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Potato virus Y (PVY) is a reemerging problem in potato production in North America. Although the "ordinary" strain, PVYO, is still the dominant isolate in U.S. seed potatoes, the recombinant strain of the virus PVYN-Wi (= PVYN:O) has become widespread. An increase in the prevalence of a PVY strain could be due to differences in the efficiency of transmission by aphid vectors. The transmission efficiency by a clone of Myzus persicae was determined for five isolates each of PVYO and PVYN-Wi. An aphid transmission assay was developed based on the use of potato seedlings from true potato seed, allowing for greater control of plant age and growth stage. No apparent differences in transmission by M. persicae were observed. Single isolates of PVYO and PVYN-Wi were tested for their ability to be transmitted from potato to potato by five aphid species: Aphis glycines, A. gossypii, A. nasturtii, M. persicae, and Rhopalosiphum padi. Both PVY isolates showed a similar transmission phenotype in being transmitted efficiently by M. persicae but very poorly or not at all by A. glycines, A. gossypii, and R. padi. The aphid A. nasturtii transmitted both isolates with an intermediate level of efficiency. The data do not support a model for a differential aphid transmissibility being responsible for the increase in the prevalence of PVYN-Wi.

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Carrot purple leaf disease was first reported in 2006 in the state of Washington and was associated with Spiroplasma citri. The disease also was reported in California in 2008. The objectives of this work were to fulfill Koch's postulates and to determine 1) whether the beet leafhopper, Circulifer tenellus (Baker) (Hemiptera: Cicadellidae), transmits carrot [Daucus carota L. subsp. Sativus (Hoffm.) Arcang] isolates of S. citri; and 2) whether carrot and citrus [Citrus sinensis (L.) Osb.]-derived spiroplasmas are pathogenic to both plant species. C. tenellus adults received a 24-h acquisition access period to a diet containing carrot-derived S. citri. After 30 d, insects were transferred to healthy carrot seedlings (five per plant). Negative controls were carrot and periwinkle [Catharanthus roseus (L.) G. Don] plants exposed to diet-only-fed insects, and positive controls were periwinkle plants exposed to insects fed on spiroplasma-supplemented diet. Purple carrot leaves and small, chlorotic periwinkle leaves were evident 10-45 d after exposure. Spiroplasmas were reisolated only from symptomatic plants, and polymerase chain reaction (PCR) confirmed their identity as S. citri. No symptoms occurred, and no spiroplasma-specific PCR amplifications or spiroplasma cultures were obtained from plants exposed to diet only-fed insects. Carrot-derived S. citri was transmitted to 15 and 50% of carrot and periwinkle plants exposed, respectively. Insects exposed to S. citri isolates from carrot or citrus transmitted the pathogen to both their host of origin and to the other plant host (carrot or citrus), showing no isolate-host specificity. Our findings confirm that carrot is a host of S. citri. Although carrot is not a preferred host of C. tenellus, it is likely that inoculative leafhoppers feed on carrot during seasonal migration.

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Spiroplasma citri, a phloem-limited pathogen, causes citrus stubborn disease (CSD). Losses due to CSD in California orchards have grown over the past decade. To investigate the possibility of introduction or emergence of a new strain, a study of genetic diversity among S. citri strains from various locations was conducted using random amplified polymorphism DNA-polymerase chain reaction (RAPD-PCR) of 35 strains cultured from 1980 to 1993, and of 35 strains cultured from 2005 to 2006. Analysis using 20 primer pairs revealed considerable diversity among strains. However, no unique genetic signatures were associated with recently collected strains compared with those collected 15 to 28 years ago, and no geographically associated pattern was distinguishable. S. citri strains from carrot and daikon radish contain some unique DNA fragments, suggesting some host plant influence. Multiple strains from single trees also showed genetic diversity. Sequencing of five RAPD bands that differed among strains showed that diversity-related gene sequences include virus fragments, and fragments potentially encoding a membrane lipoprotein, a DNA modification enzyme, and a mobilization element. No differences in colony morphology were observed among the strains. The lack of correlation between PCR patterns and isolation date or collection site is inconsistent with the hypothesis that recent infections are due to the introduction or emergence of novel pathogen strains.

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Triphenyltetrazolium chloride (TTC) staining and echocardiography (ECHO) are methods used to determine experimental myocardial infarction (MI) size, whose practical applicability should be expanded. Our objectives were to analyze the accuracy of ECHO in determining infarction size in rats during the first days following coronary occlusion and to test whether a simplified single measurement by TTC correctly indicates MI size, as determined by the average value for multiple slices. Infarction was induced in female Wistar rats by coronary artery occlusion and MI size analysis was performed after the acute (7th day) and chronic periods (after 4 weeks) by ECHO matched with TTC. ECHO and TTC showed similar values of MI size ( percent of left ventricle perimeter) in acute (ECHO: 33 ± 11, TTC: 35 ± 14) and chronic (ECHO: 38 ± 14, TTC: 39 ± 13 periods), and also presented an excellent correlation (r = 0.92, P < 0.001). Although measurements from different heart planes showed discrepancies, a single measurement acquired from the mid-ventricular level by TTC was a good estimate of MI size calculated by the average of multiple planes, with minimal disagreement (Bland-Altman test with mean ratio bias of 0.99 ± 0.07) and close to an ideal correlation (r = 0.99, P < 0.001). In the present study, ECHO was confirmed as a useful method for the determination of MI size even in the acute phase. Also, the single measure of a mid-ventricular section proposed as a simplification of the TTC method is a satisfactory prediction of average MI extension.

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RESUMEN

Triphenyltetrazolium chloride (TTC) staining and echocardiography (ECHO) are methods used to determine experimental myocardial infarction (MI) size, whose practical applicability should be expanded. Our objectives were to analyze the accuracy of ECHO in determining infarction size in rats during the first days following coronary occlusion and to test whether a simplified single measurement by TTC correctly indicates MI size, as determined by the average value for multiple slices. Infarction was induced in female Wistar rats by coronary artery occlusion and MI size analysis was performed after the acute (7th day) and chronic periods (after 4 weeks) by ECHO matched with TTC. ECHO and TTC showed similar values of MI size (% of left ventricle perimeter) in acute (ECHO: 33 +/- 11, TTC: 35 +/- 14) and chronic (ECHO: 38 +/- 14, TTC: 39 +/- 13 periods), and also presented an excellent correlation (r = 0.92, P < 0.001). Although measurements from different heart planes showed discrepancies, a single measurement acquired from the mid-ventricular level by TTC was a good estimate of MI size calculated by the average of multiple planes, with minimal disagreement (Bland-Altman test with mean ratio bias of 0.99 +/- 0.07) and close to an ideal correlation (r = 0.99, P < 0.001). In the present study, ECHO was confirmed as a useful method for the determination of MI size even in the acute phase. Also, the single measure of a mid-ventricular section proposed as a simplification of the TTC method is a satisfactory prediction of average MI extension.

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