Spot Form Of Net Blotch Research Articles

Spot form of net blotch, caused byPyrenophora teresf.maculata, is the most prevalent foliar disease of barley in Victoria, Australia

Surveys of incidence and severity of foliar diseases in a total of 127 barley (Hordeum vulgare) crops throughout Victoria were carried out during 2007 and 2008. In each crop, 100 tillers were assessed for disease symptoms on the top four leaves. Spot form of net blotch caused by Pyrenophora teres f. maculate had the highest incidence, being present in more than 90% of crops surveyed, with severity ranging from 0 to 42%. Scald caused by Rhynchosporium secalis had the second highest incidence, being found in 13 and 23% of crops in 2007 and 2008, respectively, with severity ranging from 0 to 16%. Leaf rust caused by Puccinia hordei was present in 13 and 18% of crops in 2007 and 2008, respectively, with severity of up to 3%. Powdery mildew caused by Erysiphe graminis was present in 11 and 9% of crops in 2007 and 2008, respectively, with severity below 0.1%. No other diseases, such as the net form of net blotch caused by P. teres f. teres were detected. The high incidence of spot form of net blotch, which can cause up to 44% grain yield loss, suggests that resistance traits need to be made a priority and targeted by barley breeding programs in Victoria for control of this important disease.

Genetic and pathogenic diversity inPyrenophora teresf.maculatain barley crops of Victoria, Australia

Forty-four Pyrenophora teres f. maculata isolates collected from barley crops in Victoria, Australia, were used in an analysis of genetic and pathogenic diversity. Genetic analysis with molecular markers revealed high levels of diversity. Fifteen sequence-tagged microsatellite primers revealed polymorphism among the 44 isolates, with two to five alleles (average 2.87 ± 0.42) amplified at each locus. Each isolate exhibited a unique genotype, which was likely to be the result of sexual recombination by random mating in the Victorian pathogen population. The two mating types of P. teres f. maculata were found at almost a 1: 1 ratio in the 44 isolate set indicating that sexual recombination is possible. Consistent with international studies of this pathogen, the high genetic diversity detected did not correlate with pathogenic variation. Adifferential set developed in Australia that consisted of 21 barley varieties was evaluated for reaction response towards the 44 P. teres f. maculata isolates as seedlings. None of the isolates tested were virulent on barley varieties known to possess the Rpt4 gene for seedling resistance, or the Ha4 allele associated with adult plant resistance. This indicates that use of the Rpt4 gene, Ha4 allele and other sources of resistance will provide effective control of spot form of net blotch (caused by P. teres f. maculata) in Victoria. However, the high level of genetic diversity indicates significant potential for the pathogen population to evolve rapidly to adapt to changes in selective pressures such as the deployment of host resistance.

Validation of Molecular Markers Associated with Net Blotch Resistance and Their Utilization in Barley Breeding

ABSTRACTWith the advancement of molecular marker technology and computer software, mapping quantitative trait loci (QTL) for complex traits in agricultural crops is frequent; however, exploitation of these QTL in practical breeding programs is limited. Here we report the validation of molecular markers linked to net blotch resistance QTL and their utilization in a barley (Hordeum vulgare L.) breeding program. Barley net blotch, caused by Pyrenophora teres Drechs. [anamorph: Drechslera teres (Sacc.) Shoemaker], is a serious foliar disease in Canada and other parts of the world. Simple sequence repeat (SSR) markers linked to net‐form net blotch (NFNB) resistance QTL (QRpt6) and spot‐form net blotch (SFNB) resistance QTL (QRpts4) were validated in two barley populations unrelated to the original mapping population. Marker‐assisted selection (MAS) was performed with SSR markers to select resistant and susceptible lines in two other populations. The lines homozygous for the resistant‐parent alleles at both marker loci had significantly lower infection than lines homozygous for the susceptible‐parent alleles at both markers, indicating that MAS for net blotch resistance is practical. Since the major QTL, QRpt6, may provide adequate NFNB field resistance in western Canada, the plan for the Crop Development Centre (CDC) barley breeding program is to routinely utilize MAS for QRpt6 followed by normal field screening in disease nurseries to select the most resistant lines having additional resistance provided by less critical genes associated with other identified QTL. The CDC program has implemented routine MAS for QRpt6 and recommends this approach to other barley breeding programs.

Registration of ‘Busby’ Barley

‘Busby’ (Reg. No. CV‐343, PI 656596; CFIA Reg. No. 6540; Canadian PBR Appl. No. 08‐6470) is a two‐rowed, hulled, spring feed barley (Hordeum vulgare L.) developed at the Field Crop Development Centre (FCDC), Lacombe, AB, Canada. Busby was tested in FCDC trials as H94034003 from 2001 to 2005 and in Prairie Recommending Committee for Oat and Barley trials as TR06673 during 2006 and 2007. It was registered for production in western Canada due to its good combination of yield, agronomic performance, grain quality traits, and disease resistance. Busby is resistant to the surface‐borne smuts (caused by Ustilago spp.) and moderately resistant to the spot form of net blotch (caused by Pyrenophora teres forma maculate Smedge). Busby has shown reactions to scald [caused by Rhynchosporium secalis (Oudem.) J.J. Davis] similar to the two‐rowed cultivar Seebe that has proven to have durable resistance in Alberta, Canada.

Registration of ‘Bentley’ Barley

‘Bentley’ (Reg. No. CV‐342, PI 655071; CFIA Reg. No. 6489, Canadian PBR Appl. No. 08‐6331) is a two‐rowed, hulled, spring malting barley (Hordeum vulgare L.) developed at the Field Crop Development Centre (FCDC), Lacombe, AB, Canada. Bentley was tested in FCDC trials as H93103004 from 2000 to 2004 and in Prairie Recommending Committee for Oat and Barley trials as TR05669 and FB414 during 2005, 2006, and 2007. It was registered for production in western Canada due to its high yields for both grain and biomass, good agronomic performance, and good grain quality traits especially for malting. Bentley is resistant to the spot form of net blotch (caused by Pyrenophora teres forma maculate Smedge) and moderately resistant to the surface‐borne smuts (caused by Ustilago spp.) and spot blotch [caused by Cochliobolus sativus (Ito & Kuribayashi) Drechs. ex Dastur].

Erratum to: Epidemiology and control of spot form of net blotch (Pyrenophora teres f. maculata) of barley: a review

Spot form of net blotch (SFNB), caused by the fungus Pyrenophora teres f. maculata, was first described in Denmark in the 1960s and is now a prevalent foliar disease of barley in many countries. This disease should be controlled as a separate disease-causing organism from the net form of net blotch (NFNB), which is caused by P. teres f. teres. The increase in prevalence of SFNB is primarily due to stubble retention and cultivation of susceptible varieties, which have resulted in increased inoculum. Infected barley stubble is the primary inoculum source for SFNB, producing both asexual spores (conidia) and sexual spores (ascospores) from pseudothecia. Spot form of net blotch causes significant losses in grain yield and quality in situations where inoculum is present, susceptible varieties are cultivated, and where the climate is cool and moist. Cultivation of resistant varieties is the most cost-effective method for control of SFNB and more than 12 different resistance sources have been identified in barley germplasm and wild barley relatives. The resistance loci of 11 of these have been mapped. Control of SFNB can also be achieved with application of foliar fungicides, crop rotation, and stubble destruction.

Epidemiology and control of spot form of net blotch (Pyrenophora teres f. maculata) of barley: a review

Spot form of net blotch (SFNB), caused by the fungus Pyrenophora teres f. maculata, was first described in Denmark in the 1960s and is now a prevalent foliar disease of barley in many countries. This disease should be controlled as a separate disease-causing organism from the net form of net blotch (NFNB), which is caused by P. teres f. teres. The increase in prevalence of SFNB is primarily due to stubble retention and cultivation of susceptible varieties, which have resulted in increased inoculum. Infected barley stubble is the primary inoculum source for SFNB, producing both asexual spores (conidia) and sexual spores (ascospores) from pseudothecia. Spot form of net blotch causes significant losses in grain yield and quality in situations where inoculum is present, susceptible varieties are cultivated, and where the climate is cool and moist. Cultivation of resistant varieties is the most cost-effective method for control of SFNB and more than 12 different resistance sources have been identified in barley germplasm and wild barley relatives. The resistance loci of 11 of these have been mapped. Control of SFNB can also be achieved with application of foliar fungicides, crop rotation, and stubble destruction.

Mapping quantitative trait loci associated with barley net blotch resistance

Net blotch of barley, caused by Pyrenophora teres Drechs., is an important foliar disease worldwide. Deployment of resistant cultivars is the most economic and eco-friendly control method. This report describes mapping of quantitative trait loci (QTL) associated with net blotch resistance in a doubled-haploid (DH) barley population using diversity arrays technology (DArT) markers. One hundred and fifty DH lines from the cross CDC Dolly (susceptible)/TR251 (resistant) were screened as seedlings in controlled environments with net-form net blotch (NFNB) isolates WRS858 and WRS1607 and spot-form net blotch (SFNB) isolate WRS857. The population was also screened at the adult-plant stage for NFNB resistance in the field in 2005 and 2006. A high-density genetic linkage map of 90 DH lines was constructed using 457 DArT and 11 SSR markers. A major NFNB seedling resistance QTL, designated QRpt6, was mapped to chromosome 6H for isolates WRS858 and WRS1607. QRpt6 was associated with adult-plant resistance in the 2005 and 2006 field trials. Additional QTL for NFNB seedling resistance to the more virulent isolate WRS858 were identified on chromosomes 2H, 4H, and 5H. A seedling resistance QTL (QRpts4) for the SFNB isolate WRS857 was detected on chromosome 4H as was a significant QTL (QRpt7) on chromosome 7H. Three QTL (QRpt6, QRpts4, QRpt7) were associated with resistance to both net blotch forms and lines with one or more of these demonstrated improved resistance. Simple sequence repeat (SSR) markers tightly linked to QRpt6 and QRpts4 were identified and validated in an unrelated barley population. The major 6H QTL, QRpt6, may provide adequate NFNB field resistance in western Canada and could be routinely selected for using molecular markers in a practical breeding program.

New eSSR and gSSR markers added to Australian barley maps

To enhance genetic maps of barley previously developed in Australia for identifying markers useable in molecular breeding, a new set of simple sequence repeat (SSR) and indel markers was added to the maps. These markers were developed through (i) database mining of barley expressed sequence tag (EST) sequences, (ii) comparative barley-rice genome analysis, and (iii) screening of a genomic library with SSR probes. The primer set selected for this study comprised 216 EST-SSR (eSSR) and 25 genomic SSR (gSSR) markers, which were screened for polymorphism on 4 doubled haploid (DH) or recombinant inbred line (RIL) populations. In total, 81 new markers were added to the maps, with good coverage on all 7 chromosomes, except 6H, which only had 2 new markers added. The marker order of previously published maps was re-evaluated by comparing recombination fractions calculated by 2 methods to discover the best position for each marker. The new SSR markers were then added to the updated maps. Several of these new markers are linked to important barley disease resistance genes such as those for cereal cyst nematode, spot form of net blotch, and leaf scald resistance, and are readily useable for marker-assisted barley breeding. The new maps are available on-line at www.genica.net.au.

Survey of Barley and Wheat Diseases in the Central Highlands of Eritrea

Annual surveys of barley and wheat diseases were conducted in Eritrea from 2000 to 2002. The surveys covered six zones of the central highlands where barley and wheat are grown. The main diseases of barley were netform net blotch, spot-form net blotch, leaf rust and scald. Other, less important diseases were loose smut, covered smut, barley stripe and septoria leaf blotch. Wheat was mainly affected by yellow rust and leaf rust. Loose smut, septoria leaf spot and tan spot diseases were less prevalent. The average incidence of these diseases varied according to the zone. Among barley diseases, net blotch incidence was high in four of the six zones surveyed. Leaf rust occurred at medium incidence in five zones. Loose smut was more severe in the southern highland plains, while covered smut was more common in the south-eastern highland terraces. For wheat, yellow rust incidence was high in two zones. Areas with a high incidence of yellow rust were not necessarily those with a high incidence of leaf rust. Leaf rust was important in the south-eastern and western highland terraces and in the western highland plains. The number of diseases found in the same field varied from 2 to 5. The south eastern highland terraces, the western highland terraces and the northern highland terraces had the highest proportions of individual barley fields with three or more diseases.

A comparison of the genetics of seedling and adult plant resistance to the spot form of net blotch (Pyrenophora teres f. maculata)

Spot form of net blotch (SFNB) (Pyrenophora teres f. maculata) is an economically damaging foliar disease of barley in many of the world's cereal-growing areas. The gene Rpt4 that confers seedling resistance to SFNB has been mapped on the long arm of chromosome 7H, but no genes for adult plant resistance (APR) have been identified. A lack of field resistance to SFNB in breeders' lines selected for Rpt4 led us to investigate the genetics of APR to this disease. Five doubled-haploid populations were phenotyped for seedling and adult plant reaction. Markers linked to Rpt4 explained a large part of the seedling variation, but little of the APR. In 2 mapped populations, major quantitative trait loci (QTLs) for APR distal to Rpt4 on chromosome 7H were identified. QTLs contributing to APR on chromosomes 4H or 5H were also identified in each population. Association of the 5H QTL with a gene for cereal cyst nematode resistance and the probable effect of this linkage on the historical development of cultivars with adult plant resistance to SFNB is discussed.

Mapping and QTL analysis of the barley population Mundah × Keel

The barley mapping population Mundah × Keel was devised to characterise and map chromosome regions associated with improved growth and grain yield on sandy soils of low fertility. A low level of polymorphism between the parents proved problematic for the construction of a detailed linkage map of this population. Despite this, significant quantitative trait loci (QTLs) for specific traits were detected, providing an insight into the probable chromosome regions associated with sand adaptation. In addition, this population is being employed to identify loci associated with the expression of traits for moisture stress and frost tolerance, and resistance to spot form of net blotch and leaf scald.

Development and use of an assay based on the polymerase chain reaction that differentiates the pathogens causing spot form and net form of net blotch of barley

Two forms of barley net blotch are caused by different formae of the fungus Pyrenophora teres and both are economically important pathogens. The spot form of the net blotch fungus (P. teres f. maculata) and the net form of the net blotch fungus (P. teres f. teres) cause the lesion types indicated by their disease names, although symptom overlap and similar spore morphology can make identification difficult. Randomly amplified polymorphic DNA fragments differentiated the two forms of Pyrenophora. Polymorphic bands were cloned and sequenced to develop specific primer sets. A simple assay based on the polymerase chain reaction was developed and can identify the Pyrenophora formae causing disease symptoms directly from infected plant tissues in a single multiplex reaction. The assay was validated using amplified fragment length polymorphism genotyping of isolates and was shown to be more accurate than reliance on symptom expression. This assay can now be used for routine diagnosis, epidemiological studies and resistance breeding, where correct identification of each pathogen is critical.

Inheritance and RAPD tagging of multiple genes for resistance to net blotch in barley

A doubled haploid barley (Hordeum vulgare L.) population that was created from a cross between cultivars 'Léger' and 'CI 9831' was characterized by RAPD (random amplified polymorphic DNA) markers for resistance to isolate WRS857 of Pyrenophora teres Drechs. f. sp. maculata Smedeg., the causal agent of the spot form of net blotch. Resistance, which initially appeared to be conferred by a single gene from the approximate 1:1 (resistant : susceptible) segregation ratio of the doubled-haploid (DH) progeny, was found to be associated with three different genomic regions by RAPD analysis. Of 500 RAPD random primers that were screened against the parents, 195 revealed polymorphic bands, seven showed an association to the resistance in bulks, and these seven markers were mapped to three unlinked genomic regions. Two of these regions, one of which was mapped to chromosome 2, have major resistance genes. The third region has some homology to the chromosome 2 region. This study demonstrates the simultaneous location of markers for more than one gene governing a trait by using RAPD and bulked segregant analysis (BSA).Key words: net blotch, RAPD markers, bulked segregant analysis, barley, doubled haploids.

Inheritance and RAPD tagging of multiple genes for resistance to net blotch in barley

A doubled haploid barley (Hordeum vulgare L.) population that was created from a cross between cultivars 'Léger' and 'CI 9831' was characterized by RAPD (random amplified polymorphic DNA) markers for resistance to isolate WRS857 of Pyrenophora teres Drechs. f. sp. maculata Smedeg., the causal agent of the spot form of net blotch. Resistance, which initially appeared to be conferred by a single gene from the approximate 1:1 (resistant : susceptible) segregation ratio of the doubled-haploid (DH) progeny, was found to be associated with three different genomic regions by RAPD analysis. Of 500 RAPD random primers that were screened against the parents, 195 revealed polymorphic bands, seven showed an association to the resistance in bulks, and these seven markers were mapped to three unlinked genomic regions. Two of these regions, one of which was mapped to chromosome 2, have major resistance genes. The third region has some homology to the chromosome 2 region. This study demonstrates the simultaneous location of markers for more than one gene governing a trait by using RAPD and bulked segregant analysis (BSA).

Identification and mapping of a gene conferring resistance to the spot form of net blotch (Pyrenophora teres f maculata) in barley

Spot form of net blotch (SFNB) (Pyrenophora teres f maculata) is an economically damaging foliar disease of barley in many of the world’s cereal growing areas. The development of SFNB-resistant cultivars may be accelerated through the use of molecular markers. A screen for SFNB resistance in 96 lines identified four new sources of resistance, including a feed variety, ‘Galleon’, for which a fully mapped doubled haploid population was available. Segregation data indicated SFNB resistance was conferred by a single gene in the ‘Galleon’בHaruna Nijo’ cross, positioned on the long arm of chromosome 7H. This gene is designated Rpt4 and is flanked by the RFLP loci Xpsr117(D) and Xcdo673 at distances of 6.9 cM and 25.9 cM, respectively. The marker Xpsr117(D) was validated using another population segregating for Rpt4, correctly predicting SFNB resistance with more than 90% accuracy.