Genetic analysis of 'Candidatus Phytoplasma aurantifolia' associated with witches' broom on acid lime trees.

Aisha G Al-Ghaithi,Issa H Al-Mahmooli,Abdullah M Al-Sadi,Ali M Al-Subhi

doi:10.7717/peerj.4480

Abstract

“Candidatus Phytoplasma aurantifolia” is associated with witches’ broom disease of lime in Oman and the UAE. A previous study showed that an infection by phytoplasma may not necessarily result in the physical appearance of witches’ broom symptoms in some locations in Oman and the UAE. This study investigated whether phytoplasma strains belonging to “Ca. P. aurantifolia” (based on the 16S rRNA gene analysis) in locations where disease symptoms are expressed are different from phytoplasma in locations where disease symptoms are not expressed. About 21 phytoplasma strains (15 from areas and trees with disease symptoms and six from areas and trees without disease symptoms) were included in the analysis. The study utilized sequences of the imp and SAP11 genes to characterize the 21 strains. Phylogenetic analysis of both genes showed that the 21 strains are similar to each other and to reference strains in GenBank. The study shows that there is a low level of diversity among all phytoplasma strains. In addition, it shows that phytoplasma in places where witches’ broom symptoms are not expressed are similar to phytoplasma in places where disease symptoms are expressed. This may suggest that disease expression is not linked to the presence of different phytoplasma strains, but may be due to other factors such as weather conditions.

Highlights

Phytoplasmas are prokaryotic gram-positive bacteria that are difficult to be cultured in artificial media (Contaldo et al, 2012, 2016)
Phylogenetic analysis of phytoplasma strains based on SAP11 gene Amplification using the primer pair SAP11-w-F2/and SAP11-w-R2 produced a fragment of 339 bp (Fig. 2)
Based on SAP11 gene sequences showed that all samples clustered together with the reference isolates belonging to “Ca. P. aurantifolia” (Fig. 3)

Summary

Introduction

Phytoplasmas are prokaryotic gram-positive bacteria that are difficult to be cultured in artificial media (Contaldo et al, 2012, 2016) They are phloem limited and transmitted by phloem-sucking insects of the order Hemiptera, mostly leafhoppers (Cicadellidae), planthoppers (Fulgoroidea), and psyllids (Psyllidae) (Frost et al, 2013; Rashidi et al, 2014; Queiroz et al, 2016). They have a wide range of host plants from over 100 plant families, including many citrus species (Hogenhout et al, 2008).

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