Microbes and Plant Diseases

Phytophthora infestans is a fungus-like organism (oomycete) that causes late blight of potato, which was responsible for the Irish Potato Famine. Loose smut of wheat is caused by Ustilago tritici, wilt of pigeon pea by Fusarium udum, and blight of chickpea by other pathogens.

Earcockle disease of wheat is caused by Anguina tritici (a nematode). Puccinia tritici causes stem rust of wheat, not earcockle. Corynebacterium tritici causes bacterial leaf streak. 'Angunia' appears to be a typo for 'Anguina' but given the options, C is clearly intended as the correct answer.

Though witches' broom is caused by bacteria but in legumes it is caused by fungus.

Loose smut of wheat is caused by Ustilago tritici (1-c). White rust of crucifers is caused by Albugo candida (2-d). Crown gall is caused by Agrobacterium tumefaciens (3-b). Pierce's disease of grape is caused by Xylella fastidiosa (4-a). Option B matches all pairings correctly.

Rhizobium is a symbiotic bacterium, which can do nitrogen fixation.

Up to 20% of the dry weight of the endospore consists of calcium dipicolinate within the core which is thought to stabilize the DNA. Dipicolinic acid could be responsible for the heat resistance of the spore and calcium may aid in resistance to heat and oxidizing agents.

Some bacteria make glycocalyx material that forms capsules around their cell walls. This property increases the virulence of the species. The capsule resists the host’s defenses by impairing phagocytosis (the process by which certain cells of the body engulf and destroy microbes) by evading the complement and antibody body defense responses. The chemical nature of the capsule appears to prevent the phagocytic cell from adhering to the bacterium.

 In many species including B. subtilis, the coat is the outermost spore structure and in other species such as the pathogenic organisms B. anthracis and B. cereus, the spore is encased in an additional layer called the exosporium. Both the coat and the exosporium have roles in protection of the spore and in its environmental interactions. The spore coat also protects the spore from some chemicals such as hydrogen peroxide (H₂O₂) but not others such as organic solvents.

A fungus is a simple organism that lacks flowers, leaves, and chlorophyll, spreads rapidly via spores, and can cause various diseases in plants and animals. Bacteria and viruses have different biological classifications.

This amino acid has a free amino group for the formation of peptide bond. Peptidoglycan of bacterial cell wall is made up of N-acetyl glucosamine (NAG)-N-acetyl muramic acid (NAM). To NAM, a tetra-peptide chain is attached consisting of L-alanine, D-glutamic acid, L-lysine and D-alanine. The L-lysine is attached to a penta-glycine chain sideways, which is further attached to D-alanine of the neighbouring NAG-NAM complex. Since L-lysine needs to form the penta-glycine chain, it should have a free amino group for peptide bond formation. This extensive cross linking gives rigid structure to the peptidoglycan moiety.

Most peptidases can only cleave L-amino acids. Peptidases are enzymes that act on short protein chains into individual amino acids. Many bacteria secrete peptidases that act on L-amino acids and help in their nutrition. But these enzymes cannot degrade their cell walls due to the presence of D-amino acids in their cell walls.

Deuteromycetes are commonly known as imperfect fungi because only the asexual or vegetative phases of these fungi are known.

Citrus canker is caused by bacterium.

Mycorrhiza is a symbiotic association between fungi and plant roots. The fungi help plants absorb nutrients (especially phosphorus) from soil, while receiving carbohydrates from the plant. This mutualistic relationship is crucial for most terrestrial plants. Bacteria-root associations would be called rhizobia, not mycorrhiza.

The most poisonous mushroom is amanita.