-Maize seeds, infected by Stenocarpella species, are important sources of inoculum for the introduction and dissemination of stalk and ear rot and macrospore leaf spot diseases. the use of healthy seeds is an important strategy for the preventive control of these diseases. However, one of the difficulties in the health quality control programs for maize seeds is the availability of a reliable and quick method for detecting these fungi during routine seed analyses. Therefore, the objective of the present study was to investigate the possibility of using the PCR technique as an alternative method for accurately detecting these pathogens in maize seed samples. Maize seeds were kept in contact with S. maydis colonie developed in PDA media containing mannitol at -1.4 MPa for 72 h. the seed samples used in this study were prepared with infected seeds at incidences of 100, 20, 10, 2, 1 and zero %.the primers used were able to detect S. maydis fungi in association with seeds with a maximum of 2% , however those primers were not able to differentiate between the two species.Index terns: fungus, molecular detection, stalk and ear rot, macrospore leaf spot.Sensibilidade da técnica PCR na detecção de Stenocarpella sp. associados às sementes de milho RESuMo -Sementes de milho infectadas por Stenocarpella são importantes fontes de inóculo para a introdução e disseminação da podridão do colmo e da espiga e mancha foliar de macrospora em campos de produção. o uso de sementes sadias constitui uma importante estratégia para o controle preventivo dessas doenças. A disponibilidade de métodos rápidos para a detecção desses fungos em análises de rotina é uma das dificuldades em programas de controle de qualidade de sementes de milho, já que o método utilizado demanda longo tempo e sua identificação é bastante subjetiva. o objetivo desse trabalho foi investigar o uso da técnica PCR para a detecção desses patógenos em sementes de milho. Para isto sementes de milho inoculadas com S. maydis foram misturadas a sementes sadias de modo que formassem lotes com incidências de 100, 20, 10, 2, 1 e zero%. o par de primers utilizado para detectar S. maydis foi capaz de detectar o máximo de 2% de incidência, todavia os primers não foram suficientes para diferenciar as duas espécies.termos para indexação: fungo, detecção molecular, podridão do colmo e da espiga, mancha foliar de macrospora.
Maize seeds infected by Stenocarpella macrospora can cause stalk and ear rot and leaf spot. Transmission of this pathogen through seeds may vary according to the cultivar, climatic conditions, and virulence of the pathogen among other factors. The aim of this study was to assess the transmission rate of S. macrospora from seeds of the maize cultivars C1-RB9308YG and C2-RB9108 using artificially infected seeds grown under two temperatures (20 ºC and 25 ºC). Seeds were inoculated by the osmotic conditioning method for 24 h (inoculum potential - P1), 48 h (P2), 72 h (P3) and 96 h (P4). After inoculation, 25 seeds were distributed individually in plastic cups with substrate, with 4 replicates per treatment. At the end of twenty-eight days of daily assessments, all plants were analyzed for the presence of the pathogen by biological methods, and some were sampled at random and analyzed Bio-PCR. The maximum percentages of dead seeds/seedlings in pre-emergence were 74.5% and 82.5% for P3 and P4, respectively. The highest total rate of transmission of the pathogen under study was 85.8% for seeds of the cultivar C1 at the highest inoculum potential (P4), grown at the temperature of 20 ºC.
RESUMOA cultura da aveia, representada pelas espécies Avena sativa L. e Avena strigosa Schreb, é uma das principais alternativas para o cultivo durante o inverno no Sul do Brasil. Os patógenos dessa cultura, como Drechslera avenae causador da helmintosporiose, sobrevivem em sementes e nos restos culturais. Em experimentos conduzidos em laboratório foram testados dois métodos de detecção, incubação em substrato de batata-dextrose-ágar (BDA) e em meio semi-seletivo de Reis, visando selecionar o mais sensível na detecção de D. avenae, Alternaria alternata e Bipolaris sorokiniana e quantificar a incidência destes fungos em sementes de aveia produzidas em diferentes municípios do Rio Grande do Sul. O método semi-seletivo de Reis mostrou-se mais sensível na detecção de D. avenae e A. alternata em aveia branca, para B. sorokiniana, o método com BDA foi o mais sensível em aveia branca, não diferindo do seletivo de Reis para aveia preta. A menor e maior incidência de D. avenae em sementes de aveia branca variaram de 12 a 76% e em aveia preta de 4 a 90% , para A. alternata variaram de 3 a 53% e 2 a 31% em aveia branca e preta respectivamente e B. sorokiniana em aveia branca de 0 a 16% e 0 a 3% em preta. Palavras-chave: Drechslera avenae, Alternaria alternata, Bipolaris sorokiniana helmintosporiose, patologia de sementes. ABSTRACT Sensitivity of methods for detection of pathogenic fungi in white and black oat seeds in Rio Grande do Sul stateThe oat crop, represented by the species Avena sativa and Avena strigosa, is one of the most important alternatives for agriculture during winter in Southern Brazil. Oat pathogens such as Drechslera avenae, the causal agent of helminthosporiosis, survive in seeds and in crop residues. In experiments conducted in the laboratory two media substrates were tested, potato-dextrose-agar and Reis semi-selective, aiming to select the most sensitive in the detection of D. avenae. Two other fungi in seeds were also evaluated, Alternaria alternata and Bipolaris sorokiniana. Another objective of this work was to quantify the incidence of fungi in oat seeds produced in some counties of Rio Grande do Sul state. A total of 38 samples had been plated in gerboxes containing the culture medium and incubated in a climatized chamber. The semi-selective medium was more sensitive in the detection of D. avenae and of A. alternata in white and black oats; on the other hand, for B. sorokiniana, the PDA media was more sensitive in white oats, while for black oats there was no statistical difference. In the quantification of fungi in white and black oat seeds in the various counties, the lowest and highest incidence of D. avenae in white oat seeds varied from 12 to 76% and in black oats from 4 to 90%; for A. alternata it varied from 3 to 53% in white oats and 2 to 31% in black oats; for B. sorokiniana it varied from 0 to 16% in white oats and 0 to 3% in black oats. Keywords: Drechslera avenae, Alternaria alternata, Bipolaris sorokiniana helminthosporiosis, seed pathology.A aveia é uma das principais culturas util...
Cotton Ramulosis (Gossypium hirsutum) is an important disease affecting cotton plantations in Brazil, and its causal agent, Colletotrichum gossypiivar.cephalosporioides(Cgc), according to the Brazilian phytosanitary authority, was considered a regulated non quarantine pest. It makes this microorganism subject to standardization in seed certification programs. The current seed health testing for detecting that pathogen in seed samples does not provide reliable results for routine analysis. On this paper, attempts were made to design specific primers for detection of Cgc associated with cotton seed. Two primer sets were selected based on the analysis of a multiple alignment of gene’s sequence encoding the glyceraldehyde 3-phosphate dehydrogenase from Cgc, C. gossypii and reference strains of the C. gloeosporioides species complex. The conserved sites unique to Cgc strains were used to design specific fragment of 140 bp. The primer specificity was confirmed by using other fungi. The primers produced a detectable band of target DNA of Cgc in all inoculum potentials of the pathogen artificially inoculated by the water restriction technique. The developed primer pair represents, therefore, a reliable and rapid mean to diagnose the Ramulosis agent in cotton seed.
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