Population genetic analysis reveals a low level of genetic diversity of 'Candidatus Phytoplasma aurantifolia' causing witches' broom disease in lime.

Rashid Al-Shariqi,Elham A Kazerooni,Abdullah M Al-Sadi,Mohammed S Al-Hammadi,Rashid A Al-Yahyai,Assunta Bertaccini,Shaikha Y Al-Abadi,Matthew Dickinson

doi:10.1186/s40064-016-3401-0

Abstract

Witches’ broom disease of lime (WBDL) is a serious phytoplasma disease of acid lime in Oman, the UAE and Iran. Despite efforts to study it, no systemic study attempted to characterize the relationship among the associated phytoplasma, ‘Candidatus Phytoplasma aurantifolia’, from the three countries. This study utilized sequences of the 16S rRNA, imp and secA genes to characterize 57 strains collected from Oman (38), the UAE (9) and Iran (10). Phylogenetic analysis based on the 16S rRNA gene showed that the 57 strains shared 98.5–100 % nucleotide similarity to each other and to strains of ‘Ca. P. aurantifolia’ available in GenBank. The level of genetic diversity was low based on the 16S rRNA (0-0.011), imp (0–0.002) and secA genes (0–0.015). The presence of low level of diversity among phytoplasma strains from Oman, the UAE and Iran can be explained by the movement of infected lime seedlings from one country to another through trading and exchange of infected plants. The study discusses implication of the findings on WBDL spread and management.

Highlights

Citrus fruits are among the most important fruits in the world due to their high nutritional value and possibility to be consumed fresh as well as processed
Witches’ broom disease (WBDL) is the most destructive disease of lime trees in Oman, the UAE and Iran (Chung et al 2006; Al-Yahyai et al 2015; Al-Sadi et al 2012b; Bové et al 2000) where it killed more than a million lime trees
‘Candidatus Phytoplasma aurantifolia’ is the phytoplasma associated with Witches’ broom disease of lime (WBDL) (Zreik et al 1995)

Summary

Introduction

Citrus fruits are among the most important fruits in the world due to their high nutritional value and possibility to be consumed fresh as well as processed. Orange trees are the most widely cultivated citrus species, with Brazil being the largest orange exporter in the world. Lime and lemon trees are cultivated extensively around the globe. With about 16 % of the world’s overall lemon and lime production, tops the production list, followed by Mexico (~14.5 %), Argentina (~10 %), Brazil (~8 %), and Spain (~7 %) (FAO 2015). Citrus aurantifolia Swingle, known locally as Omani lime, has many other names in other parts of the world, Witches’ broom disease (WBDL) is the most destructive disease of lime trees in Oman, the UAE and Iran (Chung et al 2006; Al-Yahyai et al 2015; Al-Sadi et al 2012b; Bové et al 2000) where it killed more than a million lime trees. WBDL was first observed in Shinas and Liwa in the northern coast of Al-Batinah

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