For example, if we want to estimate the disease severity percentage of leaf spotting disease of eggplant, we can suggest the following scale:
0 Leaves with No symptoms
1 1-5 spots on the eaf
2 6-10 spots on the leaf
3 11-15 spots on the leaf
4 More than 15 spots and/or leaf dryness
Then we can use Mckinney equation to calculate the percent of disease severity.
Hi,
I would suggest you to have a look at this guide. It depends on many factors such as geographical area, crop and pest/pathogen.
https://www.bioversityinternational.org/fileadmin/user_upload/A_field_guide_Manandhar.pdf
Which kind of crop are you working with? Which kind of pathogen are you working with?
Best regards
The measurement of disease intensity plays the same key role for plant pathology as does the diagnosis. Without quantification of disease, no studies in epidemiology, no assessment of crop losses, and no plant disease surveys and their applications would be possible. Disease assessment is also needed for many other applications in plant pathology, such as screening for resistance and fungicides. It expresses the effects of various treatments or factors on the disease in experiments, and disease control. Kindly check the following RG link:
Chapter Measuring Plant Disease
This is another RG link, kindly check, it may be useful:
Article Quantitative assessment of disease severity and rating of ba...
https://www.researchgate.net/profile/Jawad_Al-Janabi3/post/How_can_I_quantify_disease_percentage_on_pictures_of_leaves/attachment/59d6466779197b80779a16b8/AS%3A457721381167104%401486140689056/download/ASSESSMENOT+F+DISEASEA+ND+EFFECTSO+N+YIELD.pdf
It depends on the type of the pathogen and the symptoms which have been seen on the plant. For example the pathogen wich cause leaves spotting, we can measure disease severity of it with a method differs from the method of measuring the disease severity of the pathogen wich causes root rot or damping off or other diseases.
According to pathogen and symptoms, we can suggest a suitable scale consists of many degrees depending on the type of symptoms, each degree represents a type of symptom, then we can estimate the percentage of disease severity according to this scale.
For example, if we want to estimate the disease severity percentage of leaf spotting disease of eggplant, we can suggest the following scale:
0 Leaves with No symptoms
1 1-5 spots on the eaf
2 6-10 spots on the leaf
3 11-15 spots on the leaf
4 More than 15 spots and/or leaf dryness
Then we can use Mckinney equation to calculate the percent of disease severity.
If we want to estimate the disease severity of the fungus Fusarium solani, we can suggest the follwoing scale:
0 The plant is healthy, and the root system is white colour.
1 Discolouration 1-25 from the root light brown colour.
2 Discolouration of more than 25-50 dark brown colour.
3 Discolouration of more than 50-75 of the root in a dark brown colour with
yellowing of leaves.
4 Discolouration of more than 75-100 of the root in a dark colour with the death
of infected plant.
Then we can apply Mckinney equation to caculate the disease severity percentage.
When we want to calculate the disease index of the fungus Rhizoctonia solani we can suggest the following scale:
0 The plant is healthy, and the root system is white colour.
1 Discolouration of the root in a yellowish-brown colour and ulceration with a
diameter less than 10 mm around the stem.
2 Dark brown discolouration of the root and canker with diameter of 11-20 mm
around the stem.
3 Reddish-brown canker fully surrounding the stem.
4 Plant death.
Then we use the same equation to estimate the disease severity.
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