This set of Class 12 Biology Chapter 9 Multiple Choice Questions & Answers (MCQs) focuses on “Plant Diseases caused by Viruses and Bacteria”.
1. Which of the following group of viruses generally attack plants?
a) Retroviruses
b) Riboviruses
c) Rheoviruses
d) Enteroviruses
View Answer
Explanation: Viruses that generally affect plants are riboviruses with ssRNA genome. Viruses are obligate parasites which are nucleoprotein entities consisting of DNA or RNA as the genetic material. 50% of the plants are rod-like.
2. Which of the following is not a method by which viral infection spreads in plants?
a) Exuding sap of infected plants
b) Infected seeds
c) Through meristem
d) Infected pollen
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Explanation: Virus infection spreads from either an infected plant or plant residue by agricultural implements, exuding sap of infected plants, vegetative propagules, infected seeds or pollen, Aphids, mites or other insect vectors, Nematodes and Fungal spores.
3. Which of the following is not a method by which a virus enters a healthy host?
a) By vectors
b) Meristem
c) Infected fungal spores
d) Through wounds
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Explanation: Virus enters the healthy host through wounds made mechanically or by vectors, infected fungal spores and infected pollen. They enter the cells, multiply and reach phloem which helps in spreading the virus throughout the plant.
4. Common symptoms of viral infection in plants are local lesions and ring spots.
a) True
b) False
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Explanation: Common symptoms of viral diseases in plants are mosaics, local lesions, necrosis, ring spots, pitting, stunting, proliferation, leaf rolls, etc. Variegation of flowers (flower breaking) produces unique designs.
5. Which of the following is not a common measure of controlling viral infections?
a) Using healthy virus-free seeds
b) Antibiotics
c) Using resistant varieties
d) Protection from insect vectors
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Explanation: Pesticides and antibiotics are useless in controlling viral infections. Control is achieved through resistant varieties, using healthy virus-free seeds, protection from insect vectors, sterilisation of agricultural implements and sanitation.
6. Which of the following organism causes Bean Mosaic Disease in plants?
a) Virus
b) Bacteria
c) Fungi
d) Nematode
View Answer
Explanation: Bean Mosaic Disease is caused by mainly two viruses, Common Mosaic Virus and Yellow Mosaic Virus. It is a common disease of beans of all types like Soya bean, Mung bean, Urd bean, French bean, Broad bean, Winged bean, etc.
7. Which of the following is not a symptom of Bean Mosaic disease?
a) Plants are bunchy
b) Leaves show mottling
c) Mosaic appearance on leaves
d) Blackening of leaflets
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Explanation: Bean mosaic infected plants are stunted and bunchy. Their leaves show mottling, yellowing and malformations. Mosaic appears due to the occurrence of light and dark green areas with clearing or yellowing of veins. Seeds are small, malformed or aborted.
8. Which of the following is not a method of overcoming the infection of Bean mosaic disease?
a) Virus-free seeds
b) Cutting leaves
c) Delayed planting
d) Sowing resistant varieties
View Answer
Explanation: Infection of mosaic virus can be overcome by using virus-free seeds, delayed planting, sowing resistant varieties, by removal of weeds and hosts of the virus, soil treatment with insecticides and foliar spray to restrict vectors.
9. Which of the following is not a bacterial plant pathogen?
a) Pseudomonas
b) Clostridium
c) Puccinia
d) Xanthomonas
View Answer
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.
10. Bacteria spread from infected plants to healthy plants only by air currents.
a) True
b) False
View Answer
Explanation: Bacteria spread from infected plants to healthy plants by air, water, mechanical contact, insects, other animals and human beings. Some insects function as vectors in which bacteria can survive and multiply.
11. Which of the following is not a symptom of bacterial diseases in plants?
a) Blight
b) Mosaic
c) Wilts
d) Rots
View Answer
Explanation: The symptoms of bacterial disease in plants include local lesions and necrosis, blights, rots, wilts, overgrowths, thickness and galls, stunting, scabs and cankers.
12. Which of the following is not a method of controlling bacterial diseases in plants?
a) Roguing of infected plants
b) Sanitation methods
c) Quarantine
d) Virus-free seeds
View Answer
Explanation: Bacterial diseases in plants can be controlled by roguing of infected plants, sanitation measures, use of healthy disease-free seeds, chemical sprays, antibiotics, periodic sterilisation of soil and by growing resistant varieties.
Sanfoundry Global Education & Learning Series – Biology – Class 12.
To practice all chapters and topics of class 12 Biology, here is complete set of 1000+ Multiple Choice Questions and Answers.
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- Practice Class 12 - Physics MCQs
- Practice Class 12 - Chemistry MCQs
- Practice Class 11 - Biology MCQs
- Check Class 12 - Biology Books
- Practice Class 12 - Mathematics MCQs
