Assessment of the genetic diversity of Frankia microsymbionts of Elaeagnus angustifolia L. plants growing in a Tunisian date-palm oasis by analysis of PCR amplified nifD-K intergenic spacer

Diversity of Frankia microsymbionts of non-native Elaeagnus angustifolia L. plants spontaneously growing in a Tunisian desertic retreat area, the date-palm oasis of Tozeur, was investigated by polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP) and PCR-sequencing techniques targeting the nifD-K intergenic spacer. Three PCR-RFLP haplotypes (I, II, and III) were detected among collected nodules. Haplotype I was detected at all five sampling sites and dominated the other haplotypes present at these sites. This haplotype was also exhibited by strain BMG5.10, which was isolated by a plant-capturing assay in 1998 from soil collected in the same locality, qualifying it to be the most competitive haplotype in the edapho-climatic condition of the studied desertic date-palm oasis. nifD-K sequences of the three haplotypes formed a closely related phylogenetic subgroup. These results suggest that Frankia variability is constrained by severe edapho-climatic conditions of retreated desert in Tunisian area.