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“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.

"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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Acid lime (Citrus aurantifolia) is the fourth largest fruit crop in terms of cultivated area and production in Oman. However, over half a million lime trees were lost in Oman over the past 35 years due to witches’ broom disease of lime (WBDL) which is caused by Candidatus phytoplasma aurantifolia. This study was conducted to examine genetic diversity of acid lime in Oman. AFLP analysis of 143 acid lime samples from Oman, 2 from Brazil and one from Pakistan using 4 primer pair combinations produced 980 polymorphic loci (100 %) and 146 AFLP genotypes. Despite the long history of acid lime cultivation in Oman, populations of lime from different districts were found to have low levels of genetic diversity (0.0888–0.2284). AMOVA analysis indicated the existence of high level of genetic differentiation (FST = 0.271) among populations of acid lime from Oman and Brazil, which indicates that both populations have evolved independently for a considerably long period of time. On the other hand, AMOVA analysis showed that only 11 % of the genetic variation exists among populations from the 18 different districts in Oman. This suggests frequent exchange of acid lime planting material across geographical regions in Oman. Findings from this study suggest that the low level of genetic diversity of acid lime in Oman and frequent movement of acid lime planting material across districts are two main factors which contributed to the rapid spread and high susceptibility of acid limes to WBDL in the country. [ABSTRACT FROM AUTHOR]

The leafhopper Hishimonus phycitis has received considerable attention as a vector of witches' broom disease of lime phytoplasma. In the present study, nine polymorphic microsatellite loci were isolated from a repeat-enriched genomic library of H. phycitis. The number of alleles varied between 2 and 4 with an average of 2.80 per locus. The observed and expected heterozygosities ranged from 0.28 to 0.84 and 0.28 to 0.80, respectively. The Polymorphism Information Content varied from 0.25 to 0.75 with an average of 0.55. These microsatellites will be useful for future genetic studies of H. phycitis populations and could help in the development of an efficient control strategy against this vector. [ABSTRACT FROM AUTHOR]

Witches' broom disease of lime (WBDL), caused by 'Candidatus Phytoplasma aurantifolia', is a very serious disease of acid limes. The disease destroyed more than one million lime trees in the Middle East. WBDL results in the production of small, clustered leaves in some branches of lime trees. Branches develop symptoms with time and become unproductive, until the whole tree collapses within 4-8 years of first symptom appearance. This study was conducted to investigate differences in minerals between symptomatic and asymptomatic leaves of infected lime trees. The study included one set of leaves from uninfected trees and two sets of infected leaves: symptomatic leaves and asymptomatic leaves obtained from randomly selected acid lime trees. Nested polymerase chain reaction detected phytoplasma in the symptomatic and asymptomatic leaves from the six infected trees, but not from the uninfected trees. Phylogenetic analysis showed that all phytoplasmas belong to the 16S rRNA group II-B. Mineral analysis revealed that the level of Na significantly increased by four times in the symptomatic leaves compared to the non-symptomatic leaves and to the uninfected leaves. In addition, symptom development resulted in a significant increase in the levels of P and K by 1.6 and 1.5 times, respectively, and a significant decrease in the levels of Ca and B by 1.2 and 1.8 times, respectively. There was no significant effect of WBDL on the levels of N, Cu, Zn, and Fe. The development of witches' broom disease symptoms was found to be associated with changes in some minerals. The study discusses factors and consequences of changes in the mineral content of acid limes infected by phytoplasma.