Phylogenetic relationships among species of Citrullus and the placement ofC-rehmii De Winter as determined by Internal Transcribed Spacer (ITS) sequence heterogeneity

The internal transcribed spacer regions (ITS1 and ITS2) of the 18S-25S nucl ear ribosomal DNA from the four recognized 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) and Acanthosicycos naudinianus (Sond.) C. Jeffrey were amplified b y PCR, and direct sequenced. Within the taxa examined, the length of ITS1 v aried from 216 bp to 219 bp, and ITS2 varied from 239 bp to 249 bp. The ave rage %CG content ranged from 59 to 64% and from 62 to 66% for ITS1 and ITS2 , respectively. The greater length variation observed in ITS2 was primarily attributable to the occurrence of a (CC)(n) microsatellite. Cladistic (PAU P) and phenetic (MEGA) analyses resulted in highly resolutive trees. ITS se quence analysis placed the recently described C. rehmii adjacent to the cul tivated watermelon and supported the validity of the species classification of this taxa.