Phylogenetic and population genetic analysis of Ceratocystis radicicola infecting date palms

A study was conducted to investigate the genetic diversity of C. radicicola from different regions of Oman and its relationship to populations of C. radicicola from other parts in the Arabian peninsula and the USA. A total of 32 C. radicicola isolates from Oman (23), the United Arab Emirates (UAE) (2), Kuwait (1) and the USA (6) were analyzed using sequences of the internal transcribed spacer region of the ribosomal DNA (ITS rDNA) and amplified fragment length polymorphism (AFLP). AFLP analysis of the 32 isolates produced 32 different genotypes and 999 polymorphic alleles (100% polymorphism). The Omani population of C. radicicola was found to be more genetically diverse (H = 0.274) than the USA population (H = 0.186), which may suggest a longer history of C. radicicola in Oman. UPGMA analysis based on Nei's genetic distance as well as phylogenetic analysis based on ITS rDNA sequences separated the USA isolates from those from Oman, UAE and Kuwait with a very high bootstrap support. This was supported by low to moderate levels of genetic differentiation between populations of C. radicicola within the Arabian peninsula (FST = -0.0297-0.1341) as compared with high levels of genetic differentiation (FST = 0.2939-0.3913) of the population from the USA. These findings may imply that populations of C. radicicola from the USA and the Arabian peninsula have been evolving independently for a considerably long period of time as opposite to constant gene flow between regions in the Arabian peninsula. Analysis of molecular variance (AMOVA) showed that genetic variation is more associated with geographical regions (F_ST = 0.1807, P < 0.0001) than hosts (F_ST = 0.0307, P = 0.1681), which may imply the lack of host "cultivar" specialization in C. radicicola.