Effect of temperature on symptom expression of witches’ broom disease in commercial citrus species

Previous studies showed that environmental factors like temperature affected symptom development and phytoplasma concentration within the plant tissues. However, no study has been conducted to investigate the effects of temperature on the development of “ Candidatus Phytoplasma aurantifolia” and witches’ broom disease. Four citrus species including Mexican lime, Persian lime, Lisbon lemon, and sour orange grafted on Mexican lime rootstocks were inoculated with two barks of “ Ca . P. aurantifolia”-infected Mexican lime. Plants were maintained at warm (35–37 °C in the day and 25–27 °C in the night) and cool (24–26 °C in the day and 18–20 °C) temperatures under greenhouse conditions, monitored for witches’ broom symptom development and phytoplasma concentration. It took 20 weeks for the symptom expression in Mexican lime shoots grown in cool conditions; however, in warm conditions, plants expressed symptoms 10 weeks earlier. Witches’ broom symptoms appeared in Persian lime, Lisbon lemon, and sour orange incubated in warm conditions but no symptoms were observed in cool conditions. Quantitative polymerase chain reaction results showed that the concentration of the phytoplasma was higher in all citrus species kept at the warm conditions in comparison with the cool conditions. These results indicate that temperature plays an important role in “ Ca . P. aurantifolia” concentration and symptom development in citrus species.