Question

Potato spindle tuber disease is caused by (a) Virus (b) Viroids (c) Lichens (d) Fungi

Short answer

The Potato Spindle Tuber Disease is caused by Viroids.

Step-by-step solution

Understand the Question

The question asks for the cause of the Potato Spindle Tuber Disease. The options given are Virus, Viroids, Lichens, and Fungi.

Recall Information

Viroids are infectious agents that consist of a short, circular, single-stranded RNA that do not encode protein yet can replicate in host plants and cause disease. In this case, Potato spindle tuber disease is famously known to be caused by a viroid, named Potato spindle tuber viroid (PSTVd).

Select the correct option

Upon correlating the information, it can be identified that the Potato Spindle Tuber Disease is caused by Viroids.

Key concepts

Viroids

Viroids represent a unique class of infectious agents, distinct from viruses in several ways. The term 'viroid' was coined to denote 'virus-like' due to their capability to cause disease but are, in fact, much simpler in structure. Unlike the more complex viruses, viroids consist solely of a short strand of circular single-stranded RNA without a protective protein coat.

Consider Potato Spindle Tuber Disease as a classic example. It is caused by the Potato spindle tuber viroid (PSTVd), which is an infectious piece of RNA with no genes encoding proteins. As a plant pathogen, PSTVd enters the host cells and hijacks the plant's own cellular machinery to replicate, disrupting normal plant development and leading to characteristic symptoms like stunted growth and, as the name suggests, a spindle-shaped tuber in potatoes.

Though they are small and seemingly simple, the impact of viroids on agriculture can be significant. They spread through various means, including mechanically via contaminated equipment and contact with infected plants, making them challenging to control. By studying viroids, scientists aim to better understand their mechanisms of infection and develop strategies to mitigate their effects on crops.

Infectious Agents in Plants

Plants, like all living organisms, are subject to infection by a variety of pathogens including viruses, bacteria, fungi, and viroids. These infectious agents can cause a range of plant diseases that impact agricultural productivity and biodiversity. For students learning about plant biology, understanding these infectious agents is crucial for effective disease management.

Viruses

Plant viruses are made up of nucleic acids (either RNA or DNA) surrounded by a protein coat. They require living cells to multiply and often cause mottled leaves, stunted growth, or reduced yields in affected plants.

Fungi

Fungi can colonize living or dead plant tissue and obtain nutrients by breaking down the plant's cellular structures. There is a diverse range of fungal pathogens, leading to diseases such as rusts, smuts, and mildews.

Viroids and Prions

These agents are even more simple than viruses. Viroids consist of a short strand of circular RNA, causing diseases such as the Potato Spindle Tuber Disease. Prions, on the other hand, are protein-based infectious agents that can affect plant development.

Each type of infectious agent has distinct characteristics that influence how they interact with their host plants. The route of transmission, ability to survive outside the host, and the host's defense mechanisms all play roles in the spread and severity of plant diseases.

Single-stranded RNA

Single-stranded RNA (ssRNA) is a type of nucleic acid that, unlike double-stranded DNA, consists of only one strand. In the realm of infectious agents in plants, ssRNA is significant because many viruses and viroids, including the Potato Spindle Tuber Viroid (PSTVd), have genomes composed of single-stranded RNA.

ssRNA can fold upon itself to form complex secondary structures due to base pairing between the nucleotides. These structures are critical for the viroid's survival, replication, and pathogenicity. Host enzymes mistakenly recognize viroids as normal cellular RNA and help them to replicate, leading to a buildup of viroid RNA and subsequent plant disease symptoms.

Understanding the structure and function of ssRNA is fundamental in molecular biology and virology. For example, RNA silencing is a natural defense mechanism in plants that can target ssRNA to prevent the replication of viruses and viroids. Research into this and other ssRNA characteristics can aid in developing genetic resistance to such infectious agents, thereby protecting crops from diseases like Potato Spindle Tuber Disease.