By using imaging techniques, plant physiological parameters can be assessed without contact with the plant and in a
non-destructive way. During plant-pathogen infection, the physiological state of the infected tissue is altered, such as
changes in photosynthesis, transpiration, stomatal conductance, accumulation of Salicylic acid (SA) and even cell death.
In this study, the different temperature distribution between the leaves infected by tobacco mosaic virus strain-TMV-U1
and the noninfected leaves was visualized by digital infrared thermal imaging with the microscopic observations of the
different structure within different species tomatoes. Results show a presymptomatic decrease in leaf temperature about
0.5-1.3 °C lower than the healthy leaves. The temperature difference allowed the discrimination between the infected and
healthy leaves before the appearance of visible necrosis on leaves.
Biological cells have components acting as electrical elements that maintain the health of the cell by regulation of the
electrical charge content. Plant impedance is decided by the state of plant physiology and pathology. Plant physiology
and pathology can be studies by measuring plant impedance. The effect of Cucumber Mosaic Virus red bean isolate
(CMV-RB) on electrical resistance of tomato leaves was studied by the method of impedance measurement. It was found
that the value of resistance of tomato leaves infected with CMV-RB was smaller than that in sound plant leaves. This
decrease of impedances in leaf tissue was occurred with increased severity of disease. The decrease of resistance of
tomato leaves infected with CMV-RB could be detected by electrical resistance detecting within 4 days after inoculation
even though significant visible differences between the control and the infected plants were not noted, so that the
technique for measurement of tomato leaf tissue impedance is a rapid, clever, simple method on diagnosis of plant
disease.
Automatic diagnosis of plant disease is important for plant management and environmental preservation in the future.
The objective of this study is to use multispectral reflectance measurements to make an early discrimination between the
healthy and infected plants by the strain of tobacco mosaic virus (TMV-U1) infection. There were reflectance changes in
the visible (VIS) and near infrared spectroscopy (NIR) between the healthy and infected plants. Discriminant models
were developed using discriminant partial least squares (DPLS) and Mahalanobis distance (MD). The DPLS models had
a root mean square error of calibration (RMSEC) of 0.397 and correlation coefficient (r) of 0.59 and the MD model
correctly classified 86.7% healthy plants and up to 91.7% infected plants.
There is increase pressure to reduce the use of pesticides in modern crop production to decrease the environment impact of current practice and to lower production costs. It is therefore imperative that sprays are only applied when and where needed. However it is difficult to measure the severity of plant disease as a result of the irregular leaf and disease spots shapes. In this research, a pixel method is proposed, and the severity of plant disease was graded accuracy by using technology of image analysis, and then the method was compared with traditional method for measured of plant infection severity. The leaves images were acquired by a CCD camera and transferred to a host computer and were stored as files in TIFF format. From the experimental results, it shows that the image method has an acceptable accuracy; and image processing is a rapid and non-destructive way to gain the plant infection severity.
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