Tratamento de sementes com fungicidas e inseticidas como redutores dos efeitos do estresse hídrico em plantas de soja

O objetivo do trabalho foi avaliar o efeito de quatro tratamentos de sementes: água (T1), carbendazim + thiram (T2), fipronil + tiofanato metílico + piraclostrobina (T3) e abamectina + thiamethoxam + fludioxonil + mefenoxan + thiabendazole (T4) sobre parâmetros de crescimento de plantas de soja submetidas a dois regimes hídricos (presença e ausência de estresse hídrico) estabelecidos logo após a emergência das plântulas. O experimento foi conduzido em casa de vegetação e campo. Na casa de vegetação, nos tratamentos sem estresse hídrico, foram feitas quatro irrigações por dia e, nos tratamentos com estresse hídrico, foi realizada uma irrigação a cada três dias. Neste ensaio, foi avaliada a estatura de plantas, comprimento radicular, volume radicular, massa seca da parte aérea, massa seca radicular e área foliar. No ensaio de campo, o estresse hídrico foi estabelecido pela construção de túneis baixos de polietileno que impediram o fornecimento de água pela irrigação e chuva. No campo, foram avaliados estatura de planta, teor relativo de clorofila, emergência, ataque de lagarta-elasmo e rendimento de grãos. Nos dois ambientes, as plantas foram mantidas sob estresse até 28 dias após a emergência. Em casa de vegetação, todos os parâmetros foram influenciados pelo tratamento de sementes na presença e ausência de estresse hídrico. No campo, o tratamento com fipronil + tiofanato metílico + piraclostrobina (T3) e abamectina + thiamethoxam + fludioxonil + mefenoxan + thiabendazole (T4) proporcionaram maior estatura de planta e teor relativo de clorofila em ambos os regimes hídricos e maior emergência e rendimento de grãos em plantas sem e com restrição hídrica, respectivamente. Conclui-se que o tratamento de sementes com esses produtos promove alterações benéficas nas plantas, aumentando sua tolerância ao estresse hídrico, com efeito positivo sobre o rendimento de grãos da soja.The objective of this research was evaluate four seed treatments: water (T1), carbendazim + thiram (T2), fipronil + thiophanate methyl + pyraclostrobin (T3) and abamectin + thiamethoxam + fludioxonil + mefenoxan + thiabendazole (T4) on growth parameters of soybean plants with or without low water availability. The experiments were conducted under field conditions and greenhouse. In greenhouse, in treatments without low water availability, it was made four irrigations by day and in treatments with low water availability, it was made one irrigation each three days. In this trial, it was evaluated the plant height, root length, root volume, dry shoot weight, dry root weight and foliar area. In the field trial, low water availability was established by construction of low tunnels of polyethylene which prevented the water supply by irrigation and rain. In the field, it was also evaluated the plant height, the relative chlorophyll content, emergence, lesser cornstalk borer attack and grain yield. In the both environment, the plants were kept on stress until 28th days after emergence. In greenhouse, all the parameters were influenced by seed treatments with or without low water availability. In field, the treatment with fipronil + thiophanate methyl + pyraclostrobin (T3) and abamectin + thiamethoxam + fludioxonil + mefenoxan + thiabendazole (T4) promoted higher plant height and relative chlorophyll content in both hydric schemes, higher emergence and grain yield in plants without and with lower water availability, respectively. It was concluded that seed treatment with these products promote benefit changes in plant, increasing its tolerance to hydric stress, with positive effect on soybean grain yield

Biochemical and physiological changes in wheat plants infected with Pyricularia oryzae

A brusone, causada pelo fungo Pyricularia oryzae, constitui a doença mais importante da cultura do trigo no cerrado brasileiro. No entanto, informações na literatura da interação trigo-P. oryzae ainda são limitadas. Neste estudo foram investigadas as alterações bioquímicas e fisiológicas em plantas de trigo das cultivares BR 18 e BRS 229, suscetível e parcialmente resistente à brusone no estádio de planta jovem, respectivamente, durante o processo infeccioso de P. oryzae. As variáveis estudadas foram a severidade da brusone, a atividade de enzimas do sistema antioxidativo, as concentrações de superóxido (O2-), peróxido de hidrogênio (H2O2) e aldeído malônico (MDA), e o extravasamento de eletrólitos (EE), bem como os parâmetros de trocas gasosas às 48, 72 e 96 horas após a inoculação (hai) com P. oryzae. Adicionalmente, foram determinadas a taxa máxima de carboxilação (Vcmax), a taxa máxima de transporte de elétrons usados na regeneração da ribulose-1,5-bisfosfato (RUBP) (Jmax), a respiração (Rd) e calculada a relação Jmax/Vcmax com base na resposta da taxa líquida de assimilação de CO2 (A) a diferentes concentrações internas de CO2 (Ci) (curva A/Ci). A severidade da brusone foi menor nas plantas da cultivar BRS 229 do que nas plantas da cultivar BR 18. A atividade das enzimas do sistema antioxidativo foi fortemente afetada pela infecção por P. oryzae e usualmente maior nas plantas inoculadas do que nas plantas não inoculadas. O aumento na atividade das enzimas superóxido dismutase, peroxidase, peroxidase do ascorbato e glutationa- S-transferase às 96 hai foi mais pronunciado para a cultivar BRS 229 do que para a cultivar BR 18. A atividade da redutase da glutationa (GR) e catalase (CAT) aumentou somente nas plantas inoculadas da cultivar BRS 229 às 96 hai em relação às plantas não inoculadas. Para a cultivar BR 18, a atividade da GR não foi afetada pela inoculação com P. oryzae e a atividade da CAT foi menor nas plantas inoculadas do que nas não inoculadas. A atividade da peroxidase da glutationa aumentou nas plantas inoculadas da cultivar BR 18 em relação às plantas não inoculadas às 48 e 72 hai, e não foi afetada pela inoculação com P. oryzae nas plantas da cultivar BRS 229. A concentração de O2- aumentou em 153viii e 72% às 96 hai nas plantas inoculadas das cultivares BR 18 e BRS 229, respectivamente, comparadas com as plantas não inoculadas. A concentração de H2O2 foi 59% maior nas plantas inoculadas da cultivar BR 18 em relação às plantas não inoculadas às 96 hai, porém não houve diferença entre plantas inoculadas e não inoculadas na concentração de H2O2 para a cultivar BRS 229. A concentração de MDA foi maior nas plantas inoculadas às 48, 72, e 96 hai para a cultivar BR 18 e somente às 48 hai para a cultivar BRS 229, em relação às plantas não inoculadas. O EE aumentou em 323 e 188% às 96 hai nas plantas inoculadas das cultivares BR 18 e BRS 229, respectivamente, comparadas com as plantas não inoculadas. Os parâmetros de trocas gasosas A, condutância estomática e taxa de transpiração, bem como Vcmax e Jmax foram significativamente reduzidos nas plantas de trigo inoculadas das duas cultivares em relação às plantas não inoculadas. Essa redução, no entanto, foi menos pronunciada nas plantas da cultivar BRS 229 do que nas plantas da cultivar BR 18, o que esteve associado com a menor severidade da brusone observada para a cultivar BRS 229. Ci aumentou em 32 e 14% às 96 hai nas plantas inoculadas das cultivares BR 18 e BRS 229, respectivamente. A relação Jmax/Vcmax aumentou nas plantas inoculadas das duas cultivares em relação às plantas não inoculadas. Rd aumentou 208% nas plantas inoculadas da cultivar BR 18 em relação às plantas não inoculadas às 96 hai, porém não houve diferença em Rd entre plantas inoculadas e não inoculadas para a cultivar BRS 229. Os resultados do presente estudo demonstraram a importância de um sistema antioxidativo eficiente para remover o excesso de espécies reativas de oxigênio gerado durante a infecção de plantas de trigo por P. oryzae, limitando o dano celular causado pelo fungo. Adicionalmente, esse sistema antioxidativo mais eficiente parece contribuir para uma maior resistência do trigo à brusone. As avaliações fisiológicas demonstraram que a fotossíntese de plantas de trigo foi significativamente reduzida pela infecção por P. oryzae, a qual esteve associada principalmente à menor atividade aparente da Rubisco, seguido pela menor regeneração de RuBP. O conhecimento das alterações bioquímicas e fisiológicas de plantas de trigo infectadas por P. oryzae é de suma importância para o desenvolvimento de estratégias de controle eficientes da brusone.Blast, caused by the fungus Pyricularia oryzae, is the most important disease of wheat in brazilian Cerrado. However, information in the literature about wheat-P. oryzae interaction is still limited. In this study, it was investigated biochemical and physiological changes in wheat plants from cultivars BR 18 and BRS 229, susceptible and partially resistant to blast at young plant stage, respectively, during the infectious process of P. oryzae. The variables studied were: blast severity, activity of antioxidant enzymes and superoxide (O2-), hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations, and electrolyte leakage (EL), as well as gas exchange parameters at 48, 72 and 96 hours after inoculation (hai) with P. oryzae. Additionally, it was determined the maximum rate of carboxylation (Vcmax), the maximum rate of electron transport used on ribulose- 1,5-bisphosphate (RUBP) regeneration (Jmax), and respiration (Rd) and calculated the Jmax/Vcmax ratio based on the response of net carbon assimilation rate (A) to different internal CO2 concentration (Ci) (A/Ci curve). The blast severity was lower in plants from cultivar BRS 229 than in plants from cultivar BR 18. The activity of antioxidant enzymes system was strongly affected by infection with P. oryzae and usually higher in inoculated plants than in noninoculated plants. The increase in activity of superoxide dismutase, peroxidase, ascorbate peroxidase and glutathione-S-transferase at 96 hai was more pronounced for cultivar BRS229 than for cultivar BR 18. The activity of glutathione reductase (GR) and catalase (CAT) increased only in inoculated plants from cultivar BRS 229 at 96 hai compared with noninoculated plants. For cultivar BR 18, GR activity was not affected by inoculation with P. oryzae and CAT activity was lower in inoculated plants than in noninoculated plants. The activity of glutathione peroxidase increased in inoculated plants from cultivar BR 18 in relation to noninoculated plants at 48 and 72 hai, and it was not affected by inoculation with P. oryzae on plants from cultivar BRS 229. O2- concentration increased 153 and 72% at 96 hai in inoculated plants from cultivars BR 18 and BRS 229, respectively, compared with noninoculated plants. H2O2 concentration was 59% higher in inoculatedx plants from cultivar BR 18 in relation to noninoculated plants at 96 hai, but there was no difference between inoculated and noninoculated plants for cultivar BRS 229. MDA concentration was higher in inoculated plants at 48, 72, and 96 hai for cultivar BR 18 and just at 48 hai for cultivar BRS 229, in relation to noninoculated plants. EL increased 323 and 188% at 96 hai in inoculated plants from cultivars BR 18 and BRS 229, respectively, compared with noninoculated plants. The gas exchange parameters A, stomatal conductance and transpiration rate as well as Vcmax and Jmax were significantly reduced in inoculated plants from both wheat cultivars compared with noninoculated plants. This reduction, however, was less pronounced in the plants from cultivar BRS 229 than in the plants from cultivar BR 18, which was associated with lower blast severity observed for BRS 229. Ci increased 32 and 14% at 96 hai in inoculated plants from cultivars BR 18 and BRS 229, respectively. The Jmax/Vcmax ratio increased in inoculated plants from both cultivars in relation to noninoculated plants. Rd increased 208% in inoculated plants from cultivar BR 18 in relation to noninoculated plants at 96 hai, but there was no difference in Rd between inoculated and noninoculated plants for cultivar BRS 229. The results of this study demonstrated the importance of an efficient antioxidant system to remove excess of reactive oxygen species generated during infection of wheat plants with P. oryzae limiting the cellular damage caused by the fungus. Additionally, the more efficient antioxidant system appears to contribute to a greater resistance to wheat blast. The physiological evaluations showed that the photosynthesis of wheat plants was significantly reduced by infection with P. oryzae, what was mainly associated with lower apparent activity of Rubisco, followed by the lower RuBP regeneration. Knowledge of biochemical and physiological changes of wheat plants infected with P. oryzae is of great importance to develop effective strategies for control of wheat blast.Conselho Nacional de Desenvolvimento Científico e Tecnológic

Aspectos fisiológicos, bioquímicos e microscópicos da interação arroz-Bipolaris oryzae mediados por um fungicida do grupo das estrobilurinas

Strobilurins are among the most important fungicides that are used for plant disease control worldwide. In addition to their fungicide effect, strobilurins can also affect some physiological and biochemical aspects of treated plants. Nonetheless physiological, biochemical and microscopic alterations caused by azoxystrobin (Az), the main marketed strobilurin, in rice crop remain elusive. To address this issue, detailed gas exchange measurements and chlorophyll a fluorescence analysis, antioxidant and defense systems assays as well light microscopy analysis were performed on rice plants (cultivar Metica-1) that were sprayed or non-sprayed with Az (+Fu and -Fu plants) and either challenged or not with Bipolaris oryzae, the causal agent of brown spot. The +Fu non-inoculated plants displayed lower carbon (C) fixation than -Fu plants, and such decrease was not related to photochemical or biochemical limitations but rather to decreased stomatal conductance that limited the CO 2 influx into the mesophyll cells. The photosynthesis of -Fu plants decreased upon B. oryzae infection, which was chiefly governed by photochemical and biochemical limitations. The energy surplus that was caused by limited C fixation in the +Fu inoculated plants was thermally and effectively dissipated until 72 hours after inoculation (hai). For the -Fu plants, however, this mechanism was not sufficient to prevent chronic photoinhibition to photosynthesis. The inoculated plants were not able to fully capture and exploit the collected light energy, but these constraints were greatly limited in the presence of Az. In general, the +Fu plants did not show changes in the activities of antioxidant enzymes, but displayed higher concentrations of reduced glutathione (GSH) than -Fu plants. The activities of superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione peroxidase, glutathione reductase, and glutathione-S-transferase were increased upon B. oryzae infection, but such increases were lower in the +Fu plants. Catalase activity decreased in the inoculated plants compared to the non-inoculated plants regardless of fungicide treatment. The GSH concentration increased in response to the B. oryzae infection, and the +Fu plants sustained higher levels of GSH at advanced stages of fungal infection than did the -Fu plants. The inoculated plants exhibited an extensive oxidative stress as evidenced by higher concentrations of hydrogen peroxide and malondialdehyde compared to the non-inoculated plants, but lower and later increases were recorded in the +Fu plants than in the -Fu plants. The +Fu plants displayed higher activities of β- 1,3-glucanase, peroxidase, polyphenol oxidase (PPO) and lipoxygenase (LOX) in the absence of B. oryzae inoculation and of phenylalanine ammonia lyase, PPO and LOX at 24 hai compared to the -Fu plants. Concentrations of total soluble phenols (TSP) were transiently reduced by fungal infection in the +Fu plants, but such plants presented higher TSP levels at 144 hai relative to their -Fu counterparts. Irrespective of the fungicide treatment, B. oryzae infection increased activities of all defense enzymes studied, but such increases usually were higher for the -Fu plants than for the +Fu plants. Concentrations of lignin thioglycolic acid derivatives were increased following fungal infection in the -Fu plants. Microscopic analyses revealed that hyphae from B. oryzae colonized bulliform, bundle sheath, epidermal, guard, mesophyll and vascular bundle cells besides intercellular spaces, but fewer and smaller fungal cells were noticed in the +Fu than in the -Fu plants. However, the constrained fungal invasion verified in the +Fu plants was not accompanied by amplified defense reactions since cells of the - Fu plants reacted by accumulating phenol-like material, whereas such reaction was only limited in cells of the +Fu plants. Overall, our results showed that Az impaired the photosynthetic performance of non-infected plants by diffusive constraints but prevented, to a greater extent, the damage to the photosynthetic apparatus during the infection process of B. oryzae. In addition, Az reduced B. oryzae-induced oxidative stress by limiting brown spot development rather than by activating the antioxidant system. Although Az had transiently reprogrammed activities of defense enzymes, which may have contributed for explaining the reduced brown spot severity observed in the +Fu plants, its fungicidal activity played a major role in reducing B. oryzae infection.As estrobilurinas estão entre os principais fungicidas usados no controle de doenças ao redor do mundo. Em adição ao seu efeito fungicida, elas também podem afetar aspectos fisiológicos e bioquímicos de plantas tratadas. No entanto, as alterações fisiológicas, bioquímicas e microscópicas decorrentes da aplicação de azoxistrobina (Az), a principal estrobilurina do mercado, na cultura do arroz permanecem elusivas. Para responder essas questões, foram realizadas análises detalhadas de trocas gasosas, da fluorescência da clorofila a, dos sistemas antioxidativo e de defesa, bem como análises de microscopia de luz em plantas de arroz (cultivar Metica-1) as quais receberam ou não a aplicação de Az (plantas +Fu e -Fu, respectivamente) e foram inoculadas ou não com Bipolaris oryzae, agente causal da mancha parda. Plantas +Fu não inoculadas mostraram menor fixação de carbono (C) do que plantas -Fu, sendo que tal redução não esteve relacionada a limitações fotoquímicas ou bioquímicas, mas ao decréscimo na condutância estomática, o qual limitou o influxo de CO 2 às células do mesófilo. A fotossíntese das plantas -Fu decresceu com a infeção por B. oryzae, principalmente por limitações fotoquímicas e bioquímicas. O excesso de energia decorrente da limitada fixação de C nas plantas +Fu inoculadas foi termicamente e efetivamente dissipado até 72 horas após a inoculação (hai). Para as plantas -Fu, entretanto, esse mecanismo não foi suficiente para prevenir uma crônica fotoinibição da fotossíntese. As plantas inoculadas não foram capazes de capturar e explorar completamente a energia solar coletada, mas tais restrições foram grandemente limitadas na presença de Az. Em geral, plantas +Fu não inoculadas não apresentaram alterações na atividade de enzimas antioxidativas, mas exibiram maiores concentrações de glutationa reduzida (GSH) do que plantas -Fu. A atividade da superóxido dismutase, peroxidase, peroxidase do ascorbato, peroxidase da glutationa, redutase da glutationa e glutationa-S-transferase foram aumentadas em decorrência da infecção por B. oryzae, mas tais aumentos foram menores nas plantas +Fu. A atividade da catalase foi diminuída nas plantas inoculadas comparadas às não inoculadas, independentemente do tratamento com fungicida. A concentração de GSH aumentou em resposta à infecção por B. oryzae, e as plantas +Fu sustentaram maiores níveis de GSH em estágios avançados da infecção fúngica do que as plantas -Fu. As plantas inoculadas exibiram extensivo estresse oxidativo, como evidenciado pelas maiores concentrações de peróxido de hidrogênio e aldeído malônico comparado às plantas não inoculadas, porém aumentos menos pronunciados e mais tardios foram reportados nas plantas +Fu do que nas plantas -Fu. Plantas +Fu apresentaram maior atividade da β-1,3-glucanase, peroxidase, polifenol oxidase (PFO) e lipoxigenase (LOX) na ausência de inoculação com B. oryzae e de fenilalanina amônia liase (FAL), PFO e LOX 24 hai comparadas às plantas -Fu. A concentração de fenois solúveis totais (FST) foi transientemente reduzida pela infecção fúngica nas plantas +Fu, mas tais plantas apresentaram maiores níveis de FST 144 hai comparadas às plantas -Fu. Independentemente do tratamento com fungicida, a infecção por B. oryzae aumentou a atividade de todas as enzimas de defesa estudadas, mas tais aumentos foram usualmente maiores para as plantas -Fu do que para as plantas +Fu. A concentração de derivados da lignina e ácido tioglicólico foram aumentadas pela infecção fúngica nas plantas -Fu. Análises microscópicas revelaram que as hifas de B. oryzae colonizaram as células buliformes, da bainha do feixe, epidérmicas, guarda, do mesófilo e do feixe vascular, bem como espaçoes intercelulares, porém menos e menores células fúngicas foram observadas nas plantas +Fu do que nas plantas -Fu. No entanto, a limitada invasão fúngica verificada nas plantas +Fu não foi acompanhada por amplificadas reções de defesa, visto que as células das plantas -Fu reagiram através do acúmulo de material semelhante a fenois, considerando que tal reação foi limitada nas células de plantas +Fu. Portanto, nossos resultados mostraram que Az prejudicou a performance fotossintética de plantas não infectadas através de limitações difusivas, mas preveniu, numa grande extensão, o dano ao aparato fotossintético durante o processo infecioso de B. oryzae. Em adição, Az reduziu o estresse oxidative induzido por B. oryzae por limitar o desenvolvimento da mancha parda ao invés da ativação do sistema antioxidativo. Embora Az tenha reprogramado a atividade de enzimas de defesa, fato que pode ter contribuído para explicar a reduzida severidade da mancha parda observada em plantas tratadas +Fu, seu efeito fungicida desempenhou um papel fundamental em restringir a infecção por B. oryzae

Changes in the antioxidant system in soybean leaves infected by Corynespora cassiicola

Considering the importance of target spot, caused by the fungus Corynespora cassiicola, to reduce soybean yield in Brazil and that more basic information regarding the soybean−C. cassiicola interaction is needed, the present study aimed to investigate whether the cellular damage caused by C. cassiicola infection could activate the antioxidant system and whether a more efficient antioxidant system could be associated with an increase in soybean resistance to target spot. The activities of the antioxidant enzymes superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione peroxidase, glutathione reductase, glutathione S-transferase as well as the concentrations of ascorbate (AsA), hydrogen peroxide (H2O2), superoxide (O2•−), and malondialdehyde (MDA) were measured in soybean plants from two cultivars differing in resistance to the pathogen. The number of lesions per square centimeter was significantly reduced by 14% in plants from cultivar Fundacep 59 compared with plants from cultivar TMG 132. The area under the disease progress curve was significantly lower, by 15%, in plants from Fundacep 59 than in plants from TMG 132. Generally, antioxidant enzyme activities and AsA concentration significantly increased in response to C. cassiicola infection in plants from both cultivars, however more prominent increases were recorded for plants from Fundacep 59. The concentrations of MDA, H2O2, and O2•− also increased, particularly for plants from TMG 132. The results from this study highlight the importance of a more efficient antioxidative system in the removal of reactive oxygen species generated in soybean plants during C. cassiicola infection, contributing to the resistance to target spot

Defence‐related enzymes in soybean resistance to target spot

Target spot, caused by the fungus Corynespora cassiicola, has become a serious foliar disease in soybean production in the Brazilian Cerrado. Information in the literature regarding the biochemical defence responses of soybean to C. cassiicola infection is rare. Therefore, the objective of this study was to determine the biochemical features associated with soybean resistance to target spot. The activities of chitinases (CHI), β‐1‐3‐glucanases (GLU), phenylalanine ammonia‐lyases (PAL), peroxidases (POX), polyphenol oxidases (PPO) and lipoxygenases (LOX), as well as the concentrations of total soluble phenolics (TSP) and lignin‐thioglycolic acid (LTGA) derivatives, were determined in soybean leaves from both a resistant (FUNDACEP 59) and a susceptible (TMG 132) cultivar. The target spot severity, number of lesions per cm2 of leaflet and area under the disease progress curve were significantly lower for plants from cv. FUNDACEP 59 compared to plants from cv. TMG 132. The GLU, CHI, PAL, POX and PPO activities and the concentration of LTGA derivatives increased significantly, whereas LOX activity decreased significantly on the leaves infected by C. cassiicola. Inoculated plants from cv. FUNDACEP 59 showed a higher PPO activity and concentrations of TSP and LTGA derivatives at 4 and 6 days after inoculation compared to plants from cv. TMG 132. In conclusion, the results of this study demonstrated that the defence‐related enzyme activities increased upon C. cassiicola infection, regardless of the basal level of resistance of the cultivar studied. The increases in PPO activity and concentrations of TSP and LTGA derivatives, but lower LOX activity, at early stages of C. cassiicola infection were highly associated with soybean resistance to target spot

Escala diagramática para avaliação de severidade de mancha-parda em arroz Diagrammatic scale for assessment of rice brown spot severity

Uma escala diagramática com seis níveis: 1,6; 3,2; 6,4; 12,6; 23,1 e 38,6% foi desenvolvida e validada para quantificar a severidade da mancha-parda em arroz causada por Bipolaris oryzae. A escala considerou o limite de severidade máxima da doença observado no campo, e os níveis intermediários seguiram incrementos logarítmicos, obedecendo-se à "Lei do estímulo de Weber-Fechner". Inicialmente, a estimativa da severidade foi realizada sem auxílio da escala, em 30 folhas com diferentes níveis de severidade, por oito indivíduos, sem experiência na avaliação de doenças. Em seguida, os mesmos avaliadores utilizaram a escala diagramática proposta. As avaliações com a escala diagramática foram mais precisas e acuradas nas estimativas de todos os avaliadores, não ocorrendo erro sistemático na superestimativa ou subestimativa da doença entre estes. A escala diagramática proposta foi considerada adequada para estimar a severidade da mancha-parda em arroz.<br>A diagrammatic scale with six levels of disease severity: 1.6; 3.2; 6.4; 12.6; 23.1 and 38.6% was developed and validated to assess rice brown spot, caused by Bipolaris oryzae. The scale was developed considering the maximum limit of disease severity observed in the field and the intermediate values followed logarithmic increases according to the "Stimulus Law by Weber-Fechner". Initially, the estimatives of severity were performed without the use of the scale in 30 leaves with different levels of severity by eight people without previous experience in assessing diseases severity. Then, the same people estimated the severity of leaves using the proposed diagrammatic scale. Assessments with the diagrammatic scale were of great precision for all raters and did not presented systematic errors in over- or underestimating the disease severity. The proposed diagrammatic scale was considered adequate to estimate rice brown spot severity

A set of standard area diagrams to assess white mold severity on the leaflets of common beans

The fungus Sclerotinia sclerotiorum is the major pathogen affecting common beans yield worldwide and an adequate disease quantification is demanded in some trials. However, a set of standard area diagrams (SADs) to aid visual assessment of severity of white mold (SWM) is lacking. This study developed SADs consisting of eight color images of diseased leaflets with severity values that ranged from 0.4 to 53.7%. Twenty raters [10 experienced (ER) and 10 inexperienced (IR)] validated the SADs by assessing the same set of 50 images twice, the first without SADs and the second using it as an aid. The SADs significantly improved both accuracy and precision for IR as evidenced by increases from 0.86 to 0.98 in the coefficients of bias (Cb) from 0.93 to 0.98 in correlation coefficient (r) and from 0.86 to 0.96 in overall agreement [Lin's concordance correlation coefficients (ρc)] without and with SADs, respectively, whereas for ER only precision (r) was improved by SADs. The SWM estimates were also more reliable because inter-rater reliability (coefficient of determination, R2) was significantly increased for both ER and IR by using SADs. Therefore, the SADs presented is thought to be a valuable tool to provide accurate, precise and reliable estimates of the SWM on common bean leaflets in epidemiological studies, evaluation of disease control methods, assessment of aggressiveness of pathogen isolates, disease resistance and other types of surveys regarding the common beans-S. sclerotiorum interaction