• Quae

Identify diseased plants in the field

 
 
The location of the first infected plants and the rate of spread in the field often informs us about the prevailing phytosanitary context and allows us to distinguish between biotic (parasitic, table 1) and abiotic (non-parasitic, table 2) problems .

 
In plant pathology traditionally at least five main types of disease distribution are described. They are presented in figure 1.  Examples of the phytosanitary context which determine the different distributions in tobacco fields are given in figures 2 to 5.

 

 
Figure 1 Figure 2 Figure 3 Figure 4 Figure 5  

 

Table 1 : Distribution of the major parasitic diseases in tobacco fields in France.
Field distribution types of diseased plants

random distribution

 

in small foci
            

 

in large foci
            

 

in lines
            

overall distribution
Airborne bacteria
(Pseudomonas cichorii, Pseudomonas syringae pv. tabaci, Erwinia spp.)
 +        
Airborne fungi
- Peronospora tabacina		  
+
+		  
x
- Erysiphe cichoracearum
  
+		  
+		    
x
- Botrytis cinerea
 +        
- Sclerotinia sclerotiorum
+		    
x		    
- Alternaria
alternata
+		        
+
Soilborne fungi
- Thielaviopsis basicola
    
+		  
x
- Rhizoctonia solani
 + +      
- Verticillium dahliae + +      
Contact-transmitted viruses
(TMV, PVX...)
 + +    +  
Aphid-transmitted viruses
(CMV, PVY, AMV...)
 + +     x
Thrips-transmitted viruses
(TSWV...)
 + +      
Nematode-transmitted viruses
(TRSV...)
 + +      
Phytoplasma causing stolbur
 +        x
Foliar and root nematodes
(Meloidogyne, Globodera, Pratylenchus...)
      +    

+ : commonly observed distribution
x : distribution observed when the outbreak is severe
 

Table 2 : Distribution of the major non-parasitic diseases in tobacco fields in France
Field distribution types of diseased plants random

in small foci

  in large  foci
 in lines
 overall  distribution
Nutritional problems
(deficiencies, toxicities)
     +   +
Phytotoxicities +     + +
Genetic abnormalities +        
Sunscald +        
Lightning injury     +    
Hail injury         +
Frenching
   + +    
Wet spots
 +        
Weather flecking
 +       x
Drought spots
         +
+ : commonly observed distribution
x : distribution observed when the outbreak is severe
Last change : 04/02/13
  • Author :
  • D Blancard (INRAe)