Determination of the Antagonistic Effects of Some Rhizospheric Bacteria against Macrophomina phaseolina under In Vitro Conditions

Macrophomina phaseolina (Tassi) Goid. is a fungal pathogen causes charcoal rot disease (Sin: Rhizoctonia bataticola) and is responsible for significant yield losses in many plants. In our study, we aimed to evaluate the antagonistic ability of 39 different bacteria, isolated from the fields of sugar beet in 2019, against the pathogen Macrophomina phaseolina isolated from sugar beet, beans and chickpeas. Approximately 31% of the bacteria showed antibiosis effect against the pathogen. It was determined that the effectiveness level of Lelliottia amnigena, Bacillus atrophaeus, B.pumilus and B. cereus (7 isolates) was moderate to high against Macrophomina phaseolina. Bacillus atrophaeus (PTo15-1a) showed the highest efficacy of 80%, 72.94% and 82.35% against Macrophomina phaseolina of chickpea, bean and sugar beet respectively. Lelliottia amnigena (Pto 14-1b) was moderately effective (57.78%) against the chickpea isolate of the pathogen. It was observed that of the seven Bacillus cereus isolates used in the experiment, three isolates (Pto14-1a, Pto12-1b, Pto17-1b) were highly effective against the chickpea pathogen, two (Pto12-1b, Pto14-2b) against bean pathogen, and one (Pto15-1b) against sugar beet isolate. Results have shown varied level of antagonism by different test bacterial against different Macrophomina phaseolina isolates, while the highest level of antibiosis shown by Bacillus atrophaeus against all pathogenic isolates indicated that it can be a potential future bioagent in managing the disease.

Insights into the Host-Pathogen Interaction Pathways through RNA-Seq Analysis of Lens culinaris Medik. in Response to Rhizoctonia bataticola Infection

Dry root rot (Rhizoctonia bataticola) is an important disease of lentils (Lens culinaris Medik.).To gain an insight into the molecular aspects of host-pathogen interactions, the RNA-seq approach was used in lentils following inoculation with R.bataticola. The RNA-Seq has generated >450 million high-quality reads (HQRs) and nearly 96.97% were properly aligned to the reference genome. Very high similarity in FPKM (fragments per kilobase of exon per million mapped fragments) values (R > 0.9) among biological replicates showed the consistency of the RNA-Seq results. The study revealed various DEGs (differentially expressed genes) that were associated with changes in phenolic compounds, transcription factors (TFs), antioxidants, receptor kinases, hormone signals which corresponded to the cell wall modification enzymes, defense-related metabolites, and jasmonic acid (JA)/ethylene (ET) pathways. Gene ontology (GO) categorization also showed similar kinds of significantly enriched similar GO terms. Interestingly, of the total unigenes (42,606), 12,648 got assembled and showed significant hit with Rhizoctonia species. String analysis also revealed the role of various disease responsive proteins viz., LRR family proteins, LRR-RLKs, protein kinases, etc. in the host-pathogen interaction. Insilico validation analysis was performed using Genevestigator® and DEGs belonging to six major defense-response groups viz., defense-related enzymes, disease responsive genes, hormones, kinases, PR (pathogenesis related) proteins, and TFs were validated. For the first time some key miRNA targets viz. miR156, miR159, miR167, miR169, and miR482 were identified from the studied transcriptome, which may have some vital role in Rhizoctonia-based responses in lentils. The study has revealed the molecular mechanisms of the lentil/R.bataticola interactions and also provided a theoretical approach for the development of lentil genotypes resistant to R.bataticola.

Efficacy of Fungicides against Soil Borne and Grapevine Pathogens under In vitro Conditions

In vitro bio-efficacy of the novel copper (NC101 and NCP102) and phosphonate (PN103 and PMN104) based fungicides against various soil borne and grape vine pathogens was evaluated at ICAR-National Research Centre for Grapes, Pune, Maharashtra, India during February - April 2021. The fungicides were screened against five bacterial pathogens viz. Xanthomonas campestris pv. citri, X. campestris pv. campestris, X. campestris pv. punicae, X. campestris pv. viticola and X. oryzae pv. oryzae and 10 fungal pathogens viz. Rhizoctonia bataticola, Sclerotium rolfsii, Cladosporium sp, Alternaria alternata, Colletotrichum gloeosporioides, Penicillium notatum, Magnaporthe oryzae, Fusarium oxysporium, Macrophomina phaseolina (Soyabean isolate) and Macrophomina phaseolina (Jute isolate) at different concentrations. Results indicated that among all the tested fungicides viz. NC101, NCP102, PN103 and PMN104, phosphonate based fungicides (PN103 and PMN104) were highly effective against bacterial isolates with zone of inhibition ranging between 8.75 - 31.12 mm in which X. campestris pv. viticola was found to express least inhibition zone. In case of pathogenic fungal isolates, similar trend was observed, most of the isolates showed cent percent inhibition at higher concentration of PN103 and PMN104. However Sclerotium rolfsii showed least or no inhibition when tested at different concentrations of fungicides. The chemicals exhibited wide range of inhibition and it was found to increase steadily with increase in concentrations of the test fungicides.

Disease Incidence, Severity and Phenotypic Variation Among the Isolates of Rhizoctonia Bataticola Infected in Root Rot Disease of Mulberry in Different Mulberry Fields of Karnataka

The present investigation was carried out in view of destructive nature of root rot disease of mulberry caused by Rhizoctonia bataticola. The pathogen is a soil inhabiting fungus which is causing serious threat to more than 500 plant species. This study will enable to have a clear view of the root rot pathogen, R. bataticola in respect to variability, distribution and economic impact on mulberry plant. Root rot disease of mulberry is a devastating disease among the mulberry diseases. The part of study was conducted in Ramanagara district of Karnataka which is the largest market for silk cocoons in Asia, followed by Kanakapura in Karnataka, India. A field survey was conducted on disease incidence in various mulberry cultivating fields in Kanakapura and Ramanagara areas of Karnataka. Disease incidence of 78% and 53.60% with an average leaf yield loss of 39.73% covering 80 mulberry gardens has been reported in Kanakapura and Ramanagara respectively. From the infected root samples the phytopathogen, R. bataticola was isolated and its phenotypic variation was studied by growing the fungal pathogen on different fugal isolation media such as potato dextrose agar, richard’s agar and czapek dox agar under laboratory conditions. This study revealed the prevalence of the mulberry root rot disease in major mulberry growing locations in Karnataka. Incidence and severity of the mulberry root rot disease varied significantly among the locations under cropping seasons. This study was limited to southern Karnataka and did not cover other mulberry production locations in the different agro-ecological zones in Karnataka state. Therefore a study should be undertaken to evaluate the disease prevalence in other locations.

Temperature and Soil Moisture Stress Modulate the Host Defense Response in Chickpea During Dry Root Rot Incidence

Dry root rot caused by the necrotrophic phytopathogenic fungus Rhizoctonia bataticola is an emerging threat to chickpea production in India. In the near future, the expected increase in average temperature and inconsistent rainfall patterns resultant of changing climatic scenarios are strongly believed to exacerbate the disease to epidemic proportions. The present study aims to quantify the collective role of temperature and soil moisture content (SMC) on disease progression in chickpea under controlled environmental conditions. In our study, we could find that both temperature and soil moisture played a decisive role in influencing the dry root rot disease scenario. As per the disease susceptibility index (DSI), a combination of high temperature (35°C) and low SMC (60%) was found to elicit the highest disease susceptibility in chickpea. High pathogen colonization was realized in chickpea root tissue at all time-points irrespective of genotype, temperature, and SMC. Interestingly, this was in contrast to the DSI where no visible symptoms were recorded in the roots or foliage during the initial time-points. For each time-point, the colonization was slightly higher at 35°C than 25°C, while the same did not vary significantly with respect to SMC. Furthermore, the differential expression study revealed the involvement of host defense-related genes like endochitinase and PR-3-type chitinase (CHI III) genes in delaying the dry root rot (DRR) disease progression in chickpea. Such genes were found to be highly active during the early stages of infection especially under low SMC.

Lab and Field Level Potential of Endophytic Bacteria in Managing the Dry Root Rot Disease in Black Gram Incited by Rhizoctonia bataticola (Taubenh) Butler

Background: The plant growth promotion and efficacy against phytopathogens by the endophytic bacteria are being focused now due to their ecofriendly nature. Methods: Endophytic bacteria (24 nos) isolated from the roots, stems and leaves of black gram plants collected from different locations were tested for their potential to inhibit the growth of R. bataticola under in vitro and in vivo conditions. Result: The leaf endophyte BLE 4 exhibited maximum inhibition (79.6%) of R. bataticola followed by BSE 4 (77.4%), BSE 7 (77.0%) and BLE 1 (74.0%). Among these 4 isolates tested as seed treatment and soil application, there was significant increase in dry weight (7.1 g), plant height (37.7 cm), number of branches (13.2) and number of pods (26.2) in BLE 4 treated plots. Whereas, the incidence of dry root rot and yield were insignificant. In the screening study of isolates for their phosphate solubilization potential, protease activity, siderophore and HCN production, no single isolate possessed all the properties, but siderophore production, protease activity and phosphate solubilization were found in BSE 4, BRE 3, BRE 5 and BRE 10 isolates.

Low soil moisture predisposes field-grown chickpea plants to dry root rot disease: evidence from simulation modeling and correlation analysis

Rhizoctonia bataticola causes dry root rot (DRR), a devastating disease in chickpea (Cicer arietinum). DRR incidence increases under water deficit stress and high temperature. However, the roles of other edaphic and environmental factors remain unclear. Here, we performed an artificial neural network (ANN)-based prediction of DRR incidence considering DRR incidence data from previous reports and weather factors. ANN-based prediction using the backpropagation algorithm showed that the combination of total rainfall from November to January of the chickpea-growing season and average maximum temperature of the months October and November is crucial in determining DRR occurrence in chickpea fields. The prediction accuracy of DRR incidence was 84.6% with the validation dataset. Field trials at seven different locations in India with combination of low soil moisture and pathogen stress treatments confirmed the impact of low soil moisture on DRR incidence under different agroclimatic zones and helped in determining the correlation of soil factors with DRR incidence. Soil phosphorus, potassium, organic carbon, and clay content were positively correlated with DRR incidence, while soil silt content was negatively correlated. Our results establish the role of edaphic and other weather factors in chickpea DRR disease incidence. Our ANN-based model will allow the location-specific prediction of DRR incidence, enabling efficient decision-making in chickpea cultivation to minimize yield loss.

Screening of Microflora Associated with Brinjal Seeds (Solanum melongena L.) in Western Part of India

Total 110 seed samples of brinjal (Solanum melongena L.) were collected from 12 major growing districts of Rajasthan and subjected to dry seed examination (DSE). DSE revealed asymptomatic (07.75-97.5%), moderately discolored (04.50-67.50%) and shriveled discolored (03.25-38.75%) seeds. Symptomatic seeds in DSE showed various types of discolorations, deformation like white crust on seed surface. The seeds with water soaked symptoms and spots on seed surface were also observed such seeds on incubation yielded bacterial species. The incubation of symptomatic seeds about 21 fungal species of 14 genera and 3 bacterial species were observed viz. Alternaria alternata, A. solani, Aspergillus flavus, A. niger, Cladosporium oxysporium, Curvularia lunata, Fusarium oxysporium, F. solani, Rhizoctonia bataticola and Rhizopus nigricans etc and bacterial species like Xanthomonas axonopodis var. vesicatoria, Ralstonia solanacearum and Pseudomonas aeruginosa. The microflora severely affects seed germination (failure or delayed germination), wilting and rotting of seedlings, bacterial oozing, collapse of hypocotyls and cotyledonary leaves which resulting seedling mortality. High yield of microflora was obtained on standard blotter method (SBM) and agar plate method (APM).