Barley Isolates Research Articles

Aphanomyces macrosporus sp. nov. Causing Root Rot in Barley and Some Other Plants.

In recent years, a new root rot disease in barley, which is caused by an Aphanomyces species, was found in field surveys in Southern Sweden and Denmark. Its symptoms occurred at the early tillering stage, around the BBCH 21 growth stage, and included the yellowing of leaves, brown coleoptiles, and the discolouration of roots. Prolonged soil wetness after rainfall favoured disease development, which sometimes advanced the yellowing patches to entire fields, resulting in lower yields. Oospores were found in the fine roots of diseased plants, and Aphanomyces isolates were obtained from these roots, as well as from the roots of barley plants grown in the greenhouse in soil samples from infected fields. Based on morphological analysis, we found that the new isolates were similar to those already obtained from barley and spinach roots in the 1990s in the same growing area. The morphological and molecular analyses performed in this study clearly separated and distinguished these barley isolates from other known Aphanomyces, and hereby Aphanomyces macrosporus sp. nov. is proposed as a new plant pathogenic species. It has larger oogonia and oospores than A. euteiches, A. cochlioides, and A. cladogamus, with one up to eight diclinous antheridia per oogonium. The phylogenetic analysis of the ITS rDNA region sequences grouped these new Aphanomyces isolates in a monophyletic clade, which was clearly distinguished from other plant pathogenic Aphanomyces species. The further pathogenicity of A. macrosporus on other plants is currently under investigation, but it is clear that it can at least infect barley, spinach, and sugar beet, indicating a wide host range for this species. The widespread presence and presumably broad host range of this new pathogenic Aphanomyces species must be considered in crop rotations.

Description of Clavibacter zhangzhiyongii sp. nov., a phytopathogenic actinobacterium isolated from barley seeds, causing leaf brown spot and decline.

Clavibacter michiganensis is a Gram-stain-positive bacterium with eight subspecies, five of which have been redefined as different species on the basis of their genome sequence data. On the basis of the results of phylogenetic analysis of dnaA gene sequences, strains of members of the genus Clavibacter isolated from barley have been grouped in a separate clade from other species and subspecies of the genus Clavibacter . In this study, the biochemical, physiological, fatty acids and genetic characteristics of strains DM1T and DM3, which represented the barley isolates, were examined. On the basis of results from multi-locus sequence typing and other biochemical and physiological features, including colony colour, carbon source utilisation and enzyme activities, DM1T and DM3 are categorically differentiated from the aforementioned eight species and subspecies of the genus Clavibacter . Moreover, the results of genomic analysis reveal that the DNA G+C contents of DM1T and DM3 are 73.7 and 73.5 %, respectively, and the average nucleotide identity (ANI) values between DM1T and DM3 and other species and subspecies range from 90.4 to 92.0 %. The ANI value between DM1T and DM3 is 98.0 %. These results indicate that DM1T and DM3 are distinct from other known species and subspecies of the genus Clavibacter . Therefore, we propose a novel species, C. zhangzhiyongii, with DM1T (=CFCC 16553 T=LMG 31970T) as the type strain.

دامنهی میزبانی جمعیتهای مختلف زنگ برگی گندم در ایران

In order to investigate the host range of various populations of causal agent of wheat leaf rust, Puccinia. recondita sensu lato, during 2010-2016, fifty isolates of the pathogen were collected from different hosts of Poaceae in various parts of Iran including: Ardabil, Fars, Golestan, Ilam, Kerman, Khuzestan, Khorasan Razavi, Kurdistan, Mazandaran and West Azerbaijan. Pathogenicity of all isolates on seven hosts, including bread wheat (Triticum aestivum L., cv. Boolani), durum wheat (Triticum durum Desf., cv. Karkhe & cv. Yavaroos), barley (Hordeum vulgare L., cv. Afzal), oat (Avena sativa L.), rye (Secale montanum Guss.) and triticale (Triticosecale Wittm. Ex A. Camus) was examined. Results indicated that all isolates had high disease severity on bread wheat (cv. Boolani) and triticale. Bread wheat isolates were avirulent on all hosts except for triticale, which showed a hypersensitive reaction or small, dispersed pustules. Triticale isolates were only pathogenic on triticale and bread wheat. Durum wheat isolates were virulent on bread wheat, durum wheat, and triticale, and were avirulent on barley and rye plants. Oat isolates showed an avirulence response on barley, rye and various genotypes of durum wheat and rye. Barley isolates were also pathogenic on bread wheat, triticale and barley and avirulent on durum wheat and rye. Although wild barley isolates were virulent on bread wheat, durum wheat, and triticale, they were avirulent on other hosts. Oat is a non-host for all leaf rust isolates, except for its own isolates. The findings indicate that in the absence of wheat, leaf rust populations are able to survive on other members of the Poaceae family.

Host range, mating type and population structure of Magnaporthe sp. of a single barley field in São Paulo state, Brazil

AbstractBrazil is blast disease hot spot because severe epidemics have occurred among wheat, triticale, rye, barley and oat crops. Although the first outbreak of barley blast appeared in 1998, little information is available. Therefore, this study aimed to examine host range, mating type composition and population structure of Magnaporthe sp. from a single barley field in São Paulo, Brazil. To examine pathogenicity, 25 Magnaporthe isolates were inoculated on five, three, two and two cultivars of barley, wheat, oat and rice, respectively, and one cultivar each of rye, corn, sorghum, triticale and certain weeds (Cenchrus echinatus, Setaria geniculata, Brachiaria plantaginea and Eleusine indica). Mating type distribution of 33 isolates was investigated by molecular tools. The genotypic divergence of 41 barley and five wheat isolates was investigated by 15 random amplified polymorphic DNA primers and unweighted pair group method with arithmetic mean. The host range of the barley blast pathogen included wheat, oat, rye and triticale but not rice and weeds. Sexual reproduction appeared to not be involved in the high genotypic diversity because only a single isolate, MAT1‐2, was identified. The majority of barley isolates clustered together with wheat blast, except for four, suggesting a different origin.

Rare Pyrenophora teres Hybridization Events Revealed by Development of Sequence-Specific PCR Markers.

Pyrenophora teres f. teres and P. teres f. maculata cause net form and spot form, respectively, of net blotch on barley (Hordeum vulgare). The two forms reproduce sexually, producing hybrids with genetic and pathogenic variability. Phenotypic identification of hybrids is challenging because lesions induced by hybrids on host plants resemble lesions induced by either P. teres f. teres or P. teres f. maculata. In this study, 12 sequence-specific polymerase chain reaction markers were developed based on expressed regions spread across the genome. The primers were validated using 210 P. teres isolates, 2 putative field hybrids (WAC10721 and SNB172), 50 laboratory-produced hybrids, and 7 isolates collected from barley grass (H. leporinum). The sequence-specific markers confirmed isolate WAC10721 as a hybrid. Only four P. teres f. teres markers amplified on DNA of barley grass isolates. Amplified fragment length polymorphism markers suggested that P. teres barley grass isolates are genetically different from P. teres barley isolates and that the second putative hybrid (SNB172) is a barley grass isolate. We developed a suite of markers which clearly distinguish the two forms of P. teres and enable unambiguous identification of hybrids.

Streptomyces strains producing mitochondriotoxic antimycin A found in cereal grains

Reasons for mammalian cell toxicity observed in barley and spring wheat grains were sought. Streptomyces sp. isolates from wheat and barley produced heat-stable methanol-soluble substances which inhibited the motility of exposed porcine spermatozoa used as a toxicity indicator. Several barley isolates produced antimycin A (2 to 5ng/mg wet wt of biomass), a macrolide antibiotic known to block oxygen utilization in mitochondria. The antimycin-producing isolates were members of the Streptomyces albidoflavus group. In in vitro assays with porcine kidney tubular epithelial cells, the specific toxicity of antimycin A towards mitochondria was higher than that of the mycotoxin enniatin B but lower than that of the mitochondriotoxins cereulide and paenilide, produced by food-related Bacillus cereus and Paenibacillus tundrae, respectively. The toxic wheat isolates, related to Streptomyces sedi, did not produce antimycin A and or any other known toxin. Our results suggest that the presence of toxin-producing streptomycetes in stored cereal grains may pose a thus far unrecognized threat for food and feed safety.

Sequence diversity of wheat mosaic virus isolates

Wheat mosaic virus (WMoV), transmitted by eriophyid wheat curl mites (Aceria tosichella) is the causal agent of High Plains disease in wheat and maize. WMoV and other members of the genus Emaravirus evaded thorough molecular characterization for many years due to the experimental challenges of mite transmission and manipulating multisegmented negative sense RNA genomes. Recently, the complete genome sequence of a Nebraska isolate of WMoV revealed eight segments, plus a variant sequence of the nucleocapsid protein-encoding segment. Here, near-complete and partial consensus sequences of five more WMoV isolates are reported and compared to the Nebraska isolate: an Ohio maize isolate (GG1), a Kansas barley isolate (KS7), and three Ohio wheat isolates (H1, K1, W1). Results show two distinct groups of WMoV isolates: Ohio wheat isolate RNA segments had 84% or lower nucleotide sequence identity to the NE isolate, whereas GG1 and KS7 had 98% or higher nucleotide sequence identity to the NE isolate. Knowledge of the sequence variability of WMoV isolates is a step toward understanding virus biology, and potentially explaining observed biological variation.

Rhizoctonia cerealis anastomosis group GAG-1, the common pathogen of wheat, barley and sugar beet

Isuluies of <i>Rhizoctonia cerealis</i> anastomosis group GAG-1 were obtained from sharp eyespot lesions on wheat and on barley culms and from diseased sugar beet seedlings. Isolates of <i>R. cerealis</i> were collected from a fields with crop rotation experiments: sugar beet-spring wheat-winter barley. In pathogenicity tests isolates of <i>R. cerealis</i> from sugar beet seedlings and from sharp eyespot lesions on wheat and barley were pathogenic to these crops. Isolates of <i>R. cerealis</i> from sharp eyespot lesions on wheat and barley caused severe damping-ofTof sugar beet. Isolates of <i>R. cerealis</i> from sugar beet seedlings also caused symptoms of sharp eyespot on wheat and barley. None of the wheat and barley isolates of <i>R. cerealis</i> tested caused root-rot on wheat or barley seedlings. Isolates of <i>R. cerealis</i> obtained from diseased plants of wheat, barley and sugar beet were similar in morphology of cultures and anastomosed with GAG-1 tester isolate. The relatinoship between anastomosis. colony characters, growth rate, hyphal diameter and pathogenicity of AG-4. AG-2-2 and AG-5 isolates obtained together with <i>R. cerealis</i> from diseased plants were also investigated.

Role of Melanin in Release of Extracellular Enzymes and Selection of Aggressive Isolates of Bipolaris sorokiniana in Barley

Eighteen barley isolates of Bipolaris sorokiniana belonging to wild and clonal type of black, mixed and white subpopulations were quantitatively assayed for their melanin content and aggressiveness with respect to production of some of the extracellular enzymes such as cellulase, pectinase, amylase and protease. Cellulase and pectinase constituted major portion of the enzymes recovered from the black, mixed and white isolates. Enzyme production and aggressiveness were relatively higher in melanin devoid or low melanin isolates. The melanin deficient isolates were also differentiated from black and mixed isolates on the basis of variation in internal transcribed spacer region of the ribosomal DNA. Higher enzyme productions positively correlated with area under disease progress curve (AUDPC) and lesion development. Melanin content was negatively correlated with extracellular enzymes and aggressiveness of the isolates. Based on melanin content, lesion size, AUDPC and extracellular enzymes, the isolates were grouped in two major clusters (I and II) with further division of cluster II into two sub-clusters (II-A and II-B). The results appears to indicate a possible role of melanin in release of extracellular enzymes and hence in evolution and selection of aggressive isolates of B. sorokiniana in barley.

Analysis of complete genomes of isolates of the Wheat dwarf virus from new geographical locations and descriptions of their defective forms

Recently, the importance of the Geminiviruses infecting cereal crops has been appreciated, and they are now being studied in detail. Barley and wheat strains of Wheat dwarf virus are recorded in most European countries. Information on complete sequences of isolates from the United Kingdom, Spain, and Austria are reported here for the first time. Analysis revealed that their sequences are very stable. Recombination between strains was recorded only for the barley strain. We identified several defective forms of the barley strain from barley and wheat, which do not influence symptom expression. Sequences of barley isolates infecting wheat were obtained that did not differ from the isolates from barley. Based on specific features of the SIR of the barley strains, it is suggested that they are assigned to one of the two proposed new clusters, A1 or A2.

First Report of Wheat dwarf virus and Its Vector (Psammotettix provincialis) Affecting Wheat and Barley Crops in Syria

A field survey covering the major cereal-production areas of Syria was conducted during May 2009. A total of 938 wheat and 971 barley samples with typical symptoms of viral infection were collected from 45 wheat and 58 barley fields. All collected samples were tested by the tissue-blot immunoassay (1) at the Virology Laboratory of ICARDA, Syria using six specific cereal virus antisera, including polyclonal antibody AS-0216 for Wheat dwarf virus (WDV) provided by the German Collection of Microorganisms and Cell Cultures (DSMZ). Serological tests showed that WDV was detected in 16 wheat (cv. Cham 8) and five barley (cv. Arabic abiad) samples collected from Al-Hasskah governorate (eastern region of Syria) and showing dwarfing, yellowing, and reduced heading. Samples that reacted with WDV antiserum were transmitted from infected plants to healthy plants of oat (Avena sativa L.), barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), and some grass species using four different leafhopper species, collected from Syrian wheat and barley fields, in a persistent manner. Leafhopper transmission tests indicated that only Psammotettix provincialis Ribaut was able to transmit Syrian barley WDV isolates (SB 1248-09 and SB 1249-09) from infected barley plants to healthy barley (48 plants became infected of 50 plants inoculated) and oats (45 of 50) under greenhouse conditions. The identity of P. provincialis was confirmed by the British Museum. Total DNA was extracted from six WDV-positive samples (three wheat and three barley) and tested by PCR using WDV primer set (WDV-F: 5'-TTGAGCCAATCTTCGTC-3'; WDV-R: 5'-GGAAAGACTTCCTGGGC-3') described by Oluwafemi (2). All six Syrian WDV-positive samples generated amplicons around the expected size (~253 bp). The amplicons from one isolate from wheat (SW 2131-09, GenBank Accession No. HQ113095) and one isolate from barley (SB 1248-09, GenBank Accession No. HQ113096) showed they had 86% sequence identity with each other, suggesting that both isolates can be considered to belong to the same species (3). Barley isolate SB 1248-09 had 99% sequence identity to an Iranian isolate of Barley dwarf virus (FJ620684.1) and 92% identity to most European barley-WDV isolates (e.g., Germany [AM942044.1] and Hungary [FM999832.1]), whereas, the wheat isolate (SW 2131-09) had 98 to 100% identity with most European wheat-WDV isolates (e.g., Czech Rep [FJ546191.1] and Germany [AM296023.1]) and a Chinese isolate (EF536868.1). WDV has been reported to infect cereals in few countries in West Asia and North Africa (Turkey, Tunisia, and Morocco) and causes economic losses on wheat in many countries in Europe (e.g., Sweden). WDV has been reported to be transmitted in a persistent manner only by leafhoppers (P. alienus Dahlbom) (4) to a wide range of cereal and wild grasses. Two strains of WDV are known, one that primarily infects wheat and another that infects barley. To our knowledge, this is the first record of WDV (both strains) infecting wheat and barley crops in Syria and the first report of P. provincialis as a WDV vector worldwide.

Widespread occurrence and molecular characterization of Wheat dwarf virus in Iran

Wheat dwarf virus (WDV), genus Mastrevirus, was associated with yellowing and dwarfing of wheat and barley in many parts of Iran. The complete nucleotide sequence of a barley isolate of the virus consisted of 2733 nucleotides and was most similar to barley isolates of WDV from Turkey, Czech Republic and Germany, but different enough to be regarded as a new strain of the virus. Phylogenetic analysis indicated that mastreviruses causing yellows and dwarfing in wheat and barley form two distinct groups. The Iranian and European barely isolates fall in one group while all wheat isolates are placed in another group. These results confirmed the division of WDV isolates into two distinct strains. WDV was also found in mixed infection with barley yellow dwarf viruses (BYDVs) in barley and wheat plants. Using dot blot hybridization with the full ssDNA genome of the Iranian barley isolate of WDV as a probe and PCR with primers which amplified the full length DNA of the virus, WDV was detected in 46 of 211 BYDV positive barley and wheat samples from northern, northwestern, northeastern, central and southern Iran. It is concluded that in addition to BYDVs, WDV is a major component of the yellows complex in cereal fields in Iran.

Studies on the host range of the barley strain of Wheat dwarf virus using an agroinfectious viral clone

Comparative analysis of the host ranges of the barley and wheat strains of Wheat dwarf virus (WDV; family Geminiviridae; genus Mastrevirus) in Europe has been severely hampered by the lack of an infectious clone of the barley strain. To remedy this situation an agroinfectious clone of a Hungarian isolate of the barley strain (WDV‐Bar[HU]) was constructed and its virulence tested in barley (Hordeum vulgare), wheat (Triticum aestivum), rye (Secale cereale) and oat (Avena sativa) by agroinoculation. Although all four species could be systemically infected by the isolate, infections were asymptomatic in the rye and oat cultivars tested. WDV‐Bar[HU] induced chlorosis and stunting symptoms typical of WDV in barley, while in wheat low infection rates but high mortality of infected seedlings were observed. In contrast, a much higher percentage of wheat plants agroinoculated with a wheat‐strain isolate (WDV‐[Enk1]) became systemically infected. WDV‐[Enk1] in wheat caused symptoms similar to those caused by WDV‐Bar[HU] in barley. WDV‐Bar[HU] was leafhopper‐transmissible to barley seedlings, in which it caused typical WDV symptoms; geminate virus particles were isolated from the infected leaves. Comparison of the genomic sequences of 11 barley strain isolates from Europe and Turkey revealed that whereas WDV‐Bar[HU] represents a typical barley‐strain isolate that is not detectably recombinant, the Turkish barley isolate (WDV‐Bar[TR]) is probably a recombinant between a barley‐strain isolate and an as‐yet‐undescribed WDV‐like mastrevirus species.

Four QTL in Rice Associated with Broad Spectrum Resistance to Blast Isolates from Rice and Barley

Pyricularia grisea is the most destructive and cosmopolitan fungal pathogen of rice and it can also cause disease on other agriculturally important cereals. We determined the number, location and interaction of quantitative trait loci (QTL) associated with resistance to P. grisea isolates obtained from rice (THL142 and THL222) and barley (TH16 and THL80) grown in Thailand. The isolates showed a spectrum of virulence when used to inoculate a series of differentials. We used a reference blast resistance mapping population of rice (IR64 x Azucena). IR64 was highly resistant, and Azucena was highly susceptible, to all four isolates. The numbers of resistant vs. susceptible progeny suggest that the resistance of IR64 is determined by two or three genes with additive effects. The correlation coefficients for all pairwise comparisons of disease severity were high and highest between barley isolates and between rice isolates. Four QTL were detected, one on each of the following chromosomes 2, 8, 9 and 10. IR64 contributed resistance alleles at three of the QTL (chromosomes 2, 8 and 9). Azucena contributed the resistance allele at the QTL on chromosome 10 in response to inoculation with isolate THL142. The results of the QTL analysis support interpretation of the phenotypic frequency distributions regarding the number of genes determining resistance to the four isolates in this population. Our results are novel in adding blast isolates from barley to the catalogue of pathogen specificities to which a gene, or genes, from IR64 confer resistance.

First Report of Barley yellow dwarf virus-PAS in Wheat and Barley Grown in the Czech Republic.

Barley yellow dwarf disease, an important, ubiquitous virus disease of cereal crops worldwide, is caused by a group of related single-stranded RNA viruses assigned to luteovirus (Barley yellow dwarf virus (BYDV) spp. PAV, PAS, MAV, and GAV) or polerovirus (Cereal yellow dwarf virus-RPV) genera or unassigned to a genera (BYDV-SGV, BYDV-RMV, and BYDV-GPV) in the family Luteoviridae (2). Incidence of BYDV in cereal crops (e.g., barley, wheat, and oats) was high and reached epidemic levels in recent years in many regions of the Czech Republic. Previously, only PAV isolates have been identified here on the basis of serological detection (4), although antibodies to differentiate between PAV, PAS, and MAV are not widely available. Field samples of cereal crops were routinely tested in 2006 and 2007 and BYDVs were detected by ELISA. One-step-reverse transcription (RT)-PCR (Qiagen, Hilden, Germany) was adapted for BYDV detection using primer pairs BYcpF (5'-CCACTAGAGAGGTGGTGAATG-3') and BYcpR (5'-CCGGTGTTGAGGAGTCTACC-3') designed from conserved sequences identified by aligning multiple BYDV sequences available in public databases. These primers amplify a 641-bp fragment spanning nucleotides 2839-3479 from PAV (GenBank Accession No. EF043235) or PAS (GenBank Accession No. NC_002160) that includes a region of the coat protein gene and the intergenic region. RT-PCR amplicons were generated from two field isolates, PS-RuJK (spring wheat isolate, cv. Granny, collected in July 2007 from experimental plots at the CRI in Prague) and JE-120JK (winter barley isolate, cv. Merlot, collected in January 2008 from a barley field in Rychnov), both of which induced severe BYD symptoms. Amplicons were sequenced in both directions in a CEQ2000XL sequencer (Beckman Coulter, Fullerton, CA). The partial coat protein gene sequence of 483 nt of PS-RuJK and JE-120JK was analyzed and compared with available sequences of 26 PAV, 17 PAS, and 13 MAV isolates by MEGA4 (3). PS-RuJK (GenBank Accession No. EU863652) nucleotide and amino acid sequence identities ranged from 96.3 to 99.2% and 93.7 to 98.7%, respectively, for available PAS isolates, and 89.9 to 90.5% and 85.5 to 86.9%, respectively, for available PAV isolates, and 78.3 to 79.5% and 70.0 to 72.5%, respectively, for available MAV isolates. Similarly, nucleotide and amino acid sequence identities JE-120JK (GenBank Accession No. EU863653) ranged from 95.2 to 98.6% and 90.6 to 96.9%, respectively, for PAS isolates, 88.8 to 90.1% and 83.1 to 84.4%, respectively, for PAV isolates, and 77.6 to 78.7% and 67.5 to 70.0%, respectively, for MAV isolates. Also, both of these isolates have the conserved amino acid motif "SIPGS" that is usually present in a variable region of the coat protein gene on the surface of virion (1) at position 52 to 56 of amino acid sequences of all published PAS-like isolates, including Vd29:AY167109, FH1:AJ223588, MA9516:AJ007926, FL2:AJ223586, ASL-1:AJ810418, and WS6603:DQ285680, contrary to "PVFRP" or "LISGP" motif in PAV or MAV, respectively. Therefore, the sequence data clearly confirm that these two isolates belong to the PAS species. To our knowledge, this is the first record of PAS detected in the Czech Republic.

The complete genome sequence for a Turkish isolate of Wheat dwarf virus (WDV) from barley confirms the presence of two distinct WDV strains

The complete genome for a barley isolate of Wheat dwarf virus (WDV) from Tekirdağ, Turkey, WDV-Bar[TR], was isolated and sequenced. The genome was found to be 2739 nucleotides long, which is shorter than wheat-infecting WDV isolates, and with a genome organization typical for mastreviruses. The complete genome of WDV-Bar[TR] showed 83-84% nucleotide identity to wheat isolates of WDV, with the non-coding regions SIR and LIR least conserved (72-74% identity). The deduced amino acid sequences for Rep and RepA were most conserved (92-93%), while CP and MP were less conserved (87% and 79-80%, respectively). The identity to other mastrevirus species was significantly lower. In phylogenetic analyses, the WDV isolates formed a distinct clade, well separated from the other mastreviruses with the wheat isolates grouping closely together. Phylogenetic analyses of WDV-Bar[TR], the partial sequence for another Turkish barley isolate (WDV-Bar[TR2]) and published WDV sequences further supported the division of WDV into two distinct strains. The barley strain could also be divided into three subtypes based on relationships and geographic origin. This study shows the first complete published sequence for a barley isolate of WDV.

Pathogenicity of fungi associated with wheat and barley seedling emergence and fungicide efficacy of seed treatment

Presented study focused on the influence of Cochliobolus sativus isolates origin on pathogenicity towards wheat and barley seedlings in comparison with pathogenicity of certain Fusarium species and Microdochium nivale. The efficacy of fungicide seed treatment against C. sativus was estimated. The C. sativus isolates were collected from different locations and were isolated from wheat, barley and sunflower seeds. The pathogenicity of C. sativus, Fusarium species and M. nivale towards germinating seedlings were expressed as germination (GA) retardation and coleoptile growth rate retardation (CGR). Of wheat only, the CGR was significantly influenced by the isolate origin. The C. sativus isolates obtained from sunflower seeds were the most aggressive. Of the barley seeds, the barley isolates were the most aggressive. Barley was significantly more susceptible to damage by C. sativus isolates than wheat. The pathogenicity of tested fungal species declined in the order: F. culmorum, F. graminearum, C. sativus, F. avenaceum, M. nivale, F. poae for both barley and wheat. The results highlighted high pathogenicity potential of C. sativus equal to that of F. avenaceum and M. nivale. The symptoms of C. sativus on coleoptile and roots were very similar or the same as the symptoms caused by Fusarium species and M. nivale, except of white, pink or red colours.

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

AbstractEffective 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 FST = 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.

Investigating the Antimicrobial Efficacy of a Lactococcal Bacteriocin for the Development of Microbiologically Stable Beer

Barley isolate Lactococcus lactis M30 produces an antimicrobial proteinaceous activity, which at least under laboratory conditions was shown to target beer spoiling lactic acid bacteria, including Lactobacillus brevis BSH9. The aim of this study was to investigate the application of this antibacterial activity at various stages of the brewing process and in packaged beer. Lactococcus lactis M30 was shown to produce the antimicrobial activity during growth under specific conditions in fortified unhopped wort. However, this activity was lost during wort boiling and yeast fermentation. When the bacteriocin was added directly to beer it retained in vitro activity following pasteurisation, while it was also shown to inhibit growth in situ when pasteurised beer was challenged with low levels of the beer spoiling Lactobacillus brevis BSH9 culture. The capacity of the bacteriocin to prevent microbial spoilage of beer was tested at various temperatures over a period of seven weeks. Storage of bacteriocin-containing beer at 30°C or room temperature resulted in a decrease in antimicrobial activity over time, but when refrigerated or frozen, this beer retained sufficient activity to be effective against Lactobacillus brevis BSH9.

The effect of fungal density on fungicide dose-response curves in barley powdery mildew (Erysiphe graminis f.sp. hordei)

The effect of inoculation density on fungicide dose-response curves and the estimated ED 50 value (the fungicide concentration needed to halve the infected leaf area relative to the infected area of leaves that had not been treated with a fungicide) ) were investigated theoretically, arid predictions were tested experimentally using powdery mildew of barley (Erysiphe graminis [syn. Blumeria graminis] f.sp. hordei). A host leaf was assumed to consist of a number of independent compartments, in each of which only a single fungal spore could germinate successfully. The number of fungal spores landing in a compartment was assumed to be Poisson-distributed. The spores were assumed to vary in their sensitivity toward a fungicide, and the sensitivity of the spore population was assumed to he normally distributed around a mean sensitivity. Under these assumptions, the ED 50 value was shown to be a positively biased estimate of the mean sensitivity in the fungal population, and the bias increased with inoculum density. Consequently, the estimated ED 50 value is expected to vary between experiments and laboratories if the inoculation density varies over a considerable range. The correlation between inoculum density and estimated ED 50 value is expected to be strongest when the assayed fungal population consists of several genotypes differing in sensitivity. This expectation was tested by estimating the ED 50 values for one barley powdery mildew isolate at different inoculation densities for three different fungicides. These ED 50 values were positively correlated strongly with the inoculum density for fenpropimorph and more weakly for triadimenol, whereas no correlation was observed for propiconazole.