S14 - Session O3 - Natural and synthetic compounds for pest and weed control - Characterization and management of witchesż broom disease of acid lime

Authors: Abdullah Al-Sadi *,

Ali Al-Subhi, Rashid Al-Yahyai

Witches broom disease of lime (WBDL) is a serious disease of acid lime ( Citrus aurantifolia ) in the Middle East. The disease results in excessive production of small light green to yellow leaves, followed by decline of the affected trees within 4 to 5 years of first symptom appearance. WBDL, which is associated with ' Candidatus Phytoplasma aurantifolia', killed over 1.5 million lime trees in the Middle East and still poses a major threat to the lime industry in this region. Our studies focused on investigating the causal agent, host, vectors and their interactions, in order to come up with strategies to reduce losses from this disease. Investigations revealed that acid lime has a low level of genetic diversity, which may explain why WBDL affected most acid limes grown in this region. Phytoplasma was found to interact with the host plant by downregulating the defense genes against pathogens and vectors. Symptom development was found to be accompanied by an increase in sodium to levels that are toxic to the plant. In addition, the symptomatic branches were found to be more attractive to the insect vectors compared to the asymptomatic branches. The expression of typical WBDL symptoms was not apparent under certain climatic conditions. These findings may suggest that disease levels in the infected plants can be reduced via a number of ways, including control of the vectors, removing the symptomatic branches and moving lime cultivation to areas that are less conducive for disease expression.