Doctor of Philosophy / Department of Plant Pathology / Bikram S. Gill / Segregation distortion describes the transmission of an allele or alleles of a heterozygous locus at a higher frequency than expected in a Mendelian ratio. From the organism's view, segregation distortion is the preferential retention of chromosomal blocks carrying genes beneficial to its fitness and reproductive viability. In wheat the best studied segregation distortes are those introduced from Aegilops species; these selfish genetic elements are named gametocidal (Gc) genes and the chromosomes carrying them are called Gc chromosomes. This genetic mechanism causes chromosome breakage in gametophytes lacking the Gc carrier chromosome, thus favoring its own retention in the genome. While the mode of action of the Gc genes is not yet known, they have been used extensively in wheat genetics for the development of deletion stocks, a key resource for elucidating the structure of physical regions containing important genes. The objective of this study was to develop the tools necessary to map the Gc2 gene derived from Ae. sharonensis and perform map-based cloning. Extensive physical and genetic mapping located the gametocidal gene on the distal 1% of the 4BL arm present in the T4BS[dot in middle of line]4BL-4S[sh superscript]#1L translocation chromosome. Comparative genomics using rice provided markers distal and proximal to the Gc2 locus; however, synteny broke down at the locus. The characterization of this chromosomal region has provided insight into its recombination frequency, synteny and composition; however, the dynamic architecture of the end of the chromosome has made comparative mapping of this region difficult.

This is a study of transcriptional gene regulation in wheat (Triticum aestivum, L.) in response to Russian wheat aphid (RWA) (Diuraphis noxia, Kurdjumov) infestation. The Russian wheat aphid feeds on the phloem sap in the leaves of wheat plants, and causes the leaves of susceptible wheat plants to curl. This forms a protective barrier for the RWA from insecticides and natural enemies. Chlorosis also results from the RWA feeding. In cases of high infestation, death of susceptible plants can also occur. Eleven wheat genes that confer resistance to the Russian wheat aphid have been identified, but their mechanism at molecular level is still not clearly understood. Wheat near-isogenic lines (NILs) were used in a genome-wide, transcriptome analysis using cDNA-AFLP technology. RWA-resistant cultivar ‘Tugela DN’ and RWA-susceptible cultivar ‘Tugela’ were infested with the RWA and leaves were collected from the infested plants at different (0-, 1-, 2-, 6-, 12-, 24-, 48- and 120-) hours post infestation. cDNA samples derived from these leaves was then analyzed by cDNA-AFLP which revealed 18 clusters of differential gene regulation between the two NILs. The results of this experiment show that differential regulation of transcripts occur even within the first hour of infestation. All types of regulation were observed within the clusters. Differentially expressed transcript derived fragments (TDFs) that were randomly isolated from PAGE gels and sequenced (41 TDFs) included sequences in the functional groups similar to those observed in the microarray analysis. The functional categories are cell structure and maintenance [protein synthesis (14%), chaperone (2%), protein degradation (2%), transcription factor (5%)]; photosynthesis [sugar metabolism (5%), carbohydrate metabolism (2%), energy related (7%)]; defenserelated [signaling (7%), defense-related (10%)] while the rest did not have any significant homology to any known or characterized proteins. Previous suppressive subtractive hybridization experiments identified transcripts that are differentially expressed in wheat in response to RWA feeding. More transcripts were identified by PCR from cDNA pools derived from RWA-infested plants as having conserved motifs common in pathenogenesis related proteins. The isolated transcripts were used to generate a defense response-biased microarray chip that was used to investigate the regulation of these transcripts during infestation of RWA resistant wheat plants (‘Tugela DN’) in a time trial. Dual hybridization of CyDye labeled probes derived from the induced ‘Tugela DN’ plants to the microarray chips revealed differential regulation of the immobilized transcripts in wheat, at different time points post infestation with the RWA. Statistical analysis of the CyDye intensities on the 380 spots mounted on the cDNA microarray slides showed 29 transcripts to be significantly regulated (P≤0.05) during the time of the experiment. These included ESTs that were grouped into four functional categories, namely cell structure and maintenance (9 ESTs); photosynthesis (8 ESTs); defense-related (4 ESTs) and those with no significant homology found or proteins with unknown function (8 ESTs). Patterns of regulation of these transcripts in all of the functional categories included all types of regulation e.g. mainly down-regulation, mainly up-regulation, and a combination of up-/up-/down-regulation in response to RWA feeding. In conclusion, data obtained utilizing cDNA microarray and cDNA-AFLP analyses in infested wheat suggest that the ability to maintain structures involved in photosynthesis by regulating the relevant transcripts through-out infestation is an important determinant in plant survival during RWA feeding. The timing of regulation is also important as some of the transcripts are also regulated in RWA susceptible ‘Tugela’ plants but not in a timely manner which leads to loss of energy and subsequent death of susceptible plants. / Dissertation (MSc)--University of Pretoria, 2011. / Genetics / unrestricted

The presented work provides the results of experiments with winter wheat during the growing season 2016/2017, which were established at the field research station of Mendel University in Žabčice. Eight winter wheat varieties were grown on two sites with different water regimes in the soil (optimal conditions - Obora/water-limited conditions - Písky). The varieties were evaluated for the number of spikes per area, thousand seed weight and grain number per spike. Then the grain yield per hectare and harvest index (which was calculated as the ratio of biomass and grain) were evaluated. In the water-limited conditions, there was a decrease in all monitored characters. The site had the largest influence on the number of spikes per area where the average number of spikes per area under water-limited conditions fell by 23 %. The second most affected was thousand seed weight which was decreased by 19 %, and the least affected character was grain number per spike, which was changed by 11 %. The harvest index was lower on water-limited field. The weight of biomass was reduced by 24 – 34 % and weight of grain was reduced by 50 % for evaluated varieties. The average yield at the site with optimal conditions was 10,4 t per ha and at water-limited conditions site it was 6,1 t per ha. According to the results of this harvest year 2017 varieties Patras, Gordian and Cimrmanova raná were found as suitable for worse conditions. On the other hand varieties Tobak and Hyfi seem to be unsuitable for stressful conditions.

Fusarium graminearum (Schwabe), causal organism of fusarium head blight (FHB), has become a major pathogen of wheat (Triticum aestivum L.) throughout North America. Since its discovery in the United States, the disease has spread south and east until at present it is an annual threat for growers of winter wheat in the Mid-Atlantic region. Yield losses for soft red winter (SRW) wheat averaged 908 kg ha-1 in the FHB outbreak of 1998 (Griffey et al., 1999). The economic loss from this single FHB epidemic was an estimated 8.5 million dollars. Environmental conditions favorable for FHB development, including above average rainfall and temperatures during anthesis, have become more common in the Upper-Midwestern wheat-growing region over the past decade, leading to substantial losses in wheat and barley crops. This, coupled with low prices being paid for wheat, has prompted research toward solving the problem of FHB across the nation. The majority of labor and financial resources devoted to FHB research are dedicated to incorporating FHB resistance into adapted wheat lines. While this is a prudent method of combating this disease, this process will take many years to complete. We have examined all FHB assessment parameters, which include FHB incidence, FHB severity, FHB index, percentage fusarium damaged kernels (percentage FDK), and 15-acetyl deoxynivalenol toxin (DON toxin) accumulation, to ascertain which assessment parameters best quantify FHB resistance levels in addition to grain yield and grain volume weight (GVW) losses. FHB index provides the most reliable in-field assessment of a genotype's resistance level, whereas percentage FDK provides a reliable measure of a genotype's resistance level post-harvest. FHB index and percentage FDK are also the most predictive assessment parameters with regard to grain yield and GVW loss. A wide range in both level and type of resistance was observed among genotypes examined in this study. The cultivars Agripro Patton, Ernie, INW9824, Roane, and the experimental line NY87048W-7388 consistently had lower scores for FHB assessment parameters and lower losses of grain yield and GVW. / Master of Science

Wheat is the most widely grown crop in the world and as such, is an essential source of energy and nutrition. The challenges that breeders presently face is to increase production to feed the rising population of the world, while also accounting for climate change, pollution, water and environmental stresses. As genetic uniformity of modern cultivars has increased vulnerability to pests and diseases, the wild relatives of wheat offer a rich source of genetic diversity and stress tolerance traits, that can be harnessed and transferred in to modern wheat. In this study, we used array-based genotyping to explore genetic diversity in 385 domesticated and non-domesticated lines of wheat and their wild relatives. Genetic characterization using the wheat 90K array, and subsequent filtering and validation mapped 9,570 single nucleotide polymorphic markers onto the wheat reference genome. Phylogenetic analyses illustrated four major clades, clearly separating the wild species from the domesticated, and the ancient Triticum turgidum species from modern T. turgidum cultivars. Using this diverse germplasm, a genome-wide association study (GWAS) was performed for leaf rust, the most widespread rust disease of wheat. Identification of novel sources of resistance is necessary to maintain disease resistance and stay ahead in the plant-pathogen evolutionary arms race. GWAS was conducted using eight statistical models for infection types against six leaf rust isolates and leaf rust severity rated in field trials for 3-4 years at 2-3 locations in Canada. Functional annotation of genes containing significant quantitative trait nucleotides (QTNs) identified 96 disease-related nucleotide associated with leaf rust resistance. A total of 21 QTNs were in haplotype blocks or within flanking markers of at least 16 known leaf rust (Lr) resistance genes. The remaining significant QTNs were considered loci that putatively harbor new Lr resistance genes. Future efforts to validate these loci will help understand their role in disease resistance and promote their utility for marker-assisted selection in pre-breeding.

O trigo é um alimento básico da humanidade cuja demanda cresce proporcionalmente ao aumento populacional. Existe carência de pesquisas sobre o efeito da nutrição da planta doadora na resposta androgenética. Este trabalho teve por objetivo avaliar a influência de cinco concentrações de nitrogênio e de boro (25%, 50%, 100%, 150% e 200%) a partir da solução de Sarruge modificada, no cultivo de plantas de trigo doadoras de anteras visando à obtenção de estruturas embriogênicas androgenéticas. Para tanto, foram avaliados os componentes do rendimento (número de colmos, diâmetro e comprimento do colmo principal; comprimento, largura e área da folha bandeira; teor de clorofila da folha bandeira, distância entre a folha bandeira e o último nó e comprimento da espiga); o acúmulo de graus dias e duração do ciclo da semeadura até a coleta das espigas para a cultura de anteras; a formação de estruturas embriogênicas androgenéticas e o desenvolvimento dos micrósporos (tétrade, mononucleado central, mononucleado periférico, binucleado e pólen P). Constatou-se que as concentrações de nitrogênio afetaram significativamente os componentes do rendimento, a formação de estruturas embriogênicas androgenéticas e o desenvolvimento dos micrósporos. A duração do ciclo das plantas cultivadas na concentração de 25% de nitrogênio foi menor que nas demais doses, apresentando diferença de até 3,3 dias quando comparada às plantas submetidas a doses mais elevadas. Houve aumento linear na produção de estruturas embriogênicas androgenéticas em função das doses crescentes de nitrogênio utilizadas no cultivo das plantas doadoras das anteras. As doses de nitrogênio interferiram também no estádio de desenvolvimento dos micrósporos, para todas as variáveis estudadas. Essa influência no desenvolvimento dos micrósporos foi efetiva enquanto a folha bandeira menos um encontrava-se no primeiro terço de deslocamento em relação à distância total entre a folha bandeira e o último nó do colmo. As concentrações de boro utilizadas nas soluções de cultivo das plantas de trigo doadoras de anteras não influenciaram nos componentes do rendimento, na formação de estruturas embriogênicas, na duração do ciclo da planta e na maioria das variáveis estudadas com relação ao desenvolvimento dos micrósporos. O desenvolvimento dos micrósporos na espiga seguiu o padrão normal descrito para a espécie, independentemente dos nutrientes estudados. Concluiuse que as concentrações de nitrogênio influenciaram positivamente nos componentes do rendimento (exceto no comprimento da espiga), na formação de estruturas embriogênicas e na distância entre a folha bandeira e o último nó do colmo (marcador morfológico da coleta das espigas para cultura de anteras), enquanto que as concentrações de boro utilizadas no cultivo das plantas doadoras de anteras não apresentaram esse efeito. / Wheat is the staple food of humanity whose demand grows in proportion to the population growth. There is lack of research about the effect of the nutrition of the donor plant in the androgenetic response. This work aim for evaluate the influence of five concentrations of nitrogen and boron (25%, 50%, 100%, 150% and 200%) from the solution of Sarruge modified, in the cultivation of wheat plants donors of anthers aiming the obtainment of androgenetics embryogenic structures. Both for, were evaluated the yield components (number stalks, diameter and length of the main stem; length, width and area of flag leaf; chlorophyll content of flag leaf, distance between flag leaf and the last node and ear length); the accumulation of degree-days and cycle duration of sowing until collection of ears to the anther´s culture; the formation of androgenetics embryogenic structures and the development of microporous (determination of the number of cells in stages: tetrad, central mononucleate, peripheral mononucleate and binucleated and occurrence of pollen P). It was found that the concentrations of nitrogen significantly affected the yield components, the formation of androgenetics embryogenic structures and the development of microspores. The duration of the cycle of the cultivated plants in the concentration of 25% of nitrogen was lower than in other doses, presenting difference of up to 3.3 days when compared to plants subjected to higher doses. There was a linear increase in the production of androgenetics embryogenic structures in function of increasing doses of nitrogen used in cultivation of donor plants of the anthers. The doses of nitrogen interfered also at the stage of development of microspores, for all variables studied. This influence on the development of microspores was effective while the flag leaf less one was in the first third of displacement in relation to the total distance between the flag leaf and the last node of the culm. The concentrations of boron used in solutions of cultivation of wheat donors plants of anthers did not affect the income components, in the formation of embryogenic structures, on the duration of the cycle of the plant and in the majority of the variables studied in relation to the development of the microspores. The development of microspores in spike followed the normal pattern described for the species, regardless of the nutrients studied. It was concluded that the concentrations of nitrogen positively influenced in yield components (except the length of the ear), the formation of embryogenic structures on and the distance between the flag leaf and the last node of the culm (morphological marker of collection of ears to anther culture), while the concentrations of boron used for the cultivation of plants donated anthers did not have this effect.

Made available in DSpace on 2017-07-25T19:29:37Z (GMT). No. of bitstreams: 1 melissa.pdf: 22685399 bytes, checksum: 52613e711bdb2207d8ee610ea5bcd520 (MD5) Previous issue date: 2006-08-10 / Trinexapac-ethyl is a growth reducer used in winter cereals that promote height plant reduction, preventing the lodging. With the aim of determine the rate and the time of ethyltrinexapac (Moddus) application in wheat cultivars of different lodging answers an experiment was established at the UEPG School Farm in Ponta Grossa, PR, in 2005, in a clay soil. The experimental design was complete randomized blocks, in a factorial design 2 x 2 x 6, with three repetitions for four wheat cultivars. The treatments consisted of two nitrogen rates (50 and 240 kg/ha), two times of trinexapac-ethyl application (between 1º and 2º knot and between 2º and 3º perceivable knot) and six trinexapac-ethyl rates (0; 31,2; 62,5; 93,7; 125,0 and 156,2 g/ha), applied in four wheat cultivars of different answers to the lodging (CD-104 - resistant), (Vanguarda - moderately resistant), (Supera - moderately susceptible) and (CEP-24 - susceptible). It evaluated agronomicals characteristics, diseases severity, yield components and yield. The nitrogen rate affected some plant characteristics and the yield for CEP-24. The application time of trinexapac-ethyl affect the yield of CD-104; the plant height that was lesser how much more delayed was the application in cultivars CEP-24 and CD-104; trinexapac-ethyl reduced the plants height of all the cultivars with changeable intensity with the port of the same ones. For all the cultivars the adjustment equation of the yield in relation to the trinexapac-ethyl rates was quadratic, occurring an increase of the yield with the increase of the reducer rate, until a changeable limit with the cultivar. However, for all cultivars occurred increase of the yield with the trinexapac-ethyl application. For the cultivar majority it had reduction of rust severity, head blight and foliar spots with the increase of the trinexapac-ethyl rate. / O trinexapac-ethyl é um redutor de crescimento utilizado em cereais de inverno que promove redução na altura das plantas, evitando o acamamento. Visando determinar a dose e a época de aplicação de trinexapac-ethyl (Moddus) em cultivares de trigo de diferentes respostas ao acamamento realizou-se um experimento na Fazenda Escola da Universidade Estadual de Ponta Grossa (UEPG), no ano de 2005, em um Cambissolo distrófico de textura argilosa. O delineamento experimental foi de blocos ao acaso, em esquema fatorial 2 x 2 x 6 com três repetições para quatro cultivares de trigo. Os tratamentos constaram de duas doses de nitrogênio (50 e 240 kg/ha), duas épocas de aplicação de trinexapac-ethyl (entre o 1º e o 2º nó e entre o 2º e o 3º nó perceptível) e de seis doses de trinexapac-ethyl (0; 31,2; 62,5; 93,7; 125,0 e 156,2 g/ha), aplicadas em quatro cultivares de trigo de diferentes respostas ao acamamento (CD-104 – resistente), (Vanguarda – moderadamente resistente), (Supera – moderadamente suscetível) e (CEP-24 – suscetível). Avaliou-se características agronômicas, severidade de doenças, componentes da produção e produtividade. As doses de nitrogênio afetaram algumas características da planta e a produtividade de apenas da cultivar CEP-24. A época de aplicação do trinexapac-ethyl afetou de forma substancial a produtividade apenas na CD-104; a altura das plantas foi menor quanto mais tardia foi a aplicação do redutor nas cultivares CEP-24 e CD-104; o trinexapac-ethyl reduziu a altura das plantas de todas as cultivares com intensidade variável com o porte das mesmas. Para todas as cultivares a equação de ajuste da produtividade em relação às doses de trinexapac-ethyl foi quadrática ocorrendo um aumento da produção com o aumento da dose do redutor, até um limite variável com a cultivar. No entanto, para todas as cultivares ocorreu aumento da produtividade com a aplicação do trinexapac-ethyl, e para a maioria delas houve redução da severidade de giberela e manchas foliares com o aumento da dose de trinexapac-ethyl.

Made available in DSpace on 2017-07-25T19:29:42Z (GMT). No. of bitstreams: 1 Hellen Aparecida Arantes.pdf: 691625 bytes, checksum: a3ecb17b706b52a2674dc29e0a5e82cc (MD5) Previous issue date: 2008-12-15 / The development and grain yield of the crop of wheat are influenced by several factors, among which is the interference caused by pathogens present in crops. Currently, the main tool for controlling these pathogens in crops is the use of constant application of fungicides. However, this practice is causing pathogens resistant to these groups of fungicides used, as well as encouraging the expression of the mutagenic character of these populations. In an attempt to provide more tools to control the diseases of wheat to the farmer, this study aimed to: a) assess the effect of timing of implementation and sources of phosphite and acibenzolar-S-methyl alone and combined with the fungicide pyraclostrobin + epoxiconazole in control the powdery mildew (Blumeria graminis f. sp. tritici) and the leaf rust (Puccinia triticina), b) assess the effect of different rates, sources of phosphite and acibenzolar-S-methyl isolated and associated to the fungicide pyraclostrobin + epoxiconazole in control of the spots brown (Bipolaris sorokiniana) and yellow (Drechslera tritici-repentis); c) and in vitro effect of different concentrations of phosphite and pyraclostrobin + epoxiconazole on the mycelial growth and germination of conidia of Bipolaris sorokiniana. About the control of powdery mildew and rust can be concluded that the phosphites have no effect on these pathogens and do not change their productivity. It is also clear that there is no difference between the different sources of phosphites to control the powdery mildew and leaf rust, which occurs on powdery mildew and leaf rust's only when the phosphite associated with the fungicide is applied. About the control of yellow and brown stains concluded that the dose of 1048 g i.a. ha-1 potassium phosphite reduces the severity of leaf spots and can be used as a tool in the management of leaf spots. In in vitro tests concluded that the phosphites have direct action on Bipolaris sorokiniana. / O desenvolvimento e o rendimento de grãos da cultura do trigo são influenciados por diversos fatores, entre os quais se encontram a interferência causada por patógenos presentes nas lavouras. Atualmente, a principal ferramenta de controle destes patógenos nas lavouras é o uso de constantes aplicações de fungicidas. Contudo, essa prática vem ocasionando resistência destes patógenos aos grupos de fungicidas utilizados, bem como favorecendo a expressão do caráter mutagênico destas populações. Na tentativa de disponibilizar mais uma ferramenta de controle às doenças do trigo ao agricultor, este trabalho objetivou: a) avaliar o efeito de épocas de aplicação e de fontes de fosfito e acibenzolar-S-metil isolados e combinados com o fungicida epoxiconazole + piraclostrobina no controle do oídio (Blumeria graminis f. sp. tritici) e da ferrugem da folha (Puccinia triticina); b) avaliar o efeito de diferentes doses, fontes de fosfito e acibenzolar-S-metil isolados e associados ao fungicida epoxiconazole + piraclostrobina no controle das manchas marrom (Bipolaris sorokiniana) e mancha amarela (Drechslera tritici-repentis); c) e efeito in vitro de diferentes concentrações de fosfito e epoxiconazole + piraclostrobina sobre o crescimento micelial e a germinação de conídios de Bipolaris sorokiniana. Sobre o controle de oídio e ferrugem pode-se constatar que os fosfitos não possuem efeito sobre estes patógenos e não alteram a produtividade. Concluiu-se ainda que não existe diferença entre as diferentes fontes de fosfitos no controle de oídio e ferrugem da folha, que ocorre efeito sobre o oídio e a ferrugem da folha apenas quando o fosfito é aplicado associado ao fungicida. Sobre o controle das manchas amarela e marrom conclui-se que a dose de 1048 g i.a. ha-1 de fosfito potássico reduz a severidade das manchas foliares, podendo ser utilizado como uma ferramenta no manejo das manchas foliares. Nos testes in vitro conclui-se que os fosfitos possuem ação direta sobre Bipolaris sorokiniana.

O fungo Magnaporthe oryzae, agente causal da brusone em trigo e em várias outras gramíneas, desde o seu primeiro relato no Brasil tem sido alvo de inúmeras pesquisas. O entendimento da morfologia, fisiologia e parâmetros bioquímicos deste ascomiceto é o primeiro passo para a adoção de medidas eficientes de controle da doença. Os objetivos deste trabalho foram avaliar os aspectos morfológicos, fisiológicos e bioquímicos relativos à patogenicidade do fungo M. oryzae em trigo, além de determinar in vitro as condições ótimas de temperatura e fotoperíodo para o crescimento e esporulação dos isolados testados, quantificar a pressão de turgor exercida pelo apressório no momento da penetração do substrato, verificar a presença de enzimas extracelulares produzidas pelo patógeno e o papel de cada uma delas na degradação da parede celular e, também, demonstrar a possível produção e ação de metabólitos tóxicos do fungo em plântulas de trigo. Dois isolados do fungo, Py5003 e Py6017, foram repicados para os meios de cultivo cenoura, milho-cenoura, batata-dextrose-ágar (BDA), aveia e V8, incubados, de maneira independente, sob luz contínua, escuro contínuo e fotoperíodo de 12h, por 20 dias, sendo avaliados periodicamente quanto ao crescimento micelial total e esporulação do patógeno. Em seguida, conídios germinados e com apressórios formados foram submetidos a diferentes concentrações de PEG-8000 para a mensuração da pressão de turgor apressorial. Além disso, o teor de proteínas totais foi mensurado e a atividade celulolítica determinada, por espectrofotometria indireta para os isolados cultivados em meio Merlin-Norkrans Modificado (MNM), a partir das enzimas exo e endo-?-1,4-glucanase e ?-glicosidase. A produção de metabólitos tóxicos foi determinada por condutivimetria, após o cultivo dos isolados por 5 e 10 dias em batata-dextrose (BD) e obtenção dos filtrados após esse período, sendo que, a ação destes, foi observada em plântulas de trigo com 25 dias de idade. Os resultados evidenciaram melhor crescimento micelial e esporulação dos isolados em meio de cultivo composto de aveia, incubado a 25 °C e fotoperíodo de 12 h. A pressão de turgor apressorial, tanto para Py5003 quanto para Py6017, concentrouse na faixa dos 7,5 MPa. Não houve diferença estatística entre os teores de proteínas totais apresentados pelo isolados. Os dois isolados exibiram alta atividade celulolítica, com diminuição da atividade observada para endo-?-1,4-glucanase e ?- glicosidase na presença de glicose e celobiose, respectivamente. A exposição de plântulas de trigo aos filtrados dos isolados do fungo M. oryzae provocou alta liberação de eletrólitos, sendo, em termos absolutos, Py5003 maior do que Py6017. Plântulas expostas ao filtrado, autoclavado ou não, e ao extrato bruto obtido a partir da separação dos metabólitos tóxicos em acetato de etila, apresentaram-se cloróticas e/ou necróticas. Os resultados sugerem um mecanismo de parasitismo desenvolvido por M. oryzae no desenvolvimento da brusone em trigo, indo desde a fase de pré-penetração, passando pelo estabelecimento das relações parasitárias estáveis e o aparecimento de sintomas e sinais na planta hospedeira. / The fungus Magnaporthe oryzae, causal agent of blast in wheat and several other grasses, since its first occurrence in Brazil has been the subject of extensive research. The understanding of the morphology, physiology and biochemical parameters of this ascomycete is the first step for the adoption of efficient measures to control the disease. The objectives of this study were to evaluate the morphological, physiological and biochemical aspects related to the pathogenicity of the fungus M. oryzae on wheat. Thus, it were determined in vitro the optimal conditions of temperature and photoperiod for growth and sporulation of the isolates tested, quantified the pressure exerted by appressorium at the time of substrate penetration, verified the presence of extracellular enzymes produced by the pathogen and their role in the degradation of cell wall and also demonstrated the possible production and action of toxic metabolites of the fungus in wheat seedlings. Two isolates of the fungus, Py5003 and Py6017, were grown on carrot, maize-carrot, PDA, oat and V8 media and measure periodically for 20 days and after that period, being evaluated the total mycelia growth and sporulation of the pathogen. Then, germinated conidia and appressoria were subjected to different concentrations of PEG-8000 for the measurement of appressorial turgor pressure. In addition, the concentration of total proteins was measured and enzyme activity (exo and endo-?- 1,4-glucanase, ?-glucosidase) was determined by indirect spectrophotometry, for the isolates grown in Modified Melin-Nokrans (MMN) medium. The production of toxic metabolites was determined after growing the isolates for 5 and 10 days in potatodextrose medium (PD) and obtaining the filtrate. The toxic action was evaluated in wheat seedlings (25 days old) by measuring electrolyte leakage. The results showed better mycelial growth and sporulation of the isolates in oat medium incubated at 25 °C and under a photoperiod of 12 h. Appressorial turgor pressure for both isolates were at the range of 7.5 MPa.There were no statistical differences between the levels of total protein presented by the isolates. The two isolates showed high cellulolytic activity, with decreased activity observed for endo-?-1,4-glucanase and ?- glucosidase in the presence of glucose and celobiose, respectively. The exposure of wheat seedlings to the filtrates of the fungus M. oryzae caused high electrolyte release, being, in absolute terms, Py5003 greater than Py6017. Seedlings exposed to the filtrate, autoclaved or not, and the crude extract obtained from the separation of the toxic metabolites in ethyl acetate, exibited clorotic and/or necrotic. These results suggest a mechanism of parasitism developed by M. oryzae on wheat, ranging from pre-penetration through the establishment of stable parasitic relationships and the appearance of symptoms and signals in the host plant.

O controle da ocorrência de injúrias mecânicas de sementes, assunto de preocupação constante entre pesquisadores e produtores, deve ser priorizado para assegurar que apenas lotes de sementes com alto nível de desempenho sejam comercializados e utilizados pelos consumidores. Nesse contexto, visando avaliar a ocorrência de injúrias e os diferentes horários de colheita mecânica, com variações no grau de umidade das sementes durante o dia e sua influência na obtenção de lotes de sementes com alto nível de desempenho durante o armazenamento; a eficiência do uso da técnica de raios X na identificação de injúrias mecânicas e análises SVIS®, em comparação com procedimentos tradicionalmente utilizados para avaliação do vigor entre lotes de sementes, essa pesquisa teve como objetivo avaliar os possíveis efeitos imediatos e latentes da colheita mecanizada e sua relação com a ocorrência de injúrias mecânicas em sementes de trigo e os eventuais prejuízos causados à germinação e ao vigor das sementes. Utilizaram-se amostras de sementes dos cultivares BRS 208, BRS 220 e IPR 85, colhidas mecanicamente, em três horários distintos (11h, 14h e às 17h) e amostras em plantas colhidas e trilhadas manualmente, às 14h. O desempenho das sementes foi verificado durante 18 meses de armazenamento, por meio de avaliações da germinação, vigor e técnicas de análise de imagens. Constatou-se que a colheita mecanizada de sementes de trigo, com grau de umidade adequado, não afeta o potencial fisiológico das sementes obtidas, por períodos de até 18 meses de armazenamento. O uso do sistema computadorizado de análise de imagens de plântulas (SVIS®) é alternativa promissora para pesquisas com lotes de sementes de potencial fisiológico elevado. O teste de raios X é eficiente na identificação de injúrias mecânicas em sementes de trigo e permite estabelecer relações entre a severidade das injúrias e os efeitos causados à germinação. / The control of seed mechanical injuries occurrence, a constant concern among researchers and producers, must be a priority to ensure that only seed lots with high performance are commercialized and used by consumers. In order to evaluate the occurrence of injuries and the different periods of the day of mechanical harvesting, with variations of the seed moisture content during the day and the effects to obtain seed lots of high performance during storage; the X-ray technique efficiency in identifying mechanical injuries and SVIS® analysis compared to traditional procedures used to evaluate vigor between seed lots, this research aimed to evaluate mechanized harvesting, the immediate and latent effects, and its relation with mechanical injuries occurrence in wheat seeds and the possible damage caused to seed germination and vigor. Seed samples of BRS 208, BRS 220 and IPR 85 cultivars, mechanically harvested at 11:00 a.m., 2:00 p.m. and 5:00 p.m. and samples harvested and threshed manually at 2:00 p.m. were evaluated. Seed performance was evaluated by seed germination and vigor, and also image analysis technique for 18 months of storage. Results showed that wheat seeds mechanically harvested with adequate moisture content, do not show loss in the physiological potential after 18 months of storage. The use of seedling vigor imaging system (SVIS®) is a promising alternative for seed lots of high physiological potential. The Xray test is efficient to identify mechanical injuries in wheat seeds allowing the establishment of a relationship between the injuries severity and the effects to the germination process.