Question

Describe biotrophs with a suitable example.

Answer 1

A plant-pathogenic fungi which establishes a long-term feeding relationship with the living cells of a host, without killing it as part of the infection process.

Coronata is a biotroph that can cause severe infections on smooth bromegrass and numerous other grasses.

Fungi are heterotrophs requiring external sources of carbon for energy and cellular synthesis and they have adapted three different modes of nutrition to obtain this carbon, occurring as saprotrophs, necrotrophs and biotrophs.

Answer 2

Quite a lot of plant-pathogenic fungi establish a long-term feeding relationship with the living cells of their hosts, rather than killing the host cells as part of the infection process. These pathogens are termed biotrophic [from the Greek: bios = life, trophy = feeding].

Typically, these fungi grow between the host cells and invade only a few of the cells to produce nutrient-absorbing structures termed haustoria. By their feeding acitivities, they create a nutrient sink to the infection site, so that the host is disadvantaged but is not killed. This type of parasitism can result in serious economic losses of crop plants, and in natural environments it can reduce the competitive abilities of the host; indeed, a few biotrophic pathogens have been used successfully as biological control agents of agricultural weeds.

In many ways, this type of parasitism is very sophisticated - keeping the host alive as a long-term source of food. This has led some people to suggest that biotrophic parasitism is evolutionarily advanced. But this is clearly not the case in general, because an almost identical type of parasitism is found in the arbuscular mycorrhizal fungi (see Mycorrhizas) which are thought to have developed on the earliest land plants.

Here we consider the two most important groups of biotrophic plant pathogens:

the rust fungi (Basidiomycota)

the powdery mildew fungi (Ascomycota).

A parallel can be made between the behaviour of these fungi and the biotrophic mycoparasites (see Verticillium biguttatum)