Chlorophyll fluorescence imaging as a tool to monitor the progress of a root pathogen in a perennial plant

The chlorophyll fluorescence parameter I broken vertical bar (NO) is an excellent metric for the non-destructive monitoring of disease progression, measured over a broad range of light intensities. The suitability of the slow induction chlorophyll fluorescence parameters I broken vertical bar (PSII), I broken vertical bar (NPQ), and I broken vertical bar (NO) to monitor in vivo disease progression in a host-root pathogen pathosystem was evaluated and compared to the established method of monitoring disease by measuring F (v) /F (m) . Using the infection of ginseng plants (Panax quinquefolius L.) with Pythium irregulare Buisman as a model, light response curves were used to establish the optimal irradiance for the resolution of differences between fluorescence parameters I broken vertical bar (PSII), I broken vertical bar (NPQ) and I broken vertical bar (NO). As infection progressed only changes in I broken vertical bar (NO) remained consistent with increased irradiance, and increased as infection progressed. Furthermore, I broken vertical bar (NO) showed a high sensitivity for distinguishing increased disease load. In contrast, the magnitude in change of I broken vertical bar (PSII) and I broken vertical bar (NPQ) were sensitive to irradiance levels. The magnitude of increase in I broken vertical bar (NO) per unit disease score was equivalent to the corresponding decline in F (v) /F (m) values. Thus I broken vertical bar (NO) is as sensitive as F (v) /F (m) in monitoring biotic stress. The ability to measure I broken vertical bar (NO) under a wide range of light intensities, including natural light, potentially without the need for dark adaptation, means that it can be used in the development of a general protocol for non-invasive, in vivo monitoring of plant health, from the laboratory to the field scale.