Occurrence of Pyricularia oryzae Triticum in plants of the genus Urochloa in Brazil / Ocorrência de Pyricularia oryzae Triticum em plantas do gênero Urochloa no Brasil

ABSTRACT: In this study Pyricularia spp., P. oryzae and the P. oryzae pathotype Triticum (PoT) were detected and identified in leaf segments of forage and invasive grasses located in or next to wheat fields. In 2018 and 2019, 66 samples of lesion leaf segments of Urochloa and other grasses were collected in Londrina (PR), Patos de Minas (MG), and Uberaba (MG). The detection and/or identification of the pathogens on the samples was conducted using moist chamber procedures and with the primers MoT3 and Pot2 by PCR. There were DNA amplification with the primer MoT3 (specific for PoT) for 13 (19.69%) of the samples, all of them from Urochloa. The finding that Urochloa hosts PoT at a relatively high rate raises concerns about the importance which these plants may have on the wheat blast cycle as an alternative host for the pathogen and/or source of inoculum for the disease.

RESUMO: Neste estudo Pyricularia spp., P. oryzae e o patótipo Triticum (PoT) de P. oryzae foram detectados e identificados em segmentos foliares de forrageiras e gramíneas invasoras de lavouras de trigo. Em 2018 e 2019, foram coletadas 66 amostras de segmentos foliares lesionados de Urochloa e outras gramíneas em Londrina (PR), Patos de Minas (MG) e Uberaba (MG). A detecção e/ou identificação dos patógenos nas amostras foi realizada por meio de procedimentos de câmara úmida e com os iniciadores MoT3 e Pot2 por PCR. Houve amplificações de DNA com o primer MoT3 (específico para PoT) em 13 (19,69%) das amostras, todas provenientes da Urochloa. O resultado de que Urochloa hospeda PoT em uma taxa relativamente alta levanta preocupações sobre a importância que essas plantas podem ter no ciclo de brusone do trigo como hospedeiro intermediário para o patógeno e / ou fonte de inóculo para a doença.

Occurrence of Pyricularia oryzae Triticum in plants of the genus Urochloa in Brazil / Ocorrência de Pyricularia oryzae Triticum em plantas do gênero Urochloa no Brasil

In this study Pyricularia spp., P. oryzae and the P. oryzae pathotype Triticum (PoT) were detected and identified in leaf segments of forage and invasive grasses located in or next to wheat fields. In 2018 and 2019, 66 samples of lesion leaf segments of Urochloa and other grasses were collected in Londrina (PR), Patos de Minas (MG), and Uberaba (MG). The detection and/or identification of the pathogens on the samples was conducted using moist chamber procedures and with the primers MoT3 and Pot2 by PCR. There were DNA amplification with the primer MoT3 (specific for PoT) for 13 (19.69%) of the samples, all of them from Urochloa. The finding that Urochloa hosts PoT at a relatively high rate raises concerns about the importance which these plants may have on the wheat blast cycle as an alternative host for the pathogen and/or source of inoculum for the disease.

Neste estudo Pyricularia spp., P. oryzae e o patótipo Triticum (PoT) de P. oryzae foram detectados e identificados em segmentos foliares de forrageiras e gramíneas invasoras de lavouras de trigo. Em 2018 e 2019, foram coletadas 66 amostras de segmentos foliares lesionados de Urochloa e outras gramíneas em Londrina (PR), Patos de Minas (MG) e Uberaba (MG). A detecção e/ou identificação dos patógenos nas amostras foi realizada por meio de procedimentos de câmara úmida e com os iniciadores MoT3 e Pot2 por PCR. Houve amplificações de DNA com o primer MoT3 (específico para PoT) em 13 (19,69%) das amostras, todas provenientes da Urochloa. O resultado de que Urochloa hospeda PoT em uma taxa relativamente alta levanta preocupações sobre a importância que essas plantas podem ter no ciclo de brusone do trigo como hospedeiro intermediário para o patógeno e / ou fonte de inóculo para a doença.

Resistance of Brazilian wheat cultivars to blast under controlled condition / Resistência de cultivares brasileiras de trigo à brusone sob condições controladas

The first report of wheat blast in the world was in Brazil, in 1986. Since then, a great effort has been made towards the development of wheat cultivars resistant to this disease, which is caused by the fungus Pyricularia oryzae Triticum (PoT). The objective of this research was to (i) evaluate the resistance of wheat genotypes to blast and (ii) verify the correlation between disease severity on wheat spikes and sporulation rate of PoT on spike rachises. Plants of 40 cultivars grown in pots, at the flowering stage (stage 65 on the Zadoks scale), were inoculated with a suspension of conidia of a PoT isolate representative of the main variant of the fungus reported in Brazil. Severity of blast on the spikes at 5 and 7 days after inoculation (dai) and the rate of sporulation of the fungus on the rachis (conidia per g of rachis) were evaluated. Eighty percent of the cultivars that were classified in the group with the lowest sporulation rate were also classified in the group with the highest resistance at 7 dai. However, the correlation coefficients of the analysis established between the cultivar severity at 5 and 7 dai averages and the PoT sporulation rate averages were not significant (r=0.2464 and r=0.2047, respectively). Results obtained represent the updated characterization to blast of wheat cultivars in Brazil and constitute an important exploratory framework for the evaluation of the reaction of wheat genotypes based on the sporulation rate of PoT on their tissues.

O primeiro relato da brusone do trigo no mundo foi no Brasil, em 1986. Desde então, tem-se realizado um esforço muito grande com vistas ao desenvolvimento de cultivares de trigo resistentes a esta doença, a qual é causada pelo fungo Pyricularia oryzae Triticum (PoT). O objetivo deste trabalho foi de (i) avaliar a resistência de genótipos de trigo à brusone e (ii) verificar a correlação entre severidade da doença em espigas e taxa de esporulação de PoT em ráquis de espigas. Plantas de 40 cultivares brasileiras de trigo crescidas em vasos, no estádio de florescimento (estádio 65 da escala de Zadoks), foram submetidas à inoculação com uma suspensão de conídios de um isolado de PoT representativo da principal variante do fungo encontrada no Brasil. A severidade de brusone nas espigas aos cinco e sete dias após a inoculação (dai) e a taxa de esporulação do fungo nas ráquis (conídios por g de ráquis) foram avaliadas. Oitenta por cento das cultivares que foram classificadas no grupo com menor taxa de esporulação também foram classificadas no grupo de maior resistência aos sete dai. Entretanto, os coeficientes de correlação da análise estabelecida entre as médias de severidade das cultivares aos cinco e sete dai e as médias da taxa de esporulação de PoT não foram significativos (r=0,2464 e r=0,2047, respectivamente). Os resultados obtidos representam a caracterização atualizada da reação à brusone de cultivares de trigo do Brasil e constituem-se em importante marco exploratório da avaliação da reação de genótipos de trigo baseado na taxa de esporulação de PoT em seus tecidos.

Conidia sporulation of Pyricularia oryzae in segments of wheat plants under six different temperatures / Esporulação de conídios de Pyricularia oryzae em segmentos de plantas de trigo sob seis diferentes temperaturas

Wheat blast is known for developing itself more intensely under relatively high temperature conditions but many aspects related to its epidemiology remain unknown. The objective of this research was to evaluate the sporulative capacity of Pyricularia oryzae Triticum (Pot), the causal agent of wheat blast, in tissues of wheat plants under different temperatures degrees. Wheat plants of the cultivar Anahuac 75, susceptible to blast, were inoculated in the stage of flowering with conidial suspensions (105 conidia/mL) of the Pot isolates Py 12.1.209 and Py 12.1.132. Seven days after the inoculation, plants were cut in the following segments: leaves, stems and rachis (with blast severity ranging from 40 to 60%). Groups of each one of the three plant segments with the lesions were disposed in Petri-dish moist chambers, that were submitted to six different temperature treatments (18, 21, 24, 27, 30 and 33 °C). The most appropriate model that related the conidia production with temperature was identified in the evaluations conducted with stems. The established equations allowed identifying that the highest production of conidia of Pot occurs between 24 and 27 °C.(AU)

Sabe-se que a brusone do trigo ocorre preferencialmente em condições de temperaturas relativamente altas, porém muitos aspectos sobre a epidemiologia desta doença ainda permanecem desconhecidos. O objetivo deste trabalho foi avaliar a capacidade esporulativa de Pyricularia oryzae Triticum (Pot) em tecidos de plantas de trigo sob diferentes temperaturas. Plantas de trigo do cultivar Anahuac 75, suscetível à brusone, foram inoculadas no estádio do florescimento com suspensões de conídios dos isolados Py 12.1.209 e Py 12.1.132 de Pot (105 conídios/mL). Sete dias após a inoculação, as plantas foram cortadas e separadas em três tipos de segmentos: colmos, folhas e ráquis (com severidade de brusone variando de 40 a 60%). Um grupo de cada desses três tipos de segmentos de planta contendo lesões foi disposto em câmara úmida. O material foi acondicionado em seis níveis de temperatura: 18, 21, 24, 27, 30 e 33 °C. O modelo mais apropriado que relacionou a produção de conídios com temperatura foi identificado nas avaliações feitas nas amostras de colmo. As equações estabelecidas permitiram identificar que a maior produção de conídios de Pot ocorreu entre as temperaturas de 24 e 27 °C.(AU)

Reaction of wheat plants and alternative hosts to Magnaporthe oryzae / Reação de plantas de trigo e hospedeiros alternativos a Magnaporthe oryzae

Blast disease, caused by the fungus Magnaporthe oryzae, has a major impact on wheat farming. The study of plant responses to pathogens has improved the management of this disease. Moreover, it is important to identify potential host plants in the crops' vicinity and to understand reactions caused by plant-pathogen interactions. The objective of this study was to assess the histopathology of wheat plants, Digitaria insularis and Digitaria sanguinalis inoculated with M. oryzae isolates obtained either rice or wheat plants. Thirty-three days after sowing, greenhouse-grown plants of all three species were inoculated with each M. oryzae isolate. The observed effects (48 hours after inoculation) differed depending on the particular interaction between each pathogen isolate-plant species pair. For instance, wheat and D. sanguinalis had the weakest defensive response against spore germination, production of melanized appressoria, and appressorial penetration, with average values above 87, 90, and 43%, respectively, for these events in these plants. Furthermore, germination and appressoria melanization were more aggressive in the rice isolate than in the wheat isolate. Additionally, evidence for a defensive response (such as cell death) was observed in wheat plants inoculated with rice isolates. However, such a response was absent in plants inoculated using wheat isolates, presumably because pathogen recognition failed.(AU)

A brusone é uma doença causada pelo fungo Magnaporthe oryzae e de grande impacto para a triticultura. O estudo das respostas da planta aos patógenos tem auxiliado no manejo das doenças, e a identificação das plantas hospedeiras nas proximidades da lavoura é importante, assim como conhecer as reações de interação com o patógeno. O objetivo deste estudo foi determinar os eventos histológicos de plantas de trigo Digitaria insularis e Digitaria sanguinalis inoculadas com isolados de M. oryzae de plantas de arroz e trigo. Aos 33 dias da semeadura, as plantas cultivadas em estufa foram inoculadas com dois isolados de M. oryzae. O efeito observado nas plantas, 48 horas após a inoculação, mostrou interações diferentes para cada isolado do patógeno e entre as espécies de plantas. As plantas de trigo e D. sanguinalis foram os materiais com menores respostas de defesa à germinação, de produção de apressórios melanizados e penetração do apressório, com valores acima de 87, 90 e 43%, respectivamente. Entre os isolados do patógeno, o mais agressivo para germinação e produção de apressório melanizado foi o proveniente de plantas de arroz. A resposta de defesa da planta, como a morte celular, foi observada nas plantas de trigo inoculadas com isolado proveniente de plantas de arroz, enquanto não houve resposta de defesa da planta quando inoculada com isolado obtido de plantas de trigo, provavelmente por não ocorrer o reconhecimento do patógeno.(AU)

Reaction of wheat plants and alternative hosts to Magnaporthe oryzae / Reação de plantas de trigo e hospedeiros alternativos a Magnaporthe oryzae

Blast disease, caused by the fungus Magnaporthe oryzae, has a major impact on wheat farming. The study of plant responses to pathogens has improved the management of this disease. Moreover, it is important to identify potential host plants in the crops' vicinity and to understand reactions caused by plant-pathogen interactions. The objective of this study was to assess the histopathology of wheat plants, Digitaria insularis and Digitaria sanguinalis inoculated with M. oryzae isolates obtained either rice or wheat plants. Thirty-three days after sowing, greenhouse-grown plants of all three species were inoculated with each M. oryzae isolate. The observed effects (48 hours after inoculation) differed depending on the particular interaction between each pathogen isolate-plant species pair. For instance, wheat and D. sanguinalis had the weakest defensive response against spore germination, production of melanized appressoria, and appressorial penetration, with average values above 87, 90, and 43%, respectively, for these events in these plants. Furthermore, germination and appressoria melanization were more aggressive in the rice isolate than in the wheat isolate. Additionally, evidence for a defensive response (such as cell death) was observed in wheat plants inoculated with rice isolates. However, such a response was absent in plants inoculated using wheat isolates, presumably because pathogen recognition failed.(AU)

A brusone é uma doença causada pelo fungo Magnaporthe oryzae e de grande impacto para a triticultura. O estudo das respostas da planta aos patógenos tem auxiliado no manejo das doenças, e a identificação das plantas hospedeiras nas proximidades da lavoura é importante, assim como conhecer as reações de interação com o patógeno. O objetivo deste estudo foi determinar os eventos histológicos de plantas de trigo Digitaria insularis e Digitaria sanguinalis inoculadas com isolados de M. oryzae de plantas de arroz e trigo. Aos 33 dias da semeadura, as plantas cultivadas em estufa foram inoculadas com dois isolados de M. oryzae. O efeito observado nas plantas, 48 horas após a inoculação, mostrou interações diferentes para cada isolado do patógeno e entre as espécies de plantas. As plantas de trigo e D. sanguinalis foram os materiais com menores respostas de defesa à germinação, de produção de apressórios melanizados e penetração do apressório, com valores acima de 87, 90 e 43%, respectivamente. Entre os isolados do patógeno, o mais agressivo para germinação e produção de apressório melanizado foi o proveniente de plantas de arroz. A resposta de defesa da planta, como a morte celular, foi observada nas plantas de trigo inoculadas com isolado proveniente de plantas de arroz, enquanto não houve resposta de defesa da planta quando inoculada com isolado obtido de plantas de trigo, provavelmente por não ocorrer o reconhecimento do patógeno.(AU)

Relationship between blast severity on seedlings and panicles of Brazilian oat cultivars / Relação entre a severidade de brusone em plântulas e panículas de cultivares brasileiras de aveia

Blast, caused by Pyricularia oryzae, threats black (Avena strigosa) and white (A. sativa) oats in Brazil. Little is known about the reaction of Brazilian oat cultivars to blast and if there is a relationship between the response of cultivars to the disease at seedling and adult plant stages. The goals of this research were to verify (a) the reaction of black and white Brazilian oat cultivars to infection of P. oryzae and (b) if the response to blast on seedling leaves and panicles was correlated. Seedlings and adult plants of 13 oat cultivars were inoculated with a conidial suspension of one P. oryzae isolate obtained from a black oat cultivar. The cultivars were classified according to blast severity on the leaf seedlings and panicles estimated by visual estimation. Two experiments were conducted for each one of the two evaluated stages. Cultivars with lower value to blast severity on seedling leaves were ‘UPFA Gaudéria’ (25.82%) and ‘UPF 18’ (24.88%) and, on panicles, ‘BRS Centauro’ (31.63%). Coefficients of Pearson, Spearman, and Kendall obtained from correlation analyses between blast severity on seedling leaves and panicles were -0.21232, -0.35714, and -0.30769, respectively (non-significant at 0.05). Lack of correlation between the responses of these oat cultivars to blast on seedling leaves and panicles be considered in the management of the disease in the field and the generation of new oat cultivars.

A brusone, causada por Pyricularia oryzae, ameaça as culturas da aveia preta (Avena strigosa) e branca (A. sativa) no Brasil. Sabe-se pouco sobre a reação das cultivares brasileiras de aveia à brusone e se existe relação entre a resposta destas cultivares à doença nos estádios de plântula e de planta adulta. Os objetivos deste trabalho foram: (a) verificar a reação de cultivares brasileiras de aveia à infecção de P. oryzae e; (b) se existe relação entre a resposta à brusone dessas cultivares nos estádios de plântula e de planta adulta. Plântulas e plantas adultas de 13 cultivares de aveia foram inoculadas com uma suspensão de conídios de um isolado de P. oryzae obtido de uma planta de uma cultivar de aveia preta. As cultivares foram classificadas de acordo com a estimativa visual da severidade da doença nas folhas das plântulas e nas panículas das plantas adultas. Dois experimentos foram conduzidos para cada um dos estádios avaliados. As cultivares com menor severidade de brusone nas plântulas foram a ‘Gaudéria UPFA’ (25,82%) e a ‘UPF 18’ (24,88%) e, nas panículas, foi a ‘BRS Centauro’ (31,63%). Os coeficientes de Pearson, Spearman e Kendall obtidos da análise de correlação entre os dois estádios avaliados foram -0,21232, -0,35714 e -0,30769, respectivamente (todos sem significância estatística à 0,05). A falta de correlação entre as respostas das cultivares de aveia à brusone, em plântulas e panículas, constitui-se em informação a ser considerada no manejo da doença, no campo e na geração de novas cultivares de aveia.

Relationship between blast severity on seedlings and panicles of Brazilian oat cultivars / Relação entre a severidade de brusone em plântulas e panículas de cultivares brasileiras de aveia

Blast, caused by Pyricularia oryzae, threats black (Avena strigosa) and white (A. sativa) oats in Brazil. Little is known about the reaction of Brazilian oat cultivars to blast and if there is a relationship between the response of cultivars to the disease at seedling and adult plant stages. The goals of this research were to verify (a) the reaction of black and white Brazilian oat cultivars to infection of P. oryzae and (b) if the response to blast on seedling leaves and panicles was correlated. Seedlings and adult plants of 13 oat cultivars were inoculated with a conidial suspension of one P. oryzae isolate obtained from a black oat cultivar. The cultivars were classified according to blast severity on the leaf seedlings and panicles estimated by visual estimation. Two experiments were conducted for each one of the two evaluated stages. Cultivars with lower value to blast severity on seedling leaves were ‘UPFA Gaudéria (25.82%) and ‘UPF 18 (24.88%) and, on panicles, ‘BRS Centauro (31.63%). Coefficients of Pearson, Spearman, and Kendall obtained from correlation analyses between blast severity on seedling leaves and panicles were -0.21232, -0.35714, and -0.30769, respectively (non-significant at 0.05). Lack of correlation between the responses of these oat cultivars to blast on seedling leaves and panicles be considered in the management of the disease in the field and the generation of new oat cultivars.(AU)

A brusone, causada por Pyricularia oryzae, ameaça as culturas da aveia preta (Avena strigosa) e branca (A. sativa) no Brasil. Sabe-se pouco sobre a reação das cultivares brasileiras de aveia à brusone e se existe relação entre a resposta destas cultivares à doença nos estádios de plântula e de planta adulta. Os objetivos deste trabalho foram: (a) verificar a reação de cultivares brasileiras de aveia à infecção de P. oryzae e; (b) se existe relação entre a resposta à brusone dessas cultivares nos estádios de plântula e de planta adulta. Plântulas e plantas adultas de 13 cultivares de aveia foram inoculadas com uma suspensão de conídios de um isolado de P. oryzae obtido de uma planta de uma cultivar de aveia preta. As cultivares foram classificadas de acordo com a estimativa visual da severidade da doença nas folhas das plântulas e nas panículas das plantas adultas. Dois experimentos foram conduzidos para cada um dos estádios avaliados. As cultivares com menor severidade de brusone nas plântulas foram a ‘Gaudéria UPFA (25,82%) e a ‘UPF 18 (24,88%) e, nas panículas, foi a ‘BRS Centauro (31,63%). Os coeficientes de Pearson, Spearman e Kendall obtidos da análise de correlação entre os dois estádios avaliados foram -0,21232, -0,35714 e -0,30769, respectivamente (todos sem significância estatística à 0,05). A falta de correlação entre as respostas das cultivares de aveia à brusone, em plântulas e panículas, constitui-se em informação a ser considerada no manejo da doença, no campo e na geração de novas cultivares de aveia.(AU)

Cytological aspects of incompatible and compatible interactions between rice, wheat and the blast pathogen Pyricularia oryzae

Blast, caused by the fungus Pyricularia oryzae, is an important disease affecting rice and wheat yield worldwide. This study investigated the cytological aspects of incompatible (non-host resistance) and compatible (host resistance) rice- (R_Po) and wheat- (W_Po) Pyricularia oryzae isolate interactions. Inoculations of rice and wheat with the R_Po and W_Po isolates of P. oryzae, respectively, were expected to be compatible interactions (host resistance), whereas inoculations of rice and wheat with the W_Po and R_Po isolates of P. oryzae, respectively, were considered to be incompatible interactions (non-host resistance). For the compatible interactions (rice-R_Po and wheat-W_Po), fungal hyphae penetrated and colonized the epidermal cells and also invaded many neighboring cells. By contrast, in the case of the incompatible interactions (rice-W_Po and wheat-R_Po), fungal hyphae were not able to penetrate nor colonize the epidermal cells, but when penetration did occur, the hyphae were restricted to the first-invaded epidermal cell. The frequency of appressorial sites exhibiting infection hyphae within the epidermal cell underlying an appressorium was greater in the case of the compatible interactions. By contrast, unsuccessful penetrations with cytoplasmic granulation occurred with high frequency in the incompatible wheat-R_Po and rice-W_Po interactions and the number of necrotic epidermal cells underlying the appressorium was low for the rice-W_Po interaction as well as for the wheat- R_Po interaction, where no symptoms of necrosis were exhibited. However, the opposite was observed for the compatible interactions. The present study presents cytological features associated with incompatible and compatible rice- and wheat-P. oryzae interactions that may be useful to studies involving variability, coevolution, diagnosis, and regulation of quarantine or even in a rice or wheat breeding program whose aim is to transfer genes involved in non-host resistance to host resistance due to similarities in downstream mechanisms.

Cytological aspects of incompatible and compatible interactions between rice, wheat and the blast pathogen Pyricularia oryzae

Blast, caused by the fungus Pyricularia oryzae, is an important disease affecting rice and wheat yield worldwide. This study investigated the cytological aspects of incompatible (non-host resistance) and compatible (host resistance) rice- (R_Po) and wheat- (W_Po) Pyricularia oryzae isolate interactions. Inoculations of rice and wheat with the R_Po and W_Po isolates of P. oryzae, respectively, were expected to be compatible interactions (host resistance), whereas inoculations of rice and wheat with the W_Po and R_Po isolates of P. oryzae, respectively, were considered to be incompatible interactions (non-host resistance). For the compatible interactions (rice-R_Po and wheat-W_Po), fungal hyphae penetrated and colonized the epidermal cells and also invaded many neighboring cells. By contrast, in the case of the incompatible interactions (rice-W_Po and wheat-R_Po), fungal hyphae were not able to penetrate nor colonize the epidermal cells, but when penetration did occur, the hyphae were restricted to the first-invaded epidermal cell. The frequency of appressorial sites exhibiting infection hyphae within the epidermal cell underlying an appressorium was greater in the case of the compatible interactions. By contrast, unsuccessful penetrations with cytoplasmic granulation occurred with high frequency in the incompatible wheat-R_Po and rice-W_Po interactions and the number of necrotic epidermal cells underlying the appressorium was low for the rice-W_Po interaction as well as for the wheat- R_Po interaction, where no symptoms of necrosis were exhibited. However, the opposite was observed for the compatible interactions. The present study presents cytological features associated with incompatible and compatible rice- and wheat-P. oryzae interactions that may be useful to studies involving variability, coevolution, diagnosis, and regulation of quarantine or even in a rice or wheat breeding program whose aim is to transfer genes involved in non-host resistance to host resistance due to similarities in downstream mechanisms.(AU)

Critical-point models to relate yield and disease intensity of the multiple pathosystem in rice leaf spots disease

ABSTRACT: The occurrence of leaf spots in irrigated rice can reduce the yield and compromise the quality of the grain. However it is unknown the economic damage threshold (EDT) that these spots cause the yield of crop. The objective of this study was to obtain damage functions for models of critical, to relate damage by simultaneous occurrence of blast, brown spot and scald spot with grain yield harvests in 2011/12 and 2012/2013, in Rio do Oeste, Santa Catarina State, Brazil. Gradient of diseases intensity was generated by number of applications and fungicides rates. Design was a randomized block with four replications and six treatments consisting of mixing fungicide applications of triazole (difenoconazole) and strobilurin (azoxystrobin). In 2011/12 and 2012/13 growing season were made two and three tests respectively with the same experiment. Before each application it was determined the incidence and severity of fungal diseases. The critical point models were obtained by linear regression between grain yield and incidence (I) and severity (S). In 2011/12 the functions were not significant at the beginning of tillering and 2012/2013 harvest resulted in R=13.404-92.98I and R=10.685-3.804S. Respectively in each harvest resulted in tillering (R=9.141-103.6I; R=7.605-1.538 and R=8.864-73.91I; R=7.202-77S), panicle initiation (R=9.432-188.5I; R=7.,038-1.466S and R=10.176-87.33I; R=8.258-533.55S), booting (R=7.044-71.78I; R=6.881-1.296S and R=9.993-71.74I; R=8.846-763.83S), flowering (R=7.447-82.29I; R=8.731-1.398S and R=8.347-54.36I; R=7.338-681.52S) and milky grain (R=10.143-80.5I; R=7.522-1.402S and R=8.661-60.063I; R=9.754-1.465S). The generated functions allow getting the damage coefficient for use in the calculation of EDT in multiple pathossystem leaf spots in irrigated rice.

RESUMO: A ocorrência de manchas foliares na cultura do arroz irrigado pode reduzir o rendimento e comprometer a qualidade do grão. No entanto, é desconhecido o limiar de dano econômico (LDE) que essas manchas causam no rendimento da cultura. O objetivo deste trabalho foi obter funções de dano, por modelos de ponto crítico, ao relacionar o dano pela ocorrência simultânea da brusone, mancha parda e escaldadura com o rendimento de grãos nas safras de 2011/12 e 2012/2013, em Rio do Oeste, Santa Catarina (SC). O gradiente da intensidade das doenças foi gerado por número de aplicações e doses de fungicidas. O delineamento foi de blocos casualizados, com quatro repetições e seis tratamentos, constituídos de aplicações de mistura de fungicidas triazol (difenoconazole) e estrobilurina (azoxistrobina). Na safra de 2011/12 e 2012/13, foram feitos dois e três ensaios, respectivamente, com o mesmo experimento. Antes de cada aplicação, foi determinada a incidência e a severidade das doenças foliares. Os modelos de ponto crítico foram obtidos por regressão linear entre rendimento de grãos e incidência (I) e severidade (S). Em 2011/12, as funções não foram significativas no início do perfilhamento e, na safra de 2012/2013, resultou em R=13.404-92,98I e R=10.685-3.804S. Respectivamente, em cada safra, resultaram no perfilhamento (R=9.141-103,6I; R=7.605-1.538 e R=8.864-73,91I; R=7.202-77S), iniciação da panícula (9.432-188,5I; R=7.038-1.466S e 10.176-87I; R=8.258-533,55S), emborrachamento (R=7.044-71,78I; 6.881-1.296S e R=9.993-71,74I; R=8.846-763,83S), floração (R=7.447-82,29I; R=8.731-1.398S e R=8.347-54,36I; R=7.338-681,52S) e grão leitoso (R=10.143-80,5I; R=7.522-1.402S e R=8.661-60.063I; R=9.754-1.465S). As funções geradas permitem obter o coeficiente de dano para uso no cálculo do LDE em patossistema múltiplo de manchas foliares, em arroz irrigado.

Critical-point models to relate yield and disease intensity of the multiple pathosystem in rice leaf spots disease

ABSTRACT: The occurrence of leaf spots in irrigated rice can reduce the yield and compromise the quality of the grain. However it is unknown the economic damage threshold (EDT) that these spots cause the yield of crop. The objective of this study was to obtain damage functions for models of critical, to relate damage by simultaneous occurrence of blast, brown spot and scald spot with grain yield harvests in 2011/12 and 2012/2013, in Rio do Oeste, Santa Catarina State, Brazil. Gradient of diseases intensity was generated by number of applications and fungicides rates. Design was a randomized block with four replications and six treatments consisting of mixing fungicide applications of triazole (difenoconazole) and strobilurin (azoxystrobin). In 2011/12 and 2012/13 growing season were made two and three tests respectively with the same experiment. Before each application it was determined the incidence and severity of fungal diseases. The critical point models were obtained by linear regression between grain yield and incidence (I) and severity (S). In 2011/12 the functions were not significant at the beginning of tillering and 2012/2013 harvest resulted in R=13.404-92.98I and R=10.685-3.804S. Respectively in each harvest resulted in tillering (R=9.141-103.6I; R=7.605-1.538 and R=8.864-73.91I; R=7.202-77S), panicle initiation (R=9.432-188.5I; R=7.,038-1.466S and R=10.176-87.33I; R=8.258-533.55S), booting (R=7.044-71.78I; R=6.881-1.296S and R=9.993-71.74I; R=8.846-763.83S), flowering (R=7.447-82.29I; R=8.731-1.398S and R=8.347-54.36I; R=7.338-681.52S) and milky grain (R=10.143-80.5I; R=7.522-1.402S and R=8.661-60.063I; R=9.754-1.465S). The generated functions allow getting the damage coefficient for use in the calculation of EDT in multiple pathossystem leaf spots in irrigated rice.

RESUMO: A ocorrência de manchas foliares na cultura do arroz irrigado pode reduzir o rendimento e comprometer a qualidade do grão. No entanto, é desconhecido o limiar de dano econômico (LDE) que essas manchas causam no rendimento da cultura. O objetivo deste trabalho foi obter funções de dano, por modelos de ponto crítico, ao relacionar o dano pela ocorrência simultânea da brusone, mancha parda e escaldadura com o rendimento de grãos nas safras de 2011/12 e 2012/2013, em Rio do Oeste, Santa Catarina (SC). O gradiente da intensidade das doenças foi gerado por número de aplicações e doses de fungicidas. O delineamento foi de blocos casualizados, com quatro repetições e seis tratamentos, constituídos de aplicações de mistura de fungicidas triazol (difenoconazole) e estrobilurina (azoxistrobina). Na safra de 2011/12 e 2012/13, foram feitos dois e três ensaios, respectivamente, com o mesmo experimento. Antes de cada aplicação, foi determinada a incidência e a severidade das doenças foliares. Os modelos de ponto crítico foram obtidos por regressão linear entre rendimento de grãos e incidência (I) e severidade (S). Em 2011/12, as funções não foram significativas no início do perfilhamento e, na safra de 2012/2013, resultou em R=13.404-92,98I e R=10.685-3.804S. Respectivamente, em cada safra, resultaram no perfilhamento (R=9.141-103,6I; R=7.605-1.538 e R=8.864-73,91I; R=7.202-77S), iniciação da panícula (9.432-188,5I; R=7.038-1.466S e 10.176-87I; R=8.258-533,55S), emborrachamento (R=7.044-71,78I; 6.881-1.296S e R=9.993-71,74I; R=8.846-763,83S), floração (R=7.447-82,29I; R=8.731-1.398S e R=8.347-54,36I; R=7.338-681,52S) e grão leitoso (R=10.143-80,5I; R=7.522-1.402S e R=8.661-60.063I; R=9.754-1.465S). As funções geradas permitem obter o coeficiente de dano para uso no cálculo do LDE em patossistema múltiplo de manchas foliares, em arroz irrigado.

Critical-point models to relate yield and disease intensity of the multiple pathosystem in rice leaf spots disease / Modelos de pontos críticos para relacionar o rendimento de grãos com a intensidade em patossistema múltiplo de manchas foliares em arroz irrigado

The occurrence of leaf spots in irrigated rice can reduce the yield and compromise the quality of the grain. However it is unknown the economic damage threshold (EDT) that these spots cause the yield of crop. The objective of this study was to obtain damage functions for models of critical, to relate damage by simultaneous occurrence of blast, brown spot and scald spot with grain yield harvests in 2011/12 and 2012/2013, in Rio do Oeste, Santa Catarina State, Brazil. Gradient of diseases intensity was generated by number of applications and fungicides rates. Design was a randomized block with four replications and six treatments consisting of mixing fungicide applications of triazole (difenoconazole) and strobilurin (azoxystrobin). In 2011/12 and 2012/13 growing season were made two and three tests respectively with the same experiment. Before each application it was determined the incidence and severity of fungal diseases. The critical point models were obtained by linear regression between grain yield and incidence (I) and severity (S). In 2011/12 the functions were not significant at the beginning of tillering and 2012/2013 harvest resulted in R=13.404-92.98I and R=10.685-3.804S. Respectively in each harvest resulted in tillering (R=9.141-103.6I; R=7.605-1.538 and R=8.864-73.91I; R=7.202-77S), panicle initiation (R=9.432-188.5I; R=7.,038-1.466S and R=10.176-87.33I; R=8.258-53(AU)

A ocorrência de manchas foliares na cultura do arroz irrigado pode reduzir o rendimento e comprometer a qualidade do grão. No entanto, é desconhecido o limiar de dano econômico (LDE) que essas manchas causam no rendimento da cultura. O objetivo deste trabalho foi obter funções de dano, por modelos de ponto crítico, ao relacionar o dano pela ocorrência simultânea da brusone, mancha parda e escaldadura com o rendimento de grãos nas safras de 2011/12 e 2012/2013, em Rio do Oeste, Santa Catarina (SC). O gradiente da intensidade das doenças foi gerado por número de aplicações e doses de fungicidas. O delineamento foi de blocos casualizados, com quatro repetições e seis tratamentos, constituídos de aplicações de mistura de fungicidas triazol (difenoconazole) e estrobilurina (azoxistrobina). Na safra de 2011/12 e 2012/13, foram feitos dois e três ensaios, respectivamente, com o mesmo experimento. Antes de cada aplicação, foi determinada a incidência e a severidade das doenças foliares. Os modelos de ponto crítico foram obtidos por regressão linear entre rendimento de grãos e incidência (I) e severidade (S). Em 2011/12, as funções não foram significativas no início do perfilhamento e, na safra de 2012/2013, resultou em R=13.404-92,98I e R=10.685-3.804S. Respectivamente, em cada safra, resultaram no perfilhamento (R=9.141-103,6I; R=7.605-1.538 e R=8.864-73,91I; R=7.202-77S), iniciação d(AU)

Histochemical aspects of wheat resistance to leaf blast mediated by silicon

Blast, caused by Pyricularia oryzae, has become a significant disease threat to wheat (Triticum aestivum L.) in Brazil. This study aimed to investigate at the histochemical level if silicon (Si) could enhance the production of flavonoids in the leaves of wheat plants in response to P. oryzae infection. Plants from the Aliança cultivar, which are susceptible to blast, were grown in hydroponic cultures containing 0 (-Si) or 2 mM of Si (+Si) and inoculated by spraying a conidial suspension of P. oryzae (1 × 105 conidia mL1) on all adaxial leaf surfaces of plants at 60 days after emergence (growth stage 65). The fourth and fifth leaves of each plant were used to evaluate blast severity at 24, 36, 48, 72 and 96 h after inoculation (hai). At 96 hai, leaves were collected from plants to determine the foliar Si concentration. For cytological observations, leaf samples were randomly collected from the fourth and fifth leaves of each plant at 72 hai. The foliar Si concentration was higher in +Si plants (36 g kg1) in comparison to -Si plants (2.6 g kg1). This increased Si concentration was correlated with reduced fungal growth inside the epidermal cells and the development of blast symptoms on leaves. Strong fluorescence, which is an indication of the presence of flavonoids, was detected in the leaf cells of +Si plants using Neus and Wilson's reagents. A novel item of evidence is that, at the histochemical level, Si is involved in the potentiation of the biosynthetic pathway of flavonoids that increases wheat resistance to blast.

Histochemical aspects of wheat resistance to leaf blast mediated by silicon

Blast, caused by Pyricularia oryzae, has become a significant disease threat to wheat (Triticum aestivum L.) in Brazil. This study aimed to investigate at the histochemical level if silicon (Si) could enhance the production of flavonoids in the leaves of wheat plants in response to P. oryzae infection. Plants from the Aliança cultivar, which are susceptible to blast, were grown in hydroponic cultures containing 0 (-Si) or 2 mM of Si (+Si) and inoculated by spraying a conidial suspension of P. oryzae (1 × 105 conidia mL1) on all adaxial leaf surfaces of plants at 60 days after emergence (growth stage 65). The fourth and fifth leaves of each plant were used to evaluate blast severity at 24, 36, 48, 72 and 96 h after inoculation (hai). At 96 hai, leaves were collected from plants to determine the foliar Si concentration. For cytological observations, leaf samples were randomly collected from the fourth and fifth leaves of each plant at 72 hai. The foliar Si concentration was higher in +Si plants (36 g kg1) in comparison to -Si plants (2.6 g kg1). This increased Si concentration was correlated with reduced fungal growth inside the epidermal cells and the development of blast symptoms on leaves. Strong fluorescence, which is an indication of the presence of flavonoids, was detected in the leaf cells of +Si plants using Neus and Wilson's reagents. A novel item of evidence is that, at the histochemical level, Si is involved in the potentiation of the biosynthetic pathway of flavonoids that increases wheat resistance to blast.(AU)

Fungicides evaluation to control of panicle blast in irrigated rice / Avaliação de fungicidas para o controle da brusone de panícula na cultura do arroz irrigado

Chemical control of panicle blast, caused by Pyricularia oryzae, is ineffective in many cases, due to the use of non-recommended products or applied improperly. In order to evaluate fungicides efficiency in the control of panicle blast, two experiments were performed in Itajaí and Garuva counties of Santa Catarina state, during 2008/09 planting season. The fungicides were evaluated as single application, at R3 stage (early heading) and two applications at R2 (late boot) and R4 stage (full heading), in an outflow of 200 L ha-1. It was found that when the incidence of panicle blast (PB) was 37.5%, there was a higher level of disease control in treatments with two applications of fungicides, compared to treatments receiving only one application. On the other hand, when the incidence of PB was 20.6%, no significant differences between treatments with one or two applications of fungicides were verified. Two applications of propiconazol + trifloxystrobin, tebuconazol + trifloxystrobin, the tank mixture tricyclazol + tebuconazol and the tricyclazol followed by tebuconazol + trifloxystrobin, proved to be over 90% effective to control panicle blast. It"s not observed significant gains in productivity resulting from the use of fungicides.

O controle químico da brusone de panícula, causada pelo fungo Pyricularia oryzae, é em muitos casos ineficaz, em virtude da utilização de produtos não recomendados, aplicados de forma inadequada. Com o objetivo de avaliar a eficiência de fungicidas no controle da brusone de panícula, foram conduzidos dois experimentos na safra 2008/09 nos municípios de Itajaí e Garuva, SC. Os fungicidas foram avaliados em aplicação única, realizada no estádio R3 (início do florescimento) e em duas aplicações, realizadas nos estádios R2 (emborrachamento) e R4 (pleno florescimento), utilizando-se um volume de calda de 200 L ha-1. Verificou-se que, quando a incidência da brusone de panículas (BP) foi de 37,5%, houve um maior nível de controle da doença nos tratamentos que receberam duas aplicações de fungicidas, comparado aos tratamentos que receberam somente uma aplicação. Por outro lado, quando a incidência da BP foi de 20,6%, não foram observadas diferenças entre os tratamentos que receberam uma ou duas aplicações de fungicidas. Os fungicidas propiconazol + trifloxistrobina, tebuconazol + trifloxistrobina e a mistura em tanque triciclazol + tebuconazol em duas aplicações, e a sucessão triciclazol / tebuconazol + trifloxistrobina, proporcionaram acima de 90% de controle da brusone de panícula. Não se observou ganhos significativos de produtividade em decorrência da utilização de fungicidas.

TRATAMENTO DE SEMENTES DE ARROZ, TRIGO, FEIJÃO E SOJA COM UM PRODUTO FORMULADO À BASE DE CÉLULAS E DE METABÓLITOS DE Bacillus subtilis

A biological fungicide product containing B. subtilis cells (60 g) and metabolites (60g) was transformed into a wettable powder formulated with, clay (480 g), surfactant (7,92 g) and water (2400 ml).The product showed to be similar to the conventional fungicides used in the control of Rhizoctonia solani, Aspergillus sp. and Sclerotinia sclerotiorum in bean seeds. The control of Pyricularia oryzae and Rhinchosporium sativum in rice seeds and Cercospora kikuchii, Phomopsis phaseoli and Fusarium spp. in soybean seeds was also as efficient as the comercial fungicides. For Dreschlera oryzae in rice seeds and Bipolaris sorokiniana, P. oryzae and Alternaria tenuis in wheat seeds, the treatment with the product, althought not as efficient as the chemical treatment, was statistically distinct from the control. The root nodulation of bean and soybean by nitrogen fixing bacteria, was not affected when the product was simultaneously applied with bacteria ( Rhyzobium and Bradyrhizobium japonicum). The product did not affect seedling emergence in any of the tested crops.

Um produto constituido de pó-molhável (PBBS) formulado à base de células (60g) e de metabólitos (60g) de Bacillus subtilis, argila (480g), espalhante (7,92g) e água (2400ml), moído e seco, mostrou-se semelhante aos tratamentos com fungicidas recomendados para o controle de Rhizoctonia solani, Aspergillus sp. e Sclerotinia sclerotiorum em sementes de feijão; Pyricularia oryzae e Rhinchosporium sativum em sementes de arroz; e Cercospora kikuchii, Phomopsis phaseoli e Fusarium spp. em sementes de soja. Para Dreschlera oryzae em arroz e Bipolaris sorokiniana, P. oryzae e Alternaria tenuis em sementes de trigo, o tratamento com o PBBS, embora não tenha se igualado ao tratamento com o fungicida padrão, diferiu estatisticamente do tratamento testemunha. A nodulação das raízes de feijão e soja por bactérias simbióticas, fixadoras de nitrogênio, não foi influenciada quando o PBBS foi aplicado simultaneamente ao inoculante contendo Rhyzobium sp. e Bradyrhizobium japonicum, respectivamente. O PBBS também não afetou a emergência das plântulas das culturas testadas.

TRATAMENTO DE SEMENTES DE ARROZ, TRIGO, FEIJÃO E SOJA COM UM PRODUTO FORMULADO À BASE DE CÉLULAS E DE METABÓLITOS DE Bacillus subtilis

A biological fungicide product containing B. subtilis cells (60 g) and metabolites (60g) was transformed into a wettable powder formulated with, clay (480 g), surfactant (7,92 g) and water (2400 ml).The product showed to be similar to the conventional fungicides used in the control of Rhizoctonia solani, Aspergillus sp. and Sclerotinia sclerotiorum in bean seeds. The control of Pyricularia oryzae and Rhinchosporium sativum in rice seeds and Cercospora kikuchii, Phomopsis phaseoli and Fusarium spp. in soybean seeds was also as efficient as the comercial fungicides. For Dreschlera oryzae in rice seeds and Bipolaris sorokiniana, P. oryzae and Alternaria tenuis in wheat seeds, the treatment with the product, althought not as efficient as the chemical treatment, was statistically distinct from the control. The root nodulation of bean and soybean by nitrogen fixing bacteria, was not affected when the product was simultaneously applied with bacteria ( Rhyzobium and Bradyrhizobium japonicum). The product did not affect seedling emergence in any of the tested crops.

Um produto constituido de pó-molhável (PBBS) formulado à base de células (60g) e de metabólitos (60g) de Bacillus subtilis, argila (480g), espalhante (7,92g) e água (2400ml), moído e seco, mostrou-se semelhante aos tratamentos com fungicidas recomendados para o controle de Rhizoctonia solani, Aspergillus sp. e Sclerotinia sclerotiorum em sementes de feijão; Pyricularia oryzae e Rhinchosporium sativum em sementes de arroz; e Cercospora kikuchii, Phomopsis phaseoli e Fusarium spp. em sementes de soja. Para Dreschlera oryzae em arroz e Bipolaris sorokiniana, P. oryzae e Alternaria tenuis em sementes de trigo, o tratamento com o PBBS, embora não tenha se igualado ao tratamento com o fungicida padrão, diferiu estatisticamente do tratamento testemunha. A nodulação das raízes de feijão e soja por bactérias simbióticas, fixadoras de nitrogênio, não foi influenciada quando o PBBS foi aplicado simultaneamente ao inoculante contendo Rhyzobium sp. e Bradyrhizobium japonicum, respectivamente. O PBBS também não afetou a emergência das plântulas das culturas testadas.

Fungicides evaluation to control of panicle blast in irrigated rice / Avaliação de fungicidas para o controle da brusone de panícula na cultura do arroz irrigado

Chemical control of panicle blast, caused by Pyricularia oryzae, is ineffective in many cases, due to the use of non-recommended products or applied improperly. In order to evaluate fungicides efficiency in the control of panicle blast, two experiments were performed in Itajaí and Garuva counties of Santa Catarina state, during 2008/09 planting season. The fungicides were evaluated as single application, at R3 stage (early heading) and two applications at R2 (late boot) and R4 stage (full heading), in an outflow of 200 L ha-1. It was found that when the incidence of panicle blast (PB) was 37.5%, there was a higher level of disease control in treatments with two applications of fungicides, compared to treatments receiving only one application. On the other hand, when the incidence of PB was 20.6%, no significant differences between treatments with one or two applications of fungicides were verified. Two applications of propiconazol + trifloxystrobin, tebuconazol + trifloxystrobin, the tank mixture tricyclazol + tebuconazol and the tricyclazol followed by tebuconazol + trifloxystrobin, proved to be over 90% effective to control panicle blast. It"s not observed significant gains in productivity resulting from the use of fungicides.

O controle químico da brusone de panícula, causada pelo fungo Pyricularia oryzae, é em muitos casos ineficaz, em virtude da utilização de produtos não recomendados, aplicados de forma inadequada. Com o objetivo de avaliar a eficiência de fungicidas no controle da brusone de panícula, foram conduzidos dois experimentos na safra 2008/09 nos municípios de Itajaí e Garuva, SC. Os fungicidas foram avaliados em aplicação única, realizada no estádio R3 (início do florescimento) e em duas aplicações, realizadas nos estádios R2 (emborrachamento) e R4 (pleno florescimento), utilizando-se um volume de calda de 200 L ha-1. Verificou-se que, quando a incidência da brusone de panículas (BP) foi de 37,5%, houve um maior nível de controle da doença nos tratamentos que receberam duas aplicações de fungicidas, comparado aos tratamentos que receberam somente uma aplicação. Por outro lado, quando a incidência da BP foi de 20,6%, não foram observadas diferenças entre os tratamentos que receberam uma ou duas aplicações de fungicidas. Os fungicidas propiconazol + trifloxistrobina, tebuconazol + trifloxistrobina e a mistura em tanque triciclazol + tebuconazol em duas aplicações, e a sucessão triciclazol / tebuconazol + trifloxistrobina, proporcionaram acima de 90% de controle da brusone de panícula. Não se observou ganhos significativos de produtividade em decorrência da utilização de fungicidas.