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Macrophomina phaseolina is the most devastating and emerging threat to groundnut production in India. An increase in average temperature and inconsistent rainfalls resulting from changing climatic conditions are strongly believed to aggravate the disease and cause severe yield losses. The present study aims to conduct a holistic survey to assess the prevalence and incidence of dry root rot of groundnut in major groundnut growing regions of Southern India, viz., Andhra Pradesh, Telangana, Karnataka, and Tamil Nadu. Furthermore, the pathogenic variability was determined using different assays such as morphological, cultural, pathogenic, and molecular assays. Results indicate that disease incidence in surveyed locations ranged from 8.06 to 20.61%. Both temperature and rainfall played a major role in increasing the disease incidence. The pathogenic variability of M. phaseolina isolates differed significantly, based on the percent disease incidence induced on cultivars of JL-24 groundnut and K-6 groundnut. Morphological variations in terms of growth pattern, culture color, sclerotia number, and sclerotia size were observed. The molecular characterization of M. phaseolina isolates done by ITS rDNA region using ITS1 and ITS4 primers yielded approximately 600 bp PCR amplicons, sequenced and deposited in GenBank (NCBI). Molecular variability analysis using SSR primers indicated the genetic variation among the isolates collected from different states. The present investigation revealed significant variations in pathogenic variability among isolates of M. phaseolina and these may be considered important in disease management and the development of resistant cultivars against groundnut dry root rot disease.

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Plants deposit lignin in the secondary cell wall as a common response to drought and pathogen attacks. Cell wall localised multicopper oxidase family enzymes LACCASES (LACs) catalyse the formation of monolignol radicals and facilitate lignin formation. We show an upregulation of the expression of several LAC genes and a downregulation of microRNA397 (CamiR397) in response to natural drought in chickpea roots. CamiR397 was found to target LAC4 and LAC17L out of twenty annotated LACs in chickpea. CamiR397 and its target genes are expressed in the root. Overexpression of CamiR397 reduced expression of LAC4 and LAC17L and lignin deposition in chickpea root xylem causing reduction in xylem wall thickness. Downregulation of CamiR397 activity by expressing a short tandem target mimic (STTM397) construct increased root lignin deposition in chickpea. CamiR397-overexpressing and STTM397 chickpea lines showed sensitivity and tolerance, respectively, towards natural drought. Infection with a fungal pathogen Macrophomina phaseolina, responsible for dry root rot (DRR) disease in chickpea, induced local lignin deposition and LAC gene expression. CamiR397-overexpressing and STTM397 chickpea lines showed more sensitivity and tolerance, respectively, to DRR. Our results demonstrated the regulatory role of CamiR397 in root lignification during drought and DRR in an agriculturally important crop chickpea.

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The present study evaluated the effect of thiamine loaded chitosan nanoparticle (TChNp) on chickpea plant growth under greenhouse condition. TChNp treated plants showed increased number of leaves, branches, shoot/root length, number of secondary roots and plant dry weight. Enhanced nodulation with larger nodules was observed in TChNp treated chickpea plants. A significant increase in the number of flowers, pods and grain yield was observed in the TChNp treated chickpea plants compared to the chitosan and untreated control. The TChNps showed direct antifungal activity towards Rhizoctonia bataticola as evidenced by in vitro and SEM analyses, which might be due to the solubility and size of the nanoparticle. TChNps treated chickpea plants challenged with R. bataticola showed significant reduction in plant mortality compared to infected untreated control under pot condition. These results indicate the potential of the TChNps in enhancing the yield and suppressing the dry root rot disease in chickpea.

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Charcoal rot is an important soilborne disease caused by a range of Macrophomina species, which affects a broad range of commercially important crops worldwide. Even though Macrophomina species are fungal pathogens of substantial economic importance, their mechanism of pathogenicity and host spectrum are poorly understood. There is an urgent need to better understand the biology, epidemiology, and evolution of Macrophomina species, which, in turn, will aid in improving charcoal rot management strategies. Here, we present the first high-quality genome assembly and annotation of Macrophomina tecta strain BRIP 70781 associated with charcoal rot symptoms on sorghum. Hybrid assembly integrating long reads generated by Oxford Nanopore Technology and short Illumina paired-end reads resulted in 43 contigs with a total assembly size of ∼54 Mb, and an N50 of 3.4 Mb. In total, 12,926 protein-coding genes and 7,036 repeats were predicted. Genome comparisons detected accumulation of DNA transposons in Macrophomina species associated with sorghum. The first reference genome of M. tecta generated in this study will contribute to more comparative and population genomics studies of Macrophomina species.

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Macrophomina phaseolina, a fungus that causes dry root rot, is a relatively new threat to blackgram in South Asia. Because this pathogen is a polyphagic necrotroph, it remains viable in the soil for several years, making disease management challenging. One of the most economical methods for managing dry root rot in blackgram is through an integrated approach that uses resistant varieties. This study examined M. phaseolina associated with dry root rot in blackgram and screened 41 blackgram genotypes for dry root rot resistance. The present work also characterized morphological features and internal transcribed sequence regions of the nuclear rDNA operon to identify M. phaseolina from blackgram. Evaluation of the 41 blackgram genotypes against M. phaseolina by the paper towel technique identified two genotypes, CO-5 and IPU 07-3, with dry root rot resistance (disease scores: ≤3) and 18 genotypes with moderate resistance (disease scores: >3 to ≤5). Five genotypes with disease scores <4.0 and two susceptible genotypes were reevaluated using the paper towel method, which revealed moderate resistance reactions of CO-5, IPU 07-3, and MASH 1-1. To confirm dry root rot resistance of these seven genotypes, further screening was done in a greenhouse using the sick pot assay. Results revealed moderate resistance of CO-5, IPU 07-3, and MASH 1-1 genotypes. As compared with susceptible check (VO 2135-B-BL), CO-5 consistently excelled in plant survival with 13.4% disease incidence, followed by IPU 07-3 (16.7%) and MASH 1-1 (19.9%). Therefore, these three genotypes can be used as parents in blackgram breeding programs for developing blackgram cultivars with improved dry root rot resistance.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

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Drought plays a central role in increasing the incidence and severity of dry root rot (DRR) disease in chickpea. This is an economically devastating disease, compromising chickpea yields particularly severely in recent years due to erratic rainfall patterns. Macrophomina phaseolina (formerly Rhizoctonia bataticola) is the causal agent of DRR disease in the chickpea plant. The infection pattern in chickpea roots under well-watered conditions and drought stress are poorly understood at present. This study provides detailed disease symptomatology and the characteristics of DRR fungus at morphological and molecular levels. Using microscopy techniques, the infection pattern of DRR fungus in susceptible chickpea roots was investigated under well-watered and drought-stress conditions. Our observations suggested that drought stress intensifies the progression of already ongoing infection by weakening the endodermal barrier and overall defense. Transcriptomic analysis suggested that the plant's innate immune defense program is downregulated in infected roots when subjected to drought stress. Furthermore, genes involved in hormonal regulation are differentially expressed under drought stress. These findings provide hints in terms of potential chickpea genes to target in crop improvement programs to develop climate-change-resilient cultivars.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

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Chickpea is an essential crop for protein nutrition and is grown around the world in rain-fed conditions. However, chickpea cultivation is under threat due to emerging diseases favored by drought stress. Dry root rot (DRR), an economically devastating disease, is an example. Chickpea-specific strains of a necrotic fungal phytopathogen, Macrophomina phaseolina, cause DRR. Microsclerotia of this fungus, which are capable of withstanding harsh environmental conditions, serve as primary inoculum. Initial symptoms are scattered necrotic spots in roots, progressing to rotting and withering lateral roots, accompanied by prematurely dried, straw-colored foliage. The recent rise in global temperature and worsening of drought spells have aggravated DRR outbreaks in chickpea. To date, DRR epidemiology has not been clarified in detail. Also, the literature lacks clarity on M. phaseolina taxonomy, morphology, disease progression, and diagnosis. In this article, research progress on patterns of DRR occurrence in the field and belowground and aboveground symptoms are clarified. In addition, the current understanding of taxonomy and management practices is elaborated. We also summarize knowledge of the impact of drought and high temperature on DRR severity. Furthermore, we provide future perspectives on the importance of host resistance, quantitative trait loci identification, and genotype screening for the identification of resistant genotypes. The article proposes new research priorities and a corresponding plan for the mitigation of DRR.

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PREMISE: A comprehensive field-based screening protocol is lacking for dry root rot (DRR) disease in chickpea, which is caused by Macrophomina phaseolina (formerly referred to as Rhizoctonia bataticola). Here, we describe a protocol for establishing a sick plot for DRR to enable disease assessment of a large number of chickpea plants during the natural growing season. METHODS AND RESULTS: We used a chickpea plot with >30% DRR incidence, and enriched the inoculum by cultivating highly susceptible chickpea plant genotypes and incorporating infected plant material into the soil. The chickpea plants were then subjected to infection in developed sick plots with various levels of soil moisture under natural field conditions. CONCLUSIONS: Our protocol provides a robust way to impose M. phaseolina infection on chickpea plants under natural field conditions and to investigate plant responses to the infection at morphological, physiological, and molecular levels. This method can also be used to screen for other soil-borne diseases in a variety of plants.

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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.

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Citrus trees face threats from several diseases that affect its production, in particular dry root rot (DRR). DRR is a multifactorial disease mainly attributed to Neocosmospora (Fusarium) solani and other several species of Neocosmospora and Fusarium spp. Nowadays, biological control holds a promising control strategy that showed its great potential as a reliable eco-friendly method for managing DRR disease. In the present study, antagonist rhizobacteria isolates were screened based on in vitro dual culture bioassay with N. solani. Out of 210 bacterial isolates collected from citrus rhizosphere, twenty isolates were selected and identified to the species level based on the 16S rRNA gene. Molecular identification based on 16S rRNA gene revealed nine species belonging to Bacillus, Stenotrophomonas, and Sphingobacterium genus. In addition, their possible mechanisms involved in biocontrol and plant growth promoting traits were also investigated. Results showed that pectinase, cellulose, and chitinase were produced by eighteen, sixteen, and eight bacterial isolates, respectively. All twenty isolates were able to produce amylase and protease, only four isolates produced hydrogen cyanide, fourteen isolates have solubilized tricalcium phosphate, and ten had the ability to produce indole-3-acetic acid (IAA). Surprisingly, antagonist bacteria differed substantially in their ability to produce antimicrobial substances such as bacillomycin (five isolates), iturin (ten isolates), fengycin (six isolates), surfactin (fourteen isolates), and bacteriocin (subtilosin A (six isolates)). Regarding the PGPR capabilities, an increase in the growth of the bacterial treated canola plants, used as a model plant, was observed. Interestingly, both bacterial isolates Bacillus subtilis K4-4 and GH3-8 appear to be more promising as biocontrol agents, since they completely suppressed the disease in greenhouse trials. Moreover, these antagonist bacteria could be used as bio-fertilizer for sustainable agriculture.