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Hyphal Growth Questions

Question 1

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Answer 1

Spore germination is followed by an indeterminant growth process. Initially a spherical colony is formed. In soil, organic nutrients are unevenly dispersed and growth becomes fragmented according to availability of nutrients. The fungus may contact hyphae of different mating types, enabling establishment of dikaryotic mycelium. After establishment of an adequate store of energy reserves, environmental cues may trigger formation of the sporocarp. Most agaric sporocarps are formed in autumn when the temperatures are declining and the relative humidity is maintained. However, some species fruit throughout the year, and in these cases, the energy store appears to be of overriding importance. In the absence of dikaryotisation, the fungus remains as a haploid mycelium, which never forms a fruiting structure. Thus the cycle is completed with the release of spores from the sporocarp.


Question 2

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Answer 2

Available nutrients, especially carbon , are extremely important for the maintenance of all fungi. Saprotrophic Agarics tend to be found in leaf litter. Overall, continuation of the thallus will require moist conditions and temperatures within a range optimal for growth. Litter is complex, with fresh nutrients associated with the recently fallen leaves, and more complex carbohydrates in the lower layers. Any one thallus will have some hyphae in recently fallen leaves and others in more recalcitrant materials. The thallus will be constrained by a variety of factors. Appropriate pH and available oxygen will limit the spread of the thallus. Competitive interactions with other organisms, especially mycophagous arthropods, will reduce hyphal survival. Thus any one thallus will be in a set of overlapping stages within the thallus.


Question 3

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Answer 3

Generally speaking, hyphae will continue to elongate while-ever available nutrients can sustain the thallus. The cues which determine developmental pathways differ from fungus to fungus. In principle, the deficiency of a critical nutrient such as carbon will induce the formation of survival structures such as sclerotia, and escape structures such as hyphal strands. Reduced concentrations of critical nutrients will alter the pattern of hyphal branching. Low concentrations of nutrients generally are associated with open networks of sparsely spaced hyphae. High nutrient concentrations are associated with abundant mycelium. Formation of sexual structures may be triggered by starvation or more specific triggers such as UV light or declining temperatures. The formation of asexual structures tend to be associated with starvation.


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Question 7

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