Chlorophyll a fluorescence and leaf temperature are early indicators of oil palm diseases

ABSTRACT Bud rot (BR) caused by Phytophthora palmivora and lethal wilt (LW) whose causal agent is unknown, are two diseases currently posing a threat to the oil palm ( Elaeis guineensis . Jacq) industry. BR, first reported in 1964, has destroyed more than 85,000 ha. LW, first reported in 1994 in the Llanos Orientales in Colombia, has destroyed more than 5,000 ha. Chlorophyll a fluorescence is useful as a provider of information about the efficiency of the photosynthetic process when plants are subjected to biotic or abiotic stresses. Oil palms affected by BR and LW showed anomalies in the photosynthetic system, manifested by reductions in Fv / F M and ΦPSII. Changes in ΦPSII, variable fluorescence yield ( Fv ) and maximum fluorescence in light-adapted leaves ( F M ’ ) were observed from the start of BR infection. The most sensitive and early indicators of LW disease were leaf temperature and basal fluorescence ( F 0 ). Fv/F 0 significantly changed in diseased palms, indicating problems with movement of electrons through the electron transport chain. Leaf temperature changed in response to both diseases, but variation was greater in LW. We concluded that damage to the photochemical system caused by the diseases affected the processes by which the plant captures and transports energy, causing a physiological imbalance in the plant reflected in the observed variations in chlorophyll a fluorescence and leaf temperature. The two parameters began to change early in the onset of BR and before visual symptoms appeared in LW, which is very important to the management of both diseases, the foundation of which is early detection.

摘要：由棕榈疫霉（Phytophthora palmivora）引发的芽腐病（Bud Rot, BR）以及病原物尚未明确的致死性萎蔫病（Lethal Wilt, LW），是当前威胁油棕（Elaeis guineensis Jacq）产业的两大病害。芽腐病于1964年首次被报道，已造成超过8.5万公顷的油棕种植面积被毁；致死性萎蔫病于1994年首次在哥伦比亚东部奥里诺科平原（Llanos Orientales）被发现，已造成超过5000公顷的种植面积被毁。叶绿素a荧光（chlorophyll a fluorescence）可作为有效指标，反映植物遭受生物或非生物胁迫时光合过程的效率。感染芽腐病与致死性萎蔫病的油棕光合系统均出现异常，具体表现为Fv/FM与ΦPSII水平降低。研究发现，从芽腐病感染初期即可观测到ΦPSII、可变荧光产额（variable fluorescence yield, Fv）以及光适应叶片最大荧光（maximum fluorescence in light-adapted leaves, FM’）的变化。致死性萎蔫病最敏感且出现最早的检测指标为叶片温度与基础荧光（basal fluorescence, F0）；感病油棕的Fv/F0比值发生显著变化，表明电子传递链的电子转运过程出现异常。两种病害均可导致叶片温度发生改变，但致死性萎蔫病引发的温度波动幅度更大。本研究得出结论：上述病害对光化学系统造成的损伤，会干扰植物捕获与转运能量的生理过程，引发植株生理失衡，具体反映为观测到的叶绿素a荧光与叶片温度变化。两项检测参数在芽腐病发病初期以及致死性萎蔫病出现可见症状之前即发生改变，这对两大病害的防控具有重要意义——而早期检测正是病害综合防控的核心基础。