|Jarret, Robert - Bob|
Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/7/1999
Publication Date: 6/1/2000
Citation: Jarret, R.L. Newman, M. Phylogenetic relationships among species of citrullus and the placement of C. Rehmii de Winter as determined by internal transcribed spacer (ITS) sequence heterogeneity. Genetic resources and crop evolution, 2000, vol 47, pg 215-222. Interpretive Summary: A new species of plant related to the cultivated watermelon was recently found in the Namib Desert in Southern Africa. We compared this plant with the cultivated watermelon and other plants known to be related to the watermelon. Our analysis indicated that this newly described plant (Citrullus rehmii) is very closely related to the watermelon. The close relationship between this new species and the cultivated watermelon indicates that it may be useful as a source of genes for improving the cultivated watermelon.
Technical Abstract: The internal transcribed spacer regions (ITS1 and ITS2) of the 18S-25S nuclear ribosomal DNA from 4 species of Citrullus (C. Lanatus var. Lanatus (Thunb.) Matsum. & Nakai., C. lanatus var. citroides (Bailey) Mansf., C. colocynthis (L.) Schrad., C. ecirrhosus Cogn., and C. rehmii De Winter), Acanthosicycos naudiniamus (Sond.) C. Jeffrey, and Cucumis melo (L.) were amplified by PCR, and direct sequenced. Within the taxa examined, the length of ITS1 varied from 216 bp to 219 bp, and ITS2 varied from 239 bp to 249 bp. The average %CG content ranged from 55 to 64% and from 61 to 65% for ITS1 and ITS2, respectively. The greater length variation observed in ITS2 was primarily attributable to the occurrence of a (CC)n microsatellite. Cladistic (PAUP) and phenetic (MEGA) analyses resulted in highly resolutive trees. ITS sequence analysis placed the recently described C. rehmii adjacent to the cultivated watermelon and supported the evalidity of the species classification of this taxa.