Development of an international standard set of barley differential genotypes for Pyrenophora teres f. teres

International comparison of virulence profiles of Pyrenophora teres f . teres (Ptt), the cause of barley net blotch, is seriously restricted by inconsistencies in differential testers used among researchers. This paper reports an attempt to develop an appropriate set of differentials to standardize characterization of Ptt populations globally. Fourteen barley genotypes (Canadian Lake Shore (CLS), Harbin, c-8755, c-20019, Manchurian, Tifang, CI 9825, CI 5791, CI 9819, Beecher, CI 9214, Skiff, Prior and Corvette) were selected from among genotypes previously used as Ptt differentials. Three cultivars (Pirkka, Haruna Nijo and Harrington) were included to identify a universally susceptible control. Genotypes were inoculated with approximately 1000 Ptt isolates from Russia, Europe, Australia and Canada. The mean reaction frequency of genotypes ranged from highly resistant (CI 9819, CI 5791, c-8755 and CI 9825) to highly susceptible (Harrington, Haruna Nijo and Pirkka). The best differential abilities were demonstrated by Harbin, CLS, c-20019, Manchurian and Prior. Application of cluster analyses identified genotypes with similar reaction patterns, which supported a reduction of genotypes in the set. When combined with an algorithm comparing the ability of individual genotypes to discriminate among Ptt isolates, a further reduction of genotypes was justified. A new, concise set of barley genotypes for differentiating virulences in Ptt was formulated. It is proposed that these genotypes be adopted as the standard, international differential set to characterize and identify the virulence properties of Ptt populations across environments. The new Ptt differential set consists of the genotypes c-8755, c-20019, CI 5791, CI 9825, CLS, Harbin, Prior, Skiff and Harrington.     

Diversity among Finnish net blotch isolates and resistance in barley

Summary Seedlings of a differential barley (Hordeum vulgare L.) series (21 genotypes) and of six check genotypes were used in the greenhouse to assess variation in virulence among 20 single-spore isolates of the net blotch pathogen. Pyrenophora teres Drechs. f.teres Smedeg., collected from various sites in Finland. The experiment was run twice and symptom expression was recorded on the first three leaves. Analysis of second leaf symptom scores from Run 1 indicated differences in virulence between isolates, all of which were pathogenic, and differential resistance among the barleys. The virulence of P. teres isolates appeared to be conditioned by the host barley from which the isolate derived; the average virulence of isolates collected from a susceptible host was greater than that of isolates collected from a less susceptible host. Results from Run 2 were similar regarding resistance within the barleys, but variation in virulence among the P. teres isolates was not consistent with that from Run 1. CI 9819 caries duplicate genes for resistance to P. teres (Rpt1b and Rpt1c), and CI 7548 possesses Rpt3d. Both genotypes were highly resistant to all isolates. The Rpt1a gene of Tifang (CI4407) conferred resistance to all isolates in Run 2, but only to about half of the isolates in Run 1. The checks, including two of the symptomatically most resistant Nordic barley genotypes, were universally susceptible during these stringent tests. No selective pressure has been placed on Finnish isolates of P. teres through previous deployment of major resistance genes, and it is speculated that any variation in virulence among isolates is likely to be due to a combination of evolutionary forces including, natural selection, random genetic drift and gene flow.     

Detectability and prevalence of Brachyspira species in herds rearing health class feeder pigs in Finland

Faeces samples were taken three times at two-week intervals, from the farrowing units of four herds of known Brachyspira (formerly Serpulina) status and one of unknown Brachyspira status. Brachyspira hyodysenteriae, Brachyspira pilosicoli, Brachyspira intermedia and Brachyspira group III were isolated from the faecal samples from the weaners in the herds using either a maximum of 50 ppm of olaquindox or no feed additives. The detection rates were relatively consistent. However, B hyodysenteriae was not detected at one sampling in a known positive herd. The prevalence of Brachyspira species was also studied in feeder pigs originating from LSO 2000 health class farrowing units, comparable with specific pathogen-free herds. These farms were free from swine dysentery, sarcoptic mange, swine enzootic pneumonia and progressive atrophic rhinitis. Fifty of 428 herds were sampled once. B hyodysenteriae was not isolated from any of them, but B intermedia, B pilosicoli and Brachyspira group III were isolated from five, 14 and 37 of the herds, respectively. The detection of Brachyspira species did not relate to the prevalence of diarrhoea in the herds, as judged by the farmers. The herds using carbadox (40 to 50 ppm) had a lower prevalence of Brachyspira species than those using olaquindox (40 to 50 ppm).     

Stable resistance in barley to Pyrenophora teres f. teres isolates from the Nordic-Baltic region after increase on standard host genotypes

Results from tests of a mixture of Finnish net blotch, Pyrenophora teres Drechs. f. teres Smedeg., isolates on a differential series of barley seedlings, comprising 17genotypes, indicated that patterns of infection response (IR)and percentage leaf area damaged (PLAD) were unaffected by differences in seedling size. Variation of the concentration of inoculum between 1,250 conidia ml^-1 and 20,000 conidia ml^-1 produced similar patterns of IR and PLAD on the differential series. IR and PLAD scored on the second seedling leaf differentiated resistance to P. teres f. teresamong the genotypes better than on the first seedling leaf. Ina second experiment, 120 single-spore P. teres f. teres isolates from Finland, Sweden, Norway, Latvia, Estonia and Ireland were used in tests conducted in the greenhouse to differentiate them in terms of virulence reaction on seedlings of six differential barley genotypes. Each isolate was tested directly following isolation from the leaf material and after having passaged each through barley cvs. Arve or Pohto, to produce 360 isolates in total. Virulence of the isolates differed significantly on the members of the differential series, but differences associated with country of origin and passaging, and interactions, were small. It is concluded that little variation between virulence of P. teres f. teres isolates is evident over a large geographic area, incorporating Nordic and Baltic countries, and Ireland. Barley genotype response to P. teres f. teres appeared to be of more significance than relative virulence of the pathogen isolates. This could simplify breeding barley for improved resistance to this phytopathogen. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of Indian mustard [Brassica juncea (L.) Czern.] core collection based on agro-morphological traits

Genetic Resources and Crop Evolution - Indian mustard [Brassica juncea (L.) Czern.] is a major edible oil crop of India. The Indian Council of Agricultural Research—National Bureau of Plant...     

Evaluation of resistance to <Emphasis Type="Italic">Fusarium graminearum</Emphasis> in oats

Fusarium head blight (FHB) is a serious threat for the production of high-quality oats, a crop known for its health beneficial traits. The fungal pathogen, Fusarium graminearum, which is the main causal agent of FHB in cereals has become more common in the main oat production areas. FHB reduces yield quality due to the accumulation of several mycotoxins such as deoxynivalenol. Strong environmental dependence of infection and variable causal agents make FHB only partly controllable by agricultural or manufacturing practices. This underlines the need for resistant cultivars. In recent years various improvements in the FHB resistance breeding of oats have been reported including improved inoculation and screening methods as well as resistance and association studies. This review demonstrates the current techniques used in the phenotyping of oats resistance to FHB. Resistance found in breeding material and gene bank accessions is described and several resistance related traits are discussed. In addition, an outlook to the future prospects of FHB resistance breeding in oats is provided.     

Genes for resistance in barley to Finnish isolates of Rhynchosporium secalis

Summary Twenty Finnish isolates of Rhynchosporium secalis (Oud.) J.J. Davis, the causal agent of scald, were taken from infected barley (Hordeum vulgare L.) plants and inoculated on to seedlings of a differential series of barley containing a range of major genes for resistance to the fungus, as well as on to six Nordic 6-row spring barleys and three winter ryes (Secale cereale L.). These fungal isolates derived from four sites and three host varieties. Disease development was monitored on two leaves of seedlings in the greenhouse employing a standard scale, and on adult plants in the field by assessing the diseased area on the three uppermost leaves. A comparison was also made between the pathogenicity and virulence of ten Finnish and ten Canadian R. secalis isolates. The Finnish isolates varied in virulence, but with the exception of Algerian (CI 1179) seedlings and adult La Mesita (CI 7565) all seedlings and adult plants of the entire differential series were resistant to all isolates. Canadian isolates were, on average, less virulent than Finnish isolates. All the Nordic checks were susceptible to all Finnish and seven Canadian isolates, but differences in the degree of susceptibility were evident. Isolates of R. secalis from barley were non-pathogenic on rye, isolates from Elymus repens L. were non-pathogenic on barley and rye, and isolates from rye were only pathogenic on rye. Finnish R. secalis isolates contain no redundant pathogenic diversity. The differential series represents a useful, but as yet untapped, source of resistance to R. secalis for Finnish barley breeders.     

Resistance to Rhynchosporium secalis in six Nordic barley genotypes

Six six-row Nordic spring barley genotypes (Hordeum vulgare L.) were assessed in the field in Finland (1994 and 1995) for resistance to Rhynchosporium secalis (Oud.) J.J. Davis, the causal pathogen of scald, in artificially inoculated plots. The barleys were known not to contain major genes for resistance to scald and the purpose of these experiments was to identify quantitative differences in resistance to scald which might be exploitable in a breeding programme. Disease development was monitored, grain yield and yield components were recorded, and these data were compared with measurements taken from plants in plots kept free of disease. Data, averaged over both years, for disease development on the uppermost three leaves — areas under disease progress curves, terminal severity and apparent infection rates — indicated that ‘Verner’, ‘Pohto’ and ‘Pokko’ were symptomatically significantly more resistant to scald than ‘Arve’, ‘Loviisa’ and Jo 1599. Grain yields, thousand-grain weights, test weights and proportions of plump grains were all significantly reduced in plots inoculated with scald compared with those kept free of disease; ‘Verner’ appeared to be the most useful genotype for use in crossing programmes to improve scald resistance in Finnish barleys.     

Pathogenic variation in populations of Drechslera teres f. teres and D. teres f. maculata and differences in host cultivar responses

The current study examined the variability in the pathogenicity of populations of Drechslera teres f. teres and D. teres f. maculata (the net and spot forms of D. teres) from Ireland and northern Europe. A population of progeny isolates from a mating of net and spot forms was also examined. Significant variation in virulence was found both between and among net form and spot form isolates (p<0.001). In the Irish population, significant differences were found between the net and spot forms, with the spot form isolates more virulent (p<0.05). Progeny isolates were significantly more virulent than net form or spot form populations (p<0.001). Significant differences were found in cultivar reactions, with cv. Botnia most susceptible to both forms of the pathogen (p<0.001). Cultivar Boreal 94145, although quantitatively resistant, was found to be very susceptible to both forms of the pathogen and to progeny isolates. Cultivars CI 5791, CI 2330 and CI 9819 were all less susceptible to infection by both forms, but were more susceptible to spot form isolates. Significant correlations were found between whole plants and detached leaf experiments for the net form isolates only (p<0.001). This study illustrates the importance of including both net form and spot form isolates in resistance studies and the need for a clearer understanding for the genetic basis of resistance to the net and spot forms. It also highlights the limitations of using a detached leaf assay for screening of net blotch of barley.