First Report of Pseudomonas viridiflava Causing a Bacterial Blight of Artichoke Bract Leaves.

In 2006, a disease was observed on two artichoke (Cynara scolymus L. cv. Lardati) fields in Crete, Greece, covering ~2 ha. Symptoms developed after several days of rainy and windy weather and >70% of capitula were affected, resulting in unmarketable produce. Initial symptoms were water-soaked, dark green spots on bracts with many sunken, necrotic, often elongated lesions, each with a brown-black center and surrounded by a water-soaked halo with a dark red-brown margin. Symptoms were more severe on inner bracts. Isolations from symptomatic, surface-disinfected bracts onto King's B agar medium (KB) consistently yielded yellow bacterial colonies that produced a green-blue fluorescent pigment. Ten selected artichoke isolates, all gram-negative, presented the LOPAT profile (- - + - +) and were levan negative, oxidase negative, potato rot positive, arginine dihydrolase negative, and showed tobacco hypersensitive reaction. All isolates used L-arabinose, D(-)-tartrate, and L-lactate, but not sucrose, L(+)-tartrate, or trigonelline. Results were identical to those obtained with the reference strain of Pseudomonas viridiflava NCPPB 1249 (3), and strains PV3005 and PV3006 from eggplant (1). Based on these biochemical tests, 10 isolates were identified as P. viridiflava group II members of the LOPAT determinative scheme of Lelliott (1,2). Two artichoke isolates (PV608 and PV609) were selected for molecular characterization. The identity and phylogenetic analysis were determined by multilocus sequence typing with the gyrB, rpoD, and rpoB genes (PV608 Accession Nos. JN383375, JN383363, and JQ267546; PV609 Accession Nos. JN383376, JN383364, and JQ267547). BLAST searches showed highest nucleotide sequence identity (96%) with GenBank sequences of P. viridiflava reference strains NCPPB 963 and CFBP 2107. Pathogenicity of 10 artichoke isolates and reference strains was tested twice on detached capitulum bracts of artichoke cv. Lardati, as well as 4-week-old tomato plants of cv. ACE, and Chrysanthemum indicum cv. Reagan plants. Each isolate was inoculated onto 10 bracts by placing 15 µl of bacterial suspension (5 × 106 CFU/ml) of a 48-h culture in KB broth on the surface of the bract, and pricking the bract through the drop of bacterial suspension with a sterile needle. Each isolate was also inoculated onto five tomato and five chrysanthemum plants by dipping a sterile toothpick in the appropriate bacterial culture and pricking the surface of the stem. Ten control plants were inoculated similarly with sterile, distilled water. Inoculated bracts and plants were kept in boxes lined with moist filter paper at 25 to 30°C and 80 to 100% relative humidity. Lesions developed on detached bracts within 72 h and were similar to those observed on the naturally infected plants. On tomato and chrysanthemum plants, pith necrosis and wilting symptoms were induced within 1 week of inoculation. Symptoms were not observed on control bracts and plants. Bacterial colonies were reisolated from bract lesions and stems with pith necrosis, but not from control plants, and the reisolates had the same LOPAT profile as the original isolates of P. viridiflava, thus fulfilling Koch's postulates. To our knowledge, this is the first report in the world of P. viridiflava causing a disease of artichoke bracts. References: (1) D. E. Goumas et al. Eur. J. Plant Pathol. 104:181, 1998. (2) Lelliott et al. J. Appl. Bacteriol. 29:470, 1966. (3) M. L. Saunier et al. Appl. Environ. Microbiol. 62:2360, 1996.

The role of bulking agent in pile methane and carbon dioxide concentration during wastewater sludge windrow composting.

Wastewater sludge and wood chips were used as feedstock for the construction of two piles, Pile I ("PI") and Pile II ("PII"), at a ratio of 1:1 and 1:2 v/v, respectively. Each pile was originally 1.3-m high, 2.0-m wide, and approximately 9.0-m long. A mechanical turner was used to turn the two windrows every 1 to 2 weeks. Three 500-mL-volume glass funnels were inverted and introduced into each pile: one in the core (named, respectively, "PIC" and "PIIC"), one at the top ("PIT" and "PIIT"), and one at the side ("PIS" and "PIIS"). Every 2 to 3 days, gas samples were collected using gas-tight syringes and analyzed in a gas chromatograph determining carbon dioxide (CO2) and methane (CH4) concentrations. An average gas concentration value between turnings was calculated and a two-way analysis of variance test was used to determine the significance of the differences between piles and pile location, followed by a Post Hoc Tukey test. During the thermophilic period, the mean CO2 concentration in PIC was 103 mL/L, 65 mL/L in PIT, and 24 mL/L in PIS, whereas, for PII, these values were 102mL/L, 59 mL/L, and 24 mL/L, respectively. The mean CH4 concentration between turnings in PIC was 9.2 mL/L, 1.9 mL/L in PIT, and 0.9 mL/L in PIS, whereas, for PII, the corresponding values were 6.4 mL/L, 0.4 mL/L, and 0.1 mL/L. For methane, there were no significant differences between these mean values, not only between the same placement in different piles, but also between different placements and different piles. This is probably due to the relatively frequent turnings (10 turnings during a period of 100 days), which did not allow the development of more anaerobic pockets in PI than in PII, indicating that both piles had similar greenhouse gas impacts. Results for carbon dioxide were similar in both piles, with some differentiation appearing between the core and top placements compared to the side placement. Reduction of the decomposition rate further from the core and a typical windrow chimney effect (gases from the core flowing through the top) explain this similarity between placements. The similarity between piles can be explained by the similar amounts of easily decomposable organic matter found in both piles, indicating that the effect of the bulking agent ratio on the concentration of gases within the pile was not significant.

Evaluating the use of electrical resistivity imaging technique for improving CH(4) and CO(2) emission rate estimations in landfills.

In order to improve the estimation of surface gas emissions in landfill, we evaluated a combination of geophysical and greenhouse gas measurement methodologies. Based on fifteen 2D electrical resistivity tomographies (ERTs), longitudinal cross section images of the buried waste layers were developed, identifying place and cross section size of organic waste (OW), organic waste saturated in leachates (SOW), low organic and non-organic waste. CH(4) and CO(2) emission measurements were then conducted using the static chamber technique at 5 surface points along two tomographies: (a) across a high-emitting area, ERT#2, where different amounts of relatively fresh OW and SOW were detected, and (b) across the oldest (at least eight years) cell in the landfill, ERT#6, with significant amounts of OW. Where the highest emission rates were recorded, they were strongly affected by the thickness of the OW and SOW fraction underneath each gas sampling point. The main reason for lower than expected values was the age of the layered buried waste. Lower than predicted emissions were also attributed to soil condition, which was the case at sampling points with surface ponding, i.e. surface accumulation of leachate (or precipitated water).