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Jinguo Hu, Beiquan Mou, and Brady A. Vick

Target region amplified polymorphism (TRAP) markers were used to evaluate genetic variability among 48 accessions of spinach (Spinacia oleracea L.), an economically important leafy vegetable crop in many countries. Thirty-eight accessions collected and preserved by the USDA National Plant Germplasm System (NPGS) and 10 commercial hybrids were used in the current study. For assessing genetic diversity within accessions, DNA samples were prepared from nine to 12 individual seedlings from six germplasm accessions and two hybrids. Relatively high levels of polymorphism was found within accessions based on 61 polymorphic TRAP markers generated with two fixed primers derived from the Arabidopsis-type telomere repeat sequence and two arbitrary primers. For evaluating inter-accession variability, DNA was extracted from a bulk of six to 10 seedlings of each accession. Of the 1092 fragments amplified by 14 primer combinations, 96 (8.8%) were polymorphic and discriminated the 48 accessions from each other. The average pair-wise genetic similarity coefficient (Dice, Nei) was 57.5% with a range from 23.2 to 85.3%. A dendrogram was constructed based on the similarity matrix. It was found that the genetic relationships were not highly correlated with the geographic locations in which the accessions were collected. However, seven commercial hybrids were grouped in three separate clusters, suggesting that the phenotype-based breeding activities have effect on the genetic variability. This study demonstrated that TRAP markers are effective for fingerprinting and evaluating genetic variability of spinach germplasm.

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Zhanao Deng, Jinguo Hu, Fahrettin Goktepe, Brady A. Vick, and Brent K. Harbaugh

Cultivated caladiums are valued for their bright colorful leaves and are widely used in containers and landscapes. More than 1500 named cultivars have been introduced during the past 150 years, yet currently only about 100 cultivars are in commercial propagation in Florida. Caladium tubers produced in Florida account for 95% of the world supplies. Loss of caladium germplasm or genetic diversity has been a concern to future improvement of this plant. In addition, the relationship among the available cultivars, particularly those of close resemblance, has been lacking. This study was conducted to assess the genetic variability and relationship in commercial cultivars and species accessions. Fifty-seven major cultivars and 15 caladium species accessions were analyzed using the target region amplification polymorphism marker technique. This marker system does not involve DNA restriction or adaptor linking, but shares the same high throughput and reliability with the amplified fragment length polymorphism system (AFLP). Eight primer combinations amplified 379 scorable DNA fragments among the caladium samples. A high level of polymorphism was detected among the species accessions as well as among cultivars. These markers allowed differentiation of all the cultivars tested, including those hardly distinguishable morphologically. Clustering analysis based on these DNA fingerprints separated the cultivars into five clusters and Caladium lindenii far from other caladium species. The availability of this information will be very valuable for identifying and maintaining the core germplasm resources and will aid in selecting breeding parents for further improvement.