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Margaret Pooler and John S. Hartung

Xylella fastidiosa is a fastidious gram-negative, xylem-limited, leafhopper-transmitted bacterium that has proven to be the casual agent of many economically important diseases, including Pierce's disease of grapevine and citrus variegated chlorosis. Genetic relationships among 11 Xylella fastidiosa strains isolated from mulberry, almond, ragweed, grape, plum, elm, and citrus were determined using random amplified polymorphic DNA (RAPD). Twenty-two 10 base primers amplified a total of 77 discrete polymorphic bands. Phenetic analysis based on a similarity matrix corresponded well with previous reports on X. fastidiosa RFLP-based similarity relationships, indicating that RAPD-PCR amplification products can be used as a reliable indicator of genetic distance in X. fastidiosa. Cladistic analysis suggests the existence of five groups of X. fastidosa: the citrus group, the plum-elm group, the grape-ragweed group, the almond group, and the mulberry group.

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Margaret R. Pooler and John S. Hartung

Xylella fastidiosa is a fastidious gram-negative, xylem-limited leafhopper-transmitted bacterium that has proven to be the causal agent of many economically important horticultural plant diseases, including Pierce's disease of grapevine and citrus variegated chlorosis. Genetic relationships among 11 X. fastidiosa strains isolated from mulberry, almond, ragweed, grape, plum, elm, and citrus were determined using randomized amplified polymorphic DNA (RAPD). Twenty-two 10-base primers amplified a total of 77 discrete polymorphic bands. Phenetic analysis based on a similarity matrix corresponded well with previous reports on RFLP-based similarity relationships, indicating that RAPD-PCR amplification products can be used as a reliable indicator of genetic distance in X. fastidiosa. RAPD products have been cloned and sequenced, and pairs of 21-nucleotide PCR primers have been developed that detect X. fastidiosa in general and the causal agent of citrus variegated chlorosis specifically.

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Amnon Levi, Lisa J. Rowland and John S. Hartung

A procedure for identifying reproducible RAPD markers from woody plant DNA is presented. The procedure relies on using a PCR buffer that contains 1% Triton-X-100 and 0.1 % gelatin [previously described for successful polymerase chain reaction (PCR) amplification of 16S/23S rRNA intergenic spacer regions from eubacteria], and amplification conditions of 50 cycles: 30 sec at 94C, 70 sec at 48C, and 120 sec at 72C. The combination of this buffer and these conditions amplified consistent fragments in higher amounts, as compared to other standard PCR buffers and conditions generally used for RAPD analysis. This procedure resulted in reliable RAPD patterns for all organisms tested. Chemical name used: α-[4-(1,1,3,3,-tetramethylbutyl)phenyl]-cohydroxypoly(oxy-l,2-ethanediyl) (Triton-X-l00).

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John L. Maas, John S. Hartung, Cristina Gouin-Behe and Stan C. Hokanson

Bacterial angular leafspot disease (BALD) of strawberry (Fragaria sp. and F. ×ananassa Duchesne cultivars) has become increasingly destructive to strawberry fruit and plant production in Canada and the United States, as well as in other countries. The disease, caused by Xanthomonas fragariae Kennedy and King, was first documented in Minnesota in 1960, and has become of worldwide concern because of the economic impact of BALD in strawberry fruit and nursery-plant production and the lack of adequate disease control strategies. We tested 81 Fragaria genotypes, including representatives of F. ×ananassa, F. chiloensis (L.) Duchesne, F. virginiana Duchesne, and F. vesca L., for resistance to two pathogenic strains of X. fragariae. Two genotypes, a native F. virginiana from Minnesota and an F. virginiana × F. ×ananassa hybrid, were found to resist infection by both bacterial strains and may be potential sources of resistance to other strains of X. fragariae.