Comparative analysis of core collection sampling methods for mandarin germplasm based on molecular and phenotypic data

Gene banks have been established to conserve the genetic diversity of crop species. Large germplasm collections lead to management problems (space, maintenance costs, etc.), especially in collections involving species with recalcitrant seeds that must be maintained as growing plants. Core collections (CCs) are thus developed to reduce the size of large germplasm collections while keeping the maximum variability. This also facilitates fine phenotypic evaluation. In this study, several software packages (DARwin, PowerMarker and MSTRAT) and methods (Max length subtree, M strategy, simulated annealing and MinSD) were compared to define a mandarin (Citrus reticulata) CC. One hundred and sixty‐seven accessions were sampled from two germplasm collections, which were genotyped with 50 SSR, 24 InDel and 68 single nucleotide polymorphism markers. All the CC obtained were tested for the maintenance of the genetic variability parameters (Ho and He) of the initial collection, the level of linkage disequilibrium (LD) and the phenotypic diversity retention. The Max length subtree function from DARWin seemed to be the most appropriate method for establishing a CC in C. reticulata. It maintained 96.82% of the allelic richness and 17.96% of the size of the initial collection with only 30 accessions. Besides it did not increase the LD (r² value) of the initial collection and retained the vast majority of the phenotypic variability. However, a CC with 70 accessions would be more helpful for genetic association studies.     

Genetic differentiation analysis of African cassava (Manihot esculenta) landraces and elite germplasm using amplified fragment length polymorphism and simple sequence repeat markers

Molecular‐marker‐aided evaluation of germplasm plays an important role in defining the genetic diversity of plant genotypes for genetic and population improvement studies. A collection of African cassava landraces and elite cultivars was analysed for genetic diversity using 20 amplified fragment length polymorphic (AFLP) DNA primer combinations and 50 simple sequence repeat (SSR) markers. Within‐population diversity estimates obtained with both markers were correlated, showing little variation in their fixation index. The amount of within‐population variation was higher for landraces as illustrated by both markers, allowing discrimination among accessions along their geographical origins, with some overlap indicating the pattern of germplasm movement between countries. Elite cultivars were grouped in most cases in agreement with their pedigree and showed a narrow genetic variation. Both SSR and AFLP markers showed some similarity in results for the landraces, although SSR provided better genetic differentiation estimates. Genetic differentiation (Fst) in the landrace population was 0.746 for SSR and 0.656 for AFLP. The molecular variance among cultivars in both populations accounted for up to 83% of the overall variation, while 17% was found within populations. Gene diversity (H_e) estimated within each population varied with an average value of 0.607 for the landraces and 0.594 for the elite lines. Analyses of SSR data using ordination techniques identified additional cluster groups not detected by AFLP and also captured maximum variation within and between both populations. Our results indicate the importance of SSR and AFLP as efficient markers for the analysis of genetic diversity and population structure in cassava. Genetic differentiation analysis of the evaluated populations provides high prospects for identifying diverse parental combinations for the development of segregating populations for genetic studies and the introgression of desirable genes from diverse sources into the existing genetic base.     

SEXUAL REPRODUCTION AND GENETIC VARIATION IN THE SUBAERIAL ALGA CEPHALEUROS VIRESCENS (ULVOPHYCEAE,CHLOROPHYTA)

Cephaleuros virescens is a pantropical subaerial green alga with no known long‐range dispersal mechanisms. Sexual reproduction is relatively rare and may involve intragametangial fusion of identical, mitotically produced gametes. This situation may be a consequence of adaptation to the subaerial habitat. Genetic variation among populations of C. virescens may be very low and might be positively correlated to the distance (hence, time) separating populations. Thus, assessing the global biogeography of C. virescens requires analysis of what might be low levels of variation. Because C. virescens occurs on literally hundreds of different host species, the question of host‐races must also be considered. Preliminary analysis of local populations of C. virescens, originally obtained as field collections from three different host species and subsequently raised in culture, is the first step in addressing the biogeography of this alga. We are using the AFLP plant mapping protocol by PE Applied Biosystems to detect genetic variability in the three isolates of C. virescens. AFLP is a PCR‐based DNA fingerprinting technique that detects the presence or absence of restriction fragments rather than fragment length differences. Because the number of restriction fragments that can be detected with the AFLP technique is “virtually unlimited,” it is a very powerful tool for assessing the degree of relatedness or variability among cultivars or isolates. AFLP techniques have been used successfully to distinguish morphologically identical bacteria, determine relatedness among soybean accessions, reveal genetic variability within bee samples, and identifyfall armyworm strains and hybrids.     

Clonal genetic diversity and populational genetic differentiation in Phragmites australis distributed in the Songnen Prairie in northeast China as revealed by amplified fragment length polymorphism and sequence-specific amplification polymorphism molecular markers

Genetic variation within and between four naturally occurring Phragmites australis land populations, DBS, QG, SS1 and SS2 (named after locality), which colonise distinct habitats (different edaphic conditions) in the Songnen Prairie in northeast China, were investigated by amplified fragment length polymorphism (AFLP) and sequence‐specific amplification polymorphism (S‐SAP) markers. It was found that the selected primer combinations of both markers were highly efficient in revealing the inter‐clonal genetic diversity and inter‐populational genetic differentiation in P. australis from a molecular ecological perspective. Cluster analysis categorised the plants into distinct groups (DBS, QG and SS groups), which were in line with their localities, albeit the two SS group populations (SS1 and SS2) showed a lower degree of inter‐populational differentiation. These results were strongly supported by multiple statistical analysis including Mantel’s test, principal coordinate analysis, allocation test and analysis of molecular variance, which further suggested that gene flow, genetic drift and differences in as yet unidentified edaphic factors may all underpin the inter‐clonal genetic diversity and inter‐populational differentiation at the nucleotide sequence level. Analysis of intra‐population clonal diversity also revealed that the QG population harboured a strikingly lower amount of within‐population variation compared with those of the other three populations, presumably being caused by genetic drift and followed by physical and/or biological isolation. Homology analysis of a subset of population‐specific or population‐private AFLP and S‐SAP bands suggested that regulatory genes and retroelements might play important roles in the ecological adaptation and differentiation of the P. australis populations. Possible causes for and implications of the extensive genetic variability in P. australis were discussed for its future genetic conservation and use in ecological revegetation.     

Recovery and virulence phenotyping of the historic ‘Stubbs collection’ of the yellow rust fungus Puccinia striiformis from wheat

A unique collection of spore samples of Puccinia striiformis, often referred to as the ‘Stubbs collection’, has been stored in liquid nitrogen from 18 to 45 years. A subset of samples representing 35 countries and 28 years was investigated to assess recovery rate, race identity and previously undetected virulence. A new method for recovery using an airbrush sprayer and Novec? 7100 for inoculating the host plants was highly successful. Ninety‐six percent of 231 isolates were recovered. Virulence phenotyping was done using differential sets of wheat genotypes representing specific‐resistance genes. A total of 181 samples represented single genotypes (isolates), whereas 40 samples consisted of at least two genotypes. Race identity was confirmed for 102 of 181 single‐genotype isolates. The virulence phenotype was updated for additional 44 isolates based on improved resolution of results because of updated and more informative wheat‐differential sets. The remaining 35 isolates showed discrepancies for one or more virulences when compared with past results. Additional virulences corresponding to Yr17, Yr25 and Yr27, respectively, which were not assayed originally, were discovered. The value of biological collections for research and plant breeding is discussed along with the challenges of maintaining collections of biotrophic microorganisms.     

Reproductive ecology and genetic variability in natural populations of the wild potato,Solanum kurtzianum

The cultivated potato (Solanum tuberosum ssp. tuberosum) has more than 200 related wild species distributed along the Andes, adapted to a wide range of geographical and ecological areas. Since the last century, several collection expeditions were carried out to incorporate genetic variability into the potato germplasm around the world. However, little is known about the reproductive ecology and genetic population structure of natural potato population from field studies. The aim of this work is to study, in the field, the genetic variability and reproductive strategies of populations of one of the most widely distributed potato species in Argentina, Solanum kurtzianum, growing in Mendoza province. AFLP markers showed that the genetic variability is mainly present among plants within populations, indicating that in the sampled populations, sexual reproduction is more relevant than clonal multiplication (by tubers). Additional evidence was obtained evaluating the genetic diversity in populations with a distribution in patches, where several genotypes were always detected. From a field study performed in the Villavicencio Natural Reserve, we found that the average number of plump seeds per fruit was 94.3, identified and calculated the foraging distance of four insect pollinators, and demonstrated the seed dispersal by storm water channels. We argue that the breeding system, the two modes of reproduction and the ecological interaction described here may have a prominent role in determining the genetic structure of S. kurtzianum populations, and discuss the importance of field studies on population genetics, reproductive biology and ecology to design collections and conservation strategies.     

Genetic Similarity among Isolates of Pyrenophora tritici-repentis, Causal Agent of Tan Spot of Wheat

Tan spot, a foliar disease of wheat, is caused by the fungus Pyrenophora tritici‐repentis. On susceptible wheat cultivars, P. tritici‐repentis induces two distinct symptoms: tan necrosis and extensive chlorosis. Presently isolates of P. tritici‐repentis are classified into 11 races based on their virulence on a set of wheat differential genotypes. In nature, this pathogen reproduces both sexually and asexually, but the extent of genetic variability in the P. tritici‐repentis population of western Canada is unknown. This study was conducted to assess the genetic variability among different isolates of P. tritici‐repentis and to determine if similarities among isolates are correlated with race classification or geographic origin of the isolates. Thirty‐three isolates of P. tritici‐repentis and one isolate each of P. teres f. sp. teres, P. teres f. sp. maculata, P. graminea, Helminthosporium sativum and an uncharacterized isolate were studied with 30 random amplified polymorphic DNA (RAPD) primers. Cluster analysis showed that all isolates had unique banding patterns and that clustering of isolates was independent of their race designation or geographic origin. Analysis of molecular variation (amova ) showed that 96.8% of variability occurred among isolates and among race variability accounted for only 3.2% of the total variability.     

Teliospore-inducing activity for wheat leaf rust in the extracts of various host plant leaves infected with telia of rust fungi

MeOH and water extracts were obtained from 16 species of infected leaves with rust fungi belonging to 18 species in 6 families: Pucciniaceae, Melampsoraceae, Coleosporiaceae, Pileolariaceae, Phragmidiaceae, and Phakopsoraceae. All the extracts of rust-infected plants with telia showed the teliospore-inducing activity for wheat leaf rust (Puccinia recondita f. sp. tritici).     

Morphological and molecular diversity among populations of Quercus brantii Lindl. in western forest of Iran

Abstract

This study represents a preliminary step toward understanding the genetic structure of Persian oak in Iran. The genetic variability of Quercus brantii in Western forest of Iran was evaluated by amplified fragment length polymorphism (AFLP), chloroplast microsatellite and leaf morphology. Fifty-five trees from eight regions were sampled from across the range of Chaharmahal va Bakhtiari province of Iran. Twenty morphological traits were analyzed through clustering and ordination method. At morphological level, the applied statistics suggest that macromorphological traits significantly differentiate between populations. The overall sample shows a proportion of AFLP polymorphic markers of 92.1%, denoting a high level of variability. Based on AFLP data, differences among populations within geographic regions account for 11.6% of the total variation and only 0.57% is attributed to variation among regions. Based on chloroplast microsatellite (cpSSR), 34% of total variation was found among populations, suggesting a high within-population haplotype diversity. The dendrogram obtained from cpSSR showed a general pattern quite different from the pattern obtained from morphological analysis and AFLP markers.     

Genetic Diversity of Pyrenophora teres Isolates as Detected by AFLP Analysis

Amplified fragment length polymorphism (AFLP) analysis has been used to analyse mainly 83 Czech isolates of Pyrenophora teres, P. graminea, P. tritici‐repentis and Helminthosporium sativum. Each species had distinct AFLP profiles. Using 19 primer combinations 948 polymorphic bands were detected. All main clusters in dendrogram correspond to the studied species. Even the two forms of P. teres–P. teres f. teres (PTT) and P. teres f. maculata (PTM) – formed different clusters. Genetic diversity, with regard to the locality and the year of the sample's collection, was analysed separately within the AFLP‐based dendrogram cluster of PTT and PTM. Unweighted pair‐group method (UPGMA) analysis of the 37 isolates of PTT and 30 isolates of PTM, using 469 polymorphic bands, showed that the variability seemed to have been influenced more by the year of sampling than by the geographic origin of the isolate. The presence of intermediate haplotypes with a relatively high number of shared markers between the two groups indicated that hybridization between the forms of P. teres could happen, but it is probably often overlapped by selection pressure or genetic drift.     

Genetic variation in field and laboratory populations of the spined soldier bug,Podisus maculiventris

The predatory spined soldier bug, Podisus maculiventris (Say) (Heteroptera: Pentatomidae), is an economically important and highly valued biological control agent. There is substantial information on the biology, ecology, behavior, and rearing of this stink bug. However, virtually nothing is known of its genetic variation, in natural or domesticated populations. To address this lacuna, we used amplified fragment length polymorphism (AFLP) to assess the genetic variability of field and laboratory populations. Four AFLP universal primer combinations yielded a total of 209 usable loci. The AFLP results showed greater genetic variability between populations from Missouri and Mississippi (both USA), and relatively low variability within Missouri populations. We infer little genetic isolation among Missouri field populations and within laboratory populations, but a significant genetic isolation between Missouri and Mississippi populations.     

Genetic structure in cultivated and wild carrots (Daucus carota L.) revealed by AFLP analysis

Genetic variation within and among five Danish populations of wild carrot and five cultivated varieties was investigated using amplified fragment length polymorphism (AFLP). Ten AFLP primer combinations produced 116 polymorphic bands. Based on the marker data an UPGMA-cluster analysis and principal component analysis (PCA) separated the Daucus collections into three groups, consisting of the wild populations, the old varieties, and the recently bred varieties. The genetic distance between the wild populations reflected the physical distance between collection sites. Analysis of genetic diversity showed that the old varieties released between 1974 and 1976 were more heterogeneous than the newly developed F₁ hybrid varieties. The analysis of molecular variation (AMOVA) showed that the major part of the genetic variation in the plant material was found within populations/varieties. The presence of markers specific to the cultivated carrot makes it possible to detect introgression from cultivated to wild types. Received: 6 October 1999 / Accepted: 4 November 1999     

Molecular diversity and landscape genomics of the crop wild relative Triticum urartu across the Fertile Crescent

Modern plant breeding can benefit from the allelic variation that exists in natural populations of crop wild relatives that evolved under natural selection in varying pedoclimatic conditions. In this study, next‐generation sequencing was used to generate 1.3 million genome‐wide single nucleotide polymorphisms (SNPs) on ex situ collections of Triticum urartu L., the wild donor of the A^u subgenome of modern wheat. A set of 75 511 high‐quality SNPs were retained to describe 298 T. urartu accessions collected throughout the Fertile Crescent. Triticum urartu showed a complex pattern of genetic diversity, with two main genetic groups distributed sequentially from west to east. The incorporation of geographical information on sampling points showed that genetic diversity was correlated to the geographical distance (R² = 0.19) separating samples from Jordan and Lebanon, from Syria and southern Turkey, and from eastern Turkey, Iran and Iraq. The wild emmer genome was used to derive the physical positions of SNPs on the seven chromosomes of the A^u subgenome, allowing us to describe a relatively slow decay of linkage disequilibrium in the collection. Outlier loci were described on the basis of the geographic distribution of the T. urartu accessions, identifying a hotspot of directional selection on chromosome 4A. Bioclimatic variation was derived from grid data and related to allelic variation using a genome‐wide association approach, identifying several marker–environment associations (MEAs). Fifty‐seven MEAs were associated with altitude and temperature measures while 358 were associated with rainfall measures. The most significant MEAs and outlier loci were used to identify genomic loci with adaptive potential (some already reported in wheat), including dormancy and frost resistance loci. We advocate the application of genomics and landscape genomics on ex situ collections of crop wild relatives to efficiently identify promising alleles and genetic materials for incorporation into modern crop breeding.     

Methods of constructing core collections by stepwise clustering with three sampling strategies based on the genotypic values of crops

A genetic model with genotype×environment (GE) interactions for controlling systematical errors in the field can be used for predicting genotypic values by an adjusted unbiased prediction (AUP) method. Mahalanobis distance, calculated based on the genotypic values, is then applied to measure the genetic distance among accessions. The unweighted pair-group average, Ward’s and the complete linkage methods of hierarchical clustering combined with three sampling strategies are proposed to construct core collections in a procedure of stepwise clustering. A homogeneous test and t-tests are suggested for use in testing variances and means, respectively. The coincidence rate (CR%) for range and the variable rate (VR%) for the coefficient of variation are designed to evaluate the property of core collections. A worked example of constructing core collections in cotton with 21 traits was conducted. Random sampling can represent the genetic diversity structure of the initial collection. Preferred sampling can keep the accessions with special or valuable characteristics in the initial collection. Deviation sampling can retain the larger genetic variability of the initial collection. For better representation of the core collection, cluster methods should be combined with different sampling strategies. The core collections based on genotypic values retained larger genetic variability and had superior representatives than those based on phenotypic values. Received: 15 October 1999 / Accepted: 24 November 1999     

AFLP and RAPD Characterization of Phaeoacremonium aleophilum Associated with Vitis vinifera Decline in Spain

The genetic diversity among Spanish isolates of the fungus Phaeoacremonium aleophilum, one of the major causes of grapevine decline, was determined using random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) techniques. Using RAPD, a large genetic variation was observed among 36 Pm. aleophilum single‐spore cultures, with 76 (82.6%) polymorphic bands generated by 12 RAPD primers. A neighbour‐joining dendrogram showing the RAPD patterns of diversity revealed four groups of haplotypes. The Bayesian and principal components clustering analysis revealed three groups of haplotypes. When more than one isolate of Pm. aleophilum was obtained from a single vine, different haplotypes were found. Seventeen single‐spore isolates were used for AFLP analysis. Five primer combinations produced 358 scorable markers, of which 309 (86.3%) were polymorphic. The analysis based on genetic distance as well as clustering analysis confirmed three main groups largely in agreement with those returned by the RAPD results. The Mantel correlation between the RAPD and AFLP distance matrices ranged from R = 0.5931 to R = 0.6294. The high level of haplotype diversity among the RAPD and AFLP markers suggests that sexual reproduction and genetic recombination may occur between Pm. aleophilum haplotypes in Spain. The AFLP approach revealed a greater number of polymorphic markers. A relationship between the genetic profile of the infecting isolate of Pm. aleophilum and the age or decline symptoms of the grapevines may exist.     

Growth inhibition of plant pathogenic fungi by hydroxy fatty acids

Hydroxy fatty acids are plant self-defense substances (Masui et al, Phytochemistry1989). Three types of hydroxy fatty acids: 10-hydroxystearic acid (HSA), 7S,10S-dihydroxy-8(E)-octadecenoic acid (DOD), and 12,13,17-trihydroxy-9(Z)-octadecenoic acid (THOA) were tested against the following plant pathogenic fungi: Erysiphe graminis f sp tritici (common disease name, wheat powdery mildew); Puccinia recondita (wheat leaf rust); Pseudocercosporella herpotrichoides (wheat foot rot); Septoria nodorum (wheat glume blotch); Pyricularia grisea (rice blast); Rhizoctonia solani (rice sheath blight); Phytophthora infestans (potato late blight); and Botrytis cinerea (cucumber botrytis). At a concentration of 200 ppm, both HSA and DOD showed no fungal disease control activity. However, THOA at the same concentration showed weak activity and provided disease control (percent) of the following plant pathogenic fungi: Erysiphe graminis 77%; Puccinia recondita 86%; Phytophthora infestans 56%; and Botrytis cinerea 63%. The position of the hydroxy groups on the fatty acids seems to play an important role in activity against specific fungi. Journal of Industrial Microbiology & Biotechnology (2000) 24, 275–276. Received 12 August 1999/ Accepted in revised form 06 January 2000     

AFLP analysis shows high incongruence between genetic differentiation and morphology‐based taxonomy in a widely distributed tortoise

Morphology has traditionally been used to diagnose the taxa of various taxonomic ranks. However, there is growing evidence that morphology is not always able to reveal cryptic taxa, and that pronounced morphological variation could reflect phenotypic plasticity rather than evolutionary divergence. Spur‐thighed tortoises (the Testudo graeca complex), distributed in the western Palaearctic region, are characterized by high morphological variability and complicated taxonomy, which are under debate. Previous molecular studies using mainly mitochondrial DNA (mtDNA) sequences have revealed incongruence between genetic differentiation and morphology‐based taxonomy, suggesting that morphological variability is the result of phenotypic plasticity and stabilizing selection, which masks the true genealogies. In the present study, we used a range‐wide sampling and nuclear Amplified fragment length polymorphism (AFLP) markers to investigate genetic differentiation within the T. graeca complex. We found that spur‐thighed tortoises are differentiated into four geographically well‐defined AFLP groups: Balkans–Middle Eastern, western Mediterranean, Caucasian and central‐eastern Iranian. Compared with the distribution of mtDNA lineages, the groups are largely concordant, although the AFLP markers are less sensitive and distinguish fewer groups than do mtDNA sequences. The AFLP groups show an allopatric or parapatric distribution. The AFLP differentiation conflicts with the previously proposed morphology‐based taxonomy of the complex, suggesting that local adaptation to different environmental conditions may have led to the great extent of morphological variation within the same lineages. We propose a re‐evaluation of the taxa that were confirmed genetically using a thorough morphological analysis corrected for phenotypic plasticity. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Population Structure of Puccinia recondita in Western Europe During 1995, as Assessed by Variability in Pathogenicity and Molecular Markers

The population structure of Puccinia recondita f. sp. tritici (Prt) in western Europe was examined by assessing variability in pathogenicity and in randomly amplified polymorphic DNA (RAPD) among 61 single uredinial isolates. The isolates were chosen to represent pathotypes detected in a previous survey of pathogenic variability in the fungus in western Europe in 1995. Thirty‐five pathotypes were identified by assessing infection types produced by the 61 isolates on 24 differential lines, each with a single gene for resistance to Prt. In contrast, only 18 RAPD phenotypes were identified by scoring 19 polymorphic RAPD bands generated with eight RAPD primers. When analysed by cluster and bootstrap analyses, the pathogenicity and RAPD results revealed little evidence for robust distinct clusters among the isolates. Multiple isolates of several pathotypes collected from widely separated locations such as Belgium, Germany, France, Italy and Switzerland had the same RAPD phenotype, providing evidence of clonal migration over considerable distances in western Europe. Some variability (one or two band differences) was observed in RAPD phenotype within several pathotypes, indicating the possible occurrence of genetic changes independent of pathogenicity, and/or the independent development of pathotypes with different genetic backgrounds. Two groups of isolates identified in the 1995 survey, differentiated by pathogenicity for genes Lr3a, Lr3bg, Lr3ka and Lr30, were not distinguished by RAPD phenotype, indicating that the groups probably do not constitute separate lineages within the pathogen population. Little correlation was apparent between the polymorphisms observed in pathogenicity and RAPD phenotypes. The similarity in the genetic backgrounds of the isolates, as assessed by RAPD markers, suggest that the observed differences in pathogenicity may have arisen by selection for specific virulences corresponding to genes for resistance in wheat cultivars grown in the region. Three isolates of pathotype 3, restricted in its distribution to southern France during 1995, were distinct from all other isolates in RAPD phenotype. Circumstantial evidence suggests that this pathotype originated from northern Africa, and that it belongs to a group of leaf rust pathogens specialized to durum wheats.     

Evidence for regional diversity and host adaptation in Iranian populations of the Russian wheat aphid

Effective pest management is greatly facilitated by knowledge of the genetic structure and host adaptation of the pest species in question. The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) (Homoptera: Aphididae: Macrosiphini), is an important economic pest in many cereal‐growing areas of the world, and in this study we investigated these aspects of its populations, using microsatellite markers and host plant response assays. Diuraphis noxia was sampled from 38 locations in Iran and genotyped at four polymorphic microsatellite loci that had been isolated from various Sitobion species. We identified 50 multilocus genotypes in 376 individuals. The overall observed heterozygosity was 0.134. F‐statistics showed a regional partitioning in D. noxia populations with overall F_ST = 0.231. In addition, there was a significant correlation between genetic and geographic distances. In order to test for the ecological consequences of genetic variability in D. noxia, biotypic variation amongst the isolates collected from wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) was evaluated on a number of resistant and susceptible wheat varieties. The plant variables we measured were damage rating (based on leaf chlorosis, leaf rolling, wilting, and death of the host plant), host plant dry weight, and root length. Damage rating was the best criterion for detecting biotypic variation in D. noxia. Discriminant analysis correctly classified the isolates in respective groups in 80–91.8% of the cases. The barley isolate showed no differences in performance on resistant and susceptible wheat, indicating a lack of gene‐by‐gene relationship with wheat plants. In contrast, wheat isolates differentially damaged the resistant and susceptible plants and showed moderate to severe virulence.     

A reconsideration of the domestication geography of tetraploid wheats

The domestication of tetraploid wheats started from their wild progenitor Triticum dicoccoides. In this paper, the geographical distribution of this progenitor is revised to include more sampling locations. The paper is based on a collection of wild and domesticated lines (226 accessions in total) analyzed by AFLP at 169 polymorphic loci. The collection includes the 69 wild lines considered by Mori et al. (2003) in their study on chloroplast DNA haplotypes of T. dicoccoides. The goal of the experiment was to reconsider which location thought to have generated the domesticated germplasm has the highest chance of being the actual site from which wild progenitors were sampled during domestication. Phylogenetic analysis of the nuclear AFLP databases indicates that two different genetic taxa of T. dicoccoides exist, the western one, colonizing Israel, Syria, Lebanon and Jordan, and the central-eastern one, which has been frequently sampled in Turkey and rarely in Iran and Iraq. It is the central-eastern race that played the role of the progenitor of the domesticated germplasm. This is supported by the cumulative results of the AFLP data from the collections of Ozkan et al. (2002) and of Mori et al. (2003), which indicate that the Turkish Karacadag population, intermixed with some Iraq-Iran lines, has a tree topology consistent with that of the progenitor of domesticated genotypes. The Turkish Kartal population belongs genetically to the central-eastern T. dicoccoides race but at the nuclear DNA level is less related to the domesticated gene pool. A general agreement between published work on tetraploid wheat domestication emerges from these results. A disagreement is nevertheless evident at the local geographical scale; the chloroplast DNA data indicate the Kartal mountains while AFLP fingerprinting points to the Karacadag Range as the putative site of tetraploid wheat domestication.