Rice Bakanae Disease Research Articles

Fusarium species associated with Bakanae Disease of Rice in Bangladesh.

Bakanae disease has become a serious threat for sustainable rice production in Asian countries including Bangladesh. Fusarium species are important seedborne pathogens that cause bakanae disease of rice. Typical bakanae symptomatic samples were collected through a series of sampling conducted in several districts of Bangladesh for 4 consecutive years from 2019 - 2022. The pathogens were confirmed using morphological characteristics, DNA sequences, and phylogenetic analyses of two genes, namely, translation elongation factor 1-alpha (TEF1-α), and RNA polymerase subunit II (RPB2). A total of 121 Fusarium isolates were recovered from diseased rice samples at different geographical locations. From the phylogenetics analyses of TEF1-α and RPB2 gene sequences coupled with morphological characterization revealed that the collected isolates belonged to five species viz. F. fujikuroi (75.2% isolation frequency), F. incarnatum (17.35%), F. commune (4.95%), F. verticillioides (1.65%), and F. proliferatum (0.82%). Phylogenetic analysis also showed that 28 representative strains were attributed to five species. Finally, four Fusarium spp. F. fujikuroi, F. commune, F. verticillioides and F. proliferatum were found to be pathogenic under virulence assays of the isolates. The pathogenicity test results demonstrated that F. fujikuroi caused typical symptoms of bakanae, leaf elongation and chlorosis, whereas F. proliferatum and F. verticillioides only caused stunting of seedlings and F. commune caused wilt and root rot. F. incarnatum was found to be associated with bakanae disease of rice, however their pathogenicity could not be established. This study provides insight into the diversity and pathogenicity of Fusarium populations associated with bakanae disease in Bangladesh, which will help in formulating effective strategies and policies for better control of the bakanae disease.

Regional propolis extracts suppress Fusarium fujikuroi and boost rice seedling growth and response against Bakanae disease

Bakanae, caused by Fusarium fujikuroi, is a serious seed-borne disease affecting rice production worldwide. Herein, we investigated the potential of propolis, a natural honeybee product, collected from three geographic locations in Egypt: North (Menofia), Middle (Cairo), and South (Sohag), and extracted with four different solvents (ethanol, olive oil, hexane, and water) as a sustainable eco-friendly alternative to control the Bakanae disease in rice. In vitro experiments showed that propolis extracts exhibited antifungal activity against F. fujikuroi and significantly suppressed its mycelial growth and sporulation. The antifungal activity of propolis extracts was associated with its chemical composition which varied depending on geographical origin, and the extraction solvents. Moreover, SEM-based analysis revealed that ethanolic extract of northern propolis prominently altered the microconidia morphology of F fujikuroi, which shrunken and seemed to lose their viability. These findings were further confirmed in vivo under greenhouse conditions. Soaking F fujikuroi-inoculated rice seeds in 1000 ppm of propolis extract significantly reduced the bakanae disease incidence, and disease severity index compared to mock-treated controls. Although infection with F fujikuroi induced the accumulation of H2O2, the application of propolis extracts alleviated oxidative stress and significantly reduced the H2O2 levels within infected rice seedlings. Moreover, propolis extracts enhanced the profile of enzymatic antioxidants (guaiacol-dependent peroxidase [POX] and polyphenol oxidase [PPO]) in F. fujikuroi-infected rice seedlings. Finally, Propolis extracts-treated rice seedlings exhibited higher transcript levels of three PTI-marker genes including nonexpressor of pathogenesis-related genes 1 (OsNPR1), WRKY transcription factor 21(OsWRKY21), and phenylalanine ammonia-lyase (OsPAL1), which are associated with systemic acquired resistance (SAR) and crucial for the plant's defense response against pathogens. Collectively, these findings suggest that propolis might be a promising sustainable, eco-friendly alternative to control bakanae disease and other fungal seed-borne phytopathogens due to its antifungal properties and ability to induce a complex multilayered defense system within infected plants.

Effect of Cow Urine and Culture Filtrates of Trichoderma isolate S-13 on Fungal Pathogens of Basmati Rice

Rice (Oryza sativa L.) is the principle food crop for majority population of the world. Basmati rice is a unique crop of Himalaya comprising good quality characters and aroma. Basmati rice is being infected by numerous diseases. To manage these diseases, fungicides being used for years. This leads to the residual effects of fungicides on grains and soils so there is needs for alternate approaches to the manage disease. Hence use of cow urine and Trichoderma isolate S-13 is considered as the sustainable approach for management of important diseases of basmati rice. In this study we used different concentration of cow urine, Trichoderma isolate S-13, and Propiconazole (control check) against brown spot and bakanae disease of rice. Among these the maximum mycelial inhibition observed in Trichoderma isolate S-13 @15per cent (66.33per cent) followed by cow urine @15per cent (52.59 per cent). In Bakanae disease the maximum inhibition observed in Trichoderma isolate S-13 @ 15per cent (58.89 per cent) followed by cow urine@15per cent (49.26 per cent).

Ultrasensitive and on-site diagnosis of rice bakanae disease based on CRISPR-LbCas12a coupled with LAMP.

Rice bakanae disease (RBD) has longstanding challenges impacted rice production, which is predominantly induced by Fusarium fujikuroi Nirenberg. Early diagnosis of F. fujikuroi is important to control RBD and improve quality and quantity of rice production. This study presents a novel on-site diagnosis platform combined with CRISPR/LbCas12a and LAMP to detect F. fujikuroi. LAMP amplification of TEF1-α, a characteristic gene of F. fujikuroi were performed, followed with trans-cleavage reaction of LbCas12a, cleaving the single-stranded DNA reporter, which is modified by the terminal fluorophore and quencher groups, producing fluorescence signal. The platform was confirmed with high specificity and sensitivity (LOD <1 aM). Furthermore, we designed a lateral flow strip experiment based on the trans-cleavage activity of LbCas12a, which was identified with similar sensitivity and specificity to the fluorescence detection method. In summary, this study achieved a platform with remarkable sensitivity and specificity for F. fujikuroi detection and provide potential for on-site and ultrasensitive diagnostic tools for RBD. © 2024 Society of Chemical Industry.

Fusarium andiyazi, a Pathogenic Species Associated with Rice Bakanae Disease in Malaysia.

Rice is the main staple food crops for the Malaysian population. Rice is also susceptible to bakanae diseases caused by some Fusarium species and reducing yield, and quality of rice also profit. In this study, several rice fields were surveyed to collect Fusarium isolates associated with bakanae disease. The morphological features of Fusarium andiyazi isolates found on infected rice plants were identified in this investigation. For biological species identification, MAT-1 (Mating type idiomorphs) bearing isolates were crossed with MAT-2 isolates. Crossing was succeeded between cross of two different mating type bearing field isolates. Consequently, there is a possibility of exchange of genetic material within the F. andiyazi population in Malaysia. The identity of the isolates was further determined up to the species level by comparing DNA sequences and phylogenetic analysis of two genes. The phylogenetic analyses of the joined dataset of translation elongation factor 1-alpha (TEF1-α) and RNA polymerase subunit II (RPB2) revealed that all the isolates were F. andiyazi. In pathogenicity tests, F. andiyazi were found to be pathogenic on the susceptible rice cultivars MR211 and MR220. Inoculated rice seedling produced typical bakanae symptom like elongation, thin and yellow leaves. F. andiyazi was further confirmed as pathogenic species by Ultra High-Performance Liquid Chromatography (UPLC) detection of Gibberellic acid (GA3) and Fusaric acid. In this study, F. andiyazi strains have been identified as the responsible pathogen for causing rice bakanae disease in Malaysia and it is the first report of F. andiyazi, as a pathogenic species on rice in Malaysia.

Characterization, Molecular Mechanism of Prochloraz-Resistance in Fusarium fujikuroi and Development of Loop-Mediated Isothermal Amplification Rapid Detection Technique Based on the S312T Genotype of Resistances.

Rice bakanae disease (RBD) is a typical seed-borne fungal disease caused by Fusarium fujikuroi. Prochloraz is a sterol demethylation inhibitor, which is among the most important classes of active ingredients for the management of RBD. In 2022, the total resistance frequency of F. fujikuroi to prochloraz in Zhejiang Province was 62.67%. The fitness of the prochloraz-resistant population was lower than that of the susceptible population, but its pathogenicity was slightly stronger. The S312T and F511S double mutations of Ffcyp51b were detected in the resistant isolates. Loop-mediated isothermal amplification (LAMP) technology based on S312T was established to rapidly determine prochloraz resistance in F. fujikuroi. LAMP primer mismatch design was performed based on the cyp51b gene, and 100-300 bp sequences containing a mutation at codon 312 were amplified. In a 25 µL reaction tube, 1 pg/µL DNA of F. fujikuroi could be detected. The detection limit for the frequency of prochloraz resistance was 0.498% using this method. We performed LAMP detection on rice seedlings inoculated with prochloraz-sensitive and -resistant isolates and treated them with prochloraz. Prochloraz demonstrated good control in rice seedlings. A chromogenic reaction was observed in seedlings treated with prochloraz-resistant isolates, and the results were verified using electrophoresis. It has been demonstrated that LAMP technology based on the S312T genotype can quickly and specifically detect prochloraz-resistant isolates in rice seedlings.

Functional analysis of all succinate dehydrogenase subunits in Fusarium fujikuroi

Fusarium fujikuroi, the causal agent of rice bakanae disease (RBD), contains five succinate dehydrogenase (Sdh) subunits: FfSdhA, FfSdhB, FfSdhC1, FfSdhC2, and FfSdhD. However, the role of these subunits in regulating sensitivity to succinate dehydrogenase inhibitors (SDHIs) is largely unknown. Here, we conducted targeted gene disruption and phenotypic assays for all Sdh subunits and found that the deletion mutants of FfSdhA, FfSdhB, and FfSdhD exhibited severe defects in hyphal growth, conidiation, virulence, and sensitivity to CaCl2 and oxidative stresses. To a lesser extent, the mycelial growth rate and conidial production of ΔFfSdhC1 were also decreased as compared to those of the wild-type strain JS16. In addition, fungicide sensitivity assays showed that deletion of FfSdhA, B, C1, or D led to decreased sensitivity to all SDHIs tested. Unexpectedly, we were unable to obtain a FfSdhC1 + C2 double mutant and further found significant up-regulation of FfSdhC2 in ∆FfSdhC1, indicating that FfSdhC1 and -C2 might be essential for fungal growth although the FfSdhC2 deletion mutant was indistinguishable from the wild-type strain. These findings provide useful information for enhancing our understanding of the biological functions of the Sdh subunits in pathogenic fungi.

Map-Based Cloning and Characterization of a Major QTL Gene, FfR1, Which Confers Resistance to Rice Bakanae Disease.

Bakanae disease (BD), caused by the fungal pathogen Fusarium fujikuroi, is a serious threat to rice production worldwide. Breeding elite rice varieties resistant to BD requires the identification of resistance genes. Previously, we discovered a resistant quantitative trait locus (QTL), qFfR1, in a Korean japonica rice variety, Nampyeong. In this study, we fine-mapped qFfR1 with a Junam*4/Nampyeong BC3F3 population and delimited its location to a 37.1 kb region on chromosome 1. Complementation experiments with seven candidate genes in this region revealed that OsI_02728 is the gene for qFfR1. This gene encodes a protein with a typical leucine-rich repeat (LRR) receptor-like protein structure. RNA-sequencing-based transcriptomic analysis revealed that FfR1 induces the transcription of defense genes, including lignin and terpenoid biosynthesis genes, pathogenesis-related genes, and thionin genes. These results may facilitate investigations into the molecular mechanisms underlying BD resistance, including molecular patterns of Fusarium fujikuroi interacting with FfR1 and players working in signal transduction pathways downstream of FfR1, and the breeding of new BD-resistant varieties by providing a BD resistance gene with its precise selection marker. This will contribute to efficient control of BD, which is becoming more prevalent according to temperature rises due to climate change.

Early surveillance of rice bakanae disease using deep learning and hyperspectral imaging

Bakanae disease, caused by Fusarium fujikuroi, poses a significant threat to rice production and has been observed in most rice-growing regions. The disease symptoms caused by different pathogens may vary, including elongated and weak stems, slender and yellow leaves, and dwarfism, as example. Bakanae disease is likely to cause necrosis of diseased seedlings, and it may cause a large area of infection in the field through the transmission of conidia. Therefore, early disease surveillance plays a crucial role in securing rice production. Traditional monitoring methods are both time-consuming and labor-intensive and cannot be broadly applied. In this study, a combination of hyperspectral imaging technology and deep learning algorithms were used to achieve in situ detection of rice seedlings infected with bakanae disease. Phenotypic data were obtained on the 9th, 15th, and 21st day after rice infection to explore the physiological and biochemical performance, which helps to deepen the research on the disease mechanism. Hyperspectral data were obtained over these same periods of infection, and a deep learning model, named Rice Bakanae Disease-Visual Geometry Group (RBD-VGG), was established by leveraging hyperspectral imaging technology and deep learning algorithms. Based on this model, an average accuracy of 92.2% was achieved on the 21st day of infection. It also achieved an accuracy of 79.4% as early as the 9th day. Universal characteristic wavelengths were extracted to increase the feasibility of using portable spectral equipment for field surveillance. Collectively, the model offers an efficient and non-destructive surveillance methodology for monitoring bakanae disease, thereby providing an efficient avenue for disease prevention and control.

Optimization of green silver nanoparticles as nanofungicides for management of rice bakanae disease

Rice bakanae, a devastating seed-borne disease caused by Fusarium species requires a more attractive and eco-friendly management strategy. The optimization of plant-mediated silver nanoparticles (AgNPs) as nanofungicides by targeting Fusarium species may be a rational approach. In this study, Azadirachta indica leaf aqueous extract-based AgNPs (AiLAE-AgNPs) were synthesized through the optimization of three reaction parameters: A. indica leaf amount, plant extract-to-AgNO3 ratio (reactant ratio), and incubation time. The optimized green AgNPs were characterized using ultraviolet–visible light (UV–Vis) spectroscopy, field emission scanning electron microscopy (FESEM) with energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS), and powder X-ray diffraction (XRD) techniques. The optimal conditions for producing spherical, unique, and diminutive-sized AgNPs ranging from 4 to 27 nm, with an average size of 15 nm, were 2 g AiLAE at a 1:19 ratio (extract-to-AgNO3) and incubated for 4 h. Fusarium isolates collected from infected soils and identified as F. fujikuroi (40) and F. proliferatum (58 and 65) by PCR were used for seed infestation. The AgNPs exhibited concentration-dependent mycelial growth inhibition with EC50 values ranging from 2.95 to 5.50 μg/mL. The AgNPs displayed exposure time-dependent seed disinfectant potential (complete CFU reduction in F. fujikuroi (40) and F. proliferatum (58) was observed at a concentration of 17.24 μg/mL). The optimized green AgNPs were non-toxic to germinating seeds, and completely cured bakanae under net-house conditions, suggesting their great nano-fungicidal potency for food security and sustainable agriculture.

Analysis of the difference in endophytic bacterial community structure between infected and non-infected rice plants with rice bakanae disease

Abstract. Yu Y, Liu H, Xu Z, Yan P, Wu H, Wu L. 2024. Analysis of the difference in endophytic bacterial community structure between infected and non-infected rice plants with rice bakanae disease. Biodiversitas 25: 197-204. Rice bakanae disease, caused by the main pathogen Fusarium fujikuroi, is an important fungal disease that seriously threatens rice production. This study analyzed the effect of Fusarium fujikuroi on the community structure and diversity of endophytic bacteria in different rice tissues. The total DNA of different tissues, such as root, stem, and leaf, was extracted after artificial inoculation, and the bacterial 16SrRNA gene library was constructed. The high-throughput sequencing was used to analyze the biological information of bacterial community composition, diversity and function. The results showed that a total of 467841 effective sequences were obtained. Alpha diversity analysis showed that the diversity and richness of the endophytic bacterial community in infected plants were higher than in non-infected plants. At the phylum level, Cyanobacteria, Proteobacteria, Firmicutes, Acidobacteria, Bacteroidetes, Chloroflexi, and Actinobacteria were the dominant phyla. The infection of rice seedling bacteria causes changes in the abundance of endophytic bacteria in rice. Compared with non-infected plants, the abundance of Streptophyta and Acidovorax in the root decreased by 1.29 and 0.74%, respectively. The abundance of Geobacter, Devosia, Pleomorphomonas, and Herbaspirillum increased by 1.05, 1.55, 1.28, and 1.76%, while the abundance of Streptophyta in stem decreased by 7.83%. The abundance of Xanthomonas, Acidovorax, Pseudomonas and Sphingomonas increased by 1.55, 1.49, 1.11 and 1.15%, whereas the abundance of Streptophyta in the leaf decreased by 12.03%, Actinomycetales, Pseudomonas, Sphingomonas are significant biological differences between different tissues of infected and non-infected plants. The study provides a theoretical basis for the biological control of rice bakanae disease.

Variations in Morpho-Cultural Characteristics and Pathogenicity of Fusarium moniliforme of Bakanae Disease of Rice and Evaluation of In Vitro Growth Suppression Potential of Some Bioagents

Bakanae is one of the important diseases of rice in Bangladesh that causes substantial yield loss every year. We collected thirty isolates of Fusarium spp. from bakanae-infected rice plants from different agroecological zones of Bangladesh and investigated the variations in cultural and morphological characteristics and pathogenicity. Diversity was found in cultural characteristics, viz., colony features, phialide, chlamydospore formation, shape, and size of macro- and microconidia. Three variants of Fusarium species such as F. moniliforme, F. fujikuroi, and F. proliferatum were identified on PDA media based on their cultural and morphological characteristics. Isolate FM10 (F. moniliforme) exhibited the highest disease aggressiveness in developing elongated plants (26.50 cm), the highest number of chlorotic leaves (5.75), and a lower germination percentage. We evaluated different bioagents against the virulent isolate of F. moniliforme to develop a rice bakanae disease management approach. Four bioagents, viz., Trichoderma spp., Bacillus subtilis, Pseudomonas fluorescens, and Achromobacter spp., were evaluated for growth suppression of F. moniliforme. Among the bioagents, Achromobacter spp. and B. subtilis (BS21) showed 73.54% and 71.61% growth suppression, respectively. The investigation revealed that the application of Achromobacter spp. and B. subtilis (BS21) would be a potential candidate for effective and eco-friendly management of the bakanae disease of rice.

Performance analysis of various deep learning models for detecting rice diseases

&lt;p&gt;A major portion of the world’s population relies on rice as a staple diet, hence rice is essential to maintaining food security worldwide. Unfortunately, rice crops are susceptible to a number of illnesses that, if detected and treated promptly, can result in significant output losses. Expert visual inspection is a time-consuming and arbitrary part of the conventional procedures for diagnosing diseases in rice. An effective method for automated illness diagnosis in agriculture has evolved in recent years: deep learning, a branch of artificial intelligence. The objective of this research is to compare AlexNet, DCNN, MobileNet, GoogleNet, VGG16, ResNet50 and Xception, these are various deep learning models in order to choose the one that would produce the highest levels of accuracy, precision recall, specificity, and F1-score for detecting rice diseases. In this study we train the model for nine different types of rice diseases named as Rice Blast (Pyricularia oryzae), Rice Sheath Blight (Rhizoctonia Solani), Bacterial Leaf Blight (Xanthomonas oryzae pv. oryzae), Tungro Disease, Rice Grassy Stunt Virus (RGSV), Rice Yellow Mottle Virus (RYMV), Bakanae Disease (Fusarium moniliforme), Brown Spot (Cochliobolus miyabeanus) and Rice Tungro Bacilliform Virus (RTBV) with 30,000 images. For this we used the secondary dataset for analyzing the performance of models. We trained the model for both normalized and non-normalized dataset. After comparing the various models we get the better result from ResNet50 model with accuracy of 97.50%.&lt;/p&gt;

Activity of fungicide cyclobutrifluram against Fusarium fujikuroi and mechanism of the pathogen resistance associated with point mutations in FfSdhB, FfSdhC2 and FfSdhD

Rice bakanae disease (RBD) is a devastating plant disease caused by Fusarium fujikuroi. This study aimed to evaluate the potential of cyclobutrifluram, a novel succinate dehydrogenase inhibitor (SDHI), to control RBD, and determine the risk and mechanism of resistance to cyclobutrifluram in F. fujikuroi. In vitro experiments showed that cyclobutrifluram significantly inhibited mycelial growth and spore germination, and altered the morphology of mycelia and conidia. Treatment with cyclobutrifluram significantly decreased mycotoxin production and increased cell membrane permeability in F. fujikuroi. The baseline sensitivity of 72 F. fujikuroi isolates to cyclobutrifluram was determined using mycelial growth and spore germination inhibition assays, which revealed EC50 values of 0.0114 – 0.1304 μg mL-1 and 0.0012 – 0.016 μg mL-1, with mean EC50 values of 0.0410 ± 0.0470 μg mL-1 and 0.0038 ± 0.0015 μg mL-1, respectively. Pot experiments demonstrated that the protective effect of cyclobutrifluram against F. fujikuroi was more significant than that of phenamacril and azoxystrobin, indicating that cyclobutrifluram is a promising antifungal agent for the control of RBD. Six cyclobutrifluram-resistant mutants of F. fujikuroi were obtained via fungicide adaptation. Moreover, these mutants exhibited weaker fitness than their parental isolate and positive cross-resistance with other SDHI fungicides, including pydiflumetofen and penflufen; however, no cross-resistance was detected with other classes of fungicides, including phenamacril, fludioxonil, prochloraz, or azoxystrobin. These results indicated that the resistance risk of F. fujikuroi to cyclobutrifluram might be moderate. Sequencing analysis revealed that mutations, including H248D in FfSdhB, A83V in FfSdhC2, and S106F and E166K in FfSdhD, contributed to resistance, which was confirmed by molecular docking and homologous replacement experiments. The results suggest a high potential for cyclobutrifluram to control RBD and a moderate resistance risk of F. fujikuroi to cyclobutrifluram, which are meaningful findings for the scientific application of cyclobutrifluram.

In vitro production of gibberellic acid and fusaric acid by Fusarium spp. and their role in bakanae disease development

Gibberellic acid (GA3) and fusaric acid (FA) are directly correlated with the symptom development of bakanae disease in rice plants. The role of GA3 and FA, produced in vitro by several Fusarium species associated with bakanae disease, was studied to understand the disease’s etiology and its impact on symptom development. In total, 121 Fusarium strains were obtained from bakanae-infected rice plants collected from various rice cultivation regions in Bangladesh. Finally, 18 highly virulent Fusarium strains were selected based on virulence assay and further evaluated for GA3 and FA production through ultra-performance liquid chromatography analysis. Among the Fusarium strains, Fusarium fujikuroi strains produced a high amount of GA3 and a low amount of FA. In contrast, Fusarium proliferatum and Fusarium verticillioides strains produced a high amount of FA and a low amount of GA3. In exception, the Fusarium strain BD117R of F. fujikuroi produced no GA3 but a high amount of FA. Interestingly, Fusarium commune produced only FA in high concentration. In bakanae disease development, GA3 production was positively related to elongation symptoms whereas FA contributes to stunting symptoms. This is the first record of the production of GA3 and FA by Fusarium species causing bakanae disease of rice in Bangladesh.

Rapid detection of Fusarium fujikuroi in rice seeds and soaking water samples based on recombinase polymerase amplification‐lateral flow dipstick

AbstractBakanae disease is a rice seedborne disease caused by the Fusarium (Gibberella) fujikuroi species complex (FFSC), among which F. fujikuroi is the dominant pathogen. Pathogens usually hide inside or on the surface of seeds, and infection occurs mainly at the germination stage. In this study, a method for the detection of F. fujikuroi in rice seeds and seed soaking water samples was established using recombinase polymerase amplification (RPA) technology with lateral flow device (LFD) chromatography test strips. A pair of specific primers and probes based on the cyp51c gene were screened. RPA‐LFD was used to detect 10 F. fujikuroi strains, and the results showed that all of them tested positive and there was no cross‐reaction with other Fusarium or non‐Fusarium species. The target production of the RPA‐LFD assay was obtained at 35–45°C for 8–14 min, and optimal reaction conditions of amplification at 39°C for 8 min is recommended. The sensitivity test showed that the detection limit of the RPA‐LFD test for F. fujikuroi genomic DNA in rice seeds was 100 fg/μL, and the detection limit for F. fujikuroi spores in submerged water samples was 100 spores/mL. In the assay for field samples, it successfully detected F. fujikuroi carried in the seeds of three out of five rice varieties. In addition, the whole RPA‐LFD assay can specifically detect F. fujikuroi within 30 min. This method is expected to become an early field monitoring tool for rice bakanae disease.

Dual Role of Potassium Silicate and Salicylic Acid: Plant Growth Promotor and Plant Immunity Booster Against Bakanae Disease of Rice

Dual Role of Potassium Silicate and Salicylic Acid: Plant Growth Promotor and Plant Immunity Booster Against Bakanae Disease of Rice

Integrated management practices against an emerging Bakanae disease of rice under the hot-humid climate of Indo-Gangetic plains of India

Bakanae disease caused by Fusarium fujikuroi is emerging in India. In this work, fungicides and biocontrol agents were evaluated as seed, seedling treatment, and foliar spray(s) against bakanae disease in rice under field conditions. Carbendazim (50% WP) was found to be the most effective fungicide for seed and seedling root dip treatments. Soil drenching with 0.25% carbendazim (50% WP) 5 days before transplanting of seedlings was effective for large scale treatments. Foliar spray of 0.1% tebuconazole 50%+ trifloxystrobin 25% w/w (75 WG) significantly reduced the percentage of infected seeds (7.17%) compared with the control (32.50%). The minimum disease incidence (31%) was observed when seeds were treated with Talaromyces flavus. Individual treatments were integrated in the form of six management modules and evaluated under the field conditions of New Delhi (India) and Pusa Bihar (India) with the susceptible cultivars ‘Pusa Basmati 1121’ and ‘Pusa 1176’. Bakanae disease incidence was lower in the modules tested compared with the inoculated control or the individual treatment. The most favorable results at two locations achieved the lowest disease incidence of 7% and 2.41%.

First Report of Fusarium Root Rot of Tobacco Caused by Fusarium fujikuroi in Guangdong Province, China.

From March to June 2022, Fusarium tobacco root rot broke out in Shaoguan Guangdong Province, China, affecting approximately 15% of tobacco production fields, with an incidence of 24% to 66%. In the early stage, the lower leaves showed chlorosis, and the roots became black. In the later stage, the leaves became browned and withered, the root cortices were broken and shed, and only a small number of roots were left. Eventually, the entire plant died. Six diseased plant samples (cv. yueyan 97) from Shaoguan (113.8°E, 24.8°N) were collected as test materials. The diseased root tissues (4×4 mm) were surface-sterilized using 75% ethanol for 30 s and 2% NaOCl for 10 min, rinsed 3 times with sterile water and incubated for 4 days on potato dextrose agar (PDA) medium at 25 °C. Fungal colonies were subcultured on fresh PDA, grown for the next 5 d and purified by single-spore separation. Eleven isolates with similar morphological characteristics were obtained. Their colonies were white and fluffy, and the bottoms of the culture plates were pale pink after 5 days of incubation. The macroconidia were slender, slightly curved and measured 18.54~45.85 µm×2.35~3.84 µm (n=50), with 3 to 5 septa. The microconidia were oval or spindle shaped, with one to two cells, and measured 5.56~16.76 µm×2.32~3.86 µm (n=50). Chlamydospores were absent. Such characteristics are typical of the genus Fusarium (Booth C, 1971). The SGF36 isolate was chosen for further molecular analysis. The TEF-1α and β-tubulin genes (Pedrozo et al.2015) were amplified. Based on a phylogenetic tree (neighbor-joining method and 1,000 bootstrap values) obtained using multiplex alignments of concatenations of these two genes from 18 Fusarium species, SGF36 was grouped into a clade with Fusarium fujikuroi strain 12-1 (MK443268.1/MK443267.1) and F. fujikuroi isolate BJ-1 (MH263736.1/MH263737.1). To further identity the isolate, five additional gene sequences (rDNA-ITS (OP862807.1), RPB2, histone 3, calmodulin, and mitochondrial small subunit) (Pedrozo et al.2015), were subjected to BLAST searches in GenBank, and the results indicated that they were most similar to F. fujikuroi sequences, with sequence identities greater than 99%. The phylogenetic tree obtained using six genes except mitochondrial small subunit gene showed that SGF36 was grouped together with four F. fujikuroi strains to form a single clade. Pathogenicity was determined by the inoculation of wheat grains with fungi in potted tobacco plants. The SGF36 isolate was inoculated onto sterilized wheat grains, which were then incubated at 25 °C for 7 d. Thirty wheat grains with fungi were added to 200 g of sterilized soil, which was then mixed well and placed into pots. One six-leaf-stage tobacco seedling (cv. yueyan 97) was planted in each pot. A total of 20 tobacco seedlings were treated. Another 20 control seedlings were treated with wheat grains without fungi. All seedlings were placed in a greenhouse at 25 °C with 90% relative humidity. After 5 d, the leaves of all inoculated seedlings showed chlorosis, and the roots became discolored. No symptoms were observed in the controls. The fungus was reisolated from symptomatic roots and confirmed to be F. fujikuroi based on the TEF-1α gene sequence. No F. fujikuroi isolates were recovered from control plants. F. fujikuroi was previously reported to be associated with rice bakanae disease (Ram et al., 2018), soybean root rot (Zhao et al., 2020) and cotton seedling wilt (Zhu et al., 2020). To our knowledge, this is the first report of F. fujikuroi causing root wilt on tobacco in China. The identification of the pathogen may help to establish appropriate measures for controlling this disease.

Current insights on rice (Oryza sativa L.) bakanae disease and exploration of its management strategies.

Bakanae is an emerging rice disease caused by the seed- and soil-borne pathogen Fusariumfujikuroi. It is becoming a more serious threat to sustainable rice production throughout rice-growing regions. Bakanae disease infection is responsible for high yield losses ranging from 3% to 95%, and disease incidence varies based on the region and cultivars. Hence, understanding the nature of the pathogen, its pathogenicity, disease epidemiology, symptoms, host‍-‍pathogen interaction, and the role of secondary metabolites in the disease cycle will be helpful in the development of effective and sustainable management strategies. However, very few comprehensive studies have described the details of rice bakanae disease. Thus, in this review we summarize and discuss in detail the information available from 1898 to 2023 on various critical facets of bakanae disease, and provide perspectives on future research.