Single Pustule Research Articles

First Report of a New TTKSF Race of Wheat Stem Rust (Puccinia graminis f. sp. tritici) in South Africa and Zimbabwe.

Seven races have been described in the Ug99 race group of Puccinia graminis f. sp. tritici (2). Ug99-related races previously recorded in South Africa are TTKSF, TTKSP, and PTKST (4). In December 2010, severe stem rust infection of the winter wheat cv. Matlabas was observed for the first time in South Africa. Race analysis using the 20 North American (NA) stem rust differential lines and letter code system classified the race as TTKSF. In comparative infection studies in a greenhouse, cv. Matlabas seedlings were susceptible (infection type [IT] 4) to isolate UVPgt61/1 (TTKSF+) collected from Afrikaskop in the eastern Free State, whereas the cultivar was resistant (IT 1 to 2) to stem rust isolates 2013 (TTKSF), UVPgt55 (TTKSF), UVPgt59 (TTKSP), and UVPgt60 (PTKST). Isolate 2013 represents the original collection of race TTKSF in South Africa (1). In addition to the NA differentials, no variation in the IT range of seedlings of lines with Sr7a, 8b, 12, 13, 14, 16, 18, 19, 22, 25, 26, 27, 28, 29, 32, 33, 34, 35, 39, 41, 42, 43, 44, Em, R, Tt2, and Satu was observed between UVPgt61/1 and UVPgt55. With the exception of cv. Matlabas, ITs of 106 South African cultivars likewise did not differentiate UVPgt61/1 and UVPgt55. Seedling IT studies were conducted at least twice. Microsatellite analysis (4) showed that all single pustule isolates established from the original Matlabas isolate formed part of the Ug99 group. When characterized with selected single nucleotide polymorphisms (SNPs), all single pustule isolates shared an identical genotype that differed from UVPgt55 (TTKSF), a foreign introduction into South Africa (1,3). SNP genotype analysis suggests that UVPgt61/1 is genetically dissimilar to UVPgt55, as is Zim1009, another TTKSF+ isolate that was collected from Birchenough in Zimbabwe. Studies are underway to determine the identity of the defeated Sr gene in Matlabas and the cultivar has been added to the South African stem rust differential set. TTKSF+ is the eighth race detected in the Ug99 group. Since no other cultivars or advanced lines were found to carry the Matlabas gene, it is unlikely that race TTKSF+ will threaten wheat production in South Africa. However, the occurrence of a new Ug99-related race emphasizes the variability within this internationally important group.

Outbreak of coffee leaf rust (Hemileia vastatrix)in Colombia

In Colombia, coffee cultivation covers 850,000 ha, of which 41% comprises cultivars of Coffea arabica that are susceptible to leaf rust (CLR) caused by Hemileia vastatrix Berk. et Br.CLR, first recorded in Colombia in 1983, is the most damaging coffee disease, causing 30% crop losses when left unmanaged. In Colombia, major epidemics of CLR had not been reported since 1987 (Leguizamón & Arcila, 1991). However, during the 2008 to 2011 growing seasons, an unusual increase in disease incidence and high leaf severities (>30%) were recorded in several susceptible commercial coffee fields, predominantly in the Departments of Tolima, Caldas, Cauca and Antioquia. We performed assays for the molecular and phenotypic characterisation of coffee rust isolates taken before and during the current epidemics. Thirty new pure cultured isolates were derived from single rust pustules taken from distinct coffee regions and contrasting altitudes. Tests on a set of coffee differential plants performed at CIFC in Oeiras, Portugal, showed that the majority of isolates were race II of H. vastatrix. Only two isolates could not be assigned to any known H. vastatrix races. Aggressiveness tests including incubation and latency period, and spore density showed that the isolates causing the epidemics were not more aggressive than pre-2008isolates.The use of 100 SSR markers (GenBankAccession Nos. JF288615 to JF288714) showed genetic identity among 30 H. vastatrix isolates taken during the rust outbreak and 30 isolates collected before 2008. The multi-line cultivars Colombia and Castilloderived from crosses between Caturra and Timor Hybrid 1343 continued exhibiting resistance against CLR. Differences in environmental and agronomic conditions during the period 2008-2011were considered as possible causes of the CLR epidemics. The rust outbreak was associated with high rainfall resulting from La Niña together with sunlight reductions due to cloudy skies and a narrower range between maximum and minimum daily temperatures. In the Colombian central coffee-growing region, annual precipitation has exceeded 3,000 mm during the last seven years, being close to the average (2,400 mm) only in 2007. A similar pattern was observed in most of the climatic stations located all over the coffee growing regions where solar irradiation was below average (1,775 hours per year); a condition that favours H. vastatrix development (Rayner, 1961; Bock, 1962; Avelino, 2006). Inadequate fertiliser application evidenced by low fertiliser sales (due to major price increases) and deficient nutrient uptake in water-saturated soils slowed shoot growth, thus preventing plant recovery. The CLR outbreak responsible for coffee production losses in Colombia in 2008 to 2011 was caused by isolates belonging to race II, the prevalent race of Hemileia vastatrix in Colombia since 1983. There does not appear to have been an increase in host susceptibility to this race. It is considered that optimal weather and agronomic conditions for disease development favoured major CLR epidemics from 2008 to 2011.

Determination of Puccinia graminis f. sp. tritici races of wheat in Turkey

Stem rust, caused by the fungus Puccinia graminis f. sp. tritici (Pgt), is one of the most important diseases limiting wheat production in Turkey. Surveys were conducted in 2007 and 2008 in order to determine the races of the pathogen present in Turkey. In 2007, it was found that 91 (43%) out of 207 inspected wheat fields were infected with stem rust, and in 2008, it was found that 61 (25%) out of 242 inspected fields were infected. From these samples, 40 single pustule isolates were obtained. The North American differential set, which includes 20 genotypes with different resistance genes, was employed to identify the races present. Seedling tests were used for race analysis under greenhouse conditions. A total of 21 different stem rust races were found. Pgt race TKTTC, which was found in 11 Pgt isolates, was the most common race. Genotypes possessing at least 1 of the Sr24, Sr31, Sr26, and Sr27 resistance genes showed low infection types for 40 Pgt isolates. The resistance genes determined in this study could be used in breeding programs for developing stem rust-resistant genotypes.

First Report of Rust Caused by Puccinia psidii on Paperbark, Melaleuca quinquenervia, in California.

Infections by Puccinia psidii Winter were detected on Melaleuca quinquenervia (Cav.) Blake (paperbark, tea tree) during a regular inspection of a San Diego, California nursery in November 2010 by San Diego County inspectors. Urediniospore morphology, production of bright-yellow uredinia on both upper and lower leaf surfaces, DNA sequencing, and inoculation tests confirm the identity of the pathogen. From digital image analysis, dimensions of 49 urediniospores from the paperbark rust collection were 25 (19 to 30) × 21 (18 to 23) μm, typical of uredinia of P. psidii (3). Some urediniospores also had a distinctive, unornamented "tonsure" near the base, and all pustules lacked teliospores. Both latter features are considered by some (3) as more typical of an asexual sub-taxon, Uredo rangelii Simpson, Tho., Grgur. which however, has narrower urediniospores than we report. U. rangelii is also considered less of a threat to Eucalyptus than other variants of P. psidii in the broad sense (1). The 627-bp DNA sequence of the internal transcribed spacer (ITS) region of the paperbark rust (GenBank Accession No. JF960255) obtained by John Hanna at the USDA Forest Service, Forestry Sciences Lab, Moscow, ID using PCR and ITS1/ITS4 primers had over 99% identity with 18 GenBank sequences of P. psidii from diverse Myrtaceae, including Melaleuca, Psidium, and Eucalyptus. In January and February of 2011, inoculations of 7- to 10-cm cuttings of active terminal growth demonstrated pathogenicity to the three species of Myrtaceae that were tested: paperbark, common myrtle Myrtus communis L., and brush cherry Syzygium australe (J.C. Wendl. ex Link) B. Hyland (=Eugenia australis, =E. myrtifolia) cv. Monterey Bay. Uredinia developed within 10 days of inoculation on inoculated host cuttings. Proportions of cuttings infected for paperbark, common myrtle, and brush cherry were 5 of 7, 6 of 6, and 1 of 6, respectively; pustules were most abundant on common myrtle and least abundant (a single pustule) on brush cherry. Similarly treated control cuttings were not infected. P. psidii has previously caused severe outbreaks on paperbark in Florida (2). California interceptions and nursery detections of P. psidii are recorded in the California Department of Food and Agriculture's internal, unpublished, Pest Detection Database, have all occurred since 2003, and include Florida sources. From the Database, detections on materials shipped into California nurseries have been: brush cherry from Florida, March and April, 2004 at Valley Center, CA; allspice (Pimenta dioica (L) Merr.) from Florida, June 2005 at Gilroy, CA; and Java apple/rose apple (Syzygium samarangense [Blume] Merr. & L.M. Perry [= Eugenia javanica Lam.]) from Hawaii, 2008 at Anaheim, CA. Other California nursery infestations have been: brush cherry, April 2004, at Valley Center, CA; pohutukawa (Metrosideros excelsa Solander ex J. Gaertner), July 2007 at Bonsall, CA; and common myrtle, November 2008 at Fallbrook, CA. The rust has not been reported in California on any plants outside of nursery settings or on Eucalyptus in any setting. The current strains of P. psidii in California appear likely to remain a recurrent problem for ornamental plant and foliage crops in the myrtle family grown in some nursery settings.

Physiologic specialization of Puccinia triticina, the causal agent of wheat leaf rust, in Canada in 2008

Commercial fields and research plots of wheat across Canada were surveyed for leaf rust during 2008. Leaf samples infected with the causal fungus, Puccinia triticina, were used to generate 407 single pustule isolates, 13 from Alberta, 302 from Manitoba and Saskatchewan, 71 from Ontario, 10 from Quebec and 11 from Prince Edward Island. Single pustule isolates were tested for virulence to 16 lines of ‘Thatcher’ wheat with single leaf rust resistance genes. Forty-six virulence phenotypes were identified; the most common were TDBJ (23.6%), TDBG (23.1%) and MLDS (18.9%). The frequency of virulence to both Lr9 and Lr17 increased compared with 2007, whereas it decreased for Lr24 and Lr2a. The populations from eastern Canada were more diverse than those from western Canada and contained many unique virulence phenotypes, and virulence to gene Lr18, which was not found in western Canada. Fifty-five isolates, representing each of the virulence phenotypes, were tested on six and 12 additional differential wheat lines at the adult and seedling stages, respectively. On the adult plant differentials, no isolates were virulent to Lr22a or Lr34, whereas all isolates except two were virulent to Lr13, and virulence varied for Lr12, Lr35 and Lr37. On the additional seedling differentials, all isolates were avirulent to Lr19, Lr21, Lr29 and Lr32, and only one isolate was virulent to Lr25. All isolates had similar infection types to Lr2b and Lr2a, varied in virulence to Lr3bg, Lr14b, Lr20, Lr23 and Lr28, and except for two were virulent to Lr15.

From a pimple to a crater

In January, 2010, a 31-year-old woman was transferred to our intensive care unit with multiorgan failure, severe inflammatory response syndrome, and the working diagnosis of necrotising fasciitis. 2 weeks before admission she had presented to another hospital with a purulent ulcer that had started as a single painful pustule of the left leg. The lesion measured 4×4 cm and was surrounded by extensive reddening and induration of the adjacent skin (see webappendix). Antibiotic treatment was started with amoxicillin/clavulanic acid and surgical debridement was done.

Pathogenic Diversity in and Sources of Resistance to Uromyces appendiculatus in Southern Africa

The reaction of the first (1983) common bean international differential set and other germplasm to 248 single pustule isolates of the rust fungus Uromyces appendiculatus, collected from various southern African countries, was evaluated. Eleven of the most important isolates were re-purified and re-inoculated, this time also on the second (2002) revised and smaller international differential set. The 248 isolates could be grouped into 44 race-groups. These were subjected to principal coordinates analysis (PCoA). A second PCoA was carried out using 25 of the most important of the 44, together with 34 African races reported by previous authors. Isolates were generally avirulent on accessions with the resistance genes Ur-3+, -5 or -11, as well as Compuesto Negro Chimaltenango (CNC) and A 286, all small seeded, and the most useful sources were accessions carrying both Ur-3 and Ur-11, for instance BelMiNeb-RMR-7, BelDakMi-RMR-14 and -18. Isolates were generally virulent on large seeded accessions (with, among others Ur-4, -6 or -9), reflecting the preference for large seeded beans in southern Africa and co-evolution of host and pathogen. No large seeded accessions showed broad resistance. The least susceptible was Plant Introduction 260418, which rated resistant to moderately susceptible to the 11 races. These observations were confirmed by field ratings on the same accessions over multiple seasons. According to the PCoA, which proved useful for the identification of differentiating accessions, southern African isolates fell into three main clusters, for which Redlands Pioneer and the South Africa cultivar Teebus were the most discriminating differentials. Other accessions that showed particularly useful differentiating ability were Olathe and 51051. Of these, only Redlands Pioneer has been included in the 2002 differential set. The PCoA grouping of the African races was similar to that of the southern African race-groups.

SRAP Technique Efficiently Generates Polymorphisms in Puccinia striiformis Isolates

Wheat stripe rust, caused by the fungal pathogen Puccinia striiformis f.sp. tritici (PST), is a major disease of wheat in temperate-cold climates. The identification of new markers would ease the procedure for evaluating the ongoing pathogen evolution. Twelve single pustule isolates were generated from samples of PST obtained in UK during 1987–2001. They were evaluated for their pathogenic behaviour on a set of differential cultivars and were analysed by sequence-related amplified polymorphisms (SRAP) technique, to identify polymorphisms useful to evaluate variability among isolates. This is the first report of the application of SRAP technique to Uredinales order.

First Detection of Virulence in Puccinia striiformis f. sp. tritici in China to Resistance Genes Yr24 (=Yr26) Present in Wheat Cultivar Chuanmai 42.

Stripe rust disease of wheat caused by Puccinia striiformis f. sp. tritici was observed on previously resistant bread wheat (Triticum aestivum L.) cv. Chuanmai 42 during the 2008-2009 crop season in Pi County, Sichuan Province, China. More than 10 single pustules were isolated from the diseased leaf samples collected in the field and inoculated on 7-day-old susceptible wheat seedlings cv. Mingxian 169. After 18 to 24 h of incubation at 100% relative humidity in darkness, the plants were moved into the greenhouse, maintained at 15 to 18°C, and supplemented with 10,000 lx of fluorescent light for 10 h per day. The second leaves were clipped when chlorotic spots appeared on leaves (~7 days postinoculation), and plants were covered with glass cylinders to prevent cross contamination. Urediniospores of each isolate were collected 16 days after inoculation and temporarily kept in a dryer at low temperature (3 to 4°C). The virulence spectra of the isolates were tested on Chinese differentials and wheat lines with known Yr genes at the seedling stage (1). A new Yr24 (=Yr26) virulent pathotype, different from currently known pathotypes in China, was identified. To our knowledge, this is the first detection of Yr24 virulence in Puccinia striiformis f. sp. tritici populations on Chuanmai 42. In addition, the new pathotype was also virulent to Lantian 17, Guinong 22 (Chinese differential), and 92R137 derived wheat lines Nannong 04Y10 and Nannong 05Y628, known to carry Yr24 (2,3). The avirulence/virulence formula of the new pathotype is Yr1, 3, 4, H46, 5, 6, 15, 17, 18, 32, Sp, Sd/Yr2, 8, 9, 10, 12, 24 (=26), 31, and Su. Wheat cultivars and breeding materials, previously protected by Yr24 gene, are now vulnerable to stripe rust epidemics in the region. Pure isolates of the new pathotype (Accession No. 09-6-16-3) are stored in the Chinese Academy of Agricultural Sciences (CAAS; Beijing) stripe rust collection.

First Report of Virulence Phenotypes of Puccinia helianthi, Causal Agent of Sunflower Rust in Illinois.

Sunflower rust caused by Puccinia helianthi (Schw.) is an autoecious and macrocyclic rust that occurs on wild perennial, wild annual, and cultivated sunflower species (Helianthus annuus L.). Severe epidemics of sunflower rust can significantly reduce yield and quality of cultivated sunflower (4). Uredinia of P. helianthi were observed in individual sunflower fields in four Illinois counties in 2008, namely; Champaign, LaSalle, McLean, and Livingston. Leaves with uredinia from each field were collected and shipped to the USDA-ARS Sunflower Pathology Laboratory in Fargo, ND. Urediniospores were harvested by rinsing leaves with Soltrol 170 isoparaffin solvent (Chevron Phillips Chemicals, Woodlands, TX). Urediniospores were increased by inoculating the spore suspension onto 21-day-old seedlings of susceptible oilseed hybrid Myc-7350 with a vacuum-pump powered atomizer. After the Soltrol 170 evaporated, plants were placed in a dew chamber for 24 h and then moved to a greenhouse at approximately 20 to 25°C with a 14-h photoperiod. When sporulating uredinia were visible, a bulk collection of urediniospores was made from samples of each location. Additionally, one single-pustule derived isolate from each location was obtained by harvesting urediniospores from a single pustule and increasing as above. To determine the virulence phenotypes, each single-pustule derived isolate and bulk collection were inoculated as above onto at least two replicated sets of the nine international differential lines (each set containing three plants per line) and evaluated after 14 days (1,2). The single-pustule isolates from LaSalle, Livingston, and McLean counties were determined to be virulence phenotype 300. The single-pustule isolate from Champaign produced no infection on any differential lines, including the susceptible, and was therefore considered not viable. The virulence phenotypes of the bulk samples were coded as 330 (Champaign), 324 (McLean), and 336 (Livingston and LaSalle). Virulence of all aforementioned virulence phenotypes was found to be common in a recent survey of 400 Midwestern P. helianthi samples collected in 2007 and 2008 (1). Although sunflower production is limited in Illinois, expansion could occur. This is particularly true in southern Illinois, where double cropping sunflower after winter wheat is a possibility. Urediniospore germination and infection is favored by free moisture and temperatures ranging from 10 to 25°C, while optimum temperature for spore development ranges from 20 to 35°C (3). These environmental conditions are often more common in Illinois than in the major sunflower-producing states in the Great Plains, where sunflower rust is a concern annually. Thus, determination of P. helianthi virulence phenotypes in Illinois may be important for future management of sunflower rust.

Susceptibility of G-genome tetraploid species of the genus Triticum L. to powdery mildew

According to the literature data, G-genome tetraploid species Triticum timopheevii and T. araraticum are highly resistant (immune) to powdery mildew. Unde-epephytoty of the disease, not a single pustule was found on the leaves of any T. timopheevii accessions or on most of the T. araraticum accessions. Infection of the spikes of accessions of the given species by this disease was found for the first time.

First Report of Soybean Rust Caused by Phakopsora pachyrhizi in Iowa and its Statewide Occurrence.

On 25 September 2007, soybean leaves with lesions typical of soybean rust were found in two commercial fields located in Dallas County, Iowa. Growth stage of the infected soybean plants was near physiological maturity. Diagnosis of Phakopsora pachyrhizi on leaves was confirmed by morphological observation of uredinia and urediniospores and conventional PCR conducted by the Iowa State University Plant and Insect Diagnostic Clinic using P. pachyrhizi-specific primers Ppm1 and Ppa2 as described (1). Water blanks were used as negative controls in PCR testing. Leaves were collected from additional counties throughout Iowa and examined microscopically. Soybean rust was identified on leaves from 14 counties, almost all the counties sampled, ranging from far western to far eastern Iowa. The northernmost detection was at 42.9°N in Hancock County, which also is the northernmost detection of soybean rust in the continental United States so far. In a commercial field in Fremont County, in the southwestern corner of Iowa along the Missouri River, disease incidence was approximately 20% and disease severity was 5%. Observed disease incidence was 1 to 2% and severity was less than 1% from all other samples. Most uredinia were scattered on the leaves as single pustules or clustered in groups of three to five pustules. Pustules on some leaf samples were sporulating, depending on weather conditions at the time when samples were collected. Fresh urediniospores collected from the leaf samples were placed on glass slides with free water on the surface and incubated in a dew chamber under darkness for 8 h to test for germination. Germination rates ranged from 80 to 90%. Rust spores also were used to inoculate detached soybean trifoliate leaves, which were kept in a dew chamber under darkness for 12 h with water-soaked cotton wrapped around the petioles. Typical soybean rust pustules developed within 10 to 14 days after incubation. The detections of soybean rust in Iowa were consistent with the predictions of an aerobiological spore dispersal model, which predicted spore showers in central to western Iowa in August. Above normal wet weather in the Great Plains and Iowa may have favored the statewide disease occurrence. To our knowledge, this is the first report of soybean rust in Iowa. Reference: (1) R. D. Frederick et al. Phytopathology 92:217, 2002.

Occurrence of Late Leaf Rust Caused by Pucciniastrum americanum in Red Raspberry (Rubus idaeus) in Buenos Aires, Córdoba, and Entre Ríos, Argentina.

In the fall of 2003, severity of late leaf rust in leaves and fruits of red raspberry (Rubus idaeus L.) reached 50% in Buenos Aires (Azul, Baradero, Capilla del Señor, Gral. Rodríguez, Mar del Plata, and Tandil), Córdoba (Villa de Las Rosas), and Entre Ríos (Concordia). The south of Argentina, Río Negro (El Bolsón), and Chubut (El Hoyo, Lago Puelo) remained rust free. The abaxial side of the field infected leaves had pustules filled with masses of yellow spores. Chlorotic areas corresponded in the adaxial side. Urediospores were vacuum harvested from field infected leaves collected in the Tandil area and placed onto a healthy 1-year-old greenhouse-grown plant (cv. Heritage). Spores from a single pustule were increased on plants of the same cultivar. Spores were studied with optic and electronic microscopy. Uredial ostiolar cells were warted, laterally free, and constricted in the middle. The obovoid, echinulate urediospores, from infected leaves averaged 24 × 16 μm (16 to 30 × 11 to 21 μm). Morphological characteristics and spore measurements agreed with those reported for Pucciniastrum americanum (1). Urediniospores were suspended in mineral oil and sprayed onto three raspberry cultivars that were maintained in a darkened mist chamber at 20°C for 48 h and the transferred to a 20°C and 12-h light cycle chamber. Control plants were inoculated with sterile water. There were three replicate plants of each treatment. After 11 days, large sporulating uredia (0.5 mm) were produced on inoculated leaves of cv. Autumn Bliss and smaller uredia (0.1 to 0.3 mm) were produced on cv. Heritage. There were necrotic flecks and the least and smallest uredia were produced on cv. Himbo Queen. No symptoms were present in control plants. To our knowledge, this is the first report of P. americanum causing disease on raspberry in Argentina. Reference: (1) G. F. Laundon and A. F. Rainbow. Pucciniastrum americanum. No. 210 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, England, 1969.

First Detection of Virulence to Genes Lr9 and Lr25 Conferring Resistance to Leaf Rust of Wheat Caused by Puccinia triticina in Mexico

Leaf rust resistance gene Lr9 was transferred to wheat from Triticum umbellulatum (1). In 1971, 4 years after cultivars with this gene were released in the United States, leaf rust races with virulence to Lr9 were detected. In Mexico, cultivars with Lr9 have not been released and leaf rust races with Lr9 virulence have not been detected. Resistance gene Lr25 was transferred to wheat from Rosen rye (1) and has been effective worldwide, but this gene has not been used commercially because of possible negative effects on yield (1). Rust samples collected at different locations in Nuevo Leon State of Mexico during the 2004-2005 and 2005-2006 wheat crop seasons were analyzed on seedlings of wheat leaf rust differentials in the greenhouse from single pustule isolates. The race nomenclature used is described in Singh (2). Among the races identified from this area, seven, MLJ/SP, TNM/JP, TLB/JP, TNM/KP, TNR/JP, TNB/JN, and TMB/JP, were virulent to both of these genes. Virulence to Lr9 and Lr25 were confirmed by repeating tests using Lr9 differentials 'RL6010' and 'McNair 701' and Transec and three other Lr25 wheat lines developed at CIMMYT, which carry Lr25. To our knowledge, this is the first confirmed report of virulence to Lr9 in Mexico and virulence to Lr25 in the world. These isolates are conserved at CIMMYT for future reference.

Resitência de Eucalyptus globulus e Eucalyptus nitens à ferrugem (Puccinia psidii)

Avaliou-se a resistência das espécies de Eucalyptus globulus e Eucalyptus nitens inoculadas com um isolado uredinospórico monopustular de Puccinia psidii origininário de plantio de Eucalypstus grandis (UFV-2) em Itapetininga, SP. A avaliação foi realizada aos 12 dias após a inoculação, e quantificou-se a doença por meio de uma escala de notas com quatro classes de severidade da doença (S0, S1, S2 e S3). Em média, aproximadamente 60% das plantas de E. globulus e 50% de E. nitens foram resistentes a P. psidii. A variabilidade intra-específica nos materiais estudados indica ser possível a clonagem de genótipos resistentes para plantio comercial ou para uso em programas de melhoramento genético.

Development and characterization of EST-SSR markers for the crown rust pathogen of ryegrass (Puccinia coronataf.sp.lolii)

The causative organism of crown rust in ryegrasses (Puccinia coronata f.sp. lolii) is an obligate biotroph that causes significant economic losses within the temperate grazing industries of dairy, meat, and wool production. This study reports on the development, transferability, and utility of gene-associated simple sequence repeat (SSR) molecular markers for crown rust. Analysis of 1,100 expressed sequence tag (EST) sequences from a urediniospore-derived cDNA library detected 55 SSR loci. The majority of EST-SSR arrays contained perfect trinucleotide repeats with consistently low repeat numbers, and the motifs (ACC)n and (CAT)n were most commonly represented. DNA extraction from single pustules, in conjunction with multiple displacement amplification, provided the basis for PCR-based screening to evaluate genetic marker performance. An example of the identification of intraspecific genetic diversity was obtained from the analysis of 16 P. coronata isolates originating from the United Kingdom, Australia, New Zealand, and Japan. A subset of 12 robust EST-SSR markers was informative for determination of pathogen diversity within and between these localities. It was also demonstrated that crown rust EST-SSR markers were capable of cross-amplification in closely related fungal taxa (Puccinia spp.) and filamentous fungi within the Ascomycota.

First Report of Virulence in Puccinia graminis f. sp. tritici to Wheat Stem Rust Resistance Genes Sr8b and Sr38 in South Africa.

During the 2000 to 2001 season, 27 stem rust samples were collected from wheat (Triticum aestivum), barley (Hordeum vulgare), and triticale (× Triticosecale) cultivars and lines in the Western Cape, South Africa. Following inoculation and multiplication on McNair 701 seedlings, 40 single pustule isolates of P. graminis f. sp. tritici were established. Twenty-six isolates obtained from wheat, barley, or triticale that produced a similar reaction pattern on a set of differentiating host lines, were designated as pathotype Pgt-2SA55. Pgt-2SA55 is avirulent to Sr5, -6, -7b, -8b, -9b, -9e, -9g, -23, -24, -27, -30, -38, and -Gt, and virulent to Sr11, and -Agi. The remaining 14 isolates, all from wheat and designated as pathotype Pgt-2SA88, were avirulent to Sr24, -27, and -Agi, and virulent to Sr5, -6, -7b, -8b, -9b, -9e, -9g, -11, -23, -30, -38, and -Gt. On an expanded differential set, representative isolates of each pathotype were all avirulent to Sr13, -15, -21, -22, -25, -26, -29, -31, -32, -33, -35, -39, -43, and -Em, and virulent to Sr7a, -8a, -9a, -9d, -9f, -10, -12, -14, -16, -19, -20, -34, and Lc. Pgt-2SA55 was avirulent on cv. Renown (Sr2, -7b, -9d, and -17), whereas Pgt-2SA88 was virulent on this cultivar and Line R Sel carrying only Sr17. Both pathotypes differ from those identified previously in South Africa (1) and to our knowledge, Pgt-2SA88 is the first local isolate to have virulence towards Sr8b and the T. ventricosum-derived gene Sr38. Virulence to Sr38 has been reported in a P. graminis f. sp. tritici isolate collected in Uganda (2). Pathotype Pgt-2SA88 is virulent to seedlings of the previously resistant South African cvs. SST 57 (heterogeneous), Tugela, Tugela DN, and PAN 3377. Furthermore, 20% of the elite breeding lines in the spring and winter wheat breeding program of the Small Grain Institute expressed susceptible seedling reactions to Pgt-2SA88. Triticale cvs. Rex and Kiewiet were heterogeneous in their seedling reaction towards Pgt-2SA55. Seedling and field reactions recorded for the barley cvs. Sterling and SSG 532 and the experimental varieties Puma and Jaguar, showed an increase in stem rust susceptibility to Pgt-2SA55 when compared with existing South African pathotypes. The higher incidence of stem rust in commercial fields and experimental plots of wheat and barley in the Western Cape may be attributed to a recent increase in the cultivation of stem rust-susceptible cultivars in the region. The detection of two new pathotypes of P. graminis f. sp. tritici is of concern to the local small grain industry and requires continued resistance breeding.

Variability in isolates of Puccinia polysora in Brazil

The main objective of this work was to evaluate the variability of the southern rust pathogen Puccinia polysora in Brazil, based on its virulence on a set of maize (Zea mays) cultivars. Sixty single pustule isolates, from different areas of occurrence of southern rust, were evaluated for their virulence to 50 maize experimental hybrids. Six cultivars showed a clear distinction between susceptible and resistant reaction, and were used to characterize the variability of the pathogen. Seventeen virulence patterns were identified among the 60 isolates tested. The most frequent virulence patterns identified, were observed in all locations of sampling, which suggests the absence of geographical differentiation among prevalent populations of P. polysora in Brazil.

Virulence of Blumeria graminis f. sp. tritici Populations in Morocco.

The incidence and severity of powdery mildew, caused by Blumeria graminis f. sp. tritici, have increased in Morocco during the past decade as a result of the introduction and intensive production of a few semidwarf cultivars of bread wheat (Triticum aestivum) and durum wheat (Triticum turgidum) that are genetically uniform, and the increased utilization of nitrogen fertilizers and irrigation. The virulence of the pathogen population has not been characterized in Morocco, and little is known about the spectra and distribution of virulence in B. graminis populations. Such knowledge will facilitate the identification and utilization of effective resistance genes in cultivar development and deployment. Isolates of B. graminis collected in 1999 and 2000 from three Moroccan wheat production areas were analyzed for virulence using a host differential series comprised of 13 known genes conferring resistance to powdery mildew. Segments of primary leaves from 12-day-old seedlings of the wheat differentials were inoculated with isolates of B. graminis derived from a single pustule. Powdery mildew reactions were assessed on a 0 to 9 scale 12 days after inoculation. Virulence frequencies, complexity, and racial composition of the pathogen population were determined. Data were analyzed for associations among pairs and triplets of virulence genes and for distribution of virulence genes among pathotypes. High frequencies of virulence to genes Pm1, Pm3c, Pm3f, Pm4a, pm5, and Pm7 were found over both years and across all three regions. Frequencies of virulence for Pm17 and Pm2 were intermediate, while virulence frequencies for Pm3a, Pm3b, Pm3d, and Pm4b were low. Virulence to Pm8 increased to high levels, while virulence to Pm4a decreased across the area surveyed from 1999 to 2000. The random distribution of virulence genes among patho-types indicates that sexual reproduction contributes to the variability of the pathogen. The Moroccan population of Blumeria graminis f. sp. tritici is composed of complex and highly variable pathotypes (87% of the isolates had five or more virulence genes), and strategies for deployment of resistance genes should take into account this complexity.

Virulence of isolates of Albugo Candida from western Canada to Brassica species

Isolates of Albugo Candida, collected from different geographical locations in western Canada, were tested for virulence on a set of differentials from Brassica species to determine the variability and distribution of different races and pathotypes. Most isolates were classified as race 7 based on virulence to Brassica rapa accessions and these could be subdivided broadly into two pathotypes, 7A or 7V, on the basis of their virulence to B. rapa cvs. Torch and Reward. Some isolates were classified as race 2 based on virulence to Brassica juncea and these could also be subdivided into pathotypes, 2A or 2V, based on their virulence to B. juncea cvs. Burgonde and Cutlass. The predominant pathotype was 7V. Two isolates of race 7, 28-7 and 29-1, appeared to be less virulent as they were avirulent on all of the differentials except rapid-cycling B. rapa accession CrGCl-18. Race 7 was most prevalent in collections from Alberta and Manitoba. In British Columbia, pathotypes 2A, 2V, 7A, and 7V were commonly observed and about 50% of the sample collections were mixtures of races 2 and 7. A few single pustule isolates from the Peace River region of Alberta and British Columbia appear to be hybrid pathotypes combining virulence characteristics of pathotypes 2A or 2V with 7A or 7V. These isolates are pathogenic on both B. juncea and B. rapa cultivars.