Development of a non-radiometric method for measuring the arterial input function of a C-11-labeled PET radiotracer

Positron emission tomography (PET) uses radiotracers to quantify important biochemical parameters in human subjects. A radiotracer arterial input function (AIF) is often essential for converting brain PET data into robust output measures. For radiotracers labeled with carbon-11 (t(1/2)=20.4 min), AIF is routinely determined with radio-HPLC of blood sampled frequently during the PET experiment. There has been no alternative to this logistically demanding method, neither for regular use nor validation. A C-11-labeled tracer is always accompanied by a large excess of non-radioactive tracer known as carrier. In principle, AIF might be obtained by measuring the molar activity (A(m); ratio of radioactivity to total mass; Bq/mol) of a radiotracer dose and the time-course of carrier concentration in plasma after radiotracer injection. Here, we implement this principle in a new method for determining AIF, as shown by using [C-11]PBR28 as a representative tracer. The method uses liquid chromatography-tandem mass spectrometry for measuring radiotracer A(m) and then the carrier in plasma sampled regularly over the course of a PET experiment. A(m) and AIF were determined radiometrically for comparison. The new non-radiometric method is not constrained by the short half-life of carbon-11 and is an attractive alternative to conventional AIF measurement

Selection of downy mildew resistant somaclones, from a susceptible B line of pearl millet

Plants regenerated from seed-derived callus of a PNMS 6B line of pearl millet (Pennisetum glaucum (L.) R. Br.) were evaluated for their resistance induced by somaclonal variation for downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroter. Among the 201 lines regenerated, only 3 lines consistently proved highly resistant (free from disease incidence) for up to 5 generations; whereas, 17 lines were resistant (disease incidence ranging from 1 to 9%). Resistance was confirmed by testing the plants under both laboratory and field conditions. The plants were evaluated for their agronomic traits

Transmission of seed-borne infection of chilli by Burkholderia solanacearum and effect of biological seed treatment on disease incidence

A survey of chilli fields in the state of Karnataka, India, showed the presence of bacterial wilt disease in important chilli growing regions. The disease incidence ranged from 26-32%. The pathogen was isolated from infected plant material and seeds. Infected plant material showed the release of milky white bacterial ooze. Burkholderia solanacearum was detected from chilli seeds by liquid assay and its identity was confirmed by biochemical tests, hypersensitive reaction and pathogenicity tests. Seed transmission of the pathogen up to 45% was observed in seeds artificially infested with the pathogen. Among different tissues of the seed, endosperm showed the presence of the pathogen. Biological seed treatment with antagonistic Pseudomonas fluorescens significantly (p=0.05) improved the seed quality parameters under laboratory conditions and drastically reduced the bacterial wilt incidence under field conditions. Seed-borne nature, transmission and effect of Pseudomonas fluorescens in both the forms of pure culture and formulation on seed quality parameters and bacterial wilt incidence are discussed in the present work

Lytic activity in pearl millet: its role in downy mildew disease resistance, Plant Sci. 157 (2000) 33–41

Abstract Sclerospora graminicola causes downy mildew disease in susceptible pearl millet. Molecular basis of downy mildew disease resistance has been studied. Coleoptile region has been shown earlier to be the most susceptible site for attack by the pathogen. Lytic activity is differentially expressed in the coleoptile region of 3-day-old pearl millet seedlings of resistant and susceptible cultivars. Significantly higher levels of lytic factors were measured in the coleoptile region of resistant cultivars (100%) than in that of susceptible cultivars (20%). Both constitutive and inducible lytic factors were observed in different resistant cultivars, and they were able to lyse the pathogen. The level of lytic activity correlated well with the degree of resistance as evaluated by field screening studies. The present study, therefore, proposes that lytic factors found in the coleoptile region of the pearl millet seedling, are responsible for the lysis of the pathogen in the resistant plant, and may therefore provide resistance to downy mildew disease. This study also provides a simple method to evaluate downy mildew resistance in pearl millet cultivars

Selection of downy mildew resistant somaclones, from a susceptible B line of pearl millet

Plants regenerated from seed-derived callus of a PNMS 6B line of pearl millet (Pennisetum glaucum (L.) R. Br.) were evaluated for their resistance induced by somaclonal variation for downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroter. Among the 201 lines regenerated, only 3 lines consistently proved highly resistant (free from disease incidence) for up to 5 generations; whereas, 17 lines were resistant (disease incidence ranging from 1 to 9%). Resistance was confirmed by testing the plants under both laboratory and field conditions. The plants were evaluated for their agronomic traits

Lytic activity in pearl millet: Its role in downy mildew disease resistance

Sclerospora gramninicola causes downy mildew disease in susceptible pearl millet. Molecular basis of downy mildew disease resistance has been studied. Coleoptile region has been shown earlier to be the most susceptible site for attack by the pathogen. Lytic activity is differentially expressed in the coleoptile region of 3-day-old pearl millet seedlings of resistant and susceptible cultivars. Significantly higher levels of lytic factors were measured in the coleoptile region of resistant cultivars (100%) than in that of susceptible cultivars (20%). Both constitutive and inducible lytic factors were observed in different resistant cultivars, and they were able to lyse the pathogen. The level of lytic activity correlated well with the degree of resistance as evaluated by field screening studies. The present study, therefore, proposes that lytic factors found in the coleoptile region of the pearl millet seedling, are responsible for the lysis of the pathogen in the resistant plant, and may therefore provide resistance to downy mildew disease. This study also provides a simple method to evaluate downy mildew resistance in pearl millet cultivars. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved

Biocontrol of downy mildew disease of pearl millet using Pseudomonas fluorescens

Pseudomonas fluorescens was tested against pearl millet downy mildew disease by treating seeds with a pure culture and formulated in talc powder. The bioagent was also tested as a foliar spray to pearl millet under greenhouse and field conditions. Treated seeds increased seedling vigour and inhibited sporulation of downy mildew pathogen. P. fluorescens controlled downy mildew disease both by seed treatment and foliar application, but efficacy was significantly higher when seed treatment was followed by a foliar application. Seed treatment was better than foliar application alone

Characterization of fast-decaying PET radiotracers solely through LC-MS/MS of constituent radioactive and carrier isotopologues

BACKGROUND: The characterization of fast-decaying radiotracers that are labeled with carbon-11 (t(1/2) = 20.38 min), including critical measurement of specific radioactivity (activity per mole at a specific time) before release for use in positron-emission tomography (PET), has relied heavily on chromatographic plus radiometric measurements, each of which may be vulnerable to significant errors. Thus, we aimed to develop a mass-specific detection method using sensitive liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) for identifying (11)C-labeled tracers and for verifying their specific radioactivities. METHODS: The LC-MS/MS was tuned and set up with methods to generate and measure the product ions specific for carbon-11 species and M + 1 carrier (predominantly the carbon-13 isotopologue) in four (11)C-labeled tracers. These radiotracers were synthesized and then analyzed before extensive carbon-11 decay. The peak areas of carbon-11 species and M + 1 carrier from the LC-MS/MS measurement and the calculated abundances of carbon-12 carrier and M + 1 radioactive species gave the mole fraction of carbon-11 species in each sample. This value upon multiplication with the theoretical specific radioactivity of carbon-11 gave the specific radioactivity of the radiotracer. RESULTS: LC-MS/MS of each (11)C-labeled tracer generated the product ion peaks for carbon-11 species and M + 1 carrier at the expected LC retention time. The intensity of the radioactive peak diminished as time elapsed and was undetectable after six half-lives of carbon-11. Measurements of radiotracer-specific radioactivity determined solely by LC-MS/MS at timed intervals gave a half-life for carbon-11 (20.43 min) in excellent agreement with the value obtained radiometrically. Additionally, the LC-MS/MS measurement gave specific radioactivity values (83 to 505 GBq/μmol) in good agreement with those from conventional radiometric methods. CONCLUSIONS: (11)C-Labeled tracers were characterized at a fundamental level involving isolation and mass detection of extremely low-abundance carbon-11 species along with the M + 1 carrier counterpart. This LC-MS/MS method for characterizing fast-decaying radiotracers is valuable in both the development and production of PET radiopharmaceuticals

Transmission of seed-borne infection of muskmelon by Didymella bryoniae and effect of seed treatments on disease incidence and fruit yield

Infected muskmelon plants were collected and a fungus was isolated during field survey of muskmelon conducted in 4th, 5th, and 6th agroclimatic zones of Karnataka state. The pathogen was identified as Didymella bryoniae upon incubation on potato dextrose agar plates. The pathogen causes gummy stem blight disease in muskmelon. Spore concentration of 12×105ml−1 was found to be very effective in reestablishment of the pathogen upon artificial inoculation. The pathogen was located both externally and internally on the seed. Naturally infected seeds were subjected to transmission studies in vitro and in vivo. Four fungicides and two biological agents were evaluated for their efficacy against gummy stem blight disease incidence and fruit yield in field conditions. In water agar, primary seedling infection occurred on hypocotyls and cotyledons while pycnidia on ungerminated seeds and stunted seedling were also noticed due to severity of the infection. Typical symptoms expressed from 35 to 67 days after sowing until harvest experimentally, the fungus was more prevalent at the collar region of the plant. Mean disease incidence from all the cultivars significantly reduced except Bavistin (Carbendazim 50 WP), among which fungicides Dithane M-45 0.2 (Mancozeb 75 WP) and Wanis 0.3 significantly (P=0.001) reduced the disease incidence where only 10.2 and 13.0, disease was recorded, respectively and severity of gummy stem blight compared with Captaf 0.3 (Captan 50 WP) with 24.2 disease, whereas Bavistin (Carbendazim 50 WP) seed treatment was par with the control. Among antagonists, Pseudomonas fluorescens applied as pure culture (1×108cfuml−1) and formulation of (26×107cfug−1) at the rate of 8 and 10gkg−1 significantly (P=0.001) reduced the disease incidence, which showed 17.7, 21.5, and 20.5, disease respectively. On the contrary pure culture of Trichoderma harzianum (1×108cfuml−1) recorded 18.2 D. bryoniae incidence followed by its formulation (21×107cfug−1), which recorded 24.0 and 21.2 disease in 8 and 10gkg−1, respectively. Mean fruit weight from all the tested cultivars were increased at higher concentration (0.3) by as much as 265g in Dithane M-45, 154g in Captaf and only 55g in Bavistin treated seeds, while Wanis treatment resulted in decreased fruit weight when compared to untreated control. Seeds treated with P. fluorescens both as pure culture and formulation significantly (P=0.001) effective in increasing the fruit yield by 370, 350, and 363g, respectively. Though slight decrease in the yield was noticed in T. harzianum both as pure culture and formulation were significantly (P=0.001) effective in increasing the fruit yield. However, both P. fluorescens and T. harzianum treatments showed significant increase in fruit weight over fungicides and untreated seeds