Journal of Plant Pathology Archive

Abstract:

Lethal yellowing (LY) is the most devastating phytoplasma disease affecting coconut palm (Cocos nucifera) in the Americas. Based on symptoms, different pathogenicity models and factors have been proposed, including hormone unbalance and changes in endogenous cytokinins content. Symptomatology and PCR were used to determine LY phytoplasma presence in coconut palms from Yucatan, Mexico. To determine Z-type and iP-type endogenous cytokinin content, young leaf and primary and secondary root meristem tissue were analyzed by HPLC-ELISA. The content of six cytokinins, three of the Z-type (Z, Z9G, ZR) and three of the iPtype (iP, iP9G and iPR) were determined in nine palms, three of which were healthy, three were in disease stage 2; and three in stage 6. Both cytokinin types decreased drastically compared with healthy controls in stage-2 leaf tissue: 13.3-fold in Z; 11 in Z9G; 17.8 in ZR; 17.7 in iP; 382 in iP9G; and 17.5 in iPR. Decreases in stage-6 leaf tissue were more pronounced, so that Z9G, ZR, iP and iP9G were not detected. Z-type cytokinins decreased also in primary root meristem from affected palms at both stages (346 fold in Z; 3.9 in Z9G; and 6 in ZR), but iP9G increased 7 times in stage-2 tissue and iPR increased 26.45 times in stage-6 tissue. In stage-2, secondary root meristem tissue, Z increased 20.78 times, iP increased 4 times and iPR 14 times. Lethal yellowing clearly affects endogenous Z-type and iP-type cytokinin levels in coconut palm, which may lead to some of the symptoms associated with this disease.