Ariano M. Prestes

Chromosome characterization in Thinopyrum ponticum (Triticeae, Poaceae) using in situ hybridization with different DNA sequences

Thinopyrum ponticum (2n = 10x = 70, JJJJsJs) belongs to the Triticeae tribe, and is currently used as a source of pathogen resistance genes in wheat breeding. In order to characterize its chromosomes, the number and position of 45S and 5S rDNA sites, as well as the distribution of the repetitive DNA sequences pAs1 and pSc119.2, were identified by fluorescent in situ hybridization. The number of nucleoli and NORs was also recorded after silver nitrate staining. Seventeen 45S and twenty 5S rDNA sites were observed on the short arms of 17 chromosomes, the 45S rDNA was always located terminally. On three other chromosomes, only the 5S rDNA site was observed. Silver staining revealed a high number of Ag-NORs (14 to 17) on metaphase chromosomes, whereas on interphase nuclei there was a large variation in number of nucleoli (one to 15), most of them (82.8%) ranging between four and nine. The pAs1 probe hybridized to the terminal region of both arms of all 70 chromosomes. In addition, a disperse labeling was observed throughout the chromosomes, except in centromeric and most pericentromeric regions. When the pSc119.2 sequence was used as a probe, terminal labeling was observed on the short arms of 17 chromosomes and on the long arms of five others. The relative position of 45S and 5S rDNA sites, together with the hybridization pattern of pAs1 and pSc119.2 probes, should allow whole chromosomes or chromosome segments of Th. ponticum to be identified in inbred lines of wheat x Th. ponticum.

Genetic control of resistance to soilborne wheat mosaic virus in Brazilian cultivars of Triticum aestivum L. Thell.

In Southern Brazil, under ideal conditions Soilborne Wheat Mosaic Virus (SBWMV) induces yield reductions to the wheat crop of over 50%. The only effective way of controlling the disease is through resistance. However, the inheritance of resistance is not been fully understood. The purpose of this work was to study the genetic control of resistance to SBWMV. Crosses were carried out between the resistant wheat cultivar Embrapa 16 and the susceptible cultivars BR 23 and IAC 5-Maringá, at the National Wheat Research Centre, Passo Fundo, RS, Brazil. The parents, F1, F2, and backcrosses were sown in plots in a field where soil was naturally infested with the vector of the virus, the fungus Polymyxa graminis, in order to promote natural infection. All plants were individually evaluated for severity and type of lesions, according to a scale of 0 to 5, where, 0 = absence of symptoms and 5 = plants severely affected by mosaic plus dwarfing and rosetting. The statistical analyses of the data showed broad sense heritability values between 43% and 55%. The data suggested the presence of two genes controlling resistance to SBWMV in the segregating population of both crosses.

Mitotic instability in wheat×Thinopyrum ponticum derivatives revealed by chromosome counting, nuclear DNA content and histone H3 phosphorylation pattern

To evaluate the mitotic stability of Triticum aestivum×Thinopyrum ponticum derivatives (BC2F7 and BC2F5 doubled haploids), chromosome counting by both conventional and immunostaining techniques, and measurement of DNA content were performed. The wheat progenitor line, PF 839197, the wheat recurrent parent CEP 19 and the control Chinese Spring were also investigated. In the hybrid derivatives, chromosome number ranged from 2n=36 to 60, with a predominance of chromosome numbers higher than 2n=42, that was confirmed by determination of nuclear DNA content. Chinese Spring’ and PF 839197 were stable, but CEP 19 showed chromosome number variation (20%). Analyses of non-pretreated cells revealed the presence of anaphase bridges, lagging chromatids, chromosome fragments and micronuclei. Immunostaining with an antibody recognizing histone H3 phosphorylated showed dicentric chromatids forming anaphase bridges and pericentromeric phosphorylation at centric chromosome fragments but not at lagging chromatids. The possible causes of the observed mitotic instability are discussed.

Virulência, atividade enzimática e padrões de isoesterases de isolados de Pyrenophora chaetomioides, agente etiológico da mancha de grãos e folhas de aveia

The complexity of the population of Pyrenophora chaetomioides, the major causal agent of the oat (Avena sativa) leaf and kernel spot, is not well known in south Brazil. Therefore, studies on population diversity are useful to the breeding programs aimed at obtaining genetic resistance. In this work, eight isolates were selected from oat seeds harvested in the three southern Brazilian States. In order to test their virulence, the isolates were inoculated on six oat varieties and evaluated for disease severity and lesion type. All cultivars were susceptible to the isolates tested although variation in disease intensity among them was noticed. In another study, the isolates were evaluated in relation to their amilolytic, proteolytic and lipolytic activities on enzyme-specific media. Results from the inoculations on six oat cultivars showed a correlation between higher enzymatic activity and virulence of the isolates. Also, their a and b esterase patterns were compared by polyacrylamide gel electrophoresis. Seven distinct isoenzymatic patterns of a and b esterase were observed among the isolates, although they were not correlated with virulence on oat seedlings

Resistance of barley genotypes to brown leaf spot

Resistance of 59 barley cultivars to three distinct isolates of Bipolaris sorokiniana, causing brown leaf spot was tested on seedlings and adult plants in a screen house and in a growth room, by determination of disease incidence, disease severity, and rate of lesion expansion. The disease reaction and severity at the seedling stage differed among cultivars. The cultivars MNS Brite, NDB 112, Kindred, Parkland, and Oderbrucke were moderately resistant to brown leaf spot, but the resistance was partial to all three isolates. None genotype with complete resistance was found. The cultivars CI 9539, Svanhals, and Chevron, considered as sources of resistance, were classified as moderately susceptible, and susceptible, respectively. Disease severity, disease reaction, and incidence of B. sorokiniana in grains also differed among the cultivars at the adult plant stage. Nevertheless, none of the genotypes was resistant to B. sorokiniana. The rate of lesion expansion differed among cultivars BR 2, MN 698, Kitchin, Svanhals, and NDB 112, with NDB 112 having the slowest expansion rate (0.194–0.205 mm2/day).

Incidência e índice de doença do mosaico do trigo em cereais de inverno e em gramíneas de verão, associados ao Polymyxa graminis

The Soil-borne wheat mosaic virus (SBWMV) is transmitted by the fungus Polymyxa graminis. To evaluate the incidence and the disease index (DI%) and the presence of the vector in the root system, an experiment was carried out using: oat (Avena strigosa and A. sativa), barley (Hordeum vulgare), triticale (Triticum secale), wheat (Triticum aestivum), Lilium multiforum, mayze (Zea mays), sorghum (Sorghum bicolor), Pannisetum americanum, Digitaria sp. and Brachiaria sp. The experiment was conducted during two sowing periods. Incidence was calculated based on the percentage of the symptomatic plants and grades (0-5) were given to determine the DI (%). Root segments were collected, then stained with solution of cotton blue-lactofenol and visualized in optical microscope. The quantity of resting spores groups was rated. No symptoms were observed on oat species, however, the presence of resting spores in moderate quantities was observed on barley. The incidence and DI (%) for the triticale and wheat in the first sowing period were higher than in the second one. A direct relationship between DI (%) and the quantity of resting spores on root was observed. No symptoms of SBWMV or resting spores in the root system of summer grasses were observed.

Atividade isoenzimática em plantas de trigo infectadas com o vírus SBWMV

O objetivo deste trabalho foi elucidar a atividade e a expressao isoenzimatica das esterases, das peroxidases e das aspartato aminotransferases em funcao da infeccao de plantas de trigo pelo Soil-borne wheat mosaic virus (SBWMV). Foram analisadas, aos 45 dias apos a emergencia, quatro cultivares e uma linhagem de trigo, com diferentes niveis de resistencia ao SBWMV: BRS Guabiju, BRS 194, BRS 179, BR 23 e PF 980524. De modo geral, ocorreram diferencas qualitativas e quantitativas intra e interpopulacional, quando comparadas plantas assintomaticas e sintomaticas ao SBWMV. Para o sistema esterase, nove padroes de bandas foram determinados e para peroxidase e aspartato aminotransferase foram detectados tres padroes de bandas, para ambas as condicoes. Padroes eletroforeticos foram observados para plantas infectadas, quando comparadas com as nao infectadas, destacando-se a atividade da esterase, o que permitiu identificar com maior precisao o estado metabolico e diferenciado das celulas.

Cultivo de embriões em retrocruzamentos entre Triticum aestivum Thell. e Agropyron elongatum host. & beauv.

Resistance to fungal diseases of wheat has been transferred from perennial species of tribe Triticeae, but the hybrid so formed presents immature embryos. Although rescue and in vitro culture of these embryos has been widely utilized, its efficiency is still very low. This work aimed to obtain backcrossing progenies in hybrid F1 (2n=56), derived from crossing between wheat (Triticum aestivum) (2n=42) and Agropyron elongatum (2n=70), through in vitro culture of immature embryos. Starting from the perennial material of F1 generation, several backcrosses were made using wheat as the recurrent parent. Polinization efficiency was 6.0% in BC1 and 12.4% in BC2. All plants from the BC1 were obtained by in vitro embryo culture. The culture medium used was potato regeneration plus vitamins. From 22 seeds collected 18 embryos were cultured in vitro and gave rise to 12 plants. Fifty percent of those embryos were normal. The remaining 27.8% showed reduced size, 16.7% were deformed and 5.5% had slow growing. The efficacy of immature embryo culture was 66.6%. This result indicates that rescue and culture medium techniques used were efficient for cultivation and regeneration of hybrid embryos, allowing viable backcrosses progenies from intergeneric hybrids.

Efeito do Soil-borne wheat mosaic virus sobre o metabolismo de cinco genótipos de trigo com diferentes níveis de resistência à doença

Com o objetivo de conhecer as alteracoes metabolicas promovidas pelo Soil-borne wheat mosaic virus (SBWMV), um dos virus economicamente mais importantes da cultura do trigo (Triticum aestivum), foram analisados os niveis de proteinas soluveis e determinadas as atividades da peroxidase e da protease em quatro cultivares (BRS Guabiju, BRS 194, BRS 179, BR 23) e uma linhagem (PF 980524) de trigo com diferentes niveis de resistencia ao virus. Os dados obtidos foram submetidos a analise de variância, comparando-se as medias, pelo Teste de Duncan a 5%. Os niveis de proteinas soluveis foram mais elevados nas plantas sem sintomas, enquanto que as atividades da peroxidase e da protease foram maiores em plantas com sintoma de mosaico do que em plantas assintomaticas. Alem disso, pode-se constatar que quanto maior a suscetibilidade do genotipo, maior o nivel de atividade da protease. Estes resultados sao promissores para estudos de inibicao da protease para controle de viroses.

Crop Rotation and Tillage Systems to Control Root Rot and Leaf Spot Diseases of Wheat in Brazil

Soil degradation under conventional tillage is a major ecological problem in Brazil. It has been reported that more than 240 million tons of soil were lost every year in the southernmost Brazilian state up to the end of the 1980 decade due to excessive soil cultivation and heavy rainfall. To prevent erosion farmers were recommended to adopt no-till with debris preserving practices. However, the maintenance of crop residues on soil surface promotes a suitable environment for survival and rapid increase of necrotrophyc pathogens. Tests of crop rotation and soil tillage systems were carried out in Passo Fundo, State of Rio Grande do Sul, Brazil, over the past ten years, aiming to control root rot and leaf spot diseases of wheat. The incidence of leaf spot diseases was reduced by crop rotation, but their severity was not. Nevertheless, crop rotation and tillage systems significantly reduced root rots and increased wheat yields. Although chisel plowing was efficient in controlling root rots and increasing wheat yield, the benefits of disease control by incorporating crop residues into the soil by plowing do not justify the high risk of soil erosion losses.