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  • Author or Editor: H.H. Wen x
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In an anthracnose [Colletotricum obiculare (Berk. & Mont.) Arx.] screening test of 76 plant introductions (PIs), commercial Chinese watermelons [Citrullus lanatus (Thunb.) Matsum. & Nakai], and `Crimson Sweet', PI 512385 had the highest disease resistance with a mean rating of 4.5 (1= resistant, 9 = susceptible). In a second test with PI 512385, which included material with previously reported resistance (PIs 270550,326515, 271775,271779,203551, 299379, and 189225), and `Crimson Sweet' (susceptible control), PI 512385 had significantly higher resistance than `Crimson Sweet' but was not significantly more resistant than the other PIs evaluated. PI 512385 had a mean rating of 2.2 in the second test.

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Citrus canker disease caused by the bacterial pathogen Xanthomonas axonopodis pv. citri is becoming a worldwide problem. Xa21 gene is a member of the Xa21 gene family of rice, which provides broad spectrum Xanthomonas resistance in rice. `Hamlin' sweet orange [Citrus sinensis (L.) Osbeck) is one of the leading commercial cultivars in Florida because of its high yield potential and early maturity. `Hamlin' also has a high regeneration capacity from protoplasts and is often used in transformation experiments. Since the citrus canker pathogen is in the same genus, this gene may have potential to function against canker in citrus. The wild-type Xa21 gene contains an intron, and there are some questions whether dicot plants can process genes containing monocot introns (the cDNA is intron-free). Plasmids DNA, encoding the non-destructive selectable marker EGFP (Enhanced Green Fluorescent Protein) gene and the cDNA of the Xa21 gene were transformed or co-transformed into `Hamlin' orange protoplasts using polyethylene glycol. More than 200 transgenic embryoids were recovered. More than 400 transgenic plants were developed from 75 independent transgenic events. PCR analysis revealed the presence of the cDNA of the Xa21 and the GFP genes in the transgenic plants. Some of the plants have the GFP only. Southern analysis is showing integration of the cDNA into different sites ranges from one to five sites. Western analysis is showing the expression of the cDNA of the Xa21 gene in the transgenic citrus plants. This is the first time that a gene from rice has been stably integrated and expressed in citrus plants. Canker challenge assay is in progress.

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