Fungal Spore Germination on Natural and Sterile Soil

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Abstract
SUMMARY The germination process of spores of several fungi which require exogenous energy-sources was initiated in non-amended natural soil, a medium deficient in energy-yielding substrates. As measured by subsequent germination time on sterilized soil, this phase accounted for about 8 to 25 yo of the total germination time. In conidia of Penicillium frequentans it was irreversible, was inhibited by temperatures of I "C and was dependent on water alone. Continued progress towards germ-tube formation required exogenous energy-yielding nutrients. When incubation on sterilized soil was interrupted by exposure to non-amended natural soil or a model system designed to imitate the microbial energy-source sink of natural soil, progress towards germination ceased in several fungi. Progress already made towards germination was maintained if the exposure to deprived conditions was short (about 3 days or less), but if longer the germination process reverted towards the water-dependent phase. The reversal, in P. frequentans conidia, paralleled the loss of 14C from spores labelled with (14C_lglucose. When 14C-labelled conidia were incubated in an artificial nutrient sink, the label lost was about equally divided between 14C02 and non-gaseous 14C-labelled metabolites. Pretreatment of P. frequentans conidia in water stimulated uptake of (14C)glucose. The results support the view that soil fungistasis in many instances is caused by nutrient deprivation.

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