Physiology and biochemistry of lethal yellowing-affected Cocos nucifera L. palms

Abstract

Lethal yellowing (LY) is a disease which is associated with phloem-inhabiting mycoplasmalike organisms (MLO) [3, 15, 30]. According to Zimmermann [38], if MLOs can only be transported via the sieve tubes, movement of MLOs is expected to be from mature leaves to phloem sinks such as roots, flowers, fruits and the shoot apex. Therefore, it is unlikely that many MLOs are present in mature leaves. Evidence of such a distribution of LY-MLOs in coconut (Cocos nucifera L.) palms has been obtained using molecular techniques (Escamilla et al., this volume, Harrison et al., this volume). However, leaf senescence, perhaps the most conspicuous symptom in yellows-type diseases, occurs in all leaves, including the mature leaves. Therefore, leaf damage, or the changes therein, probably takes place as an indirect effect of the MLO action. This paper updates a previous review [29] on the physiological and biochemical changes in LY-affected coconut palms and discusses how they may arise by MLO action. An understanding of the physiology and biochemistry of the disease will contribute to a better understanding of the mode of action of the LY-causing MLO, and this in turn, may lead to the development of more effective control measures.KeywordsStomatal ConductanceMature LeafLeaf SenescenceStomatal ClosureSieve TubeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.