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S.D. Reid, M. Ali-Ahmad, and H.G. Hughes

The use of random amplified polymorphic DNA (RAPD) markers has been shown to be a potentially useful technique for identifying buffalograss breeding lines. Analysis of RAPD markers has also revealed considerable variation within, as well as among, each of four natural buffalograss populations surveyed. Identification of genetic markers for quantitative traits, such as physiological components of tolerance to salt stress, can provide important information for plant improvement programs. The objectives of this study were to develop DNA fingerprints for buffalograss clones selected from an in vitro seedling screening program for survival at high NaCI (200–250 mM) levels, identify markers for future analysis, and assess the variability among the lines. DNA was extracted from leaves of 10 salt-selected and 15 non-selected buffalograss clones. Fifty-two 10-mer primers were screened for ability to produce bands with DNA from four clones as visualized on ethidium-stained agarose gels. Bands were most reproducible with a genomic template DNA concentration of 1 ngμl–1 reaction volume. Primers selected for ability to produce a moderate number of clear bands were used to produce RAPD profiles of the 25 clones. Abundant polymorphism to distinguish among clones was found. Four primers produced a total of 45 polymorphic markers. The primer 5′-CGGAGAGCCC-3′ produced 11 readily scored markers, allowing identification in 94.67% of pair-wise comparisons. As a group, RAPD profiles of salt-selected clones are more variable than non-selected clones from the same population; however, no unique pattern of markers generated by primers screened to date differentiates all salt-selected clones from the non-selected group.

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Y. Liu, B.S. Patil, H. Ahmad, and D.T. Gardiner

Pectin is a class of complex polysaccharides that function as hydrating agents and cementing materials for the cellulose network. Pectin has various health benefits, such as decreasing serum cholesterol levels, alleviating diabetes mellitus, and preventing cancer. It has been reported that the cancer prevention effect is closely related to the structure of pectin (galactose-rich, molecular weight <10,000, and methylation degree 50% to 70%). This study was conducted to investigate the variation of grapefruit pectin content due to harvest time. `Rio Red' grapefruit on sour orange rootstock grown at Texas A&M Univ.-Kingsville Citrus Center were harvested every 2 months and analyzed for pectin content, galacturonic acid concentration, methylation degree, and neutral sugar composition. Results showed that lamella contains more pectin than flavedo and albedo. In the lamella, the edible section, the uronic acid content ranged from 85% to 90% from August to April the following year. Methylation degree increased from August (31.89%) to April (46.99%). Total neutral sugar content of lamella pectin decreased from 110.54 to 61.77% mg·g -1. Galactose, arabinose, and rhamnose are the major sugar contents of pectin (85%), and glucose content increased with the season from 3.14 to 13.34 mg·g-1. Molecular weight of pectin was also determined.

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Ahmad A. Omar, Wen-Yuan Song, James H. Graham, and Jude W. Grosser

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.