Hint: There are mainly two types of bacteria, beneficial bacteria that help in digestion in animals, nitrogen fixation in roots, etc. and pathogenic bacteria that cause severe diseases and infections in animal, plants, and humans. In plants, the pathogenic bacteria can disrupt the certain metabolic process of the plant by infecting the xylem or phloem, and other parts of the plant.
Complete step by step answer: Potato ring rot is caused by the bacterium Clavibacter michiganensis, subspecies- Sepedonicus and its symptoms initially include wilting in the lower leaves, the margins of the leaves roll inwards and upwards and the leaf surface becomes progressively dull light green, then grey-green yellow and then finally brown and necrotic. Then there is a soft cheese-like rotting of the vascular ring, thus called "ring rot” and in severe cases, the vascular ring rots completely. Tikka disease mainly occurs in the groundnut by Cercospora arachidicola, it is a fungal ascomycete plant pathogen that causes early circular spot on the surface of the leaf and the main source of this infection is conidia of fungus present in the soil or in fruit shell. Downy mildew of grapes is caused by fungus Plasmopara viticola and causes a decrease in the quality and quantity of the crop. Red rot infection in sugarcane, caused by the fungus Colletotrichum falcatum, and the symptom of the disease is reddening of the internal intermodal tissues along with white patches in between. Hence, the correct answer is option (C).
Note:Bacterial cells can be rod-shaped, spherical, spiral-shaped or filamentous, they can be motile and have whip-like flagella that propel them through films of water. The bacteria that infect the plants are called Phytoplasmas and Spiroplasmas.