A basidiomycete fungus producing uredospores on wheat plant is
A)Ustilago
B)Puccinia
C)Phytophthora
D)Alternaria

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Hint: Of the rust diseases of wheat, the foremost common nowadays is termed leaf or brown rust. It occurs on the leaf blades, although leaf sheaths may also be infected under favourable conditions, high inoculum densities, and intensely susceptible cultivars. It frequently lacks the abundant teliospore production of stem rust at the top of the season, leading to a brown leaf lesion instead of a black stem lesion that happens with stem rust.

Complete answer:
Wheat rust pathogens belong to genus Puccinia, family Pucciniaceae, order Uredinales and class Basidiomycetes. These rust fungi are highly specialized plant pathogens with narrow host ranges.When leaf rust teliospores are produced, they typically emanate from telia on the lower leaf surfaces, which remain covered by the epidermal cells. Losses because of leaf rust are usually small but are severe.

Puccinia graminis causes stem rust in wheat, rye, oat etc. The isolate of wheat cannot infect oats or the other host and the other way around, which indicate their host specificity. The phenomenon where a particular pathogen infects only a particular host is termed biological specialisation.

Vegetative body of Puccinia graminis:
1.The vegetative body is mycelium. Mycelia are of two types: dikaryotic and monokaryotic. 2.Both of these are septate, branched, grow intercellularly and produce special haustoria.
Simple pore if present within the septum, maintains protoplasmic continuity between neighbouring cells. The cytomembrane consists of chitin and glucan.
3.The dikaryotic mycelium occurs in wheat plant i.e., the first host and therefore the monokaryotic mycelium occurs on barberry plant i.e., the alternate host of the pathogen.

Different kinds of spores found in Puccinia graminis: Puccinia graminis tritici produces five different kinds of spores in its life cycle. These are uredospore, teleutospore, basidiospore, pycniospores and aeciospore.Uredospores and teleutospores grow on wheat, the first host; basidiospores on soil or on dead plants upon soil that developed from teleutospore; and also the pycniospores and aeciospores on barberry plant, the alternate host of the pathogen.

Hence, the correct answer is option (B)

Note: Puccinia graminis tritici could be a heteroecious, macrocyclic and polymorphic pathogen:
1.Heteroecious- It requires two unrelated hosts like wheat, the first host and Barberry, the secondary host; to finish the life cycle.
2.Macrocyclic- It's extended life cycle, consists of 5 kinds of spores i.e., uredospores, teleutospores, basidiospores, pycniospores or spermatia and aeciospores.
3.Polymorphic- It produces 5 different kinds of spores in its life cycle.