Question

Little leaf disease and plant yellows are caused by
A. Halobacterium
B. Mycoplasma
C. Bdellovibrios
D. Chlamydia

Answer 1

Hint: Plants are affected by a number of pathogens belonging to different genera and species. The little leaf disease is commonly found in various plants in which leaf growth is retareded leading to the bad functioning of photosynthesis as well as transpiration. The bacteria are one of the most dominant pathogens as their rate of multiplication is very high.

Complete answer:
The correct answer is option (B) that is Mycoplasma.
The characteristics and diseases/disorders caused by the given pathogens are listed below :
Halobacterium – It is an Archaebacteria, and does not cause any disorders in humans or plants. This type of bacteria can tolerate extreme harsh conditions such as saline, extremely hot atmosphere and methanogenic environment.
Mycoplasma – A canopy term for many pathogens such as PPLO, PLT. Even mycoplasma like organisms (MLO = phytoplasma) are generally called Mycoplasma. This category of pathogens includes animal pathogens and plant pathogens.
Bdellovibrios – It is a predator bacteria this is found in the human gut. It usually attacks gram-negative bacteria, and are used to control cystic fibrosis in human lungs.
Chlamydia – It is a bacterium that causes one of the most common sexually transmitted diseases known simply as Chlamydia infection.
Mycoplasma is the one that is causing little leaf and plant yellows. These disorders are caused by Phytoplasma, which is characterized as a Mycoplasma-like organism upon its discovery. Characteristic symptoms of plant yellows include a proliferation of axillary buds, reduced leaf size together with shortening internodes. This gives rise to witch’s broom growth.The Little leaf has the following symptoms: interveinal chlorosis of young leaves, and distortion and failure of leaves along the midrib to expand. General stunting of plants is also seen.

Note: The disease-causing organism is actually Phytoplasma which is a bacteriophage. The Mycoplasma is the only pathogen of the plant among the given options. Rest all act in animal systems, except Halobacterium, which doesn’t have a prominent pathogenic activity. Mycoplasma is a kind of prokaryotic cell which does not have a cell wall. It is always found to be pathogenic.