Diseases of Vegetable, Ornamental and Spice Crops

Exercise-13: DISEASES CAUSED BY BACTERIA

a) Black rot of crucifers (Causal organism Xanthomonas campestris pv. campestris)

Kingdom : Prokaryotae
Division : Gracilicutes
Class : Proteobacteria
Family : Pseudomonadaceae
Genus : Xanthomonas
Species : campestris
Pathovar : campestris

Symptoms: ‘V’ shaped chlorotic lesions with the base towards the midrib appear on the leaves. Affected tissues turn yellow. The veins and veinlets in the chlorotic tissues become dark.
Bacteria: Small, rod shaped aerobic, non spore forming with single polar flagella (Fig. 1).
Gram-reaction: -tive.
Colony colour: Yellow.


b) Solanaceous wilt (Causal organism Ralstonia solanacearum)

Kingdom : Prokaryotae
Division : Gracilicutes
Class : Proteobacteria
Family : Pseudomonadaceae
Genus : Ralstonia
Species : solanacearum

Symptoms: Sudden drooping of leaves, without yellowing accompanied by rotting of the stem. Bacterium is mostly confined to the vascular system where it produces polysaccharides, which mechanically block the system and checks the translocation of water resulting in wilting of the plants.

Bacteria: Rod shaped, aerobic, frequently occurs in pairs, motile with 1 to 4 flagella (Fig. 1).
Gram-reaction: -tive.


c) Bacterial canker (Causal organism Clavibacter michiganensis subsp. michiganensis)

Kingdom : Prokaryotae
Division : Fermicutes
Class : Thallobacteria
Family : unknown
Genus : Clavibacter
Species : michiganensis
Subsp. : michiganensis

Symptoms: Lower leaves show wilting symptoms. On stem brown streaks and canker develop and small brown, scabby lesions surrounded by white halo appear on fruits..

Bacteria: Coryneform rod with cells growing either singly or in pairs and aerobic.
Gram-reaction: + ve.

d) Curd rot of cauliflower (Causal organism Erwinia carotovora)

Kingdom : Prokaryotae
Division : Gracilicutes
Class : Proteobacteria
Family : Enterobacteriaceae
Genus : Erwinia
Species : caratovora

Symptoms: Curds start rotting from any portion. The rotting usually starts after some injury.

Gram-reaction: -ve


e) Bacterial blight of pea (Pseudomonas syringae pv. pisi)

Kingdom : Prokaryotae
Division : Gracilicutes
Class : Proteobacteria
Family : Pseudomonadeaceae
Genus : Pseudomonas
Species : syringae
pathovar : pisi

Symptoms: Brown water-soaked spots appear on the leaf margins, nodal points and pods. Early infection results in complete wilting of plants.
Bacteria: Motile rods, non spore forming with one or more polar flagella (Fig. 1).
Gram-reaction: -ve.

Fig 1: Different arrangement of flagella on bacteria