Navegando por Autor "Dhingra, Onkar D."
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Item Effect of soil temperature, moisture, and nitrogen on competitive saprophytic ability of Macrophomina phaseolina Author links open overlay panel(Transactions of the British Mycological Society, 1981) Dhingra, Onkar D.; Chagas, DaniloThe effect of soil temperature, moisture and nitrogen on saprophytic colonization of bean or wheat stems by Macrophomina phaseolina was studied in two soils. Maximum colonization of the substrate units occurred at 15–20° and decreased with increasing soil temperature. At 15° more wheat than bean stems were colonized whereas at higher temperatures the reverse occurred. Maximum colonization of substrates occurred at 15–25% of moistureholding capacity, and percentage colonization decreased with increasing soil moisture. Addition of nitrogen to soil completely inhibited saprophytic colonization.Item Ergosterol accumulation and oil quality changes in stored soybean invaded by Aspergillus ruber (A. glaucus group)(Mycopathologia, 1998-11-03) Dhingra, Onkar D.; Jham, Gulab; Napoleão, Ivani T.Soybean seed samples inoculated with spores of Aspergillus ruber were stored for 20 to 140 days at 25 ± 1 °C with moisture content varying from 11.3% to 17.7%. Seeds were colonised by the fungus within 20 days at all moisture levels. Ergosterol concentration in seeds increased with time of storage, being slow in samples with moisture content of 11.3% to 13.1% and more rapidly in those with higher moisture content. Free fatty acid (FFA) content also increased following the pattern of ergosterol. Equations were used to predict minimum safe storage period of the seeds at 25 °C. The rise in FFA is due to increase of A. ruber mass within the seed. Fungal growth did not affect fatty acids profiles or iodine index of the extracted oil. The results suggest revision of the present recommendations regarding seed moisture during storage. The FFA concentration of a seed lot can be used as a sensitive indicator of seed deterioration due to storage fungi.Item Glucosinolate content and nematicidal activity of Brazilian wild mustard tissues against Meloidogyne incognita in tomato(Plant and Soil, 2011-04) Oliveira, Rosângela D. L.; Dhingra, Onkar D.; Lima, André O.; Jham, Gulab N.; Berhow, Mark A.; Holloway, Ray K.; Vaughn, Steven F.The wild mustard (Brassica juncea L.), an invasive weed of winter crops in Brazil, was evaluated for glucosinolate content of its plant tissues and nematicidal activity of its dry leaf meal (LM), whole seed meal (WSM) and hexane defatted seed meal (DSM) against Meloidogyne incognita on tomato plants. Sinigrin was the major glucosinolate in LM, WSM and DSM, occurring at concentration of 0.11, 12.2 and 21.9 mg/gdw, respectively. Allyl isothiocyanate (AITC) was the major degradation product and its concentration was highest in DSM followed by WSM and LM. The number of galls, egg masses and eggs on tomato plants was reduced by over 90% by amending soil with 1.6% LM, 0.2% WSM, or 0.05% DSM. Exposure to the volatiles from the amended soils reduced egg eclosion. The soil amendment with LM, WSM and DSM killed the second stage juveniles of M. javanica, M. enterolobii (=M. mayaguensis) and Heterodera glycines. The efficacy of the LM, WSM and DSM for nematode suppression was related to the amount of AITC released in soil.Item In vitro production of conidia of Alternaria solani(Tropical Plant Pathology, 2010-07) Rodrigues, Tatiana T. M. S.; Maffia, Luiz A.; Dhingra, Onkar D.; Mizubuti, Eduardo S. G.Sporulation of Alternaria solani can be scarce and is often reduced when the fungus is cultivated in vitro. A series of experiments were conducted to assess the effects of moisture, mycelial wounding, light quality and photoperiod, and culture media on conidial production. A procedure to induce sporulation based on mycelial wounding and dehydration was adapted and validated. Best results were obtained when fungal colonies were grown in V8 medium at 25ºC in the dark with agitation for seven days; the mycelium mass was ground, poured into potato dextrose agar (pH 6.5) in plates, and incubated at 25 ± 2ºC under near ultraviolet light and 12 h-photoperiod. The procedure was validated with 30 isolates of A. solani from different hosts, sampling locations, ages, and storage conditions. Conidial production, germination, and infectivity were quantified. Seventy-five percent of the isolates sporulated and the lowest germination rate was 68%. Inoculations of conidial suspension of all isolates resulted in lesions on tomato and potato plants. The effect of subculturing on A. solani sporulation was also assessed. After six subcultures, every seven days, there was no reduction in sporulation of colonies that were induced with the protocol.Item Population changes of Macrophomina phaseolina in amended soils(Transactions of the British Mycological Society, 1980-06) Santos Filho, Edgar; Dhingra, Onkar D.Population changes of Macrophomina phaseolina (Tassi) Goid. were followed in two soils amended with either wheat, corn, bean or alfalfa straw, or with nitrogen-enriched wheat straw or glucose and sodium nitrate at different C:N ratios. The population declined significantly initially in both soils with any amendment but later increased in soils amended with wheat or corn straw and in one soil amended with bean or alfalfa straw. Population declined with no subsequent increase when soil was amended with nitrogen-enriched wheat straw or glucose and sodium nitrate at C:N ratios equal to that of the natural plant residues. In general the population declined more rapidly when soil was amended with nitrogen-enriched wheat straw or glucose and nitrogen than if amended with either corn, bean or alfalfa straw and when soil was amended with low C:N ratios.Item Selection of endemic nonpathogenic endophytic Fusarium oxysporum from bean roots and rhizosphere competent fluorescent Pseudomonas species to suppress Fusarium-yellow of beans(Biological Control, 2006-10) Dhingra, Onkar D.; Coelho-Netto, Rosalee A.; Rodrigues, Fabrício Á.; Silva Jr., Geraldo J.A less resource intensive procedure was used to select an endophytic non-pathogenic isolate of Fusarium oxysporum (NPFo) and an antibiotic producing rhizosphere/rhizoplane (RS-RP) competent fluorescent pseudomonad to suppress Fusarium yellow (F. oxysporum (Schlecht) f. sp. phaseoli Kendrick and Snyder) of bean (Phaseolus vulgaris L.). Using the combined criteria of in vitro and in planta competitiveness resulted in selection of three isolates for determination of their disease suppressing attributes. Several isolates of fluorescent pseudomonads obtained from RS-RP and internal root tissues of bean were tested for antibiosis in vitro. The isolates producing large inhibition zones were selected to determine RS-RP competence through seed treatment. The three most competent isolates were tested for their capacity to reduce root colonization by the pathogen, which resulted in the selection of only one isolate, identified as Pseudomonas putida (Trevisan) Migula biotype A. The NPFo isolates Fo10 and Fo6 endophytically occupied about 80% of the root length compared to only 60% by the isolate Fo16. Mixing chlamydospores of Fo10 in non-sterile field soil, reduced RS-RP and internal root colonization by the pathogen by 95 and 89%, respectively. In the greenhouse trial, mixing chlamydospores of either of the three NPFo isolates, the area under the chlorophyll retention curve (AUCRC) increased significantly with Fo10 compared to Fo6 or F16, over the positive control. The grain yield/plants from Fo10 treated soil was 177 or 291% higher than from Fo6-soil or positive control, respectively, but remained 50% lower than in pathogen-free negative control soil. In the field plots with pathogen ID of 850 ± 150/g soil, mixing chlamydospores of Fo10 (4250 ± 113/g), increased AUCRC and grain yield by about 100% over the control. However, if the bean seeds were treated with P. putida, the grain yield increased by 211% without further increase in AUCRC. The suppressive effect of Fo10 on disease development appeared to be related to its high saprophytic competitiveness with the pathogen in the soil matrix, which resulted in lower ID in the root zone, and parasitic competitiveness by reducing the availability of infection sites and internal root colonization by the pathogen. Seed treatment with P. putida provided additional protection in the root zone.Item Selection of endemic nonpathogenic endophytic Fusarium oxysporum from bean roots and rhizosphere competent Xuorescent Pseudomonas species to suppress Fusarium-yellow of beans(Biological Control, 2006-04-25) Dhingra, Onkar D.; Coelho-Netto, Rosalee A.; Rodrigues, Fabrício Á.; Silva Jr., Geraldo J.; Maia, Claúdio B.A less resource intensive procedure was used to select an endophytic non-pathogenic isolate of Fusarium oxysporum (NPFo) and an antibiotic producing rhizosphere/rhizoplane (RS-RP) competent fluorescent pseudomonad to suppress Fusarium yellow (F. oxysporum (Schlecht) f. sp. phaseoli Kendrick and Snyder) of bean (Phaseolus vulgaris L.). Using the combined criteria of in vitro and in planta competitiveness resulted in selection of three isolates for determination of their disease suppressing attributes. Several isolates of fluorescent pseudomonads obtained from RS-RP and internal root tissues of bean were tested for antibiosis in vitro. The isolates producing large inhibition zones were selected to determine RS-RP competence through seed treatment. The three most competent isolates were tested for their capacity to reduce root colonization by the pathogen, which resulted in the selection of only one isolate, identified as Pseudomonas putida (Trevisan) Migula biotype A. The NPFo isolates Fo10 and Fo6 endophytically occupied about 80% of the root length compared to only 60% by the isolate Fo16. Mixing chlamydospores of Fo10 in non-sterile field soil, reduced RS-RP and internal root colonization by the pathogen by 95 and 89%, respectively. In the greenhouse trial, mixing chlamydospores of either of the three NPFo isolates, the area under the chlorophyll retention curve (AUCRC) increased significantly with Fo10 compared to Fo6 or F16, over the positive control. The grain yield/plants from Fo10 treated soil was 177 or 291% higher than from Fo6-soil or positive control, respectively, but remained 50% lower than in pathogen-free negative control soil. In the field plots with pathogen ID of 850 ± 150/g soil, mixing chlamydospores of Fo10 (4250 ± 113/g), increased AUCRC and grain yield by about 100% over the control. However, if the bean seeds were treated with P. putida, the grain yield increased by 211% without further increase in AUCRC. The suppressive effect of Fo10 on disease development appeared to be related to its high saprophytic competitiveness with the pathogen in the soil matrix, which resulted in lower ID in the root zone, and parasitic competitiveness by reducing the availability of infection sites and internal root colonization by the pathogen. Seed treatment with P. putida provided additional protection in the root zone.Item Wild brazilian mustard (Brassica juncea L.) seed oil methyl esters as biodiesel fuel(Journal of the American Oil Chemists' Society, 2009-07-03) Jham, Gulab N.; Moser, Bryan R.; Shah, Shailesh N.; Holser, Ronald A.; Dhingra, Onkar D.; Vaughn, Steven F.; Berhow, Mark A.; Winkler-Moser, Jill K.; Isbell, Terry A.; Holloway, Ray K.; Walter, Erin L.; Natalino, Ricardo; Anderson, Jason C.; Stelly, David M.Wild mustard (Brassica juncea L.) oil is evaluated as a feedstock for biodiesel production. Biodiesel was obtained in 94 wt.% yield by a standard transesterification procedure with methanol and sodium methoxide catalyst. Wild mustard oil had a high content of erucic (13(Z)‐docosenoic; 45.7 wt.%) acid, with linoleic (9(Z),12(Z)‐octadecadienoic; 14.2 wt.%) and linolenic (9(Z),12(Z),15(Z)‐octadecatrienoic; 13.0 wt.%) acids comprising most of the remaining fatty acid profile. The cetane number, kinematic viscosity, and oxidative stability (Rancimat method) of the methyl esters was 61.1, 5.33 mm^2 s^−1 (40 °C) and 4.8 h (110 °C), respectively. The cloud, pour and cold filter plugging points were 4, −21 and −3 °C, respectively. Other properties such as acid value, lubricity, free and total glycerol content, iodine value, Gardner color, specific gravity, as well as sulfur and phosphorous contents were also determined and are discussed in light of biodiesel standards ASTM D6751 and EN 14214. Also reported are the properties and composition of wild mustard oil, along with identification of wild mustard collected in Brazil as Brassica juncea L. (2n = 36) as opposed to the currently accepted Sinapis arvensis L. (2n = 18) classification. In summary, wild mustard oil appears to be an acceptable feedstock for biodiesel production.