Question

Which one of the following fungi is biotroph?
A. Puccinia
B. Pythium
C. Colletotrichum
D. Fusarium

Answer 1

Hint: Fungi are eukaryotic organisms that can be unicellular or multicellular. The kingdom has various modes of nutrition. They are heterotrophs, saprophytic (feed on the dead and decaying matter).

Complete answer:
Biotroph is any pathogen, which can establish a long term nutritional or feeding relation with the host. It doesn’t kill the host but exhibits parasitism for a long duration. An example of a biotroph is Puccinia, they exist as obligate parasites and are responsible for diseases such as rusts. These organisms grow between the host cells and absorb nutrition through specialized structures known as haustroia. They establish the relationship by developing a sink for the nutrients at the infection site. This keeps the host at disadvantage but does not kill the host. It results in the loss of the nutritional ability of the host organisms.
Considering the other given options:
Pythium is also a fungus, belonging to the class oomycetes, existing as parasites. But these organisms are not biotrophic as they are not obligate parasites. It causes a disease known as Pythosis. Thus it is not the right option
Colletotrichum is fungi that exhibit a symbiotic relationship with plants. They exist as endophytes as they live inside the plants. They can exhibit pathogens, but some exist as symbionts also. Thus it is not the appropriate option.
Fusarium is a filamentous fungus. They exist as harmless saprobes. They constitute the microbial community in the soil. Thus it is not an appropriate option.
Thus the most appropriate answer to the question is A-Puccinia that exists as biotrophs.

Note: Fungi are heterotrophic organisms. They derive nutrition from various organic compounds such as ethanol, nitrates, acetate, and ammonia. They have a high degree of metabolic versatility.