RESUMO Em experimentos conduzidos em câmara climatizada e laboratório, quantificou-se a ação preventiva, curativa e erradicativa dos fungicidas no controle das raças MFT-MT e TFP-HT de Puccinia triticina. Avaliou-se o efeito dos fungicidas tebuconazol (triazol) e azoxistrobina (estrobilurina), isoladamente. As plântulas foram inoculadas com uma suspensão de 50 x 103 uredosporos/mL de água destilada adicionada de 120 μL/L de adjuvante (polioxietileno sorbitano monolaurato Tween 20 - Synth). Os fungicidas foram aplicados, 24 horas antes da inoculação (controle preventivo), 96 horas após a inoculação (controle curativo) e dez dias após a inoculação (controle erradicativo), tanto nas plântulas (in vivo) cultivadas em vasos como nos segmentos foliares (in vitro) em placas de Petri. Avaliou-se o efeito dos tratamentos em função do número de urédias/cm2 e a produção de uredosporos/urédia, in vivo e in vitro. Os fungicidas aplicados preventivamente, para ambas as raças, controlaram 100% a ferrugem da folha e curativamente somentre a azoxistrobina. As raças testadas permanecem sensíveis à azoxistrobina, porém, mantendo a redução da sensibilidade ao tebuconazole. O método de folhas de trigo destacadas foi eficiente na avaliação da sensibilidade de raças de P. triticina a fungicidas tendo as folhas permanecido verdes por 18 dias.

ABSTRACT In experiments conducted in a growth chamber and in laboratory, the preventive, curative and eradicative action of fungicides was assessed for the control of Puccinia triticina races MFT-MT and TFP-HT. The effect of fungicides tebuconazole (triazole) and azoxystrobin (strobilurin) was evaluated separately. Seedlings were inoculated with a suspension of 50 x 103 uredospores/mL distilled water added of 120 μL adjuvant (polyoxyethylene sorbitan monolaurate Tween 20 - Synth). Fungicides were applied 24 hours before inoculation (preventive control), 96 hours after inoculation (curative control) and ten days after inoculation (eradicative control), both in seedlings (in vivo) grown in pots and in leaf segments (in vitro) on Petri dishes. The effect of treatments based on the number of uredia/cm2 and the production of uredospores/uredium were tested in vivo and in vitro. When applied preventively, for both races, the two fungicides controlled 100% leaf rust, and when applied curatively, only azoxystrobin led to 100% control. The tested races remain sensitive to azoxystrobin but maintain the reduction in sensitivity to tebuconazole. Detached wheat leaf assay was efficient in assessing the sensitivity of P. triticina races to fungicides and leaves remained green for 18 days.

RESUMO A ferrugem da folha do trigo causada pelo fungo Puccinia triticina, pode causar danos de até 62%. Esse trabalho objetivou testar o efeito de concentrações de uredosporos no processo infeccioso de quatro raças fisiológicas. As raças MFJ-MN, MFT-MT 4002 S, TPT-HT e TDP-HT foram inoculadas, na primeira folha expandida no estádio de plântula, respectivamente nas cultivares Ônix, Abalone, Morocco e Quartzo. Foram testadas as concentrações de 0,0; 5 x 103; 10 x 103; 20 x 103 e 40 x 103 uredosporos/mL de óleo mineral (Soltrol). As plântulas, após a inoculação, foram mantidas em câmara climatizada a 20 ± 2 ºC, umidade próxima a 100% e no escuro por 20 horas. Quinze dias após a inoculação foi avaliada a densidade de urédia/folha. A concentração de 40 x 103 uredosporos/mL resultou numa intensidade da doença que permite com segurança a diferenciação de cultivares suscetíveis e resistentes na fase de plântula, sem causar a senescência das folhas pela alta densidade de urédias.

ABSTRACT Wheat leaf rust caused by the fungus Puccinia triticina may lead to damage of up to 62%. This study aimed to test the effect of different uredospore concentrations on the infectious process of four physiological races. The races MFJ-MN, MFT-MT 4002 S, TPT-HT and TDP-HT were inoculated, when the first leaf was expanded in the seedling stage, on cultivars Ônix, Abalone, Morocco and Quartzo, respectively. The tested concentrations were 0.0; 5 x 103; 10 x 103; 20 x 103 and 40 x 103 uredospores/mL mineral oil (Soltrol). After inoculation, seedlings were kept in a growth chamber at 20°C ± 2, near 100% humidity, in the dark, for 20 hours. Fifteen days after inoculation, the density of uredia/leaf was evaluated. The concentration of 40 x 103 uredospores/mL resulted in a disease intensity that allows safe differentiation between susceptible and resistant cultivars in the seedling stage, without causing leaf senescence due to high uredinium density.

Experimentos foram conduzidos para determinar, in vivo a IC50 e CI90 para fungicidas inibidores da demetilação (IDM)(triazois) e inibidores da quinona externa (IQe) (estrobilurinas) a cinco raças de Puccinia triticina mais frequentes na safra 2007, no Sul do Brasil. Os experimentos foram realizados em câmara de crescimento com plântulas de trigo. Os fungicidas IDMs foram testados nas concentrações em mg/L de 0,0; 0,02; 0,2; 2,0; 20,0; 100,0 e 200,0 e os IQes nas concentrações de 0,0; 0,0001; 0,001; 0,01; 0,1, 1 e 10,0 mg de ingrediente activo/L de água. Os fungicidas foram aplicados preventivamente 24 horas antes da inoculação das plântulas com os esporos do fungo. O efeito dos tratamentos foi avaliado pelo número de urdias/cm². A menor IC50 (concentração inibitória) para fungicidas DMI determinados para MCG-MN, raça sensível, variaram de 0,33 a 0,91 e os maiores valores de MDP-MR, MDT-MR, MDK-MR, MFH-HT corridas, variou de 9,63 a 85,64 mg/L (suspeitas de insensibilidade). A CI50 dos fungicidas IQes variou de 0,0018-0,14 mg/L. O fator de redução da sensibilidade para os DMIs variou de 8,8-238,8 e para os IQEs de 0,3-1,5 mg/L. Foi confirmada a redução na sensibilidade de raças MDP-MR, MDT-MR, MDK-MR, MFH-HT para DMIS e sua sensibilidade aos fungicidas IQe.

Experiments were carried out to determine in vivo the IC50 and the IC90 for demethylation-inhibitor fungicides (DMIs, triazoles) and quinone outside inhibitors (QoIs, strobilurins) to the five most frequent races of Puccinia triticina in 2007 growing season in Southern Brazil. The tests were done in a greenhouse with wheat seedlings. DMI fungicides were tested at the concentrations, in mg/L, 0.0; 0.02; 0.2; 2.0; 20.0; 100.0 and 200.0, and QoIs at the concentrations 0.0; 0.0001; 0.001; 0.01; 0.1; 1 and 10.0 mg of active ingredient/L water. Fungicides were preventively applied at 24 hours before the inoculation of seedlings with the fungal spores. The effect of treatments was assessed based on the number of uredia/cm². The lowest IC50 (inhibitory concentration) for DMI fungicides determined for MCG-MN, sensitive race, ranged from 0.33 to 0.91 mg/L, while the highest values for MDP-MR, MDT-MR, MDK-MR, MFH-HT races, varied from 9.63 to 85.64 mg/L (suspected insensitivity). QoI fungicide presented an IC50 varying from 0.0018 to 0.14 mg/L. The sensitivity reduction factor for DMIs varied from 8.8 to 238.8, and for QoIs from 0.3 to 1.5 mg/L. Sensitivity reduction was confirmed for the races MDP-MR, MDT-MR, MDK-MR, MFH-HT to DMIs, as well as their sensitivity to QoI fungicides.

Os estudos da variabilidade genética de Puccinia triticina em inóculo coletado no Brasil começaram em 1941 por Vallega. O trabalho pioneiro no Brasil teve início em 1949 no Instituto Agronômico do Sul, Ministério da Agricultura (MA) em Pelotas, RSs, depois de 1975 na Embrapa Trigo em Passo Fundo, RS. Em 2002 prosseguiram as análises de identificação de raças na OR Melhoramento de Sementes, paralelamente ao programa da Embrapa, ambos em Passo Fundo. Trabalharam na identificação de raças no Brasil, Ady Raul da Silva em Pelotas (MA), Eliza Coelho em (Pelotas (MA) e em Passo Fundo (Embrapa), Amarilis Labes Barcellos em Pelotas (MA) e em Passo Fundo (Embrapa e OR), Camila Turra em (Passo Fundo (OR) e Márcia Chaves em (Passo Fundo (Embrapa). Até a safra 2010, 59 raças já foram determinadas, considerando-se a partir de 1979, de acordo com a diferenciação pela expressão de cada gene de resistência Lr. Na média surge uma a três raças por ano. A pesquisa tem se concentrado no uso da resistência vertical, porém, ultimamente, algumas instituições têm buscado a resistência mais durável, do tipo planta adulta (horizontal, menos específica a raças). A não interrupção do monitoramento da população patogênica da ferrugem da folha do trigo no Brasil durante tantas décadas possibilitou conhecer a evolução das raças e da virulência. Embora tenha havido esforço de alguns programas O uso da nomenclatura internacional adotado por alguns programas tem permitido a comparação da variabilidade do fungo ocorrida no Brasil com a de outros países e especialmente com aqueles onde as fronteiras não são barreiras para o transporte dos esporos, como confirmado pela ocorrência de mesmas raças em toda a região.

Studies on the genetic variability of Puccinia triticina in inoculum collected in Brazil started in 1941 with Vallega (20). The pioneering work in Brazil dates from 1949 (16) at "Instituto Agronômico do Sul", Ministry of Agriculture (MA), in Pelotas, Rio Grande do Sul State (RS), and continued after 1975 at Embrapa Wheat in Passo Fundo, RS. In 2002, analyses for the identification of P. triticina races continued at OR Seed breeding, simultaneously to Embrapa's program, both in Passo Fundo. The investigators involved in the identification of races in Brazil were Ady Raul da Silva in Pelotas (MA), Eliza Coelho in Pelotas (MA) and in Passo Fundo (Embrapa), Amarilis Labes Barcellos in Pelotas (MA) and in Passo Fundo (Embrapa and OR), Camila Turra in Passo Fundo (OR) and Marcia Chaves in Passo Fundo (Embrapa). From 1979 to 2010 growing season, 59 races were determined, according to the differentiation based on the expression of each Lr resistance gene. On average, one to three new races are detected per year. Research has focused on the use of vertical resistance; however, lately some institutes have searched more durable resistance, of the adult-plant type (horizontal, less race-specific). The uninterrupted monitoring of the wheat rust pathogenic population in Brazil during so many decades allowed the understanding of the evolution and virulence of races. The use of international nomenclature adopted by some programs has allowed the comparison of the fungus variability in Brazil with that in other countries, especially where frontiers are not barriers for spore transportation, confirmed by the occurrence of the same races all over one region.

A população de Puccinia triticina, agente causal da ferrugem da folha do trigo, é extremamente dinâmica na região do Cone Sul da América do Sul, onde o surgimento de novas raças é freqüente. A cultivar de trigo "BRS 194" foi a segunda variedade com maior disponibilidade de sementes para plantio no Rio Grande do Sul e em Santa Catarina em 2005, por apresentar características como rusticidade, elevado rendimento de grãos e resistência qualitativa a todas as raças de P. triticina ocorrentes no Brasil e em outros países da América do Sul. Em 2005, pústulas de ferrugem da folha foram observadas sobre plantas desta cultivar, tanto em lavouras quanto em campos experimentais, indicando a possível superação de sua resistência. O objetivo deste trabalho foi identificar a raça de P. triticina presente em amostras oriundas de "BRS 194" e verificar se esta se tratava de uma nova virulência do patógeno, a qual teria superado sua resistência. Oito amostras de ferrugem provenientes da cultivar "BRS 194" foram enviadas em 2005 à Embrapa Trigo, Passo Fundo, Rio Grande do Sul, para isolamento e identificação por meio da Série Internacional de Hospedeiros Diferenciais específica para este patógeno. Todas as amostras apresentaram a mesma combinação de virulência, a qual correspondeu ao código MFP-CT, conforme o Sistema Norte-Americano de nomenclatura do patógeno. Esta foi a primeira vez que este código foi detectado no Brasil, caracterizando o surgimento de uma nova raça de P. triticina virulenta à "BRS 194". Outras cultivares de trigo, também amplamente semeadas, foram inoculadas com a nova raça, sendo que algumas foram suscetíveis e outras resistentes. Entre as cultivares resistentes estão "Fundacep 30" e "IPR 84", as quais permanecem também resistentes a todas as raças do patógeno ocorrentes no Brasil.

The population of Puccinia triticina, the causal agent of wheat leaf rust, is extremely dynamic in the South Cone region of South America, where the appearance of new races is frequent. The wheat cultivar 'BRS 194' was the second variety in availability of seeds for planting in Rio Grande do Sul and Santa Catarina States in 2005, because it has good agronomic characteristics as rusticity, high yield and resistance to all races of P. triticina occurring in Brazil and other countries in South America. In 2005, pustules of leaf rust were observed in this cultivar on farms and in experimental fields, indicating the probable breakdown of its resistance. The objective of this research was to identify the race of P. triticina present in samples from 'BRS 194' and verify if it was a new virulence of the pathogen able to overcome its resistance. Eight samples of leaf rust from 'BRS 194' were sent to Embrapa - National Wheat Research Center, Passo Fundo, Brazil for isolation and identification in International Sets of Differential Hosts specific for this pathogen. All samples showed the same virulence combination, which corresponded to MFP-CT according to the North-American System of nomenclature for the pathogen's races. That was the first time that this letter code was detected in Brazil, characterizing the emergence of a new race of P. triticina virulent to 'BRS 194'. Other popular varieties were inoculated with the new race, some were susceptible and others were resistant. Among the resistant cultivars were 'Fundacep 30' and 'IPR 84', which also remain resistant to all races of the pathogen occurring in Brazil.

A genetic analysis of adult plant resistance to leaf rust (Puccinia triticina) was performed in in vitro obtained double haploid progenies from a cross between the Brazilian wheat cultivar Trigo BR 35, which, under the high inoculum pressure of the southern region, has been resistant to leaf rust for more than 12 years, and the susceptible cultivar IAC 13-Lorena. Haplodiploidization via in vitro gimnogenesis was done by somatic elimination of the pollen donor genome after maize pollination of the F1 plants. The advantages and usefulness of double haploids (DH) for genetic analysis of complex inherited traits like durable adult-plant resistance to wheat leaf rust were evident: it was possible to analyze inheritance patterns in this cross by using only the 35 DH homozygous segregant lines obtained by in vitro embryo culture of F1 flowers pollinated by maize, this number being equivalent to 1,225 conventional F2 lines because of lack of heterozygosity. After being infected with MCG and LPG races, the results indicated that Trigo BR 35 has two resistance genes. One of the genes expressed resistance only after the intermediate stage of plant development (5-6 leaves).

Worldwide wheat (Triticum aestivum L. em. Thell, 2n = 6X = 42, AABBDD) breeding programs aim to reorganize genotypes to achieve better yields, environmental adaptation and food quality. The necessary interdisciplinarity for breeding purposes requires an accurate choice of the most appropriate cellular and/or molecular strategies available to be integrated with agronomic approaches in order to overcome the genetic limitation of each cultivated species, at each agroecosystem. Cytogenetics has given a great contribution to wheat genetic studies and breeding, due to viability of chromosomal variants because of homoeology among genomes in this allohexaploid species and the genus Triticum. The level of development of cytogenetic techniques achieved over the last 60 years has set wheat apart from other cereal crops in terms of possibilities to introduce genetic material from other species. Cytogenetic approaches have been extensively used in chromosomal mapping and/or resistance gene transference from tribe Triticeae-related species. Monosomic analysis, entire chromosomes engineered through single additions and/or substitutions, reciprocal translocation through radiation or manipulation of homoeologous pairing, as well as synthesis of new amphiploids to allow homologous recombination by chiasmata evolved considerably since the past decades. The association of tissue culture and molecular biology techniques provides bread wheat breeding programs with a powerful set of biotechnological tools. However, knowledge on genetic system components, cytotaxonomical relationships, cytogenetic structure and evolutionary history of wheat species cannot be neglected. This information indicates the appropriate strategy to avoid isolation mechanisms in interspecific or intergeneric crosses, according to the genome constitution of the species the desired gene is to be transferred from. The development of amphiploids as "bridge" species is one of the available procedures to facilitate gene flow between wheat and related species. Since the environment at the center of origin of wheat in Southern Asia is quite different from subtropical environments, Brazilian breeding programs overcome more challenges to adapt wheat crop to biotic and abiotic stresses than some other countries. The germplasm bank of Embrapa Trigo has about 1000 registered entries of Triticum relatives, Aegilops, Secale and Agropyron species supplied from several germplasm banks distributed over the world which were multiplied and/or selected for naturally occurring or artificially inoculated fungal diseases. Since Aegilops squarrosa L. entries showed very good performance, the genetic variability observed in this species was firstly exploited. It is reported here the strategy used for transferring useful genes from Ae. squarrosa (DD, 2n = 14): crossing with tetraploid species (AABB, 2n = 28), rescue and in vitro culture of immature embryos for regeneration of the trihaploid (ABD, 2n = 21) hybrid, and colchicine treatment for genome duplication resulting in the artificial synthesis of hexaploid wheat lines (AABBDD, 2n = 42). Results of 10,739 artificial pollinations involving 28 cross combinations amongst eight T. durum L., T. dicoccum and T. cartlicum tetraploid entries used as female parents and ten selected Ae. squarrosa sources of resistance as male parents are presented here. Immature embryos from 18 cross combinations were recovered and cultured in vitro. Green plantlets from 13 combinations were regenerated. Fertile amphiploids were recovered only from crosses among entries of tetraploid T. durum and diploid Ae. squarrosa. They originated 11 fertile synthetic amphiploid lines from seven different combinations. Useful stem and leaf rust as well as powdery mildew resistance for future use in breeding programs were obtained.