Question

A wheat plant is infected by the aeciospores of black stem rust fungus produced on the alternate host. What is the correct sequence of the following stages in the disease cycle?
1. Uredo stage
2. Pycnidial stage
3. Basidial stage
4. Teleuto stage
5. Aecidial stage
Select the correct answer using the codes given.
A. 1, 4, 3, 5, 2
B. 1, 3, 4, 5, 2
C. 1, 2, 3, 4, 5
D. 1, 4, 3, 2, 5

Answer 1

The stem, black, and cereal rusts are caused by the fungus Puccinia graminis and are a significant disease affecting cereal crops. Crop species that are affected by this disease include bread wheat, durum wheat, barley and triticale.

Complete step by step answer: The stem rust fungus attacks the part of a plant that is above the ground. Spores that land on green wheat plants form a pustule that invades the outer layers of the stalk. Infected plants produce fewer tillers and set fewer seeds, and in cases of severe infection, the plant may die. Infection can reduce a healthy crop about three weeks before harvest into a black tangle of broken stems and shrivelled grains by harvest. Rust fungi can produce up to five spore types from corresponding fruiting body types during their life cycle, depending on the species. The correct sequence of the stages start with the uredo stage, followed by teleuto stage, basidial stage, aecidial stage and the last stage, i.e. the pycnidial stage.
1. Urediniospores form uredia. These serve as repeating dikaryotic vegetative spores. These spores are referred to as the repeating stage because they can cause auto-infection on the primary host.
2. Teliospores form telia. These dikaryotic spores often survive on the winter stage of the life cycle. They usually do not infect a plant directly; instead, they germinate to produce basidia and basidiospores. These windborne haploid spores often infect the alternate host in Spring. They are rarely observed outside of the laboratory.
3. Aeciospores form aecia. These serve mainly as non-repeating, dikaryotic, asexual spores, and go on to infect the primary host.
4. Pycniospores from Pycnidia. They serve mainly as haploid gametes in heterothallic rusts.
Hence, the correct answer is option (A).

Note: Stem rust on wheat is characterized by the presence of uredinia on the plant, which are brick-red, elongated, blister-like pustules that are easily shaken off. They most frequently occur on the leaf sheaths but are also found on stems, leaves, glumes, and awns. On leaves, they develop mostly on the underside but may penetrate to the upper side. On leaf sheaths and glumes pustules, they rupture the epidermis, giving a ragged appearance.