Panicle Blast Severity Research Articles

Probing the effects of silicon amendment on combined stressors on rice: Lead pollution and blast fungus (Magnaporthe oryzae) infection

As agroecology deteriorates, agricultural production is threatened by the combined stressors of exposure to environmental pollutants and pathogenic microbes. Proper agronomic practices for crop growth management and fertilization require understanding plant tolerance strategies. Both rice blast and heavy metals substantially impair rice crops, while silicon (Si) is an effective amendment to alleviate the combined stressors. Herein, this study was conducted to investigate the rice physiology and pathology perspective on the mechanism of Si alleviation against both lead (Pb) toxicity and Magnaporthe oryzae infection, utilizing pot experiments with inoculation of the virulent Magnaporthe oryzae strain. Exogenous Si reduced the phyto-availability and plant absorption of Pb, resulting in a 73.5% reduction in exchangeable Pb concentration in soil and a 40.23% reduction in rice plants. Furthermore, Si addition boosted the plant antioxidant system by increasing the activities of related enzymes, as the activities of catalase, superoxide dismutase, and polyphenol oxidase were significantly improved while the activity of peroxidase in rice panicles decreased. As a result, an improvement in dry matter quantity by 19.19% was observed compared to treatments without Si application, and the panicle blast severity (PBS) was reduced by 0.4–37.52%. Notwithstanding the interaction between the combined stressors, this study revealed that the speciation of Pb formation in the rhizosphere was the primary contributor to the alleviation of abiotic stresses, whereas the regulation of oxidative stress by enzymatic antioxidants played a dominant role in alleviating Magnaporthe oryzae colonization and impairments. The regulation process may reveal the mechanism of siliceous fertilizer functioning in the paddy system. Thereby the role of exogenous Si in anti-fungal, heavy metal toxicology, and plant physiology needs further study to fully elucidate the role of Si amendment, which is proposed to be considered from the perspective of soil chemistry and plant physiology.

Evaluation of Triazole and Strobilurin Fungicides against Leaf and Panicle Blast of Rice in Farmer's Field

Blast disease of rice caused by the ascomycetes fungus Magnaporthe grisea poses a major threat to rice production from terai to hilly region of Nepal. Field trials were conducted in two successive years, 2021 and 2022 at Bharatpur-5, Chitwan in a farmer's field producing seed of Hardinath-1 variety with the main objective of finding the effective single and/or pre-mix formulation of triazole and strobilurin fungicides against rice blast that could be an alternative to tricyclazole. The trials were conducted in randomized complete block design with three replications and eight treatments viz. azoxystrobin 18.2% + difenoconazole 11.4% SC, propiconazole 13.9% + difenoconazole 13.9% EC, azoxystrobin 11% + tebuconazole 18.3% SC, azoxystrobin 23% SC, propiconazole 25% EC, difenoconazole 25% EC, tebuconazole 25%WDG and a control. The fungicides were applied during tillering and heading stage at the rate of 0.1%. All fungicides significantly reduced the leaf and panicle blast severity resulting in a higher yield. Among the tested fungicides, pre-mix formulation fungicide azoxystrobin 18.2% + difenoconazole 11.4% SC, propiconazole 13.9% + difenoconazole 13.9% EC and azoxystrobin 11% + tebuconazole 18.3% SC gave excellent performance with the lowest leaf and panicle blast severity and higher yield. Hence, these three fungicides could be used for the management of leaf and panicle blast disease for higher yield. However, controlling rice blast disease has become increasingly challenging due to the pathogens' capacity to adapt and evolve into new, more potent strains, making the management and control of this disease more difficult.

Analysis of blast resistance genes in Longliangyou and Jingliangyou hybrid rice varieties

<p id="C3">Longke 638S and Jing 4155S, developed by Yuan Longping High-Tech Agriculture Co., Ltd. in 2014, were two thermo-sensitive genic male sterile (TGMS) lines with disease resistance, high grain quality and combining ability for producing mid-season<italic> indica</italic> hybrid rice. In this study, we analyzed the blast resistance evaluation data from the regional trials of the Longliangyou and Jingliangyou hybrid rice varieties approved by the state from 2015 to 2019. Meanwhile, to provide theoretical basis for distribution and further improvement of these hybrid rice varieties, a genotyping panel containing 16 rice blast resistance (<italic>R</italic>) genes based on KASP (Kompetitive Allele-Specific PCR) technology was developed and used for molecular detection of these hybrid rice varieties. The results showed that 43.92% of Longliangyou and Jingliangyou hybrid rice varieties conferred moderate resistance to high resistance to blast disease. The mean value of integrated disease index (IDI) and highest scale of panicle blast severity (HSPBS) was 3.3 and 4.7, respectively. These hybrid rice varieties carried different number of <italic>R</italic> genes, ranging from 3 to 7. The average number of <italic>R</italic> genes in each variety was 5.1. The distribution frequency of the five genes including <italic>Pia</italic>, <italic>Pita</italic>, <italic>Pi2</italic>, <italic>Pi5</italic>, and <italic>Piz </italic>were higher by more 50%, among which, it was 100% for <italic>Pia</italic> gene. In contrast,<italic> Pi9</italic>, <italic>Pi35</italic>,<italic> Pi36</italic>, and <italic>Pb1</italic> genes were not detected in Longliangyou and Jingliangyou hybrid rice varieties. With the increase of the number of <italic>R</italic> genes in the varieties, the mean values of IDI and HSPBS were generally decreased. In conclusion, we suggested that introduction of <italic>Pi9 </italic>into Longke 638S and Jing 4155s might lead to the further improvement of blast resistance of Longliangyou and Jingliangyou hybrid rice varieties.

Panicle blast severity identification in advance generation rice lines

Harvest failure due to blast (Pyricularia oryzae) in Indonesia was ranked fourth during 2015-2020. Establishing a panicle blast-resistant rice variety is crucial to prevent broader damage. The research aimed to evaluate the yield productivity at the blast endemic areas. The field experiment was held from April to July 2019 at Curugkembar Sukabumi. The statistic field design used Augmented with five blocks to manage 122 advanced rice lines in total, and six check varieties included leaf blast-resistant varieties. Pest and disease control based on Integrated Pest Management (IPM) standards, except for blast disease. Leaf blast infection occurs from vegetative and lasts to generative, which then continues to be a severed panicle blast. All tested lines and varieties were infected, with different severity. Two rice lines were resistant to panicle blast (scale 0), two lines were moderate resistant (scale 3), and the rest were susceptible (scale 5-9). The results of the augmented analysis for yield production showed that BP30533D-SKI-29-3-3 (8.96 t/ha) and BP31501D-SKI-28-1-0-0 (7.69 t/ha) lines were significantly better than INPARI 41 (3.6 t/ha) but susceptible to panicle blast (scaled 5 and 7). This result indicates that yield testing and blast screening would be better to run simultaneously.

Efficacy of Different Fungicides for the Control of Rice Blast (Pyricularia oryzae) Disease under Field Conditions at Pawe, Northwest Ethiopia

Rice blast disease caused by Pyricularia oryzae Cavara is the most destructive rice disease worldwide. Among the disease management options, the use of a fungicide is suitable for immediate action and remained an exclusive management method in the continents like Africa where agricultural technologies are not well advanced. The present study aimed to evaluate the effectiveness of seven chemical fungicides viz., Amistar Xtra 280 SC, Artea 330 EC, Contaf Max 350 SC, Fungozeb 80 WP, Matco, Rex® Deo and Tilt 250 EC for the control of rice blast disease under field condition at Pawe, northwest Ethiopia. The result revealed that all the test fungicides have significantly suppressed the disease development with 11.1 – 51.5% suppression of panicle blast severity and 18.9 – 67% suppression of neck blast severity compared to the control (Untreated plot). However, Contaf Max 350 SC had superior disease reduction by more than 60% and gave the maximum grain yield (5617.06 kg ha-1) among the fungicides while the lowest yield was obtained from the control (4324.73 kg ha-1) followed by Artea 330 EC (4639.35 kg ha-1). Therefore, the present results suggest that twice application of Contaf Max 350 SC fungicide at 1 Lha-1 is effective for managing rice blast disease in Pawe and other places with a similar condition.

Varietal susceptibility overcomes climate change effects on the future trends of rice blast disease in Northern Italy

CONTEXTRice blast manifests with different symptoms according to the affected plant organ, i.e., leaf and panicle blast, the latter being the primary determinant of yield losses in Italy. Forecasting models have been developed to drive fungicides application and perform scenario analyses to plan legislative measures on plant protection. An assessment of the blast pathogen pressure evolution in the Italian rice area under climate change realizations has not been done yet. OBJECTIVEWe developed the ELLE process-based forecasting model (ricE bLast simuLation modEl) to reproduce the dynamics of leaf and panicle blast severity and incidence to release a tool to perform in-season monitoring and scenario assessment. The forecasting model is delivered as a RESTful API and is ready to be used by third parties for operational monitoring activities. Here we present its application to assess future rice blast impacts in Italy after an extended calibration and evaluation with ground-truth data. METHODSThe reference dataset for model testing comprised (a) a multi-year (2013–2015) and multi-site (three locations) experimental trial, where leaf and panicle blast were assessed on four Italian rice varieties with different levels of susceptibility to blast disease, and (b) historical disease data collected at the municipality level. We then performed spatially distributed simulations at 2 × 2 km resolution on the Northern Italian rice district, considering a short- (2030) and long- (2070) term time horizon and rice varieties representative of the current variability in phenology and susceptibility to blast disease within the Italian varietal landscape. The factorial combinations of climatic projections from four General Circulation Models and two extreme CO2 Representative Concentration Pathways were used as model inputs in the scenario analysis. RESULTS AND CONCLUSIONSModel calibration and evaluation at the field level denoted an overall accurate reproduction of leaf blast severity (RRMSE <13%) and panicle blast incidence (RRMSE <17%). The climate change scenario analysis highlighted the varietal susceptibility as the critical factor determining leaf and panicle blast variability in the future, with no significant changes in 2030 and a slight decline in 2070. SIGNIFICANCEBesides delivering a reusable methodology to analyze the severity and incidence of leaf and panicle blast, our modelling study confirms that varietal susceptibility is the main feature to be pursued in rice breeding programs to counteract blast disease.

Efficacy of Bacillus tequilensis strain JN-369 to biocontrol of rice blast and enhance rice growth

Rice blast caused by Magnaporthe oryzae is one of the major threat to global food security. In this study, Bacillus tequilensis strain JN-369, which exhibited antagonistic effect against several phytopathogens, was previously isolated and identified from xiangzaoxian No. 24 healthy rice plants. To further evaluate its potential agricultural use, in vitro on detached leaves test, greenhouse and field experiments were performed to evaluate the plant growth-promotion and biocontrol efficacy of strain JN-369. The results of the study showed that strain JN-369 can promote seed germination and seedling plant growth, and improve plant defense enzyme activities. Compare with water treatment, the plant height, stem width, root length, fresh weight of above-ground, fresh weight of root, chlorophyll a, chlorophyll b, total chlorophyll, root activity, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of rice seedlings increased by 37.49%, 6.25%, 56.76%, 67.87%, 55.25%, 149.60%, 31.09%, 109.04%, 53.66%, 353.17%, 284.30% and 104.86%, respectively. Moreover, strain JN-369 also has good biocontrol effect on rice blast. The biocontrol effect of the protective test and the therapeutic test reached up to 74.08% and 62.96% on detached rice leaves, respectively. JN-369-treated rice plants showed significantly decrease in disease index in greenhouse experiment. And significantly reduced rice leaf blast and panicle blast severity and increased its yield under field conditions. In summary, B. tequilensis strain JN-369 may be developed as a potential biocontrol agent against rice blast as well as a biofertilizer for rice cultivation.

INCREASING YIELD OF SUSCEPTIBLE AND RESISTANT RICE BLAST CULTIVARS USING SILICON FERTILIZATION

&lt;p&gt;Rice blast is one of the most critical limiting factors for rice plant growth performance. Silicon has been shown to have positive effects in controlling several plant diseases. The study aimed to investigate the impact of silicon levels on rice yield, silicon content, and panicle blast in rice plants. The study was set up as a 2 x 5 factorial experiment with three replications and arranged in a randomized complete block design. The first factors were two rice cultivars, MARDI Siraj 297 (resistant) and MR 263 (susceptible). The second factors were five levels of calcium silicate (0 g, 4 g, 8 g, 12 g, and 16 g) applied to 40 kg soil per pot. The standard fertilizers, i.e., N, P2 O5, and K2 O, were applied four times at the recommended dosage. High virulent of Pyricularia oryzae conidia (4 x 104 conidia ml-1) was sprayed using a hand sprayer (30 ml pot-1) at the time of fully completed panicle development (65 days after planting). Observed parameters were plant growth (height and culm length), yields (spikelets per panicle, grain filling percentage, and harvest index), panicle blast severity, and silica content in leaf, stem, and panicle. The results showed that silicon application reduced panicle blast severity, leading to higher yield per plant. The increase of the rice yield was a result of a significant increae in panicle per m2 , spikelet per m2 , and percentage of filled grain. Panicle blast greatly affected the performance of spikelet number per m2 , percentage of filled grain, grain weight, and yield per plant for the susceptible cultivar. Application of calcium silicate 10 g 40 kg-1 soil per pot at panicle initiation is recommended to reduce panicle blast severity hereby improve grain yield.&lt;/p&gt;

Efficacy of Cladosporium cladosporioides C24G as a Multifunctional Agent in Upland Rice in Agroecological Systems

The occurrence of diseases in rice, mainly rice blast (Magnaporthe oryzae), is the main cause of yield reduction, and it has been controlled with the abusive use of fungicides in the conventional production system. To produce rice in an agroecological system, some measures, such as biological control, facilitates the transition from one system to another. The biological agent C24G classified as Cladosporium cladosporioides has been isolated from the phylloplane of rice plants and is a potential antagonist to rice pathogens. The aim of this study was to verify the efficiency of C. cladosporioides C24G under field conditions, in an agroecological system. During two growing seasons, C. cladosporioides was tested in a randomized block design in 4 replicates. The treatments consisted of: microbiolized rice seeds with C. cladosporioides, plant sprayed (2 applications), microbiolized rice seeds with C. cladosporioides + plant sprayed (2 ap.), plant sprayed (8 ap.) and microbiolized rice seeds with C. cladosporioides + plant sprayed (8 ap.) and control (no microbiolization and no spray). We evaluated leaf and panicle blast severity, physiological parameters associated with gas exchange, and grain yield. Leaf and panicle blast suppression was up to 85.58% and 79.63% in growing season 2016/2017, respectively, and 83.06% and 74.98% in growing season 2017/2018. At growing season 2016/2017, we observed an increase of the following parameters: photosynthetic rate (A) of 70.99% and 53.52% and transpiration (E) of 22.98% and 59.73% at vegetative and reproductive stage respectively, stomatal conductance (gs) of 126.66% at reproductive stage, water use efficiency (WUE) was up to 55.29% at vegetative stage, biomass 34.56% and yield 51.30%. At the growing season 2017/2018, we observed an increase at the photosynthetic rate (A) of 29.71%, at reproductive stage, biomass, 89.40%, and yield, 34.19%. We conclude that the treatments, microbiolized rice seeds or plant sprayed, allows the insertion of C. cladosporioides into the agroecological system, facilitating the agroecological transition with considerable grain yield, and leading to a final product without residues.

LOW AVAILABILITY OF EFFICIENT FUNGICIDES FOR RICE BLAST CONTROL IN LOWLAND RICE CULTIVATION IN BRAZIL

&lt;p&gt;Rice cultivation is fundamental to Brazil's economy, which is the largest grain-producing country outside the Asian continent. However, several factors harm sustainable rice production, including diseases incidence. The blast is the major rice disease, and annually, losses caused by this disease would be sufficient to feed millions of people. Due to the complexity in rice blast management, fungicide application has been most used by rice growers, however, despite the high number of registered fungicides, is questioned the real efficiency in field conditions. This work aimed to analyze the effectiveness of fungicides in rice blast control and grain yield maintenance in irrigated rice. Experiments were carried out in a randomized block design, with four replications, in 2015/2016 and 2016/2017 crop seasons, at the Rio Grande do Sul Rice Experiment Station located in Cachoeirinha city, RS, Brazil. We tested the efficiency of nine fungicides registered in Brazil with different target sites for rice blast control. The analyzed variables were the Area Under the Disease Progress Curve (AUDPC) in leaves; neck blast incidence; panicle blast severity and grains yield. In general, only the tricyclazole and trifloxystrobin + tebuconazole fungicides were efficient in rice blast control with direct reflection on grain yield. &lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;

Conservation agriculture cropping systems reduce blast disease in upland rice by affecting plant nitrogen nutrition

In the central highlands of Madagascar, blast, a serious fungal disease of rice caused by Magnaporthe oryzae, was shown to be less severe in conservation agriculture (CA) than in conventional tillage (CT) cropping systems. To assess the effects of CA cropping systems on rice susceptibility to blast and to understand the mechanisms involved, an experiment was conducted over three growing seasons in two sites (at high and mid-altitude). Two fertilization treatments, one with mineral nitrogen (N) fertilizer, and one without, were studied in interaction with two different cropping systems (CA/CT) and two rice varieties that differ in their susceptibility to blast. The performances of the two cropping systems were assessed, and results showed that yields were no higher in the CA or were lower than in CT cropping systems. The effects of the treatments on upland rice crop growth were measured by leaf N content as an indicator of N crop status, and leaf area index (LAI) as an indicator of canopy density. In all years at both sites, leaf N content during early growth stages was higher in the CT than in the CA cropping system. The LAI was lower in the CA than in the CT cropping system at the high altitude site in all three years, and in two out of three seasons at the middle altitude site. Overall, when the level of blast was high, blast was less severe in the CA cropping system and with no N fertilizer. Leaf N content and LAI were used as intermediate explanatory variables in the statistical analyses, and one or the other or both always masked the effect of the cropping system or of N fertilization. Our results show that leaf N content during early growth stages masks the effect of the cropping system on leaf blast severity. When the LAI is strongly affected by the cropping system, it also masks the effect of the cropping system on the severity of leaf and panicle blast. Very often both variables masked the effects of the cropping system and of N fertilization. These findings should help improve disease management by modifying fertilization practices and crop nutrition in conservation agriculture cropping systems.

Assessment of Rice Panicle Blast Disease Using Airborne Hyperspectral Imagery

Rice blast disease occurs in rice production areas all over the world and is the most important disease in Japan. Remote sensing techniques may provide a mean for detecting disease intensity for large area without being subjected to raters. This study evaluated the use of airborne hyperspectral imagery to measure the severity of panicle blast in field crops. Hyperspectral remote sensing imagery was acquired at the dough stage of rice grain development in northern Japan. The most consistent relationship, with high R2 and low P, was the simple band ratio R498 to 515/R700 to 717 (i.e., the reflectance at 498 to 515-nm divided by the reflectance at 700- to 717-nm). The band ratio of R498 to 515/R700 to 717 increased significantly (P &lt; 0.001) with increasing visual estimates of disease incidence, defined as the percentage of diseased spikelets (R2 = 0.83). Assessment of disease distribution and severity could provide useful information for making decisions regarding the necessity of fungicide application and estimate potential yield loss due to the disease.

Hyperspectral image analysis based on BoSW model for rice panicle blast grading

Rice panicle blast grading is very important in gauging cultivar resistance and in the precise control of a blast epidemic. However, the development of an automated, rapid, and accurate panicle blast grading system is a challenging task. This is mainly because of the complexity of the pathology, appearance, and definition of the blast disease level. In this study, a new method for grading panicle blast based on hyperspectral imaging technology is proposed. The method is based on the concept of the “bag of textons,” which is widely used in the document analysis field and which defines a “bag of spectra words” (BoSW) model for hyperspectral image data representation. Hyperspectral image data representation based on the BoSW model is used as the input to a chi-square kernel support vector machine (chi-SVM) classifier for predicting the rice panicle blast level. Specifically, the BoSW model jointly considers the image-spectrum information to attain improved classification accuracy. It reduces a high-dimension hyperspectral image into a compact, low-dimension representation. It also highlights the histogram statistics of a typical spectrum prototype to reflect the panicle blast severity level. In this way, it avoids the fine segmentation and morphological analysis of blast lesions. Experiments were conducted on a total of 312 fresh rice panicles covering more than 50 cultivars, which were collected from an experimental field under natural conditions. The results showed that the proposed method could effectively grade panicle blast with classification accuracies of up to 81.41% for six-class grading and 96.40% for two-class grading in the validation datasets. Comparison experiments were conducted on different data batches or combinations thereof. The results showed that the technique is viable for different types of rice cultivar and planting seasons, pointing to its widespread practical applicability.

Two‐component cultivar mixtures reduce rice blast epidemics in an upland agrosystem

The effect of two‐component rice cultivar mixtures on the control of rice blast disease was studied in three different experiments under rainfed upland conditions in the Madagascar Highlands. The mixtures involved a susceptible cultivar (either susceptible or very susceptible) and a resistant cultivar in different mixture arrangements (random or row mixtures) and with different proportions of the susceptible cultivar (50, 20 and 16·7%), which were compared to the susceptible cultivar grown in a pure stand. The effect of these mixtures on the incidence and severity of leaf and panicle blast was measured weekly, and on yield and yield components at harvest time. The mixture effect was more efficient in reducing disease with a proportion of 16·7% susceptible component than with a proportion of 50%. Blast epidemic was significantly reduced in all three experiments. However, under high blast pressure, there was no reduction in the disease by the end of the epidemic and yields of the susceptible cultivar were almost zero whatever the mixture. In two other experiments performed under lower blast pressure, disease incidence and severity were significantly lower in mixtures, and yields of the susceptible cultivars grown in mixtures were higher than those of their respective pure stands. Cultivar mixtures are a promising strategy that could contribute to a more sustainable cultivation of rice under upland conditions in the context of subsistence agriculture in Madagascar, where all cropping operations are manual.

Controle químico da brusone em arroz de terras altas: efeitos nos fungos não alvos do filoplano

A brusone em arroz de terras altas causa danos significa-tivos, necessitando de uma a duas aplicações de fungicidas, para o controle da doença. No entanto, o efeito de fungicidas sobre fungos não alvos do filoplano do arroz e benéficos são desconhecidos. Este trabalho objetivou avaliar o efeito de fungicidas no controle da brusone nas panículas, sobre fungos não alvos do filoplano de arroz, e estudar a antibiose de fungos não alvos para M. oryzae. Foi realizado um experimento em campo, utilizando-se duas cultivares (Primavera e Bonança), quatro fungicidas (trifloxistrobina + propiconazol, azoxistrobina, tebuconazol e triciclazol) e testemunha, com delineamento experimental em blocos ao acaso, em esquema de parcelas subdivididas, e quatro repetições. Foram avaliados a severidade da brusone nas panículas, o teor de clorofila nas folhas, o número de unidades formadoras de colônia cm-² de folha e a antibiose. A cultivar Primavera apresentou maior severidade de brusone nas panículas do que a Bonança. Os fungicidas azoxistrobina e trifloxistrobina + propiconazol diferiram significativamente da testemunha, com menores severidades de brusone nas panículas. O teor de clorofila não foi influenciado pelo tratamento com fungicida, mas houve diferença entre as cultivares. Os fungicidas tebuconazol, trifloxistrobina + propiconazol e azoxistrobina reduziram significativamente os fungos do filoplano, em relação à testemunha. O triciclazol proporcionou maior número de unidades formadoras de colônia cm-² de folha, não diferindo da testemunha. Dos quatro fungos testados, apenas Epicoccum sp. apresentou antagonismo para M. oryzae.

Relação entre o teor de clorofila nas folhas e a severidade de brusone nas panículas em arroz de terras altas

Relationship between chlorophyll content in leaves and panicle blast in upland rice Rice blast (Magnaporthe oryzae) is the most important yield limiting factor of upland rice in Brazil. The nitrogen application rate and planting date determine the level of panicle blast severity. A field experiment was conducted with the cultivar BRS Bonanca to establish the relationship between chlorophyll content in leaves and panicle blast severity. The layout was a randomized split plot design with three replications. The treatments included 12 planting dates at weekly intervals and five rates of nitrogen (0, 30, 60, 120 and 240 kg ha-1 of N). The chlorophyll content was measured on flag leaf with a chlorophyll meter. Panicle blast severity increased significantly with the increase in nitrogen fertilization. The correlation between nitrogen rate and chlorophyll content in flag leaf was positive and significant (r=0.98; p ≤ 0.01). The relationship between panicle blast severity and chlorophyll content was linear and positive (r= 0.99; p ≤ 0.01). The chlorophyll content in the flag leaf can be included as independent variable in the development of a mathematical model for panicle blast forecasting.

Danos causados por doenças fúngicas no arroz cultivado em várzeas no Sul do Estado do Tocantins

Neste estudo, foram avaliados os danos causados por doenças fúngicas no arroz cultivado sob condição de várzea no Estado do Tocantins. O delineamento experimental foi o de blocos casualizados com quatro repetições em esquema fatorial 26 (genótipos de arroz irrigado) × 2 (aplicação ou não de fungicidas). As aplicações de fungicidas foram realizadas aos 35 dias após a semeadura (tiofanato metílico; 0,5 L ha-1) nos estádios de emborrachamento (trifloxistrobina + propiconazole; 0,6 L ha-1) e com 5% das panículas emitidas (trifloxistrobina + propiconazole; 0,6 L ha-1 + tebuconazole; 0,75 L ha-1). As variáveis avaliadas foram: severidades da brusone nas folhas e nas panículas, mancha-parda nas folhas, mancha dos grãos, massa de cem sementes e produtividade. O tratamento com fungicida reduziu, em média, a severidade da brusone nas folhas em 69% e em 54% a brusone nas panículas. Não houve diferença estatística entre os tratamentos com e sem fungicida na severidade da mancha parda; porém alguns genótipos diferiram estatisticamente entre eles. Nas plantas tratadas com fungicidas, houve um acréscimo médio de 0,52 g (17,6%) na massa de cem sementes e de 1000 kg ha-1 na produtividade (12,6%). Os valores máximos obtidos na massa de cem sementes e na produtividade foram, respectivamente, de 3,2 g e 9270 kg ha-1.

Correlation between Severity of Panicle Blast and the Seedling Box Treatment in Paddy Field

Correlation between Severity of Panicle Blast and the Seedling Box Treatment in Paddy Field

Evolución el añublo del arroz en dos condiciones de fertilidad nitrogenada

Con el objetivo de evaluar la evolución de la infección producida por Pyricularia oryzae (cooke) Sacc, en la hoja y en la panícula, fueron seleccionados tres genotipos de arroz (Oryza sativa). Los genotipos: El Paso 144 (EP), Don Ignacio (DI) y H 316-1-2-1-1 (H 316) fueron sembrados en condiciones de campo, en la Estación Experimental La Plata, y en dos condiciones de disponibilidad de nitrógeno (testigo o sin nitrógeno y 150 kg N ha-1 en forma de urea). El hongo fue inoculado en la tercera hoja, con una mezcla de razas, a una concentración de 1,2 x 10(5) fragmentos de hifa/ml, incubándose durante 48 horas en cámara húmeda. Fueron evaluados la severidad y tipo de mancha en la hoja y la severidad e incidencia en la panícula. Se realizó el ANOVA, y las diferencias estadísticas fueron analizadas a través del test Tukey (p&lt;0,05). Fueron aplicados modelos Log-lineares para datos no paramétricos. No se observó interacción entre genotipo y fertilización, en las hojas, en los estadios de primer perfilo (M) y diferenciación (D). La fertilización aumentó la severidad en las hojas. El coeficiente de correlación entre el tipo de mancha y el porcentaje de severidad en la hoja fue elevado. Fue observada interacción entre genotipo y fertilización en los valores de severidad en la panícula, los mismos que disminuyeron con la fertilización en los genotipos EP y DI, pero no presentaron diferencias en H 316.

Effects of Elevated Atmospheric CO2 Concentration on the Infection of Rice Blast and Sheath Blight

ABSTRACT The effect of elevated atmospheric CO(2) concentration on rice blast and sheath blight disease severity was studied in the field in northern Japan for 3 years. With free-air CO(2) enrichment (FACE), rice plants were grown in ambient and elevated ( approximately 200 to 280 mumol mol(-1) above ambient) CO(2) concentrations, and were artificially inoculated with consist of Magnaporthe oryzae. Rice plants grown in an elevated CO(2) concentration were more susceptible to leaf blast than those in ambient CO(2) as indicated by the increased number of leaf blast lesions. Plants grown under elevated CO(2) concentration had lower leaf silicon content, which may have contributed to the increased susceptibility to leaf blast under elevated CO(2) concentrations. In contrast to leaf blast, panicle blast severity was unchanged by the CO(2) enrichment under artificial inoculation, whereas it was slightly but significantly higher under elevated CO(2) concentrations in a spontaneous rice blast epidemic. For naturally occurring epidemics of the sheath blight development in rice plants, the percentage of diseased plants was higher under elevated as opposed to ambient CO(2) concentrations. However, the average height of lesions above the soil surface was similar between the treatments. One hypothesis is that the higher number of tillers observed under elevated CO(2) concentrations may have increased the chance for fungal sclerotia to adhere to the leaf sheath at the water surface. Consequently, the potential risks for infection of leaf blast and epidemics of sheath blight would increase in rice grown under elevated CO(2) concentration.