untitled

strains of opposite mating type (designated plus and

minus) are opposed on agar plates. Nuclear fusion

and meiosis usually occur within the zygospore. This

whole process is orchestrated by volatile hormones

termed trisporic acids, discussed in Chapter 5.

In addition to the Order Mucorales, the Zygomycota

contains a wide range of fungi that parasitize other

small organisms, including nematodes, other small

invertebrates, and other fungi. For example, the

genus Piptocephalis (Fig. 2.11c), in the Order

Zoopagales, contains several species that parasitize

other Zygomycota and occasionally other fungi.

Piptocephalisis one of several genera that produce

few-spored sporangia, termed merosporangia, with

linearly arranged spores. In nature the Piptocephalis

spp. probably grow as obligate parasites on other

fungi, especially other Zygomycota, although they

can be grown in pure culture if supplied with the

necessary vitamins. They penetrate the host hyphae

without killing them, by producing specialized, nutrient-

absorbing haustoria, and in this way they tap the

host’s nutrients to support their own development. This

type of interaction seems to be governed by specific

recognition factors (lectins), discussed in Chapter 12 (see

Fig. 12.10).

DIVERSITY OF FUNGI 25

Fig 2.10(a) A 2-day-old colony of Thermomucor pusillus

(previously called Mucor pusillus), a thermophilic species

common in composts. (b) The characteristic branched

sporangiophores of this fungus; the spores have been

shed but the sporangiophores and columellae remain, like

drumsticks.

(a) (b)

Fig. 2.9(a) The characteristically unbranched sporangio-

phores of most Mucorspecies. The sporangia are still

intact and contain many darkly pigmented spores with

melanized walls. (b) Thamnidium elegans, showing one of

several variations in the production of sporangiospores by

Zygomycota. This fungus produces typical sporangia on

long sporangiophores, but complex branching structures

arise from the sporangiophore and terminate in small,

few-spored sporangioles.

(a)

(b)

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