Question

Potato Spindle Tuber disease is due to
(a) Nematode
(b) Virus
(c) Bacterium
(d) Viroid

Answer 1

Hint:Potato spindle tuber disease is caused by plant pathogens that consist of a short stretch of highly complementary, circular, single- stranded RNA (a few hundred nucleobases) without a protein coat. In potatoes and tomatoes, this disease can reduce crop yields.

Complete step by step answer:
The first viroid to be described was the Potato spindle tuber viroid ("PSTVd") . PSTVd is a thin, circular molecule of RNA closely related to the stunt viroid of Chrysanthemum. PSTVd is susceptible to all potatoes and tomatoes, and no form of natural resistance can occur. Prions, viruses, and bacteria don't cause potato spindle tuber disease.
Viroids were discovered and assigned this name in 1971 by the plant pathologist Theodor Otto Diener at the Maryland Agricultural Research Service.
Symptoms of the disease on potato:
The strains are both mild and extreme. The signs of nutrient deficiency, spray damage, insect damage or other plant diseases such as true viruses may be misunderstood. Symptoms become more evident under warm conditions and high luminous intensity.
- Stems remain upright with extreme strains, and internodes are longer and more slender than usual. Leaflets with fluted margins decrease marginally in scale.
- Leaves close to ground level are kept upright, in comparison to healthy leaves of plants that mostly lie on the ground. Even extreme strains are seen with twisted leaflets and wrinkled leaf surfaces.
- Tubers are elongated, sometimes with pointy ends, but are cross- sectionally wide. The eyes are wide, more prominent and there is cracking of the bone. Some cultivar tubers grow knobs and swellings.
So, the correct answer is, ‘(b) Virus’.

Note: PSTVd was first identified in North America as a disease in potatoes, and first observed in South Africa on tomatoes. Reportedly the disease occurs in Asia, Africa, North America, South America, Europe, and New Zealand. Previous detections and eradications of PSTVd have occurred in Australian tomatoes and potatoes, particularly in Western Australia.