Dilip Lakshman - Academia.edu (original) (raw)
Papers by Dilip Lakshman
Plants
The root nodules are a unique environment formed on legume roots through a highly specific symbio... more The root nodules are a unique environment formed on legume roots through a highly specific symbiotic relationship between leguminous plants and nodule-inducing bacteria. Previously, Rhizobia were presumed to be the only group of bacteria residing within nodules. However, recent studies discovered diverse groups of bacteria within the legume nodules. In this report soybean nodule-associated bacteria were studied in an effort to identify beneficial bacteria for plant disease control and growth promotion. Analysis of surface-sterilized single nodules showed bacterial diversity of the nodule microbiome. Five hundred non-rhizobial colonies from 10 nodules, 50 colonies per nodule, were tested individually against the tomato wilt causing bacterial pathogen Clavibacter michiganensis subsp. michiganensis (Cmm) for inhibition of pathogen growth. From the initial screening, 54 isolates were selected based on significant growth inhibition of Cmm. These isolates were further tested in vitro on a...
Plant Health Progress
Minnesota is the top sugar beet (Beta vulgaris L.) producing state in the United States. In 2020,... more Minnesota is the top sugar beet (Beta vulgaris L.) producing state in the United States. In 2020, sugar beet plants were observed for the first time in which the two to three oldest leaves had light brown to dark brown necrotic leaf lesions that eventually became yellow or brown and died but remained attached to the plant. Morphological data and sequences of internal transcribed spacer regions identified the pathogen as Sclerotinia sclerotiorum. Because over 90% of the plants in identified fields were infected it was difficult to quantify loss in yield or quality caused by this disease. All fields with symptomatic plants had soybean or edible beans in the rotation. One field planted to several different varieties indicated that all the varieties were symptomatic. It will be useful to determine any economic loss caused by S. sclerotiorum and any known varietal resistance to this pathogen.
Journal of Agricultural Chemistry and Environment
Thymol, the key component of the thyme oil and its derivatives were evaluated for their structure... more Thymol, the key component of the thyme oil and its derivatives were evaluated for their structure activity relationship as fungicide against Rhizoctonia solani. Since plant-based chemicals are considered as "Generally Recognized as Safe" (GRAS) chemicals, there is great potential to use those and synthetic derivatives against R. solani and other fungal pathogens, in vitro, and in the greenhouse or field conditions. Among the six thymol derivatives evaluated, thymol acetate was considered as the most suitable commercially viable plant-based fungicide due to its superior efficacy as well as lowest residue.
American Journal of Plant Sciences
Annals of Plant Protection Sciences
HortTechnology
Clove oil derived from the clove plant [Syzygium aromaticum (=Eugenia caryophyllata)] is active a... more Clove oil derived from the clove plant [Syzygium aromaticum (=Eugenia caryophyllata)] is active against various soil-borne plant pathogens and therefore has potential for use as a bio-based pesticide. A clove oil formulation previously found to be toxic to the southern root-knot nematode (Meloidogyne incognita) in laboratory assays was investigated in greenhouse studies for nematode suppression and phytotoxicity on vegetable crops. Phytotoxicity studies were conducted with 0.1%, 0.2%, and 0.3% clove oil applied to soil 0, 2, 5, and 7 days before transplant of cucumber (Cucumis sativus), muskmelon (Cucumis melo), pepper (Capsicum annuum), and tomato (Solanum lycopersicum) seedlings. Tomato seedlings were the most sensitive to clove oil. The 0.2% and 0.3% clove oil concentrations applied as drenches at transplant (0 day) were the most phytotoxic to seedlings of all the tested vegetable species, with only 0% to 50% seedling survival. Most of the clove oil concentrations applied as dren...
European Journal of Plant Pathology
Journal of microbiological methods, 2018
Long-term preservation of experimental fungi without genetic, morphological, and pathogenic chang... more Long-term preservation of experimental fungi without genetic, morphological, and pathogenic changes is of paramount importance in mycological and plant pathological investigations. Several cryogenic and non-cryogenic methods are available for the preservation of fungi, but the methods can be cumbersome, hazardous, expensive, and often not suitable for long-term storage of non-spore-forming (sterile) fungi. A method of preservation of spore-forming fungi in commercially available porous beads (Micrbank™) under cryogenic condition was successfully tested for three non-spore-forming basidiomycetes genera: Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) (n = 19), Ceratobasidium species (n = 1), and Waitea circinata (n = 3), and a non-spore forming ascomycetes, Sclerotinia sclerotiorum (n = 1). For comparison, spore-forming ascomycetous fungi, Alternaria alternata (n = 1), Bauveria basiana (n = 2), Botrytis cinerea (n = 1), Fusarium oxysporum f.sp. gladiolii (n = 1), Trichoderma...
Plant Disease
Eight fungal isolates (ELRF 1 to 8) were recovered from necrotic roots of Easter lilies, Lilium l... more Eight fungal isolates (ELRF 1 to 8) were recovered from necrotic roots of Easter lilies, Lilium longiflorum cv. Nellie White, grown in a field in the U.S. Pacific Northwest. The eight fungal isolates were identified by sequencing and molecular phylogenetic analyses based on their ITS rDNA region. Five isolates were identified as Fusarium oxysporum, two as F. tricinctum, and one as Rhizoctonia sp. AG-I. This constitutes the first report of Rhizoctonia sp. AG-I infecting lilies worldwide and the first report of F. tricinctum infecting lilies in the United States. To study and validate their pathogenicity, pure cultures of each isolate were used to infect the roots of Easter lily plants growing in vitro. In addition, Easter lily plants growing in vitro were infected either with or without Pratylenchus penetrans, the root lesion nematode, prior to placing a culture plug of fungus 1 cm from a lily root. Pratylenchus penetrans is a nematode species commonly found in the sampled fields. Th...
BMC Genomics
Background: The biological control agent Aspergillus aculeatus Asp-4 colonizes and degrades scler... more Background: The biological control agent Aspergillus aculeatus Asp-4 colonizes and degrades sclerotia of Sclerotinia sclerotiorum resulting in reduced germination and disease caused by this important plant pathogen. Molecular mechanisms of mycoparasites underlying colonization, degradation, and reduction of germination of sclerotia of this and other important plant pathogens remain poorly understood. Results: An RNA-Seq screen of Asp-4 growing on autoclaved, ground sclerotia of S. sclerotiorum for 48 h identified 997 up-regulated and 777 down-regulated genes relative to this mycoparasite growing on potato dextrose agar (PDA) for 48 h. qRT-PCR time course experiments characterized expression dynamics of select genes encoding enzymes functioning in degradation of sclerotial components and management of environmental conditions, including environmental stress. This analysis suggested co-temporal up-regulation of genes functioning in these two processes. Proteomic analysis of Asp-4 growing on this sclerotial material for 48 h identified 26 up-regulated and 6 down-regulated proteins relative to the PDA control. Certain proteins with increased abundance had putative functions in degradation of polymeric components of sclerotia and the mitigation of environmental stress. Conclusions: Our results suggest co-temporal up-regulation of genes involved in degradation of sclerotial compounds and mitigation of environmental stress. This study furthers the analysis of mycoparasitism of sclerotial pathogens by providing the basis for molecular characterization of a previously uncharacterized mycoparasite-sclerotial interaction.
![Research paper thumbnail of Use of [32P]RNA probes for the dot-hybridization detection of potato spindle tuber viroid](https://attachments.academia-assets.com/73050969/thumbnails/1.jpg)
](Journal of Virological Methods, Dec 1, 1986
A dot-hybridization assay using 32P-labelled RNA probes (+RNA and cRNA) transcribed from potato s... more A dot-hybridization assay using 32P-labelled RNA probes (+RNA and cRNA) transcribed from potato spindle tuber viroid (PSTV) cDNA was described. A complete cDNA copy of PSTV, originally cloned in pBR 322 (pAV 401) was subcloned in the BamHI site of a 'Riboprobe' cloning vectors pSP 64 and pSP 65 in opposite orientations. The reconstructed plasmids were designated pDX 1 and pDX 4, respectively. Transcription of pDX 1 and pDX 4 plasmids by SP6 RNA polymerase resulted in the generation of PSTV-specific RNA (+RNA) and PSTV complementary RNA (cRNA), respectively. The cRNA probe was much more sensitive than the +RNA probe and the nick-translated cDNA probe from the plasmid pAV 401 for the detection of PSTV in clarified plant sap. As little as 1.4 pg of purified PSTV mixed in clarified sap from uninoculated tomato leaves has been detected using cRNA probe. A relatively simple procedure using cetyltrimethyl ammonium bromide (CTAB) as nucleic acid precipitant and an enrichment step for the purification of PSTV was described.
Phytopathology, 1985
... ABSTRACT Lakshman, D, K,, and (Jonsalves. D. 1985. ... mosaic virus(CM V)-C,CMV-N, and large-... more ... ABSTRACT Lakshman, D, K,, and (Jonsalves. D. 1985. ... mosaic virus(CM V)-C,CMV-N, and large-lesion mutant CMV-CI.#5 and CMV-NI.#I on some diagnostic hosts Host reactions1 Cucurbita CMV pepa isolates 'President' nicol fana I a bacimi 'Н-42Э' Cucumis sai ¡vus 'Marketer ...
Plant Disease, 2016
Environmentally friendly control measures for soilborne plant pathogens are needed that are effec... more Environmentally friendly control measures for soilborne plant pathogens are needed that are effective in different soils when applied alone or as components of an integrated disease control strategy. An ethanol extract of Serratia marcescens N4-5, when applied as a cucumber seed treatment, effectively suppressed damping-off caused by Pythium ultimum in potting mix and in a sandy loam soil. Plant stand associated with this treatment was similar to that of seed treated with the chemical pesticide Thiram in the sandy loam soil. The N4-5 ethanol extract did not consistently provide significant disease control in a loam soil. The N4-5 ethanol extract was compatible with two Trichoderma isolates, not affecting in vitro or in situ colonization of cucumber by these biological control fungi. Control of damping-off of cucumber was never diminished when this ethanol extract was applied as a seed treatment in combination with in-furrow application of the Trichoderma isolates, and disease contro...
Journal of Agricultural and Food Chemistry, 2016
Journal of Plant Pathology, Jan 11, 2010
Journal of Nematology, Sep 1, 2006
Extracts from the plants Plantago lanceolata and P. rugelii were evaluated for toxicity to the ro... more Extracts from the plants Plantago lanceolata and P. rugelii were evaluated for toxicity to the root-knot nematode Meloidogyne incognita, the beneficial microbes Enterobacter cloacae, Pseudomonas fluorescens and Trichoderma virens, and the plant-pathogenic fungi Fusarium oxysporum f. sp. gladioli, Phytophthora capsici, Pythium ultimum, and Rhizoctonia solani. Wild plants were collected, roots were excised from shoots, and the plant parts were dried and ground to a powder. One set of extracts (10% w/v) was prepared in water and another in methanol. Treatments included extract concentrations of 25%, 50%, 75% and 100%, and water controls. Meloidogyne incognita egg hatch was recorded after 7-day exposure to the treatments, and second-stage juvenile (J2) activity after 48 hours. All extracts were toxic to eggs and J2, with P. lanceolata shoot extract tending to have the most activity against M. incognita. Numbers of active J2 remained the same or decreased in a 24-hour water rinse following the 48-hour extract treatment, indicating that the extracts were lethal. When data from water- and methanol-extracted roots and shoots of both plant species were combined for analysis, J2 tended to be more sensitive than eggs to the toxic compounds at lower concentrations, while the higher concentrations (75% and 100%) were equally toxic to both life stages. The effective concentrations causing 50% reduction (EC50) in egg hatch and in J2 viability were 44.4% and 43.7%, respectively. No extract was toxic to any of the bacteria or fungi in our assays.
Plant Cell, Tissue and Organ Culture (PCTOC), 2015
Plants
The root nodules are a unique environment formed on legume roots through a highly specific symbio... more The root nodules are a unique environment formed on legume roots through a highly specific symbiotic relationship between leguminous plants and nodule-inducing bacteria. Previously, Rhizobia were presumed to be the only group of bacteria residing within nodules. However, recent studies discovered diverse groups of bacteria within the legume nodules. In this report soybean nodule-associated bacteria were studied in an effort to identify beneficial bacteria for plant disease control and growth promotion. Analysis of surface-sterilized single nodules showed bacterial diversity of the nodule microbiome. Five hundred non-rhizobial colonies from 10 nodules, 50 colonies per nodule, were tested individually against the tomato wilt causing bacterial pathogen Clavibacter michiganensis subsp. michiganensis (Cmm) for inhibition of pathogen growth. From the initial screening, 54 isolates were selected based on significant growth inhibition of Cmm. These isolates were further tested in vitro on a...
Plant Health Progress
Minnesota is the top sugar beet (Beta vulgaris L.) producing state in the United States. In 2020,... more Minnesota is the top sugar beet (Beta vulgaris L.) producing state in the United States. In 2020, sugar beet plants were observed for the first time in which the two to three oldest leaves had light brown to dark brown necrotic leaf lesions that eventually became yellow or brown and died but remained attached to the plant. Morphological data and sequences of internal transcribed spacer regions identified the pathogen as Sclerotinia sclerotiorum. Because over 90% of the plants in identified fields were infected it was difficult to quantify loss in yield or quality caused by this disease. All fields with symptomatic plants had soybean or edible beans in the rotation. One field planted to several different varieties indicated that all the varieties were symptomatic. It will be useful to determine any economic loss caused by S. sclerotiorum and any known varietal resistance to this pathogen.
Journal of Agricultural Chemistry and Environment
Thymol, the key component of the thyme oil and its derivatives were evaluated for their structure... more Thymol, the key component of the thyme oil and its derivatives were evaluated for their structure activity relationship as fungicide against Rhizoctonia solani. Since plant-based chemicals are considered as "Generally Recognized as Safe" (GRAS) chemicals, there is great potential to use those and synthetic derivatives against R. solani and other fungal pathogens, in vitro, and in the greenhouse or field conditions. Among the six thymol derivatives evaluated, thymol acetate was considered as the most suitable commercially viable plant-based fungicide due to its superior efficacy as well as lowest residue.
American Journal of Plant Sciences
Annals of Plant Protection Sciences
HortTechnology
Clove oil derived from the clove plant [Syzygium aromaticum (=Eugenia caryophyllata)] is active a... more Clove oil derived from the clove plant [Syzygium aromaticum (=Eugenia caryophyllata)] is active against various soil-borne plant pathogens and therefore has potential for use as a bio-based pesticide. A clove oil formulation previously found to be toxic to the southern root-knot nematode (Meloidogyne incognita) in laboratory assays was investigated in greenhouse studies for nematode suppression and phytotoxicity on vegetable crops. Phytotoxicity studies were conducted with 0.1%, 0.2%, and 0.3% clove oil applied to soil 0, 2, 5, and 7 days before transplant of cucumber (Cucumis sativus), muskmelon (Cucumis melo), pepper (Capsicum annuum), and tomato (Solanum lycopersicum) seedlings. Tomato seedlings were the most sensitive to clove oil. The 0.2% and 0.3% clove oil concentrations applied as drenches at transplant (0 day) were the most phytotoxic to seedlings of all the tested vegetable species, with only 0% to 50% seedling survival. Most of the clove oil concentrations applied as dren...
European Journal of Plant Pathology
Journal of microbiological methods, 2018
Long-term preservation of experimental fungi without genetic, morphological, and pathogenic chang... more Long-term preservation of experimental fungi without genetic, morphological, and pathogenic changes is of paramount importance in mycological and plant pathological investigations. Several cryogenic and non-cryogenic methods are available for the preservation of fungi, but the methods can be cumbersome, hazardous, expensive, and often not suitable for long-term storage of non-spore-forming (sterile) fungi. A method of preservation of spore-forming fungi in commercially available porous beads (Micrbank™) under cryogenic condition was successfully tested for three non-spore-forming basidiomycetes genera: Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) (n = 19), Ceratobasidium species (n = 1), and Waitea circinata (n = 3), and a non-spore forming ascomycetes, Sclerotinia sclerotiorum (n = 1). For comparison, spore-forming ascomycetous fungi, Alternaria alternata (n = 1), Bauveria basiana (n = 2), Botrytis cinerea (n = 1), Fusarium oxysporum f.sp. gladiolii (n = 1), Trichoderma...
Plant Disease
Eight fungal isolates (ELRF 1 to 8) were recovered from necrotic roots of Easter lilies, Lilium l... more Eight fungal isolates (ELRF 1 to 8) were recovered from necrotic roots of Easter lilies, Lilium longiflorum cv. Nellie White, grown in a field in the U.S. Pacific Northwest. The eight fungal isolates were identified by sequencing and molecular phylogenetic analyses based on their ITS rDNA region. Five isolates were identified as Fusarium oxysporum, two as F. tricinctum, and one as Rhizoctonia sp. AG-I. This constitutes the first report of Rhizoctonia sp. AG-I infecting lilies worldwide and the first report of F. tricinctum infecting lilies in the United States. To study and validate their pathogenicity, pure cultures of each isolate were used to infect the roots of Easter lily plants growing in vitro. In addition, Easter lily plants growing in vitro were infected either with or without Pratylenchus penetrans, the root lesion nematode, prior to placing a culture plug of fungus 1 cm from a lily root. Pratylenchus penetrans is a nematode species commonly found in the sampled fields. Th...
BMC Genomics
Background: The biological control agent Aspergillus aculeatus Asp-4 colonizes and degrades scler... more Background: The biological control agent Aspergillus aculeatus Asp-4 colonizes and degrades sclerotia of Sclerotinia sclerotiorum resulting in reduced germination and disease caused by this important plant pathogen. Molecular mechanisms of mycoparasites underlying colonization, degradation, and reduction of germination of sclerotia of this and other important plant pathogens remain poorly understood. Results: An RNA-Seq screen of Asp-4 growing on autoclaved, ground sclerotia of S. sclerotiorum for 48 h identified 997 up-regulated and 777 down-regulated genes relative to this mycoparasite growing on potato dextrose agar (PDA) for 48 h. qRT-PCR time course experiments characterized expression dynamics of select genes encoding enzymes functioning in degradation of sclerotial components and management of environmental conditions, including environmental stress. This analysis suggested co-temporal up-regulation of genes functioning in these two processes. Proteomic analysis of Asp-4 growing on this sclerotial material for 48 h identified 26 up-regulated and 6 down-regulated proteins relative to the PDA control. Certain proteins with increased abundance had putative functions in degradation of polymeric components of sclerotia and the mitigation of environmental stress. Conclusions: Our results suggest co-temporal up-regulation of genes involved in degradation of sclerotial compounds and mitigation of environmental stress. This study furthers the analysis of mycoparasitism of sclerotial pathogens by providing the basis for molecular characterization of a previously uncharacterized mycoparasite-sclerotial interaction.
Journal of Virological Methods, Dec 1, 1986
A dot-hybridization assay using 32P-labelled RNA probes (+RNA and cRNA) transcribed from potato s... more A dot-hybridization assay using 32P-labelled RNA probes (+RNA and cRNA) transcribed from potato spindle tuber viroid (PSTV) cDNA was described. A complete cDNA copy of PSTV, originally cloned in pBR 322 (pAV 401) was subcloned in the BamHI site of a 'Riboprobe' cloning vectors pSP 64 and pSP 65 in opposite orientations. The reconstructed plasmids were designated pDX 1 and pDX 4, respectively. Transcription of pDX 1 and pDX 4 plasmids by SP6 RNA polymerase resulted in the generation of PSTV-specific RNA (+RNA) and PSTV complementary RNA (cRNA), respectively. The cRNA probe was much more sensitive than the +RNA probe and the nick-translated cDNA probe from the plasmid pAV 401 for the detection of PSTV in clarified plant sap. As little as 1.4 pg of purified PSTV mixed in clarified sap from uninoculated tomato leaves has been detected using cRNA probe. A relatively simple procedure using cetyltrimethyl ammonium bromide (CTAB) as nucleic acid precipitant and an enrichment step for the purification of PSTV was described.
Phytopathology, 1985
... ABSTRACT Lakshman, D, K,, and (Jonsalves. D. 1985. ... mosaic virus(CM V)-C,CMV-N, and large-... more ... ABSTRACT Lakshman, D, K,, and (Jonsalves. D. 1985. ... mosaic virus(CM V)-C,CMV-N, and large-lesion mutant CMV-CI.#5 and CMV-NI.#I on some diagnostic hosts Host reactions1 Cucurbita CMV pepa isolates 'President' nicol fana I a bacimi 'Н-42Э' Cucumis sai ¡vus 'Marketer ...
Plant Disease, 2016
Environmentally friendly control measures for soilborne plant pathogens are needed that are effec... more Environmentally friendly control measures for soilborne plant pathogens are needed that are effective in different soils when applied alone or as components of an integrated disease control strategy. An ethanol extract of Serratia marcescens N4-5, when applied as a cucumber seed treatment, effectively suppressed damping-off caused by Pythium ultimum in potting mix and in a sandy loam soil. Plant stand associated with this treatment was similar to that of seed treated with the chemical pesticide Thiram in the sandy loam soil. The N4-5 ethanol extract did not consistently provide significant disease control in a loam soil. The N4-5 ethanol extract was compatible with two Trichoderma isolates, not affecting in vitro or in situ colonization of cucumber by these biological control fungi. Control of damping-off of cucumber was never diminished when this ethanol extract was applied as a seed treatment in combination with in-furrow application of the Trichoderma isolates, and disease contro...
Journal of Agricultural and Food Chemistry, 2016
Journal of Plant Pathology, Jan 11, 2010
Journal of Nematology, Sep 1, 2006
Extracts from the plants Plantago lanceolata and P. rugelii were evaluated for toxicity to the ro... more Extracts from the plants Plantago lanceolata and P. rugelii were evaluated for toxicity to the root-knot nematode Meloidogyne incognita, the beneficial microbes Enterobacter cloacae, Pseudomonas fluorescens and Trichoderma virens, and the plant-pathogenic fungi Fusarium oxysporum f. sp. gladioli, Phytophthora capsici, Pythium ultimum, and Rhizoctonia solani. Wild plants were collected, roots were excised from shoots, and the plant parts were dried and ground to a powder. One set of extracts (10% w/v) was prepared in water and another in methanol. Treatments included extract concentrations of 25%, 50%, 75% and 100%, and water controls. Meloidogyne incognita egg hatch was recorded after 7-day exposure to the treatments, and second-stage juvenile (J2) activity after 48 hours. All extracts were toxic to eggs and J2, with P. lanceolata shoot extract tending to have the most activity against M. incognita. Numbers of active J2 remained the same or decreased in a 24-hour water rinse following the 48-hour extract treatment, indicating that the extracts were lethal. When data from water- and methanol-extracted roots and shoots of both plant species were combined for analysis, J2 tended to be more sensitive than eggs to the toxic compounds at lower concentrations, while the higher concentrations (75% and 100%) were equally toxic to both life stages. The effective concentrations causing 50% reduction (EC50) in egg hatch and in J2 viability were 44.4% and 43.7%, respectively. No extract was toxic to any of the bacteria or fungi in our assays.
Plant Cell, Tissue and Organ Culture (PCTOC), 2015