Characterization of a genetic resource collection for Miscanthus (Saccharinae,Andropogoneae, Poaceae) using AFLP and ISSR PCR

Amplified fragment length polymorphism (AFLP) and inter-simple sequence repeat markers were employed to characterize a genetic resource collection of Miscanthus, a grass under trial in Europe as a biomass crop. The 26 polymorphic markers produced by two ISSR fingerprinting primers were able to discriminate taxa and identify putative clones. AFLP fingerprints were fully reproducible and produced a larger number of markers for the three primer pairs tested, of which 998 were polymorphic (representing 79.3% of all bands). AFLP markers distinguished species, infra-specific taxa (varieties and cultivars) and putatively clonal material. They were also used to assess the inter-relationships of the taxa, to investigate the origin of important hybrid plants and to estimate the overall level of genetic variation in the collection. They were useful for assessing the species status of certain taxa such as M. transmorrisonensis, an endemic from Taiwan that was clearly distinct from M. sinensis; whereas other taxa of disputed species status, such as M. condensatus and M. yakushimanum were not genetically distinct from M. sinensis. The AFLP markers detected a high degree of infra-specific variation and allowed subdivisions of the genetic resource collection to be made, particularly within M. sinensis.     

Essential oil constituents and RAPD markers to establish species relationship in Cymbopogon Spreng. (Poaceae)

Nineteen Cymbopogon taxa belonging to 11 species, two varieties, one hybrid taxon and four unidentified species were analysed for their essential oil constituents and RAPD profiles to determine the extent of genetic similarity and thereby the phylogenetic relationships among them. Remarkable variation was observed in the essential oil yield ranging from 0.3% in Cymbopogon travancorensis Bor. to 1.2% in Cymbopogon martinii (Roxb.) Wats var. motia. Citral, a major essential oil constituent, was employed as the base marker for chemotypic clustering. Based on genetic analysis, elevation of Cymbopogon flexuosus var. microstachys (Hook. F.) Soenarko to species status and separate species status for C. travancorensis Bor., which has been merged under C. flexuosus (Steud.) Wats were suggested towards resolving some of the taxonomic complexes in Cymbopogon. The separate species status for the earlier proposed varieties of C. martinii (motia and sofia) is further substantiated by these analyses. The unidentified species of Cymbopogon have been observed as intermediate forms in the development of new taxa.     

Identification of Erythroxylum taxa by AFLP DNA analysis

Erythroxylum coca, indigenous to the Andean region of South America, is grown historically as a source of homeopathic medicine. However, in the last century, cultivation of E. coca and several closely-related species for the production of illicit cocaine has become a major global problem. Two subspecies, E. coca var. coca and E. coca var. ipadu, are almost indistinguishable phenotypically; a related cocaine-bearing species also has two subspecies (E. novogranatense var. novogranatense and E. novogranatense var. truxillense) that are phenotypically similar, but morphologically distinguishable. The purpose of this research was to discover unique AFLP DNA patterns ("genetic fingerprinting") that characterize the four taxa and then, if successful, to evaluate this approach for positive identification of the various species of coca. Of seven different AFLP primer pairs tested, a combination of five proved optimal in differentiating the four taxa as well as a non-cocaine-bearing species, E. aerolatum. This method of DNA fragment separation was selective, and faster, for coca identification, compared with analyses based on flavonoid chemotaxonomy. Using the 5-primer AFLP approach, 132 known and unknown coca leaf accessions were evaluated. Of these, 38 were collected in 1997-2001 from illicit coca fields in Colombia, and all were genetically differentiated from coca originating in Peru and Bolivia. Based on the DNA profiling, we believe that the Colombian coca now represents a hybridization of E. coca var. ipadu. Geographical profiling within Colombia also seems feasible as new coca production areas are developed or new types of coca are introduced within traditional growing areas.     

AFLP characterization of natural populations of Berberis (Berberidaceae) in Patagonia, Argentina

 AFLP markers were used to analyse the intra- and interspecific relationships among 22 natural populations of 13 Patagonian species of Berberis and the relationships among the taxa belonging to homoploid and polyploid complexes. Seven primer combinations gave rise to 231 AFLP bands, of which 199 were polymorphic. Correspondence between AFLP data, morphological traits and seed protein bands was also assessed. The dendrogram inferred from AFLP fingerprints showed that, in general, populations of the same species formed closely related groups with high coefficients of similarity. Principal co-ordinates analysis showed two separate subgroups: (i) B. bidentata and their putative ancestors –B. darwinii and B. linearifolia– which form a homogamic group, and (ii) B. buxifolia, B. heterophylla and B. parodii– which could form a polyploid hybrid complex. Received March 21, 2001 Accepted September 11, 2001     

濒危植物毛柄小勾儿茶片断化居群的遗传多样性

采用扩增片段长度多态性(AFLP)标记对我国特有的濒危植物毛柄小勾儿茶(Berchemiella wilsonii var. pubipetiolata)现存于浙江和安徽的4个片断化居群中的89株个体进行了遗传多样性和遗传结构的研究。结果表明,与其它木本濒危植物相比,毛柄小勾儿茶具有与它们相当的遗传多样性,8对选择扩增引物共扩增出122条清晰的条带,居群的平均多态位点百分率为P_p=26.4%,其中马家河居群最高(29.5%)而湍口居群最低(23.8%),居群的平均基因多样度为H_ep=0.162 8(0.140 5~0.172 4);而在物种水平上的遗传多样性为P_s=36.9%, H_es=0.202 4。居群间的遗传分化系数F_ST=0.193 9,表明居群间有显著的遗传分化,进一步利用AMOVA软件对遗传变异进行等级剖分发现:24.88%的遗传变异存在于地理宗间(浙江地理宗和安徽地理宗),14.71%的遗传变异存在于居群间,60.42%存在于居群内。该研究结果表明,由于人为干扰引起的生境片断化和居群减小导致了毛柄小勾儿茶居群的遗传多样性丧失和遗传分化,并对毛柄小勾儿茶的生存造成潜在威胁。该文还就保育策略进行了讨论。     

Molecular evolution and diversity in Bacillus anthracis as detected by amplified fragment length polymorphism markers.

Bacillus anthracis causes anthrax and represents one of the most molecularly monomorphic bacteria known. We have used AFLP (amplified fragment length polymorphism) DNA markers to analyze 78 B. anthracis isolates and six related Bacillus species for molecular variation. AFLP markers are extremely sensitive to even small sequence variation, using PCR and high-resolution electrophoresis to examine restriction fragments. Using this approach, we examined ca. 6.3% of the Bacillus genome for length mutations and ca. 0.36% for point mutations. Extensive variation was observed among taxa, and both cladistic and phenetic analyses were used to construct a phylogeny of B. anthracis and its closest relatives. This genome-wide analysis of 357 AFLP characters (polymorphic fragments) indicates that B. cereus and B. thuringiensis are the closest taxa to B. anthracis, with B. mycoides slightly more distant. B. subtilis, B. polymyxa, and B. stearothermophilus shared few AFLP markers with B. anthracis and were used as outgroups to root the analysis. In contrast to the variation among taxa, only rare AFLP marker variation was observed within B. anthracis, which may be the most genetically uniform bacterial species known. However, AFLP markers did establish the presence or absence of the pXO1 and pXO2 plasmids and detected 31 polymorphic chromosomal regions among the 79 B. anthracis isolates. Cluster analysis identified two very distinct genetic lineages among the B. anthracis isolates. The level of variation and its geographic distribution are consistent with a historically recent African origin for this pathogenic organism. Based on AFLP marker similarity, the ongoing anthrax epidemic in Canada and the northern United States is due to a single strain introduction that has remained stable over at least 30 years and a 1,000-mile distribution.     

Inter- and intra-specific variation among five Erythroxylum taxa assessed by AFLP

BACKGROUND: and Aims The four cultivated Erythroxylum taxa (E. coca var. coca, E. novogranatense var. novogranatense, E. coca var. ipadu and E. novogranatense var. truxillense) are indigenous to the Andean region of South America and have been cultivated for folk-medicine and, within the last century, for illicit cocaine production. The objective of this research was to assess the structure of genetic diversity within and among the four cultivated alkaloid-bearing taxa of Erythroxylum in the living collection at Beltsville Agricultural Research Center. METHODS: Amplified fragment length polymorphism (AFLP) fingerprinting was performed in 86 Erythroxylum accessions using a capillary genotyping system. Cluster analysis, multidimensional scaling (MDS) and analysis of molecular variance (AMOVA) were used to assess the pattern and level of genetic variation among and within the taxa. KEY RESULTS: A clear distinction was revealed between E. coca and E. novogranatense. At the intra-specific level, significant differentiation was observed between E. c. var. coca and E. c. var. ipadu, but the differentiation between E. n. var. novogranatense and E. n. var. truxillense was negligible. Erythroxylum c. var. ipadu had a significantly lower amount of diversity than the E. c. var. coca and is genetically different from the E. c. var. ipadu currently under cultivation in Colombia, South America. CONCLUSIONS: There is a heterogeneous genetic structure among the cultivated Erythroxylum taxa where E. coca and E. novogranatense are two independent species. Erythroxylum coca var. coca is most likely the ancestral taxon of E. c. var. ipadu and a founder effect may have occurred as E. c. var. ipadu moved from the eastern Andes in Peru and Bolivia into the lowland Amazonian basin. There is an indication of artificial hybridization in coca grown in Colombia.     

Multivariate analysis of morphological variation among closely related species Bromus japonicus, B. squarrosus and B. arvensis (Poaceae) in comparison with isozyme evidences

Morphological variation and taxonomic continuum of 110 specimens of Bromus arvensis, B. japonicus and B. squarrosus were analysed to assess the morphological variability of these close taxa. The importance of every morphological character was estimated by the GLM procedure. Stepwise discriminant analysis was used in order to find a set of morphological characters that maximises differences among the species. According to this, the most important characters appeared to be the length of anthers, width of lemma and lemma margin angle shape. The most important characters for the determination of Bromus arvensis was the length of anthers and for B. squarrosus width of lemma. According to the UPGMA cluster analysis, canonical discriminant, classificatory discriminant and principal component analyses, all specimens were separated into three moderately distinct groups which corresponded to the three traditional species. The study showed that qualitative characters were the best for the delimitation of the tax a by statistical analyses and demonstrated the incongruity between the pattern of morphological and genetic (allozyme) variation among the three Bromus species.     

Spatial genetic structure of Aquilegia taxa endemic to the island of Sardinia

Background and Aims

The Mediterranean Basin is one of the most important regions for the Earth''s plant biodiversity; however, the scarcity of studies on fine scale patterns of genetic variation in this region is striking. Here, an assessment is made of the spatial genetic structure of all known locations of the three Sardinian endemic species of Aquilegia in order to determine the relative roles of gene flow and genetic drift as underlying evolutionary forces canalizing the divergence of Sardinian Aquilegia taxa, and to see if the spatial genetic structure found fits the current taxonomic differentiation of these taxa.

Methods

DNA from 89 individuals from all known locations of Aquilegia across Sardinia was analysed by means of amplified fragment length polymorphism (AFLP) markers. Both principal co-ordinates analysis (PCoA) and Bayesian clustering analyses were used to determine the spatial genetic structure irrespective of any taxonomic affiliation. Historical effects of gene flow and genetic drift were assessed by checking for the existence of isolation-by-distance patterns.

Key Results

STRUCTURE and PCoA analyses revealed a pattern of genetic variation geographically structured into four spatial genetic groups. No migration–drift equilibrium was detected for Aquilegia in Sardinia, when analysed either as a whole or in individual groups. The scenario approached a Case III pattern sensu Hutchinson and Templeton, which is associated with extreme isolation conditions where genetic drift has historically played a dominant role over gene flow.

Conclusions

The pattern of genetic variation of Sardinian taxa of Aquilegia indicates that genetic drift has been historically more influential than gene flow on population structure of Sardinian species of Aquilegia. Limited seed dispersal and divergent selection imposed by habitat conditions have been probably the main causes reinforcing post-Pleistocene geographical isolation of Aquilegia populations. The spatial genetic structure found here is not fully compatible with current taxonomic affiliations of Sardinian Aquilegia taxa. This is probably a consequence of the uncoupling between morphological and genetic patterns of differentiation frequently found in recently radiated taxa.     

Karyological Studies in Cunninchamia unicanaliculata and var. pyramidalis

Cunnighamia unicanaliculata D. Y. Wang et H. L. Liu and var. pyramidalis D. Y. Wang et H. L. Lin, two new taxa recently found in south-western Sichuan Province of China, have both a very restricted yet sympatric geographical distribution, including Dechang and Miyi districts.[7] There is a debate as regards the specific status of C. unicanaliculata. A comparative karyological investigation, including chromosome numbers, karyotype analyses and measurements of nuclear volume and DNA contents, was under- taken in order to shed some light on the phylogenetic relationships between these taxa and C. lanceolata (Lamb.) Hook. The kaxyotype formulas of the above two taxa and C. lanceolata are as follows: C.unicanaliculata; K(2n) = 22 =L8m+ S12m+S2sm; C. unicanaliculata var. pyramidalis: K(2n)= 22= L8m +S10m+S4sm; C. lanceolata (Type A): K(2n) =22 = Lsm+ S14m S2sm; C. lanceolata(TypeB): K(2n) = 22 = L8m + S14m . Frown the above karyotypes, we have found that C. unicanaliculata and var. pyrami- dalis, which are very similar to each other, are closely related to C. lanceolata (Type B), but seem more strongly differentiated in the following respects: (1) the former posses- sing 1--2 pairs of chromosomes with submedian primary constrictions each, while the latter with all chromosomes possessing median primary constrictions; (2) the satellites of the former being always located on the 4th pair of chromosomes, whereas the position of satellites of the latter varying with geographical distribution, being usually on the 1st and 4th pairs of chromosomes; (3) B-chromosomes being present in the latter (predominantly in the geographical races of southwestern China) but not seen in the former; (4) the average chromosome volume of C. unicanaliculata var. pyramidalis being 623.44, while those of the four geographical races of C. lanceolata being 667.2–796.0; (5) the comparative DNA amount of C. unicanaliculata var. pyramidalis being 5.54, while those of the various geographical races of C. lanceolata being 6.20–7.67. Upon an overall comparison of the data with regard to karyology, geographical distribution, ecology, morphology and isoenzymic patterns of the taxa in question, we come to the following conclusions. Cunninghamia unicanaliculata and var. pyramidalis are most likely taxa originated from natural populations of C. lanceolata. The extreme environmental conditions of the habitats axe thought to have played an important role in the production of these two new taxa. An elevation of over 2000 meters and the periodical aridity of climate of the habitat, which differed remarkably from those of C. lanceolata, made possible the isolation of alternative populations, accompanied by selection for adaptation to extreme environments. But the differences between these two newly found taxa and C. lanceolata are karyologically minor and morphologically quantitative and tend to display a more or less continuous variation pattern. It is, therefore, suggested that they are probably geographical races or ecotypes of C. lanceolata, and are not distinct enough from the latter to warrant specific status. It seems best to treat both C. unicanaliculata and var. pyramidalis as infraspecific catorories of C. lanceolata.     

Genetic diversity in Mediterranean diploid and tetraploid Bromus L. (section Bromus Sm.) populations.

The levels of genetic diversity assessed from allozyme data were investigated in 25 populations of Mediterranean Bromus intermedius, B. squarrosus, B. lanceolatus, and B. hordeaceus from Algeria. The geographically restricted diploids B. intermedius and B. squarrosus displayed less genetic diversity (the mean population gene diversity of Nei (Hu) ranged from 0.03 to 0.12) than the widespread tetraploid colonizers B. lanceolatus and B. hordeaceus (Hu = 0.07-0.27). Deviations from Hardy-Weinberg expectations in diploid populations of B. intermedius and B. squarrosus were observed owing to heterozygote excess at several loci and suggested that these self-fertilizing species may have substantial amounts of allogamy. Tetraploid populations of B. lanceolatus and B. hordeaceus were largely homozygous at homologous loci and frequently exhibited intergenomic fixed heterozygosity in accordance with their alloploid origin. Genetic variation at the infraspecific level was mostly distributed within populations in the four species, B. hordeaceus showing the lowest level of interpopulation differentiation (Gst = 0.06) and the highest level of gene flow (Nm = 3.75). Consistent gene flows are in agreement with the strongest intercontinental invasive behaviour of B. hordeaceus. Less differentiation was reported in the literature among later introduced B. hordeaceus populations from England and Australia, indicating reduced differentiation under the process of colonization. Moderate divergence occured among the four taxa, with interspecific genetic identities ranging from 0.87 to 0.93. In spite of substantial genetic similarity, species were clearly differentiated, with each tetraploid being more closely related to a diploid: B. hordeaceus to B. squarrosus and B. lanceolatus to B. intermedius.     

Genetic divergence, range expansion and possible homoploid hybrid speciation among pine species in Northeast China

Although homoploid hybrid speciation in plants is probably more common than previously realized, there are few well-documented cases of homoploid hybrid origin in conifers. We examined genetic divergence between two currently widespread pines in Northeast China, Pinus sylvestris var. mongolica and Pinus densiflora, and also whether two narrowly distributed pines in the same region, Pinus funebris and Pinus takahasii, might have originated from the two widespread species by homoploid hybrid speciation. Our results, based on population genetic analysis of chloroplast (cp), mitochondrial (mt) DNA, and nuclear gene sequence variation, showed that the two widespread species were divergent for both cp- and mtDNA variation, and also for haplotype variation at two of eight nuclear gene loci surveyed. Our analysis further indicated that P. sylvestris var. mongolica and P. densiflora remained allopatric during the most severe Quaternary glacial period that occurred in Northeast China, but subsequently exhibited rapid range expansions. P. funebris and P. takahasii, were found to contain a mixture of chlorotypes and nuclear haplotypes that distinguish P. sylvestris var. mongolica and P. densiflora, in support of the hypothesis that they possibly originated via homoploid hybrid speciation following secondary contact and hybridization between P. sylvestris var. mongolica and P. densiflora.     

Increased inbreeding and strong kinship structure in Taxus baccata estimated from both AFLP and SSR data

Habitat fragmentation can have severe genetic consequences for trees, such as increased inbreeding and decreased effective population size. In effect, local populations suffer from reduction of genetic variation, and thus loss of adaptive capacity, which consequently increases their risk of extinction. In Europe, Taxus baccata is among a number of tree species experiencing strong habitat fragmentation. However, there is little empirical data on the population genetic consequences of fragmentation for this species. This study aimed to characterize local genetic structure in two natural remnants of English yew in Poland based on both amplified fragment length polymorphism (AFLP) and microsatellite (SSR) markers. We introduced a Bayesian approach that estimates the average inbreeding coefficient using AFLP (dominant) markers. Results showed that, in spite of high dispersal potential (bird-mediated seed dispersal and wind-mediated pollen dispersal), English yew populations show strong kinship structure, with a spatial extent of 50–100 m, depending on the population. The estimated inbreeding levels ranged from 0.016 to 0.063, depending on the population and marker used. Several patterns were evident: (1) AFLP markers showed stronger kinship structure than SSRs; (2) AFLP markers provided higher inbreeding estimates than SSRs; and (3) kinship structure and inbreeding were more pronounced in denser populations regardless of the marker used. Our results suggest that, because both kinship structure and (bi-parental) inbreeding exist in populations of English yew, gene dispersal can be fairly limited in this species. Furthermore, at a local scale, gene dispersal intensity can be more limited in a dense population.     

Genetic diversity in cultivated carioca common beans based on molecular marker analysis

A wide array of molecular markers has been used to investigate the genetic diversity among common bean species. However, the best combination of markers for studying such diversity among common bean cultivars has yet to be determined. Few reports have examined the genetic diversity of the carioca bean, commercially one of the most important common beans in Brazil. In this study, we examined the usefulness of two molecular marker systems (simple sequence repeats - SSRs and amplified fragment length polymorphisms - AFLPs) for assessing the genetic diversity of carioca beans. The amount of information provided by Roger's modified genetic distance was used to analyze SSR data and Jaccards similarity coefficient was used for AFLP data. Seventy SSRs were polymorphic and 20 AFLP primer combinations produced 635 polymorphic bands. Molecular analysis showed that carioca genotypes were quite diverse. AFLPs revealed greater genetic differentiation and variation within the carioca genotypes (Gst = 98% and Fst = 0.83, respectively) than SSRs and provided better resolution for clustering the carioca genotypes. SSRs and AFLPs were both suitable for assessing the genetic diversity of Brazilian carioca genotypes since the number of markers used in each system provided a low coefficient of variation. However, fingerprint profiles were generated faster with AFLPs, making them a better choice for assessing genetic diversity in the carioca germplasm.     

峨眉山2种重楼属植物同域分化的分子遗传学及其形态学证据初探

对峨眉山2种重楼－小重楼（Paris polyphylla Smith var. minora S.F.Wang）、黒籽重楼（P. thibetica Franch）DNA进行了AFLP (扩增的限制性片段长度多态性)分析和形态上的差异分析。AFLP分析可知小重楼和黑籽重楼在DNA分子水平上表现出极为丰富的遗传多样性,每个种内个体间的相似性很大,但有明显种间的遗传差异。形态对比分析可知小重楼和黑籽重楼在花部性状上有明显的差异。AFLP和形态分析结果表明小重楼和黑籽重楼无论是在形态还是遗传上均有明显差异。它们之间已经有了明显的分化。     

Reproductive biology and species geographical distribution in the Melastomataceae: a survey based on New World taxa

Background and Aims

Floral variation, pollination biology and mating patterns were investigated in sunbird-pollinated Babiana (Iridaceae) species endemic to the Western Cape of South Africa. The group includes several taxa with specialized bird perches and it has been proposed that these function to promote cross-pollination.

Methods

Pollinator observations were conducted in 12 populations of five taxa (B. ringens subspp. ringens, australis, B. hirsuta, B. avicularis, B. carminea) and geographic variation in morphological traits investigated in the widespread B. ringens. Experimental pollinations were used to determine the compatibility status, facility for autonomous self-pollination and intensity of pollen limitation in six populations of four taxa. Allozyme markers were employed to investigate mating patterns in four populations of three species.

Key Results

Sunbirds were the primary pollinators of the five Babiana taxa investigated. Correlated geographical variation in perch size, flower size and stigma–anther separation was evident among B. ringens populations. Experimental pollinations demonstrated that B. ringens and B. avicularis were self-compatible with variation in levels of autonomous self-pollination and weak or no pollen limitation of seed set. In contrast, B. hirsuta was self-incompatible and chronically pollen limited. Estimates of outcrossing rate indicated mixed mating with substantial self-fertilization in all species investigated.

Conclusions

Despite the possession of specialized bird perches in B. ringens and B. avicularis, these structures do not prevent considerable selfing from occurring, probably as a result of autonomous self-pollination. In eastern populations of B. ringens, smaller flowers and reduced herkogamy appear to be associated with a shift to predominant selfing. Relaxed selection on perch function due to increased selfing may explain the increased incidence of apical flowers in some populations.     

红花玉兰与玉兰亚属几个种亲缘关系的AFLP分析

应用AFLP分子标记技术对红花玉兰与玉兰亚属几个种之间的亲缘关系,以及红花玉兰的分类地位进行了分析。9对引物对7个玉兰种的36个代表样株进行选择性扩增,共得到扩增谱带874条,其中多态性谱带635条。分析结果表明：各玉兰种间,红花玉兰与白玉兰、武当木兰的遗传相似度较高;玉兰亚属种间基于AFLP分析的聚类结果与形态学对种的划分基本吻合。红花玉兰不仅形态上与其它玉兰种有明显区别,AFLP分子标记也支持红花玉兰为一个独立的新种,多瓣红花玉兰变种与红花玉兰原变种为一个种。     

Glucosinolates,flea beetle resistance,and leaf pubescence as taxonomic characters in the genus Barbarea (Brassicaceae)

Glucosinolate content of leaves and roots, diversity in leaf pubescence, and resistance to two near-isogenic lines of the flea beetle Phyllotreta nemorum with or without an R-gene, were determined for 27 accessions of 7 Barbarea taxa, i.e. B. stricta, B. orthoceras, B. intermedia, B. verna, B. vulgaris var. vulgaris, the G-type of B. vulgaris var. arcuata and the P-type of B. vulgaris var. arcuata. Four variable glucosinolate biosynthetic characters were deduced. For (formally) homophenylalanine-derived glucosinolates: (1). Presence or absence of 2-hydroxylation, and if present, R- or S-configuration of 2-hydroxylation; (2). presence or absence of p-hydroxylation; and for tryptophan-derived glucosinolates: (3). presence or absence of N-methoxyglucobrassicin; and (4). presence or absence of 1,4-dimethoxyglucobrassicin. Three phenotypes of leaf-pubescence were observed; (1). glabrous to glabrate leaves; (2). glabrous to glabrate leaves with hairs along the edge; (3). pubescent leaves. The hairs were characterized as simple by scanning electron microscopy. Full resistance to a flea beetle line (ST) was found in B. vulgaris var. vulgaris and in the G-type of var. arcuata; partial resistance was found in B. verna and B. intermedia, while the remaining taxa were fully susceptible to the ST line. All investigated Barbarea taxa were susceptible to larvae from another line containing an R-gene, indicating a similar flea beetle resistance mechanism in the three resistant species. Most Barbarea taxa could be characterized by a particular combination of the investigated characters. The most aberrant was the P-type of B. vulgaris var. arcuata, and the taxonomic status of this type should be reconsidered.     

Environmental effects on grass-endophyte associations in the harsh conditions of south Patagonia

Cool-season grasses are frequently infected by Neotyphodium endophytes and this association is often considered as a mutualistic symbiosis. We examined the incidence of Neotyphodium in populations of Bromus setifolius, Phleum alpinum and Poa spiciformis, native and wide-spread grasses from south Patagonia, Argentina. The incidence of 36 populations of Bromus setifolius was studied in association with climatic and soil variables. 31 populations of Ph. alpinum were sampled in five different plant communities. Seventeen populations of P. spiciformis were sampled in three different plant communities. The association between incidence and climatic variables in Ph. alpinum and between incidence and soil fertility in P. spiciformis was investigated. In B. setifolius endophyte incidence was positively correlated with annual average rainfall contrary to the results found in Ph. alpinum. All the populations of P. spiciformis were infected by endophytes and the incidence was associated with plant community. The Neotyphodium-grass interaction is variable in natural populations, supporting the increasing evidence that the Neotyphodium-host interaction depends, in many cases, on the environmental conditions. Field observations suggest that in detrimental low growth conditions the association is not favoured, leading to a decrease in the endophyte frequency of infection or even to the complete loss of the association.