Imaging techniques and the early detection of plant stress

Abstract

Biotrophic pathogenA pathogen that lives inside intact cells.Fluorescence transientThe evolution of fluorescence emission upon illumination of dark-adapted leaves.Hypersensitive response (HR)Reaction of a resistant plant to an incompatible pathogen, characterized by the death of infected cells, eventually forming necrotic flecks of dead tissue.Hyperspectral imagingSimultaneous measurements performed in narrow spectral bands of the order of tens of nanometres.Multispectral imagingSimultaneous imaging in different spectral regions (e.g. far infrared, near infrared, visual).Necrotrophic pathogenA pathogen that lives on dead cells.Non-photochemical quenching (ΔFm/Fm′)The decrease in chlorophyll fluorescence caused by photoprotective thermal dissipation of absorbed light energy. This parameter is calculated as (Fm−Fm′)÷Fm′, where Fm is the fluorescence measured during the first saturating light pulse at the start of the fluorescence induction transient and Fm9 is that measured during a later flash of saturating light. Thus, ΔFm/Fm′ represents the ratio of quenched to remaining fluorescence.Non-saturating illumination (actinic light)Illumination with an intensity typically <1000 mmol m−2 s−1.Photochemical quenching (FII)The decrease in chlorophyll fluorescence caused by photochemical reactions leading to CO2 fixation. Calculated as (Fm′−Fs×R)÷Fm′, where Fm′ and Fs are the fluorescences measured under saturating and non-saturating illumination, respectively, and R is the ratio of saturating to non-saturating light. This parameter is the ratio of the difference between ‘maximum’ fluorescence at saturating light and steady-state fluorescence at non-saturating light to the ‘maximum’ fluorescence at saturating light. A high FII means efficient photosynthesis.PresymptomaticIn this context, before the appearance of visual symptoms.Saturating illuminationIllumination with an intensity typically >2000 mmol m−2 s−1.Variable chlorophyll fluorescence ratio (Ratio of fluorescence decay: Rfd)This is defined as (Fm−Fs)÷Fs, where Fm is the maximum fluorescence intensity attained early during the fluorescence induction transient and Fs the final steady-state value of fluorescence reached upon activation of photosynthesis.