RESUMO
Coconut lethal yellowing disease (CLY) has had a devastating effect on the coconut (Cocos nucifera L.) industry in Jamaica and Latin America. A study was conducted in Jamaica during 2005 to identify alternate hosts of the CLY phytoplasma. Since weeds are known to act as reservoir hosts of numerous pathogens, Vernonia cinerea (L.) (Asteraceae), a prevalent weed species on coconut farms island-wide, was collected from coconut farms in areas of high and low levels of CLY incidence, although none of the plants displayed disease symptoms. DNA was extracted from plant samples by the method of Dellaporta et al. (1) and analyzed by nested PCR assay employing phytoplasma universal rRNA operon primers P1/P7 (2,4) and LY16Sf/LY16-23Sr (3). DNA derived from CLY-diseased or healthy coconut palm served as positive and negative controls, respectively, in each assay. Amplification of an rDNA product of the expected size (1.7 kb) confirmed phytoplasma infections in 53 of 118 (44.9%) V. cinerea test plants. Twenty-seven of the rDNA PCR products were analyzed by digestion with restriction enducleases RsaI, MspI, MseI, TaqI, HinfI, and HhaI. The restriction fragment length polymorphism profiles obtained were similar to that observed in the CLY-infected coconut palm. V. cinerea rDNA amplicons were cloned and sequenced (in both directions) and a representative sequence was deposited in GenBank (Accession No. EU057983). Blast analysis determined this sequence to be most similar (99%) to that of CLY phytoplasma in Jamaica (Accession No. AF49807) and Florida (Accession No. AF498309). To our knowledge, this is the first report of the 16Sr IV group of phytoplasmas infecting V. cinerea. Presence of the lethal yellowing phytoplasmas in dicotyledonous plant species has important epidemiological implications concerning vector identity and ecology. Futhermore, it is now evident that weed control on coconut farms could assist in the management of CLY disease in Jamaica. References: (1) S. L. Dellaporta et al. Plant Mol. Biol. Rep. 1:19, 1993. (2) S. Deng and C. Hiruki. J. Microbiol. Methods 14:53, 1991. (3) N. A. Harrison et al. Ann. Appl. Biol. 141:183, 2002. (4) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996.
RESUMO
In September 1998, tomato plants in Barbados exhibited symptoms of severe leaf curling without marginal chlorosis. These symptoms were often associated with an increase in whitefly (Bemisia tabaci) populations. DNA was extracted from leaf tissue from symptomatic tomato plants. Polymerase chain reaction (PCR) was performed with DNA-A degenerate primer pair PAC1v1978/PAV1c715, which amplifies part of the rep gene, the cp gene, and the common region (CR), and with DNA-B primer pair PBC1v2039/PBV1c800, which amplifies part of the bc1 and bv1 genes and the CR (2). The amplified PCR fragments of DNA-A and DNA-B were 1.3 and 1.4 kb, respectively, which are the expected sizes from bipartite, whitefly-transmitted geminiviruses of the Western Hemisphere (2). DNA sequence of the cloned fragments of DNA-A and DNA-B are available as GenBank No. AF213013 and AF213014, respectively. The 181 nucleotides of the CR of DNA-A had a nucleotide identity of 96% with the CR of DNA-B, which indicates that this is a bipartite begomovirus. Pairwise comparisons using DNASTAR (DNASTAR, Madison, WI) of the sequenced part of DNA-A was most similar to Cabbage leaf curl virus (CaLCuV, 69%, U65529) and Squash leaf curl virus extended host range isolate (SqLCV-E, 64%, M38183), and <59% to 13 other bipartite Western Hemisphere geminiviruses and Tomato yellow leaf curl virus from Israel (X15656). Pairwise comparisons of the DNA-B fragment sequence was 59 and 55% similar to CaLCuV (U65530) and SqLCV-E (M38182), respectively. Phylogenetic analysis of DNA-A of the major groups of Western Hemisphere begomoviruses placed the Barbados tomato-infecting geminivirus in the cluster with CaLCuV and SqLCV-E (1), while DNA-B analysis placed it with CaLCuV. The DNA-A amplified fragment was used as a probe at high stringency with the dot blot hybridization assay using the Genius II labeling and detection kit (Boeringer Mannheim) to detect this geminivirus in tomato and several other plant species, which had typical geminiviral symptoms. Strong hybridization signals were obtained for all 23 tomato plants with symptoms, weak signals were observed for two of three muskmelon and two of seven watermelon plants, all with leaf curling symptoms. No hybridization signals were observed for peppers with leaf curling symptoms and two weed species, Macroptilium lathyroides and Rhynchosia minima, with golden mosaic symptoms or with the symptomless plant species used as negative controls. The weak signals observed from watermelon and muskmelon samples indicated the presence of low virus titer or geminiviruses distinct from this tomato virus. The presence of viral DNA in these two plant species was confirmed by PCR with degenerate primers described above. Resulting database searches of sequences in the GenBank revealed that the Barbados tomato virus appears to be a previously unreported virus. This new virus is given the provisional name Tomato leaf curl Barbados virus (ToLCBBV). References: (1) J. C. Faria et al. Phytopathology 84:321, 1994. (2) M. R. Rojas et al. Plant Dis. 77:340, 1993.
RESUMO
OBJECTIVE: Examine the effects of asynchronously activating motor units of the human quadriceps femoris muscle during electrical stimulation. METHODS: Two stimulation channels were used to activate the muscle. One pair of electrodes was placed over the vastus medialis (Channel 1) and another pair was placed over the vastus lateralis (Channel 2). All contractions were isometric. The stimulation frequency was 10 Hz for each channel and the effect of varying the delay between the two channels was tested. RESULTS: Synchronous activation of both channels produced the greatest forces and stimulating the muscle 180 degrees out of phase (ie, with a 50-msec delay) produced the least forces. CONCLUSIONS: Activating motor units asynchronously under certain conditions will be less efficient than synchronous activation. This study, therefore, helps to define the boundary conditions when asynchronous stimulation may be helpful.
