واکنش ژنوتیپ‌های مکزیکن و پرشین‌لایم به Candidatus Phytoplasma aurantifolia در شرایط دمایی متفاوت

Witches'-broom disease of lime (WBDL) is a serious phytoplasma disease of acid lime in the world where has led to death of great amounts of Mexican lime trees in different regions in southern Iran. This study was conducted for examination the reaction of two commercial citrus genotypes including Mexican lime (Citrus aurantifolia Swingle) and Persian lime (Citrus latifolia Tanaka) to Candidatus Phytoplasma aurantifolia under controlled conditions, in two separated warm and cool units. Acid lime healthy germplasm was obtained from Citrus and Subtropical Fruits Research Center, and thirty-two two-years old healthy Mexican limes were used as rootstock. Mexican lime and Persian lime buds (five replications) from healthy sources were budded on ten infected Mexican limes which graft-inoculated with two bark patches of phytoplasma isolate originated from natural infected lime trees. Non-inoculated Persian lime and Mexican lime buds (three replications) considered as negative controls. After three weeks, all the rootstock pruned by cutting the stem above the grafted site, transferred to warm (day 35-37℃; night 25-27℃) and cool unit (day 24-26℃; night 18-20℃) and inspected regularly for symptom expression during 14 months. Samples were analyzed for presence of phytoplasma by direct and nested-PCR using the phytoplasma universal primer pairs P1/P7 and R16F2n/R16R2. In warm unit, at 9 -10 weeks after inoculation, disease symptoms observed on Mexican lime (five of five plants) and Persian lime (three of five plants). Disease symptoms in Mexican lime in cool unit were different from warm unit, so that the size of internode and leaves were larger in comparison to the warm unit. Moreover, at 56 weeks after inoculation, 80% of Persian lime (four of five plants) and all Mexican lime plants were PCR-positive for phytoplasma infection. In the cool unit, 20-21 weeks after inoculation disease symptoms were observed on all Mexican lime but not Persian lime plants. The results of this study showed that disease incubation period for Mexican and Persian lime in the warm condition was significantly shorter than disease incubation period in cool condition. Furthermore, higher temperature maybe prepares the appropriate condition for phytoplasma multiplication and may lead to occurrence the disease symptoms in cultivars which may not show the symptoms in cool condition. In this study, at temperatures between 25-37 ℃ disease symptoms were observed on Persian lime plants in less than three months after graft inoculation. This is the first report of symptoms occurrence of Ca. P. aurantifolia in Persian lime under greenhouse condition.