosum in living host sapwood. In experiment 1, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings were inoculated with H. annosum isolates, 14 each of the S-and P-intersterility groups, collected from various parts of Sweden. In pine, the P-group isolates were more virulent than the S-group isolates both in terms of infection frequency, induced mortality rate (p < 0.05), and fungal growth in sapwood (p < 0.05). In spruce, the P-group isolates were also more virulent on average, but the difference was not statistically significant. Both S and P isolates had a higher infection frequency and a significantly longer sapwood growth on spruce than on pine. The P-group caused higher mortality on pine than on spruce. The length of the lesion in the inner bark was strongly correlated with fungal growth in spruce, but not in pine where the lesions were short or absent. In experiment 2, ten Norway spruce clones were inoculated with 18 S-isolates, originating from nine live-decayed trees and from nine spore-infected stumps in a single Norway spruce stand. The objective was to test whether any selection for growth rate in sapwood was detectable among individuals of H. annosum originating either from stumps or trees. The results gave no support for such selection since no difference in sapwood growth between the two groups of isolates was found.     

Genetic variation of Fraxinus angustifolia natural populations in Greece based on nuclear and chloroplast microsatellite markers

Assessment of genetic variation within and among populations is an essential parameter for the effective conservation of forest genetic resources. In this work, the genetic diversity within and among natural populations of the forest tree species Fraxinus angustifolia Vahl in Greece was studied using selected nuclear and chloroplast microsatellite DNA loci. Eight natural populations of F. angustifolia were identified in different locations of the mainland of Greece, and a total of 230 individuals were studied. High polymorphism was observed within populations, while the genetic differentiation among populations was moderate. Intra-population diversity was correlated with geographical coordinates, but no isolation by distance was observed. Of the three haplotypes identified, only one was dominant. Putative ancestral haplotypes were found at small spatial scales suggesting that population expansions could have originated in the region. This study located in sympatry haplotypes that in other parts of Europe are in allopatry, reinforcing the notion of population expansions from the south of Balkans including Greece. Suggestions for conservation and management of F. angustifolia are also reported.     

Genetic and morphological variation in natural teak （Tectona grandis） populations of the Western Ghats in Southern India

Teak(Tectona grandis L.f.) is a popular hardwood species native to South and South-East Asia. The possible association of amplified fragment length polymorphism(AFLP) marker with morphological variables of eleven important characters viz. girth at breast height(GBH), height of tree, bole height, branch knots, presence of fluting, spiral stem, leaf hair, leaf length/breadth ratio, branching pattern, bark colour and petiole shape for nine natural populations comprising 180 genotypes of teak(9 populations × 20 trees). The phenogram constructed using Euclidean distances for the eleven morphological characters showed that the populations were not grouped according to their geographical origin. The Mantel's test for pairwise correlation between Euclidean distances of different morphological variables and genetic distances from AFLP data revealed that only petiole character(r =0.269; p =0.046) and height of tree(r =0.200; p =0.001) were significantly correlated with that of AFLP data matrix. The nine populations in this study covered a geographic area of about 1000 km stretch along the Western Ghat of South India. A test of correlation between genetic and geographic distance matrices revealed a significant positive correlation(r =0.475; p =0.009). The lack of perfect congruence between morphological and molecular data except for geographic distance, tree height and petiole character suggested that the morphological system might be useful for the morphotypes management but not appropriate to study the genetic structure of the teak populations.     

Physiological variation among Populus fremontii populations: short- and long-term relationships between delta13C and water availability

Different populations of widely distributed species can experience dramatically different climatic conditions that may influence physiological activity, specifically carbon assimilation and water use. Populus fremontii Wats. (Fremont cottonwood) populations are found near rivers of varying size along a precipitation gradient from New Mexico to northern California. Climatic differences among populations may lead to physiological differences because P. fremontii is sensitive to water availability. To assess physiological variation among populations, we collected foliage and wood samples from 13 populations that experience different precipitation and stream flow regimes and analyzed the samples for carbon isotope composition (delta13C). Wood delta13C served as a lifetime-averaged indicator of water-use efficiency (WUE), whereas foliage delta13C provided as an estimate of WUE during the growing season of collection. We found approximately 3.4 per thousand variation in delta13C among populations for both foliage (-31.1 to -27.9 per thousand) and wood (-28.3 to -24.7 per thousand). Wood delta13C was, on average, 2.8 per thousand more enriched than foliage. Some of the variation in wood delta13C can be explained by variation in elevation of the study sites. We constructed total precipitation and mean stream flow variables based on the length of the growing season at each study site and analyzed for a relationship between delta13C, precipitation and stream flow. A significant relationship between foliage delta13C and precipitation was found, but water availability did not explain a significant fraction of the variation in wood delta13C. The data suggest that water availability can account for some of the delta13C variation among populations but, given the large residual variances, other factors are important.     

Genetic variation of Tunisian Myrtus communis L. (Myrtaceae) populations assessed by isozymes and RAPDs

The genetic variation of six Tunisian Myrtus communis L. (Myrtaceae) populations was assessed using nine isozymes coding for 17 putative loci and 79 RAPD markers, amplified by five decamer random primers. The analysed populations belonged to three bioclimatic zones (lower humid, sub-humid and upper semi-arid). A high genetic diversity within populations was detected both by isozymes and RAPDs. The level of variation differed according to bioclimate. Populations collected from sub-humid bioclimate showed more polymorphism than those grown in the upper semi-arid zone. For all populations, the genetic diversity revealed by RAPDs was more pronounced than that detected with isozymes. A high differentiation among populations related to bioclimate and geographic distance was revealed by both methods. Population’s structure based on RAPD markers was more concordant with bioclimatic zones in comparison with isozymes. Differentiation between ecological groups was higher than that revealed within groups. Conservation programs should take into account the level of genetic diversity within population revealed by the two complementary classes of markers according to bioclimate.     

Genotypic variation in natural infection frequency of Heterobasidion spp. in a Picea abies clone trial in southern Sweden

Abstract

Natural root and butt rot infection with Heterobasidion spp. was recorded on three occasions in trees from a 20-year-old Norway spruce [Picea abies (L.) Karst.] clone trial. In the first assessment, carried out when the trial had been running for 15 years, 29.5% of the trees felled were infected with Heterobasidion spp., but no statistically significant differences were found between the different clones. In the second assessment, also at 15 years, bore cores were taken from 595 trees. Of these cores, 16.5% were infected, but again no statistically significant differences were found between the different clones. Combining the two first assessments also revealed no significant differences. The discrepancy in rot incidence between the two assessments was explained by the inaccuracy of the bore core method. The third assessment was carried out after the trial had been running for 20 years. At that time, 424 trees of 50 clones were felled and sampled. Visible infection was recorded in 46.5% of the trees. The differences between clones were statistically significant and the broad-sense heritability estimate was 0.18. There were no significant genotypic correlations between tree size and rot infection; this is important for the Norway spruce breeding strategy. Calculations show that economic viability would increase by 0.28 SEK per plant for every 10% decrease in root rot frequency at final felling.     

Genetic variation in natural and nursery populations of Styrax magnus (Styracaceae) for the restoration of humid mountain forests in southern Mexico

New Forests - Humid mountain forests (HMF) in Mexico have been heavily degraded by anthropogenic activities. A key conservation strategy consists of propagating HMF species in forest nurseries for...     

Phenotypic variation in Phoebe bournei populations preserved in the primary distribution area

Phoebe bournei(Hemsl.) Yang is a rare and protected plant in China. This study was conducted to determine the phenotypic variation in this species and to document phenotypic variation within and among populations of P. bournei. Nested analysis of variance, coefficient of variation, multiple comparisons, principal component analysis(PCA) and correlation analysis were used to analyze ten phenotypic traits in ten natural populations of P.bournei from both the northeastern and the primary region of the range of this species. Significant differences among and within populations were observed in leaf and seed phenotypic traits. Variation among populations(34.92%)was greater than that within populations(26.19%). The mean phenotypic differentiation coefficient was 53.77%among populations, indicating that variation among populations comprised the majority of the phenotypic variation of P. bournei. The coefficient of variance(CV) of ten traits varied from 6.44 to 18.45%, with an average of 12.03%.The CV of leaf traits among populations(15.64%) was higher than that of seed traits(8.60%), indicating that seed traits were more stable. The results from CV and PCA indicated that leaf area, leaf length and thousand seed weight were the main factors accounting for the observed phenotypic variations. Significant or highly significant correlations were observed among most leaf and/or in seed phenotypic traits, whereas no significant correlations were observed between phenotypic traits and geographic factors.Based on cluster analysis, the ten populations can be divided into three clusters. These clusters were not a result of geographic distances.