Rice Brown Spot Research Articles

Effect of Zinc on the Development of Brown Spot in Rice

AbstractBrown spot, caused by the fungus Bipolaris oryzae, is one of the most destructive diseases of rice. This study investigated the effect of zinc rates on the development of brown spot in rice. Rice plants (cv. ‘Metica‐1′) were grown in hydroponic culture amended with Zn rates (applied as ZnSO4.7H2O) of 0, 0.5, 1, 2 and 4 μm and inoculated with B. oryzae. The foliar concentration of Zn was determined. Leaf samples were assessed for disease severity, and then, area under brown spot progress curve (AUBSPC) was calculated. The relationship between Zn concentrations on leaf tissues and the rates of this micronutrient was best described by a positive linear regression model, while the relationship between the Zn rates and the AUBSPC was best described with a positive quadratic regression model. The correlation between Zn concentrations on leaf tissues and AUBSPC was positive and significant (r = 0.68, P < 0.05). The results from this study showed that high foliar concentration of Zn was associated with increasing rice susceptibility to brown spot.

A review on crop losses, epidemiology and disease management of rice brown spot to identify research priorities and knowledge gaps

Rice brown spot (BS) is a chronic disease that affects millions of hectares of rice every growing season, grown by some of the most resource-poor farmers. Despite its widespread occurrence and impact, much still needs to be understood about BS. Reported yield losses in relative terms vary widely from 4 to 52 %. However, accurate, systematic estimates are lacking. BS is conventionally perceived as a secondary problem that reflects rice crops that experience physiological stresses, e.g. drought and poor soil fertility, rather than a true infectious disease. Much remains to be understood about the mechanisms leading to epidemics and crop losses. Quantitative and qualitative knowledge gaps exist in our understanding of the epidemiological processes, sources of resistance and biocontrol methods. In this review we identify several of these gaps, which if filled, could lead to a strong impact on the management of brown spot. We also use the architecture of a simulation model to position and prioritize these knowledge gaps, assess the epidemiological consequences of disease management options on BS monocyclic processes and explore the impact changing production situations on this important disease.

Quantification of rice brown leaf spot through Taqman real-time PCR specific to the unigene encoding Cochliobolus miyabeanus SCYTALONE DEHYDRATASE1 involved in fungal melanin biosynthesis

Rice brown leaf spot is a major disease in the rice paddy field. The causal agent Cochliobolus miyabeanus is an ascomycete fungus and a representative necrotrophic pathogen in the investigation of rice-microbe interactions. The aims of this research were to identify a quantitative evaluation method to determine the amount of C. miyabeanus proliferation in planta and determine the method's sensitivity. Real-time polymerase chain reaction (PCR) was employed in combination with the primer pair and Taqman probe specific to CmSCD1, a C. miyabeanus unigene encoding SCYTALONE DEHYDRATASE, which is involved in fungal melanin biosynthesis. Comparative analysis of the nucleotide sequences of CmSCD1 from Korean strains with those from the Japanese and Taiwanese strains revealed some sequence differences. Based on the crossing point (CP) values from Taqman real-time PCR containing a series of increasing concentrations of cloned amplicon or fungal genomic DNA, linear regressions with a high level of reliability (R(2)>0.997) were constructed. This system was able to estimate fungal genomic DNA at the picogram level. The reliability of this equation was further confirmed using DNA samples from both resistant and susceptible cultivars infected with C. miyabeanus. In summary, our quantitative system is a powerful alternative in brown leaf spot forecasting and in the consistent evaluation of disease progression.

Image Reduction Method for Rice Leaf Disease Based on Visual Attention Model

Analyzing the crop growth status through leaf disease image is one of the hottest issues in agriculture and forestry fields currently. But the size of image gathered by digital camera is too large, the focus of this research is to zooming-out image at the condition of ensuring the main information which carried by the image to distort lower. Based on the further study of visual attention model proposed by Itti and Ma YF. This paper establishes visual attention and visual saliency map of rice blast and brown spot disease image, whose size is 4272*2878 pixels. Finally, determines the reduction scale of the corresponding effective target collection and provide a new way to reduce the plant leaf images.

Biological control of rice brown spot with native isolates of three Trichoderma species

Biological control of rice brown spot with native isolates of three Trichoderma species

Biological control of rice brown spot with native isolates of three Trichoderma species.

Brown spot caused by Bipolaris oryzae is an important rice disease in Southern coast of Caspian Sea, the major rice growing region in Iran. A total of 45 Trichoderma isolates were obtained from rice paddy fields in Golestan and Mazandaran provinces which belonged to Trichoderma harzianum, T. virens and T. atroviride species. Initially, they were screened against B. oryzae by antagonism tests including dual culture, volatile and nonvolatile metabolites and hyperparasitism. Results showed that Trichoderma isolates can significantly inhibit mycelium growth of pathogen in vitro by producing volatile and nonvolatile metabolites Light microscopic observations showed no evidence of mycoparasitic behaviour of the tested isolates of Trichoderma spp. such as coiling around the B. oryzae. According to in vitro experiments, Trichoderma isolates were selected in order to evaluate their efficacy in controlling brown spot in glasshouse using seed treatment and foliar spray methods. Concerning the glasshouse tests, two strains of T. harzianum significantly controlled the disease and one strain of T. atroviride increased the seedling growth. It is the first time that the biological control of rice brown spot and increase of seedling growth with Trichoderma species have been studied in Iran.

FUNGITOXIC SPECTRUM OF AMALAB-A AGAINST FUNGAL PATHOGENS IN RICE UNDER IN-VITRO

ABSTRACT Through the present study a botanically derived product Amalab-a was developed by combining Aegle marmelos leaf extract with a formulating agent (coded A+) and tested against three fungal pathogens of rice viz. Helminthosporium oryzae , Curvularia lunata and Fusarium moniliforme. Product registered complete inhibition of conidial germination at 0.01% in H.oryzae, C. lunata and F.moniliforme and mycelial growth inhibition at 1% in H.oryzae, F.moniliforme and at 0.1% in C. lunata whereas the extract alone could not at the same concentration. The shelf-life test displayed greater fungitoxic effect against all the three tested pathogens and retained its fungitoxicity upto 0.01% concentration till 12 months storage period. This formulated product has therefore improved the efficacy and shelf-life of this botanical product compared to the unformulated botanical extracttested under in-vitro, hence possesses greater potential for its integration against rice brown spot and grain discolouration control strategy but needs to be tested under in-vivo.

Brown Spot of Rice is Affected by Photon Irradiance and Temperature

Brown spot, caused by Bipolaris oryzae, is one of the most destructive diseases in rice. In this study, the effect of photon irradiance and temperature on brown spot development was evaluated. The concentration of total soluble sugars (fructose, glucose and sucrose) in rice leaves was also evaluated. Rice plants of cv. ‘Oochikara’ were inoculated with B. oryzae and kept in a greenhouse [20 ± 2°C (night time) and 35 ± 2°C (day time), ≈ 1000 μmol photons/m2/s] or two different mist chambers (25 or 32 ± 2°C, ≈ 15 μmol photons/m2/s at the top canopy). Plants kept in a mist chamber at 32 ± 2°C, under low photon irradiance, showed reduced incubation period (IP) and increase in the rate of lesion expansion. Brown spot severity in rice leaves was 67.8% at 32 ± 2°C, 27.8% at 25 ± 2°C and 11.4% under greenhouse conditions. The highest brown spot severity was found on plants grown under low photon irradiance, in which soluble sugar concentrations were lowest, suggesting that disease development was boosted under these particular growing conditions. Based on the results of this study, a continuous high temperature and low photon irradiance, in the presence of high relative humidity, and low soluble sugars contribute to an increase in brown spot development.

Escala diagramática para avaliação de severidade de mancha-parda em arroz

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.

Rice Resistance to Brown Spot Mediated by Nitrogen and Potassium

This study was undertaken to investigate the effects of both nitrogen (N) and potassium (K) rates on rice resistance to brown spot, caused by the fungus Bipolaris oryzae. Rice plants (cultivar `Metica 1') were grown in soil corrected with 0, 25, 50, 75 and 100 mg of N/kg (as NH 4 NO 3 ) of soil as well as with 25, 50, 75, 125 and 150 mg of K/kg (as KCl) of soil. Thirty-three-day-old plants were inoculated with a suspension of Bipolaris oryzae conidia and the incubation period (IP), number of lesions (NL) per cm 2 of leaf area and disease severity was evaluated. Disease severity was scored at 24, 48, 72, 96, 120 and 144 h after inoculation and data were used to obtain the area under brown spot progress curve (AUBSPC). Soil plant analysis development (SPAD) index, plant dry weight and concentration of N and K in leaf tissues were also determined for both non-inoculated (NI) and inoculated (IN) plants. Concentration of N in leaf tissue increased as the N rates in the soil increased. Concentration of K in leaf tissue increased sharply as the K rates in the soil increased for both NI and IN plants. Concentration of K in leaf tissue was not affected by N rates. The IP increased as the N rates increased, but was somewhat less impacted by increasing K rates. The NL decreased as the N rates increased. The NL dramatically declined at the highest K rates. The AUBSPC dramatically declined as the N and K rates in the soil increased. SPAD index values increased as the N and K rates in the soil increased for both NI and IN plants. Plant dry weight increased as the N and K rates in the soil increased for both NI and IN plants. Results from this study suggest that combining high N and K rates may contribute to reducing the intensity of brown spot in rice while improving plant development.

Effect of root and foliar applications of silicon on brown spot development in rice

Silicon (Si) application is a strategy to manage rice brown spot, but no studies have been conducted on Si as a foliar spray for control of this disease. The purpose of this study was to compare root and foliar Si applications on rice brown spot development, and to determine if there is a biochemical defence response. Rice plants (cv. Metica-1) were grown in a Si-deficient soil that received the following treatments: root application of calcium silicate (CS) (1.25 g/kg of soil), foliar application of potassium silicate (PS) (40 g/L), and control (leaves sprayed with distilled water). Thirty-day-old plants were inoculated with a conidial suspension of Bipolaris oryzae. Si concentration in rice tissue was markedly higher for CS compared with the other treatments. The intensity of Si deposition, as determined by X-ray microanalysis, between the adaxial and abaxial leaf blades of rice plants in the control treatment was similar. Si deposition occurred in both the adaxial and abaxial leaf blades of rice plants that received CS while this Si deposition only occurred on the adaxial leaf blades of plants that received PS. The area under brown spot progress curve (AUBSPC) was not significantly different between the PS and control treatments, but was significantly lower in plants grown in soil amended with CS. The values for the AUBSPC and the number of lesions (NL) per cm2 of leaf area decreased by 37 and 47%, respectively, with CS compared with the control. Conidial germination was not inhibited by PS. The concentration of total soluble phenolics and lignin-thioglycolic acid derivatives was not linked with the reduction observed in the AUBSPC and the NL. Although the concentration of these two biochemical variables seemed to be slightly higher in plants from the control treatment, likely due to the greater disease severity and the NL, rice tissue was not efficiently protected against colonisation by B. oryzae. The results of this study suggest that foliar-applied Si can decrease the intensity of brown spot; however, the level of control achieved was not as great as that obtained when Si was supplied to the roots.

Study of genetic variation in population of Bipolaris victoriae , the causal agent of rice brown spot disease, in Guilan Province of Iran

Isolates of Bipolaris victoriae were analysed by random amplified polymorphic DNA (RAPD) techniques to determine the amount of intraspecific genetic variability. Seven primers were applied and DNA bands of 200-5000 bp were produced. Cluster analysis using UPGMA method gave five groups. Levels of polymorphism were observed between DNA of different isolates. The pattern of RAPD bands did not show any correlation between polymorphism and climates or geographical areas.

Characterizing and Estimating Fungal Disease Severity of Rice Brown Spot with Hyperspectral Reflectance Data

Large-scale farming of agriculture crops requires real-time detection of disease for field pest management. Hyperspectral remote sensing data generally have high spectral resolution, which could be very useful for detecting disease stress in green vegetation at the leaf and canopy levels. In this study, hyperspectral reflectances of rice in the laboratory and field were measured to characterize the spectral regions and wavebands, which were the most sensitive to rice brown spot infected by Bipolaris oryzae ( Helminthosporium oryzae Breda. de Hann). Leaf reflectance increased at the ranges of 450 to 500 nm and 630 to 680 nm with the increasing percentage of infected leaf surface, and decreased at the ranges of 520 to 580 nm, 760 to 790 nm, 1550 to 1750 nm, and 2080 to 2350 nm with the increasing percentage of infected leaf surface respectively. The sensitivity analysis and derivative technique were used to select the sensitive wavebands for the detection of rice brown spot infected by B. oryzae. Ratios of rice leaf reflectance were evaluated as indicators of brown spot. R669/R746 (the reflectance at 669 nm divided by the reflectance at 746 nm, the following ratios may be deduced by analogy), R702/R718, R692/R530, R692/R732, R535/R746, R521/R718, and R569/R718 increased significantly as the incidence of rice brown spot increased regardless of whether it's at the leaf or canopy level. R702/R718, R692/R530, R692/R732 were the best three ratios for estimating the disease severity of rice brown spot at the leaf and canopy levels. This result not only confirms the capability of hyperspectral remote sensing data in characterizing crop disease for precision pest management in the real world, but also testifies that the ratios of crop reflectance is a useful method to estimate crop disease severity.

Control of brown spot pathogen of rice (Bipolaris oryzae) using some phenolic antioxidants

Bipolaris oryzae is the causal agent of rice brown spot disease and is responsible for significant economic losses. In order to control this disease, three phenolic antioxidants were tested (salicylic acid, benzoic acid and hydroquinone). The antifungal activity of the tested substances were investigated against B. oryzae at different concentrations in vitro, as well as the efficacy of their exogenous application in controlling rice brown spot disease under field conditions. In vitro, benzoic acid or salicylic acid at 9 mM completely inhibited the growth of B. oryzae. Under field conditions, spraying of benzoic acid at 20 mM led to a significant reduction in disease severity (DS) and disease incidence (DI) on the plant leaves, in addition to a significant increase in the grain yield and its components. Some biochemical responses were also detected, where the application of the previous treatment led to a significant increase in the total photosynthetic pigments (chlorophyll a and b and carotenoids) in rice leaves and in the total carbohydrate and protein contents of the yielded grains.

Glufosinate ammonium-induced pathogen inhibition and defense responses culminate in disease protection in bar-transgenic rice.

Glufosinate ammonium diminished developments of rice (Oryza sativa) blast and brown leaf spot in 35S:bar-transgenic rice. Pre- and postinoculation treatments of this herbicide reduced disease development. Glufosinate ammonium specifically impeded appressorium formation of the pathogens Magnaporthe grisea and Cochliobolus miyabeanus on hydrophobic surface and on transgenic rice. In contrast, conidial germination remained unaffected. Glufosinate ammonium diminished mycelial growth of two pathogens; however, this inhibitory effect was attenuated in malnutrition conditions. Glufosinate ammonium caused slight chlorosis and diminished chlorophyll content; however, these alterations were almost completely restored in transgenic rice within 7 d. Glufosinate ammonium triggered transcriptions of PATHOGENESIS-RELATED (PR) genes and hydrogen peroxide accumulation in transgenic rice and PR1 transcription in Arabidopsis (Arabidopsis thaliana) wild-type ecotype Columbia harboring 35S:bar construct. All transgenic Arabidopsis showed robust hydrogen peroxide accumulation by glufosinate ammonium. This herbicide also induced PR1 transcription in etr1 and jar1 expressing bar; however, no expression was observed in NahG and npr1. Fungal infection did not alter transcriptions of PR genes and hydrogen peroxide accumulation induced by glufosinate ammonium. Infiltration of glufosinate ammonium did not affect appressorium formation of M. grisea in vivo but inhibited blast disease development. Hydrogen peroxide scavengers nullified blast protection and transcriptions of PR genes by glufosinate ammonium; however, they did not affect brown leaf spot progression. In sum, both direct inhibition of pathogen infection and activation of defense systems were responsible for disease protection in bar-transgenic rice.

Characterizing and estimating rice brown spot disease severity using stepwise regression, principal component regression and partial least-square regression

Detecting plant health conditions plays a key role in farm pest management and crop protection. In this study, measurement of hyperspectral leaf reflectance in rice crop (Oryzasativa L.) was conducted on groups of healthy and infected leaves by the fungus Bipolaris oryzae (Helminthosporium oryzae Breda. de Hann) through the wavelength range from 350 to 2,500 nm. The percentage of leaf surface lesions was estimated and defined as the disease severity. Statistical methods like multiple stepwise regression, principal component analysis and partial least-square regression were utilized to calculate and estimate the disease severity of rice brown spot at the leaf level. Our results revealed that multiple stepwise linear regressions could efficiently estimate disease severity with three wavebands in seven steps. The root mean square errors (RMSEs) for training (n=210) and testing (n=53) dataset were 6.5% and 5.8%, respectively. Principal component analysis showed that the first principal component could explain approximately 80% of the variance of the original hyperspectral reflectance. The regression model with the first two principal components predicted a disease severity with RMSEs of 16.3% and 13.9% for the training and testing dataset, respectively. Partial least-square regression with seven extracted factors could most effectively predict disease severity compared with other statistical methods with RMSEs of 4.1% and 2.0% for the training and testing dataset, respectively. Our research demonstrates that it is feasible to estimate the disease severity of rice brown spot using hyperspectral reflectance data at the leaf level.

Trichoderma harzianum: a biocontrol agent against Bipolaris oryzae

Rice brown spot, caused by Bipolaris oryzae, can be a serious disease causing a considerable yield loss. Trichoderma harzianum is an effective biocontrol agent for a number of plant fungal diseases. Thus, this research was carried out to investigate the mechanisms of action by which T. harzianum antagonizes Bipolaris oryzae in vitro, and the efficacy of spray application of a spore suspension of T. harzianum for control of rice brown spot disease under field conditions. In vitro, the antagonistic behavior of T. harzianum resulted in the overgrowth of B. oryzae by T. harzianum, while the antifungal metabolites of T. harzianum completely prevented the linear growth of B. oryzae. Light and scanning electron microscope (SEM) observations showed no evidence that mycoparasitism contributed to the aggressive nature of the tested isolate of T. harzianum against B. oryzae. Under field conditions, spraying of a spore suspension of T. harzianum at 10(8)spore ml(-1) significantly reduced the disease severity (DS) and disease incidence (DI) on the plant leaves, and also significantly increased the grain yield, total grain carbohydrate, and protein, and led to a significant increase in the total photosynthetic pigments (chlorophyll a and b and carotenoids) in rice leaves.

Field efficacy of fungal and bacterial antagonists against brown spot of rice.

Efficacy of two antagonists, namely, Trichoderma harzianum and Pseudomonas fluorescens was evaluated against brown spot of rice under field conditions. Three sprays of P. fluorescens (Talc based) at weekly interval @10g per litre, proved effective in reducing the disease severity and increasing the yield. It reduced the severity from 35.8 percent to 24.5 percent in case of rice variety PR116 and from 20.1 percent to 8.5 percent in case of Basmati rice 386.

Phylloplane microorganisms as a potential biocontrol agent against Helminthosporium oryzae Breda de Hann, the incitant of rice brown spot

Fifteen pathogenic isolates of Helminthosporium oryzae were established from 15 different rice growing areas representing nine districts: Madurai, Theni, Thanjavur, Thiruvarur, Nagapatinum, Tirunelveli, Trichy, Ariyalur and Cuddalore district of Tamil Nadu. The symptoms initially appeared on the leaves as small, oval, dark brown to black spots. Under favourable conditions, the fungus attacks grain and caused grain discoloration. The isolate, collected from Ammapettai of Thanjavur district was the most virulent (Grade 7.47, PDI 82.96) on rice plants followed by Trichy isolate I2 (Grade 7.26; PDI 80.74) while I15 (Cumbum) was the least virulent (Grade 1.8, PDI 20.00). The isolates of H. oryzae varied in size (length and width) of the conidia, colour and the number of cells per conidium. The maximum (39.1 μm) length of the conidium was observed in I10 followed by I11 (37.3 μm). The maximum (17.1 μm) conidial width was observed in I8. The colour of the conidium varied from light brown (isolates I3, I6 and I14) to brown, while there was no appreciable difference in the conidial shape. The number of cells varied from 2 – 4 among the isolates. Six phylloplane microorganisms were tested against the virulent isolate of H. oryzae. Among them, Cladasporium spp was very effective in inhibiting the mycelial growth and spore germination of H. oryzae followed by Penicillum spp and Aspergillus flavus while Bacillus subtilis was least effective in inhibiting the mycelial growth and spore germination of H. oryzae.

Calcium Restores Prepenetration Morphogenesis Abolished by Methylglyoxal-Bis-Guanyl Hydrazone inCochliobolus miyabeanusInfecting Rice

ABSTRACT Cochliobolus miyabeanus forms a specialized infection structure, an appressorium, to infect its host rice plants. Curtailment of prepenetration development by spermidine and spermine was more evident in appressorium development and germination remained unaffected, whereas putrescine and methylglyoxal-bis-guanyl hydrazone (MGBG) impaired both morphogenetic events. Exogenous calcium nullified the inhibitory effect of MGBG on the prepenetration development in vitro and in vivo and the disease progression. High levels of polyamines were detected in freshly collected conidia, but the amounts were reduced during germination and appressorium formation. MGBG fortified the decrease of polyamines within conidia under development and calcium amendment did not affect the reduction. Hard-surface contact augmented messenger RNA synthesis of calmodulin gene (CmCaM) and protein kinase C (PKC) activity in germinating or appressorium-forming conidia. Calcium restored transcription of CmCaM and upregulation of PKC activity suppressed by MGBG. Taken together, fine-tuning of intracellular polyamine transition is indispensable for the conidial germination and appressorium formation in C. miyabeanus. Biochemical and molecular analyses revealed that the MGBG-acting site or sites are upstream of Ca(2+)-dependent signaling pathways regulating prepenetration morphogenesis of C. miyabeanus causing rice brown leaf spot.