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Witches'-broom of Bakraee (Citrus reticulata hybrid) in Iran

Symptoms, resembling those of witches'-broom disease of lime (WBDL), consisting of proliferation and growth of spindly shoots, rosetting, development of stunted, pale green, cupped leaves, and long thin thorns were observed on some bakraee (Citrus reticulata hybrid) trees, the major rootstock species in Ghazi-Ghale (Hormozgan Province) and Kahnouj (Kerman Province) in southern Iran. Vein clearing, mottling, and mild to severe yellowing of leaves was evident on some rosetted flushes. The disease occurred sporadically, and only some branches of the tree displayed the symptoms. Sour lime (Citrus aurantifolia) trees with symptoms of WBDL were also encountered in adjacent citrus groves in the area where an association of “Candidatus Phytoplasma aurantifolia” with diseased trees was previously established. Total nucleic acids were extracted from symptomatic as well as apparently healthy bakraee (1). The nucleic acids were subjected to nested polymerase chain reaction (PCR) amplification with the universal primers R16mF2/R16mR1, followed by R16F2n/R16R2 (2). The PCR program consisted of an initial denaturation at 94°C for 2 min, followed by 40 cycles of 1 min at 94°C, 2 min at 55°C, and 3 min at 72°C. After a final extension of 10 min at 72°C, the samples were electrophoresed on agarose gels, and the DNA fragments were stained with ethidium bromide and visualized under ultraviolet light. An expected 1.2-kb product was amplified in DNA preparations from broomed bakraee and WBDL-affected sour lime trees. No such amplicon was detected in similar DNA extracts of asymptomatic trees. These results demonstrated an association of a phytoplasma with witches'-broom disease of bakraee. However, its relationship with “Candidatus Phytoplasma aurantifolia” remains to be determined.

References: (1) S. L. Dellaporta et al. Plant Mol. Biol. Rep.1:19, 1983. (2) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998.