Chlorophyll a fluorescence and leaf temperature are early indicators of oil palm diseases
Keywords:Photosystem II, PSII quantum efficiency, Plant-Pathogen Interaction, severity
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/FM and ΦPSII. Changes in ΦPSII, variable fluorescence yield (Fv) and maximum fluorescence in light-adapted leaves (FM’) were observed from the start of BR infection. The most sensitive and early indicators of LW disease were leaf temperature and basal fluorescence (F0). Fv/F0 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.