Right option is (b) Clostridium
Explanation: About 900 species of bacteria are plant pathogens, e.g; species of Acidovorax, Pseudomonas, Rhizobacter, Rhizomonas, Xanthomonas, Bacillus, Clostridium, Clavibacter, etc. Bacterial pathogens of plants may be obligate pathogens, facultative pathogens and facultative saprophytes.