SOFT ROT AND BLACK LEG OF POTATO

PATHOGEN:
Soft rot: Erwinia carotovora pv  carotovora.
Black leg: Erwinia carotovora pv  atroseptica.

SYMPTOMS OF SOFT ROT:

1. The soft rot symptoms begin as small water soaked lesion, which enlarges rapidly in diameter and in depth.
2. The affected area becomes soft, mushy and depressed. Tissue within the affected region becomes cream coloured and slimy, disintegrating intu a mushy mass of disorganized cell.
3. The outer surface remain intact while the entire contents have changed to a turbid liquid. Cracks develop and slimy mass exudes to the surface which turns tan, grey, or dark brown in air.
4. A whole fruit or tuber may be converted to a soft watery, decayed mass within 3-5 days. Infected fruits or tubers of many plants are collapsed and then secondary bacteria grow on decomposing tissues and produce a foul odor.

EARLY BLIGHT OF POTATO AND TOMATO

SYMPTOMS:

Symptoms On Leaf:

1. Foliar symptoms of early blight first appear as small, irregular to circular dark brown to black spots on the lower (older) leaves. These may range in size from a pinpoint to an eighth of an inch in diameter.                                                                
2. As the spots enlarge, they become restricted by leaf veins and take on an angular shape. Early in the growing season, lesions on young, fully expanded succulent leaves may be larger up to half an inch in diameter and may, due to their size, be confused with late blight lesions. 
3. Leaf lesions are relatively easy to identify in the field. Because a series of dark concentric rings alternating with bands of light tan tissue are developed giving the spots a target like appearance.                                               A narrow band of chlorotic tissue often surrounds each lesion and extensive chlorosis of infected foliage develops over time. Elongated superficial brown or black lesions may also form on stems and petioles.
4. By the end of the growing season, the upper leaves of infected potato plants may be peppered with numerous small early blight lesions .                            
5. Subsequently lesions may coalesce to cover a large area of the leaf (Fig. 5a). Severely infected leaves eventually wither and die but usually remain attached to the plant (Fig. 5b). 

Severe infection of foliage by the early to mid-bulking period can result in smaller tubers, yield loss and lower tuber dry matter content.


Symptoms On Stem:

1. Dark sunken spots develop on branches and stems of plants such as tomato. Some lesions may develop on seedling stage and form cankers, which may enlarge, griddle the stem and kill the plant.



Lesion on potato stem





Lesion on tomato stem

Symptoms on Tuber (Potato):

1. On the tubers dark, slightly sunken lesions develop that may be up to 2 cm in diameter and 5-6 mm in depth.                                                        
2. Rotting and formation of undersized and reduced number of tuber is reported to this disease.                                                                

Symptoms on the Fruit:

1. Alternaria may attack during the maturity period. the spots may be small and sunken or may enlarge to cover the most of fruit. The fruits may be leathery and have a black, velvety surface layer of fungal growth and spores. Sometimes a small lesion at the surface may indicate an extensive spread of the infection inside the fruit.   

HOST: Potato, tomato, chili, Solanum nigrum etc.

PERPETUATION OF THE CAUSAL ORGANISM/SOURCE OF INFECTION:

Primary Source:

Alternaria survive as mycelium or conidia in diseased plant debris and in or on seeds which cause primary infection in the next crop.

Secondary Source:

Infected crop.

FAVORABLE CONDITION:

• Heavy dews and frequent rains are suitable for abundant conidia production.
• Weak and wounded plants.
• Mg ion deficient field is favorable for disease.