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

Witches’ broom (WB), associated with the presence of ‘Candidatus Phytoplasma aurantifolia’, 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.