Assessment of fungicide-based control of sheath blight using mobile spraying equipment

BackgroundRice sheath blight (ShB) disease, caused by the pathogenic fungus Rhizoctonia solani, causes significant yield losses globally. US weedy rice populations, which are de-domesticated forms of indica and aus cultivated rice, appear to be more resistant to ShB than local japonica cultivated rice. We mapped quantitative trait loci (QTL) associated with ShB resistance using two F8 recombinant inbred line populations generated from crosses of an indica crop variety, Dee-Geo-Woo-Gen (DGWG), with individuals representing the two major US weed biotypes, straw hull (SH) and black hull awned (BHA).ResultsWe identified nine ShB resistance QTL across both mapping populations. Five were attributable to alleles that affect plant height (PH) and heading date (HD), two growth traits that are known to be highly correlated with ShB resistance. By utilizing an approach that treated growth traits as covariates in the mapping model, we were able to infer that the remaining four QTL are involved in ShB resistance. Two of these, qShB1–2 and qShB4, are different from previously identified ShB QTL and represent new candidates for further study.ConclusionOur findings suggest that ShB resistance can be improved through favorable plant growth traits and the combined effects of small to moderate-effect resistance QTL. Additionally, we show that including PH and HD as covariates in QTL mapping models is a powerful way to identify new ShB resistance QTL.

Sheath blight caused by fungal pathogen Rhizoctonia solani can cause significant yield loss in rice, especially in warm, high rainfall environments. Integrated pest management (IPM) is the key to sheath blight control. This system utilizes disease resistance, pesticides, cultural practices and biological control to control multiple pests. Silicon fertilization is an additional cultural practice that can reduce sheath blight severity and increase grain yield. Studies were conducted in the greenhouse and field to determine the effect of calcium silicate on sheath blight severity, rice grain yield, and leaf silicon concentration. Results in the greenhouse study showed that sheath blight severity was significantly reduced in the cultivar Cypress when calcium silicate was applied to a Crowley silt loam soil. Disease severity for another cultivar Katy was inconsistent in that disease severity was significantly reduced in 1997, but not in 1995. In the same experiment but using reclaimed marsh soil, sheath blight on Katy was significantly reduced in 1997 but not in 1995. In contrast to Cypress grown in Crowley silt loam soil, disease severity was unaffected by the calcium silicate in the reclaimed marsh soil. In the 1995 field study, silicon fertilization on a Crowley silt loam soil in Vermilion Parish, Louisiana, affected yield, y-leaf Si (most recently matured leaf at panicle initiation growth stage) and mature straw Si. Rice grain yield increased 13 percent from a 3.3 Mg ha-1 application of calcium silicate. A significant reduction in sheath blight severity was detected on three different soil types in Louisiana when amended with calcium silicate. The sheath blight severity decreased linearly with slag amendment. These results show that Si fertilization can reduce fungal disease severity, improve grain yield and increase silicon concentration levels in rice tissues. Cultivars differ in their response to the slag amendment in different soils. Silicon concentration in plant tissues can be used as an indicator of yield potential and disease severity in some rice cultivars.

Labor-saving application of thifluzamide and tricyclazole to seedling trays for integrated control of rice blast and sheath blight

Sheath blight of rice is one of the most damaging diseases of rice worldwide causing serious yield losses. Several fungicide molecules with different mode of actions are available in the market. The present study was undertaken to find the best and most economical combination of fungicides in managing this disease. Hence, an experiment was conducted to evaluate the efficacy and economics of flusilazole 12.5% + carbendazim 25% SC, difenoconazole 11.4% + azoxystrobin 18.2% SC, tebuconazole 18.3% + azoxystrobin 11% SC, tricyclazole 18% + mancozeb 62% WP, zineb 68% + hexaconazole 4% WP, trifloxystrobin 25% + tebuconazole 50% WG, mancozeb 50% + carbendazim 25% WS and epoxiconazole 62.5 g/l + fluxapyroxad 62.5 g/l EC against sheath blight of rice under the field conditions. Results of the present study revealed that, out of the different fungicidal combinations, two foliar sprays of difenoconazole 11.4% + azoxystrobin 18.2% SC @ 1 ml/lit was found to be most economic that provided best incremental net benefit ratio of 6.17:1.00. It was followed by two foliar sprays of epoxiconazole 62.5 g/l + fluxapyroxad 62.5 g/l EC @ 1.5 ml/l, tebuconazole 18.3% w/w + azoxystrobin 11% SC, zineb 68% + hexaconazole 4% WP and trifloxystrobin 25% + tebuconazole 50% WG.

Field efficacy of fungicides for management of sheath blight and narrow brown leaf spot of rice

Unmanned aerial vehicle (UAV) remote sensing is a new alternative to traditional diagnosis and detection of rice diseases by visual symptoms, providing quick, accurate and large coverage disease detection. UAV remote sensing offers an unprecedented spectral, spatial, and temporal resolution that can distinguish diseased plant tissue from healthy tissue based on the characteristics of disease symptoms. Research has been conducted on using RGB sensor, multispectral sensor, and hyperspectral sensor for successful detection and quantification of sheath blight (Rhizoctonia solani), using multispectral sensor to accurately detect narrow brown leaf spot (Cercospora janseana), and using infrared thermal sensor for detecting the occurrence of rice blast (Magnaporthe oryzae). UAV can also be used for aerial application, and UAV spraying has become a new means for control of rice sheath blight and other crop diseases in many countries, especially China and Japan. UAV spraying can operate at low altitudes and various speeds, making it suitable for situations where arial and ground applications are unavailable or infeasible and where precision applications are needed. Along with advances in digitalization and artificial intelligence for precision application across fertilizer, pest and crop management needs, this UAV technology will become a core tool in a farmer’s precision equipment mix in the future.

How benthic diatoms within natural communities respond to eight common herbicides with different modes of action

Rice sheath blight (RSB), caused by the pathogenic fungus Rhizoctonia solani, poses a significant threat to global food security. The defense mechanisms employed by rice against RSB are not well understood. In our study, we analyzed the interactions between rice and R. solani by comparing the phenotypic changes, ROS content, and metabolite variations in both tolerant and susceptible rice varieties during the early stages of fungal infection. Notably, there were distinct phenotypic differences in the response to R. solani between the tolerant cultivar Zhengdao22 (ZD) and the susceptible cultivar Xinzhi No.1 (XZ). We observed that the activities of five defense-related enzymes in both tolerant and susceptible cultivars changed dynamically from 0 to 72 h post-infection with R. solani. In particular, the activities of superoxide dismutase and peroxidase were closely associated with resistance to RSB. Metabolomic analysis revealed 825 differentially accumulated metabolites (DAMs) between the tolerant and susceptible varieties, with 493 DAMs responding to R. solani infection. Among these, lipids and lipid-like molecules, organic oxygen compounds, phenylpropanoids and polyketides, organoheterocyclic compounds, and organic acids and their derivatives were the most significantly enriched. One DAM, P-coumaraldehyde, which responded to R. solani infection, was found to effectively inhibit the growth of R. solani, Magnaporthe grisea, and Ustilaginoidea virens. Additionally, multiple metabolic pathways, including amino acid metabolism, carbohydrate metabolism, metabolism of cofactors and vitamins, and metabolism of terpenoids and polyketides, are likely involved in RSB resistance. Our research provides valuable insights into the molecular mechanisms underlying the interaction between rice and R. solani.

Small UAVs (Unmanned Aerial Vehicles) have high potential to be used to detect and manage the diseases of various crops because they are low cost and user-friendly. Objective of this study is to develop a UAV platform to detect sheath blight in rice in the field. A quadrotor UAV equipped with high-resolution RGB-/multispectral camera was developed and images from these sensors were collected over research plots of different rice varieties with different levels of sheath blight. The ground truth-NDVIs (Normalized Difference Vegetation Indexes) of these rice varieties were also collected. Through comparison and analysis, there appeared to have a good correlation between the ground truth-NDVIs values and the NDVI values extracting from the UAV images. The determination coefficient and Root Mean Square Error (RMSE) are 0.907 and 0.0854, respectively. The results indicate that the multispectral images even provide higher accuracy to differentiate different levels of sheath blight. Therefore, small UAV platform mounted the proper sensors can effective detect the development of sheath blight in rice.

False smut, caused by Ustilaginoidea virens, is an important emerging disease of rice (Oryza sativa L.) in China. Up to now, as most varieties with high yielding and good quality are susceptible or even highly susceptible to false smut in most rice-growing ecological regions, especially in Anhui Province, chemical control with fungicides would be an important measure for the control of this disease. The ergosterol biosynthesis inhibitor (EBI) fungicides, such as prochloraz, difenoconazole, propiconazole and tebuconazole, are extensively used in China for the control of rice diseases, such as rice sheath blight and rice blast. In this study, a total of 102 U. virens isolates (from Anhui Province of China) were tested for their sensitivity to these four EBI fungicides during the stage of mycelial growth. The EC50 ranges of values for prochloraz, difenoconazole, propiconazole and tebuconazole inhibiting mycelial growth of the 102 U. virens isolates were 0.04–0.75, 0.04–1.08, 0.04–0.38 and 0.03–0.57 μg ml−1, with the average EC50 values of 0.32 ± 0.08, 0.45 ± 0.08, 0.19 ± 0.03 and 0.21 ± 0.06 μg ml−1, respectively. These values suggested that the tested U. virens isolates were very sensitive to these four EBI fungicides. Results of field trials showed that two sprays of three of the fungicides exhibited greater control efficacy than a single spray for the control of rice false smut. Two sprays of each was better than a single spray for the control of rice sheath blight. Two sprays of 50% propiconazole EC at 300 g a.i. ha−1 gave the best control of rice false smut at both two sites during the two consecutive years, 2010 and 2011, with the control efficacy ranging from 71.5 to 74.3%. Sensitivity of the field U. virens isolates to EBI fungicides should be monitored. Mixtures, as well as alternation with other fungicides with different modes of action, should be tested.

An effective formulated biopesticide for controlling sheath blight in rice was developed using three microbial antagonists (Bacillus megaterium, Bacillus subtilis and Aspergillus niger) isolated from the rice sheath. The efficiency of spore-based formulations of the above microbial antagonists was investigated and their effectiveness in controlling sheath blight was demonstrated. Application of talc-based formulations of individual antagonists and mixtures of the three antagonists as spray treatments or soil applications were effective in reducing the incidence by up to 45% at 27 days after inoculation of the pathogen of sheath blight and increased rice yield. The use of spores of a fungal antagonist (A. niger), in comparison to commonly used bacterial antagonists, is a novel feature of the present study. Optimum sporulation conditions of the antagonists for preparation of spore-based formulations and their commercially desirable features such as the ability to maintain spore viability in storage were also determined. Culturing in the synthetic replacement sporulation medium (SRSM-2) for 72 hours was the most effective for sporulation of the two bacterial antagonists while culturing in potato dextrose broth (PDB) for 7 days was the most effective for sporulation of the fungal antagonist. It was demonstrated that talc-based formulations of all antagonists, either in refrigerated storage (4°C) or at room temperature (28±2°C), were able to maintain greater spore viability over a longer period (>6 months) than spore suspensions. In view of the relatively shorter life spans of formulations based on vegetative cells, spore-based formulations have a distinct advantage in achieving longer-lasting control, especially under harsh field conditions.

Detoxification of oxalic acid by Pseudomonas fluorescens strain PfMDU2: Implications for the biological control of rice sheath blight caused by Rhizoctonia solani

Abstract. Prihatiningsih N, Rahayuniati RF, Djatmiko HA, Lestari P, Wulansari NK, Widnyana IK, Sutanto KD. 2024. Endophytic bacterial isolate diversity in suboptimal field rice and their potential in sheath blight control. Biodiversitas 25: 3359-3367. Rice root endophytic bacteria from suboptimal fields rice are beneficial for controlling plant pathogens. The present research aimed to characterize morphology and biochemical properties, identify secondary metabolites of rice root endophytic bacteria and evaluate their potential as biocontrol for sheath blight caused by Rhizoctonia solani. The present study focused on five endophytic bacteria, specifically Bacillus sp., with white colonies, rod-shaped cells, Gram-positive characteristics, and catalase-positive. These bacteria were selected from rice root samples due to their potential as antagonists against the pathogenic fungus R. solani. The inhibition potential of endophytes against R. solani was determined by measuring the radius of the fungal colony in the presence of the endophytic bacteria isolates. Among them, NP KR4 showed the highest inhibition percentage of 46.00 ± 6.25%, which was attributed to the antibiosis mechanism causing hyphal swelling. A molecular test using the 16S rRNA gene was conducted to determine the isolates' genetic identity. Comparing the gene sequences with those in the genetic database, it was found that NP A5, NP KR4, and NP KR7 isolates were similar to B. subtilis strain 2JKP676166, although with a few base pair differences. NP A6 exhibited a close relation to B. subtilis strain YT2 HQ143571, while NP SB3 was identified as B. subtilis subsp. stercoris strain EG1265MN704551. Further analysis of the endophytic bacteria's secondary metabolites through Gas Chromatography and Mass Spectroscopy revealed the presence of alkaloids, phenols, alcohols, and fatty acids. Among the isolates, NP KR4 demonstrated the highest biocontrol effectiveness against sheath blight, with an efficacy of 58.74%. Overall, the results indicated that the rice root endophytic bacteria isolated from suboptimal fields possess multiple contemporary traits, including antifungal activity and strain-specific differences as Bacillus subtilis. These findings suggest promising prospects for developing bio-fungicide formulations to promote sustainable rice production.

Rice blast and sheath blight disease caused by a fungus Pyricularia oryzae (Cavara) and Rhizoctonia solani, respectively, is a worldwide problem in rice and is dangerous because of its yield loss potential up to 100%. The objective of this review is to provide useful facts about rice blast and sheath blight disease and to be familiar with the different methods for controlling the diseases. Rice blast and sheath blight disease has been recognized in more than 85 rice producing countries worldwide. At present, more than 100 R genes for blast resistance have been identified in rice. Unlikely, there is no commercial variety which is resistant to sheath blight disease, but the land races can be used to achieve the novel genes for disease resistance. Rice sheath blight caused by R. solani is a destructive disease that leads to yield loss of 20–50%. Sheath blight disease management is difficult because of high genetic diversity of the causal organism and wide host range. Symptoms of this disease are generally observed from the milking stage to tillering stage of the rice crop. P. oryzae is favored by moist warm conditions and increased by fog, shade, or frequent light rains. Similarly, rice cultivar that accumulated more silicon on the shoots showed less incidence of rice blast. Among the fungal disease control method may include biological, chemical, and nutrient management; cultural practices and use of resistant varieties are the best disease management options.

About 40 per cent(2.1 Mha) of the arable land in Japan was devoted to rice production in 1988 and which in 1989 represented 42 per cent of the total fungicide market ($314-M). The most important diseases are blast and sheath blight caused by Pyricularia oryzae and Rhizoctonia solani, respectively. Fungicides for the control of these two diseases were valued at $280 M, 89 per cent of rice fungicides. The leading blast-fungicides are isoprothiolane, probenazole,tricyclazole, pyroquilon, iprobenfos, edifenphos, phthalide, kasugamycin and blasticidin-S. Flutolanil,pencycuron, diclomezine,validamycin, mepronil, organoarsenates and polyoxin are for sheath blight control. Other diseases like soil-borne seedling blight caused by Pythium, Fusarium, Rhizopus, Rhizoctonia and Trichoderma are the main problems in nurseries. These are controlled by hymexazole, hymexazole-metalaxyl and chlorothalonil. Among bacterial diseases, bacterial grain rot caused by Pseudomonas glumae is more common than bacterial leaf blight caused by Xanthomonas campestrips pv. oryzae. Most rice seeds are treated with TMTD-benomyl or TMTD-thiophanate methyl to control seed-borne diseases such as bakanae disease, blast and brown spot caused by Gibberella fujikuroi, P. oryzae and Cochliobolus miyabeanus, respectively. Nine per cent ($27M) of rice fungicides were used for the control of these seed-borne dieases. Though many diseases are effectively controlled by the current fungicides, fungicide resistance to antibiotics or organophosphorus compounds and to carbendazim generators has occured with P.oryzae and G.fujikuroi. New fungicides with different modes of action are needed to cope with them. Japanese rice culture is facing serious problems such as the decrease in rice consumption, the decrease in younger farmers and the impacts to the free trade of rice. The area under rice decrease to some extent. These problems need an urgent solution because rice culture is important being the staple food of Japan. Rice production necessarily needs fungicides as the climate in Japan favors the outbreak of many diseases.