Genetic variability among isolates of Coconut lethal yellowing phytoplasmas determined by heteroduplex mobility assay (HMA)

Heteroduplex mobility assay (HMA) was used to determine genomic diversity among African isolates of coconut lethal yellowing phytoplasmas causing Cape St. Paul wilt disease (CSPD, Ghana), lethal disease (LD, Tanzania), and lethal yellowing (LYM, Mozambique). They were also compared to the Caribbean phytoplasma associated with coconut lethal yellowing (LY). A DNA fragment of 1850 bp covering the 16S rRNA gene and 16/23S intergenic spacer region of each isolate was amplified with primers P1 and P7 and subsequently submitted to HMA analysis for sequence variation. A PCR product amplified from GH5D (CSPD isolate) as a reference was combined with each PCR product and electrophoresed on polyacrylamide gels. Three groups of phytoplasmas associated with various coconut lethal yellowing diseases were identified by HMA. The samples from Mozambique (LYM) and Ghana (CSPD) formed one group, which was different from the second group, LD from Tanzania. These two groups were different from the third group of Caribbean isolates. This grouping was consistent with the genetic diversity described in the coconut yellowing-associated phytoplasmas detected after cloning, sequencing, and phylogenetic analyses. The HMA technique described here has the potential to provide a simple and rapid means to identify and to establish the diversity of isolates within the coconut lethal yellowing disease group. (Résumé d'auteur