Population genetic analysis reveals a low level of genetic diversity of \u2018Candidatus Phytoplasma aurantifolia\u2019 causing witches\u2019 broom disease in lime.

Witches\u2019 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, \u2018Candidatus Phytoplasma aurantifolia\u2019, 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\u2013100 % nucleotide similarity to each other and to strains of \u2018Ca. P. aurantifolia\u2019 available in GenBank. The level of genetic diversity was low based on the 16S rRNA (0-0.011), imp (0\u20130.002) and secA genes (0\u20130.015). 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

Development and morphological changes in leaves and branches of acid lime (Citrus aurantifolia) affected by witches\u2019 broom disease

Witches\u2019 broom (WB), associated with the presence of \u2018Candidatus Phytoplasma aurantifolia\u2019, is one of the most serious diseases of acid lime. This study determined incidence, distribution, and development of the dis-ease, and morphological changes in leaves and branches of affected host plants. Survey in different parts of Oman showed that WB occurs in most regions in the country, where 108 out of 158 (68%) surveyed farms were found to have diseased trees. A survey of 6,926 acid lime trees showed that severity of WB was positively related (r = 0.948; P<0.01) to tree age. The mean percentage of symptomatic branches was 1% in 3-year-old trees compared to 63% in 12-year-old trees. To further characterize morphological changes in WB-affected limes, apical stems (40 cm long) were collected from three infected trees during the autumn of 2009 and spring of 2010. Increases in the numbers of leaves (1,208%), numbers of branches (309%) and total length of branches (712%) were recorded for symptomatic branches relative to non-symptomatic branches. In the spring of 2009 these respective increases were 159%, 243% and 121%.Overall area of leaves in the symptomatic branches was 81% less than for non-symptomatic branches in the autumn of 2009 and 34% less in the spring of 2010. This study is the first to characterize morphological changes in leaves and branches of acid lime affected by WB