Assessment of genetic diversity in emmer (Triticum dicoccon Schrank) × durum wheat (Triticum durum Desf.) derived lines and their parents using mapped and unmapped molecular markers

In the last few years, the renewed interest for emmer wheat (Triticum dicoccon Schrank) in Italy has stimulated breeding programs for this crop releasing improved genotypes obtained not only by selection from landraces, but even by crosses with durum wheat (Triticum durum Desf.) varieties. The purpose of this work has been to uncover the genetic make-up of some emmer × durum derivatives, specifically by comparing the differences from their parents. Genetic diversity of advanced breeding lines and varieties derived from a durum × emmer cross has been evaluated on the basis of AFLP and SSR markers in comparison with the corresponding emmer and durum wheat parent for addressing the seminal question of how much ‘wild’ variation remains after selection for agronomic type.     

Evaluation for resistance to Pyrenophora tritici-repentis in Aegilops tauschii Coss. and synthetic hexaploid wheat amphiploids

Summary A total of 59 diploid Aegilops tauschii Coss. (syn. Aegilops sguarrosa auct. non L.) and 39 synthetic hexaploid wheat accessions were evaluated for reaction to Pyrenophora tritici-repentis (Died.) Drechs. in a controlled environment, and classified using a disease rating system based on lesion type. 27 Ae. tauschii and 20 synthetic wheats were found to be resistant to tan spot disease. The overall mean disease ratings of Ae. tauschii and the synthetic wheat lines scored on a scale of 1 (resistant) to 5 (susceptible) were 1.80 and 2.38, respectively. Synthetic wheats generally showed a decrease in resistance, although several lines of synthetic wheat expressed a higher resistance than the diploid parents. Five synthetic wheat lines exhibited higher resistance than the standard resistant common wheat cultivar Red Chief.     

Agronomical,quality, and molecular characterization of twenty Italian emmer wheat (<Emphasis Type="Italic">Triticum dicoccon</Emphasis>) accessions

Emmer wheat (Triticum dicoccon Schrank, 2n = 4x = 28) consists in a hulled wheat; its cultivation has been drastically reduced during the last century as a consequence of its low yield. Recently, its agronomic and nutritive values, as well as the increase of popularity of organic agriculture, have led to a renewed interest making its cultivation economically viable in the marginal lands with an increase of the cultivated areas. In Italy, it mainly survives in few marginal lands of central and southern Italy, where local varieties, adapted to the natural environment from where they originate, are used; moreover, some selected lines have also been developed. In the present work, agro-morphological and qualitative traits, together with molecular analyses of 20 emmer accessions consisting of Italian landraces, breeding lines, and cultivars, were performed. The field experiments were conducted for two consecutive years (2001/2002–2002/2003) in two locations: Viterbo in central Italy, and Foggia in south Italy. The analyzed emmer wheat accessions showed a good amount of genetic variability for both evaluated agro-morphological and molecular traits. This study illustrates an increase in earliness, GY, TW, TKW, and YI going from landraces, breeding lines to cultivars, while the variability does not change proportionally.     

Simple sequence repeats marker polymorphism in emmer wheat (<Emphasis Type="Italic">Triticum dicoccon</Emphasis> Schrank): Analysis of genetic diversity and differentiation

Genetic diversity was investigated in 73 accessions of emmer wheat (Triticum dicoccon Schrank) from 11 geographical regions using a set of 29 simple-sequence repeat (SSR or microsatellite) markers, representing at least two markers for each chromosome. The SSR primers amplified a total of 357 different alleles with an average of 12.31 alleles per locus. The number of fragments detected by each primer ranged between 6 (Xgwm1066) and 21 (Xgwm268). Null alleles were detected in nine of the 29 primers used. A high level of gene diversity index was observed. Across the 29 primers, gene diversity ranged from 0.60 (Xgwm46) to 0.94 (Xgwm655), with a mean of 0.82. There was a highly significant correlation (r=0.882; p<0.01) between gene diversity index and the number of loci, showing the number of loci per se is a strong indicator of diversity. Analysis of genetic diversity within and among eleven geographical regions revealed most of the genetic diversity of the total sample resided within regions. The coefficient of gene differentiation (Gst = 0.27) showed that the genetic variation within and among the 11 geographical regions was 73 and 27%, respectively. High value of mean number of alleles per locus was found in Iran (4.86) followed by Morocco (4.10) and Armenia (4.03). On the contrary, lower mean number of alleles per locus was detected in Yemen (2.83). The average gene diversity index across regions ranged from 0.52 (Slovakia) to 0.67 (Morocco) with an average of 0.60. Multivariate techniques of principal component analysis and clustering were employed to examine genetic relationship among the 73 emmer wheat accessions vis-à-vis geographical regions of collections. The genetic distance coefficients for all possible 55 pairs of regional comparisons ranged from 0.63 (between Iran and Armenia, Georgia and Azerbaijan, Georgia and Slovakia) to 0.97 (between Morocco and Yemen, Spain and Georgia, and Turkey and Iran) with a mean of 0.82. From the PCA results, a two dimensional plot of PC1 versus PC2 was constructed. The scatter plot of the first two principal components which explained altogether 27% of the total variation depicted the presence of a clear pattern of geographical differentiation except in few cases like accessions from Caucasian region. Similar pattern of genetic relationships among accessions was observed in cluster analysis. The study provided genetic information of emmer wheat in relation to geographical regions of origin. The information could be utilized in crop improvement, germplasm conservation programs, and in further investigation.     

Genetic diversity of winter wheat in Shaanxi province, China, and other common wheat germplasm pools

Cultivated Chinese wheat germplasm has been a valuable genetic resourcein international plant breeding. Landraces endemic to China are a geneticresource that is distinct from other wheat germplasm. Patterns of geneticdiversity among cultivated Chinese accessions and relationship to othergermplasm pools are unknown, despite the proven value and potential novelty. Theobjective of this work was to determine the level of genetic diversity withinimproved Chinese germplasm in the context of several other wheat germplasmpools. We analyzed a set of improved accessions cultivated from the 1940s to the1990s in Shaanxi province, China, using six simple sequence repeat (SSR) primerpairs and 30 restriction fragment length polymorphism - probe enzymecombinations (RFLP-PEC) previously used to characterize 21 geographically basedgermplasm pools. Shaanxi germplasm consists of three groups based on foreignintroductions from Italy, Australia, Denmark, and Russia. There was a decreasein genetic diversity among Shaanxi accessions cultivated in the 1970s and 1980sto the 1990s, and accession classifications based on primary decade ofcultivation were found to be significantly undifferentiated. The analysis of themean genetic distance among 22 geographically based pools of germplasm suggestsseveral regions are significantly undifferentiated. A vast majority of the totalamount of variation was found within pools; therefore, pools appear to belargely differentiated based on small differences in band relative frequency andfew if any unique bands. Previous studies have identified some Chinese landracepools as morphologically and genetically unique. The Shaanxi pool does not havethe same unique morphological or genetic features, nor is it more similar to thelandrace pools than other improved germplasm pools.     

Resistance to wheat leaf rust in Aegilops tauschii Coss. and inheritance of resistance in hexaploid wheat

A collection of 164 Aegilops tauschii accessions, obtained from Gatersleben, Germany, was screened for reaction to leaf rust under controlled greenhouse conditions. We have also evaluated a selection of synthetic hexaploid wheats, produced by hybridizing Ae. tauschii with tetraploid durum wheats, as well as the first and second generation of hybrids between some of these resistant synthetic hexaploid wheats and susceptible Triticum aestivum cultivars. Eighteen (11%) accessions of Ae. tauschii were resistant to leaf rust among which 1 was immune, 13 were highly resistant and 4 were moderately resistant. Six of the synthetic hexaploid wheats expressed a high level of leaf rust resistance while four exhibited either a reduced or complete susceptibility compared to their corresponding diploid parent. This suppression of resistance at the hexaploid level suggests the presence of suppressor genes in the A and/or B genomes of the T. turgidum parent. Inheritance of leaf rust resistance from the intercrosses with susceptible bread wheats revealed that resistance was dominant over susceptibility. Leaf rust resistance from the three synthetics (syn 101, syn 701 and syn 901) was effectively transmitted as a single dominant gene and one synthetic (syn 301) possessed two different dominant genes for resistance.     

Evaluation of Gossypium arboreum L. Germplasm for resistance to thrips

Summary As part of a project to assess the U.S. Asiatic Cotton Germplasm Collection as a source of genes for pest resistance, forty-three accessions of Gossypium arboreum L. were evaluated for resistance to thrips. Thrips, Thysanoptera spp., are a minor, but widespread pest on cotton, G. hirsutum L. and G. barbadense L. Accessions were planted in free-choice field tests in 1988, 1989, and 1990 at the Cotton Branch Experiment Station, Marianna, Arkansas. Damage ratings, based on a scale of 0 (no damage) to 7 (severe damage), were made approximately one month after planting. Relative score was computed by dividing the rating of each accession by the rating of the reference, G. hirsutum Stoneville 506. The relative score averaged over all G. arboreum accessions by year varied with the year, but was less than 100 (relative score for Stoneville 506) in each case. When data were combined for all three years, twenty-five accessions were significantly better than Stoneville 506. Introgression of the better accessions into G. hirsutum is now in progress.Abbreviations NPGS National Plant Germplasm System - STV 506 G. hirsutum Stoneville 506     

Evaluation of cultivated and wild barley for resistance to pathotypes ofPuccinia hordei with wide virulence

An isolate ofPuccinia hordei (ND89-3) originally collected in Morocco is virulent on most barley genotypes reported to possess resistance, except cultivar Estate (CI 3410), which possesses theRph3 gene and exhibits a low to intermediate level of resistance (infection type 12). Isolate ND89-3 possesses one of the widest virulence spectrums reported forP. hordei. Accessions ofHordeum vulgare (1,997 in total) andH. spontaneum (885 in total), mostly originating from the Mediterranean region and parts of North Africa, were evaluated with isolate ND89-3 at the seedling stage to identify new sources of leaf rust resistance. Fifty-eight accessions ofH. vulgare, and 222 accessions ofH. spontaneum exhibited low infection types to this isolate. Further evaluations of these resistant accessions with isolates ofP. hordei virulent forRph3,Rph7, andRph12 suggested that most of the resistantH. vulgare accessions possess theRph3 gene. Data suggested additional sources of effective resistance inH. vulgare are rather limited. FiveH. vulgare accessions and 167H. spontaneum accessions were identified as possible sources of new genes for leaf rust resistance. These accessions likely possess resistance genes that are different fromRph1 toRph12, or gene combinations thereof based on their reaction to four leaf rust isolates. Utilization of these accessions in barley breeding will broaden the germplasm resources available for genetic control ofP. hordei. North Dakota Agricultural Experiment Station Journal Series No. 2123. The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.     

Variation in resistance to the cabbage aphid ( Brevicoryne brassicae) between and within wild and cultivated Brassica species

Seven Brassica species were evaluated for their resistance to the cabbage aphid, Brevicoryne brassicae, in a series of field experiments. Four wild Brassica species, two 8 chromosome species with similarities to the B genome of Brassica nigra (Brassica fruticulosa and Brassica spinescens) and two 9 chromosome species containing the C genome (Brassica incana and Brassica villosa) were identified as possessing consistently high levels of antibiosis mediated resistance to B. brassicae. None of the species were shown to possess consistently high levels of antixenosis resistance. In more detailed glasshouse experiments one B-like genome species, B. fruticulosa, showed considerable variation between accessions collected from different sites for resistance to B. brassicae. In addition, individual accessions of one A genome species (Brassica rapa) and one C genome species (Brassica alboglabra) were shown to be highly variable in their resistance to B. brassicae, some plants of each accession being highly resistant and others very susceptible. The implications of the variability in resistance to B. brassicae within wild Brassica species for exploitation in Brassica breeding programmes are discussed.     

Detection of genetic diversity in Libyan wheat genotypesusing wheat microsatellite markers

Twenty-four wheat microsatellites (WMS) wereused to estimate the extent of genetic diversity among 15 Libyanwheat genotypes. The WMS used determined 26 loci located on 20different chromosomes, and were capable of detecting 116 alleles withan average of 4.5 alleles per locus. Only two markers located on 2DSand 4DL, were monomorphic. The results indicated that the B genome(5.9 alleles per locus) was more variable than the A and Dgenomes (4.1 and 2.7 alleles per locus, respectively).Furthermore, the results obtained suggest that a relatively smallnumber of primers can be used to distinguish all genotypes used andto estimate their genetic diversity. Genetic dissimilarity valuesbetween genotypes, calculated by the WMS derived data, were used toproduce a dendrogram. The diversity within the analysed germplasm isdiscussed.     

Evaluation of wild Lactuca species for resistance of natural infection of powdery mildew (Erysiphe cichoracearum)

Summary The 99 accessions of seven wild Lactuca species (L. serriola, L. saligna, L. virosa, L. viminea, L. perennis, L. tenerrima, L. tatarica) and Mycelis muralis (syn. L. muralis) were tested for natural infection of Erysiphe cichoracearum L. serriola accessions were highly susceptible. L. saligna showed highly variable levels of resistance. Other Lactuca species were mostly resistant or only moderately susceptible.     

Genetic diversity in Ethiopian hexaploid and tetraploid wheat germplasm assessed by microsatellite markers

The genetic diversity of a subset of the Ethiopian genebank collection maintained at the IPK Gatersleben was investigated applying 22 wheat microsatellites (WMS). The material consisted of 135 accessions belonging to the species T. aestivum L. (69 accessions), T. aethiopicum Jacubz. (54 accessions) and T. durum Desf. (12 accessions), obtained from different collection missions. In total 286 alleles were detected, ranging from 4 to 26 per WMS. For the three species T. aestivum, T. aethiopicum and T. durum on average 9.9, 7.9 and 7.9 alleles per locus, respectively, were observed. The average PIC values per locus were highly comparable for the three species analysed. Considering the genomes it was shown that the largest numbers of alleles per locus occurred in the B genome (18.4 alleles per locus) compared to A (10.1 alleles per locus) and D (8.2 alleles per locus) genomes. Genetic dissimilarity values between accessions were used to produce a dendrogram. All accessions could be distinguished, clustering in two large groups. Whereas T. aestivum formed a separate cluster, no clear discrimination between the two tetraploid species T. durum and T. aethiopicum was observed.     

Resistance gene analog polymorphisms (RGAPs) in wild emmer wheat (<Emphasis Type="Italic">Triticum dicoccoides</Emphasis>) and their ecological associations

Using the 8 specific primer pairs based on the conserved motifs of plant resistance genes, the plant disease resistance gene analog polymorphisms (RGAPs) in 15 wild emmer wheat (Triticum dicoccoides) populations from Israel had been detected. High genetic variations at the RGAP loci were observed in T. dicoccoides populations. A total of 254 discernible bands were obtained among 115 accessions, and 192 bands (75.6%) were polymorphic. Each genotype had a unique banding profile, and the genetic similarity coefficient ranged from 0.094 to 0.862. In T. dicoccoides, the proportion of polymorphic loci (P), the genetic diversity (He) and Shannon’s information index were 0.756, 0.362 and 0.541, respectively. The proportion of polymorphic loci (P) per population averaged 0.732 (range: 0.515–0.932); genetic diversity (He) averaged 0.271 (range: 0.212–0.338); and Shannon’s information index averaged 0.404 (range: 0.310–0.493). The coefficients of genetic distance (D) among populations averaged 0.107 (range: 0.043–0.178), and the results of Mantel test (r = 0.168, P = 0.091) showed that the estimates of genetic distance were geographically independent. Neighbor-joining cluster analysis suggested that the genetic relationships of T. dicoccoides populations were associated with their ecogeographic distribution. The hierarchical analysis of molecular variance (AMOVA) and the coefficient of gene differentiation (G _ST ) values revealed that most of the variations were presented within populations, although significant differences among populations and regions were also detected. The values of P and Shannon’s information index were negatively correlated with the two factors: Tdd (day–night temperature difference) and Ev (mean annual evaporation), whereas they were positively correlated with one water factor: Rn (mean annual rainfall). The correlation matrix between He in the RGAPs and geographic variables contained 20 significant (P < 0.05) correlations. The present study established that T. dicoccoides in Israel had a considerable amount of genetic variations at RGAP loci at least partly correlated with ecological factors.     

Phenotypic responses of the wild wheat relative Aegilops geniculata Roth and wheat (Triticum durum Desf.) to experimentally imposed salt stress

In order to study the salt effect on the wild wheat and durum wheat, three accessions of Aegilops geniculata L. from Ain zana, Zaghouan, and Sbitla and one variety of wheat (Triticum durum L.) have been grown in the INRAT green house and treated with different salt concentrations. The morphological, phenological and yield characters have been measured for each plant and analyzed using SAS software. This study has shown a high degree of variation of these characters mainly related to geographical origin. It was observed also that Sbitla accession was less affected by the imposed salt stress than all the others while Ain zana was the most affected one.     

Genetic diversity and intra-specific phylogeny of Triticum turgidum L. subsp. dicoccon (Schrank) Thell. revealed by RFLPs and SSRs

Today, emmer wheat, T. turgidum subsp. dicoccon, widely grown in the past is a candidate crop for sustainable agriculture in Italy. As part of a research project aimed at the enhanced use of the hulled wheat germplasm, molecular characterization was carried out to understand the genetic structure of the crop and to identify accessions of interest. A collection of 194 accessions was analyzed with 15 microsatellite loci (SSRs), while only a sample of 38 accessions was tested with 19 RFLP probes. The marker loci were selected on the basis of their independent genomic distribution. Genetic distances and allelic frequencies were calculated for each marker class. The genetic relationships were visualized with dendrograms. RFLP loci were, on average, less polymorphic than SSRs. An average Dice's genetic distance of 0.22 for RFLPs vs 0.38 for SSRs was detected, while an expected average heterozygosity per locus of 0.23 for RFLPs vs 0.26 for SSRs was also estimated. With a least number of 10 loci per marker class it was possible to identify each genotype. The most diverse accessions had different geographic origins. Germplasms from Italy and Ethiopia appear to belong to a more primitive genepool, given that a group of accessions from these countries were genetically differentiated from a Russian-Iranian group.     

苯并噻二唑(BTH)诱导小麦对条锈病抗性的研究

小麦条锈病是小麦生产中的重要病害之一,为了明确苯并噻二唑(Benzothiadiazole,BTH)对小麦条锈病的诱导抗性作用,分别以BTH处理后的苗期和成株期小麦为试验材料,诱发接种小麦条锈菌后调查小麦的发病情况及防治效果。温室苗期试验结果表明,与对照相比,不同浓度BTH处理后,小麦抗锈性明显提高,病情指数降低29.69~49.77,防治效果可高达90%左右,不同浓度处理之间有一定差异,但与对照相比差异极显著;BTH诱导的最佳浓度为0.3 mmol·L-1,BTH喷雾处理后6~7 d小麦诱导抗锈性表达最强,诱导抗性的持久期在15 d以上。田间成株期试验结果表明,不同浓度处理诱导的小麦抗锈性无明显差异,浓度为0.3 mmol·L-1的BTH诱导处理小区小麦的产量最高,千粒重最重,为42.21 g,增产最高达19.3%。小麦在分蘖期、拔节前期和分蘖期+拔节前期喷施BTH,都能诱导小麦抗条锈性增强,病情指数显著降低,防治效果分别为43.07%、47.43%和50.01%,增产13.4%~16.9%。综上所述,BTH可以诱导小麦产生抗锈性,对小麦条锈病防治起到积极作用。     

Characterisation and Variation of Morphological Traits and Storage Proteins in Spanish Emmer Wheat Germplasm (<Emphasis Type="Italic">Triticum Dicoccon</Emphasis>)

Emmer wheat is hulled wheat that was wide cultivated in Spain at the past. Actually, the most of this germplasm is conserved in Germplasm Banks, and only two small populations have been found in Asturias (North of Spain) in a recent collecting mission. In this work, a collection of 31 Spanish emmer lines developed from identical number of accessions of two Germplasm Banks was analysed for morphological spike traits and seed storage protein composition. Up to seven different botanical varieties were detected, which suggest the presence of a wide diversity, although lower than the historically described 10 botanical varieties. At level of seed storage proteins, the lines showed a high diversity, although the new alleles were present with low frequency in materials with scarce agronomic interest for the farmers (var. atratum, var. lagascae or var. pycnurum). This last circumstance could translate in a lost of variability by genetic drift.     

Variation and genetic diversity for gliadins in Spanish spelt wheat accessions

Gliadin composition has been analysed in 403 accessions of spelt wheat (Triticum aestivum ssp. spelta); 61 different patterns were found for the -gliadins, 44 for the -gliadins, 19 for the -gliadins and 15 for the -gliadins. A subset of 333 accessions belonging to fifty populations from Asturias, North of Spain, showed high levels of genetic variation (A = 3.89, P = 0.88, Ne = 3.35 and He = 0.553), indicating that 82.5% of the genetic variation was within populations, and only 18.5% among populations. Thirty-five of these populations presented more of five accessions, in this new subset the values of genetic variation were higher that those of fifty populations (A = 4.49, P = 0.91, Ne = 3.80 and He = 0.595). The genetic variation within populations was 59.7% of the total, and 40.3% among populations, which could be associated to fixation effects of some alleles by genetic drift.     

Host-plant resistance to Pseudomonas solanacearum in tomato germplasm

Seedlings of two hundred and thirty-three accessions of the tomato collection maintained at the Centro Agronómico Tropical de Investigación y Enseñanza, Turrialba, Costa Rica (CATIE) and 7 cultivars used as controls were evaluated for host-plant resistance to 4 virulent strains of Pseudomonas solanacearum representing race 1 biovars 1 and 3. In general, biovar 3 strains wilted seedlings faster than biovar 1 strains but, after 20 days post-inoculation, no significant differences were noted in susceptible control ratings. Significant differences for disease index were noted, but no line with complete resistance was found. For the USA biovar 1 strain UW-25, only 5 accessions, CATIE 17331, 17334, 17349, 17739, 17740, and 2 of the control cultivars, Hawaii 7998 and UC-82B showed some degree of resistance. Conversely, both the frequency and the degree of resistance were high for Costa Rican biovar 1 strain UW-256. For biovar 3, the Costa Rican strain UW-255 was more virulent than the Peruvian strain UW-130. Eight CATIE accessions, 5539, 17331, 17333, 17334, 17345, 17349, 17742, and MIP-CH1, were as resistant as the resistant control Hawaii 7998 to 3 strains and accession 17740 was as resistant as Hawaii 7998 to all 4 strains.Journal Paper No. J-16011 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 3123.     

Chromosomal distribution and genetic expression of Lophopyrum elongatum (Host) A. Löve genes for adult plant resistance to stripe rust in wheat background

A set of wheat cv. Chinese Spring (CS)-Lophopyrum elongatum addition and substitution lines has been analyzed for its potential to offer new sources of stripe rust resistance for wheat. The adult plants of these lines, together with CS-L. elongatum amphiploid and CS, were inoculated by new physiological races CYR-30 and CYR-31 of stripe rust in China. The resistance investigation indicated that chromosome 7E1 of L. elongatum was responsible for the adult resistance in CS background. Moreover, the expression of the adults plant resistance derived from chromosome 7E1 in wheat background was dependent on the wheat genotype. In addition, the different rust resistance and glutenin composition were observed in 2 CS-L. elongatum amphiploids, indicating the genetic diversity existed in different origins of L. elongatum.