Spore Yield and Microcycle Conidiation of Colletotrichum gloeosporioides in Liquid Culture.

The effect of V8 juice concentration (5 to 40%, vol/vol), spore inoculum density (10 and 10 spores per ml), and liquid batch or fed-batch culture condition on mycelium and spore production by Colletotrichum gloeosporioides was evaluated. The amount of mycelium produced, the time required for initiation of sporulation following attainment of maximum mycelium, and the time for attainment of maximum spore concentration increased with increasing V8 juice concentration in batch culture. Cultures containing V8 juice at >10% achieved a similar spore density (apparent spore-carrying capacity) of about 0.8 mg of spores per ml (1 x 10 to 2 x 10 spores per ml) independent of inoculum density and V8 juice concentration. The relative spore yield decreased from a high of 64% of the total biomass for the low-inoculum 5% V8 culture, through 13% for the analogous 40% V8 culture, to a low of 2% for the high-inoculum 27% V8 culture. Fed-batch cultures were used to establish conditions of high spore density and low substrate availability but high substrate flux. The rate of addition of V8 juice was adjusted to approximate the rate of substrate utilization by the (increasing) biomass. The final spore concentration was about four times higher (3.0 mg of spores per ml) than the apparent spore-carrying capacity in batch culture. This high spore yield was obtained at the expense of greatly reduced mycelium, resulting in a high relative spore yield (62% of the total biomass). Microcycle conidiation occurred in the fed-batch but not batch systems. These data indicate that substrate-limited, fed-batch culture can be used to increase the amount and efficiency of spore production by C. gloeosporioides by maintaining microcycle conidiation conditions favoring allocation of nutrients to spore rather than mycelium production.

Sources of variability in the measurement of fungal spore yields.

VARIABILITY IN THE PRODUCTION OF FUNGAL SPORES AND IN THE MEASUREMENT OF SPORE YIELDS WAS INVESTIGATED IN FOUR SPECIES OF FUNGI: Colletotrichum gloeosporioides, Colletotrichum coccodes, Colletotrichum phomoides, and Acremonium strictum. When the fungi were grown on solid medium in microplates and spore yields were measured by counting the subsamples with a hemacytometer, the variability among hemacytometer squares was always the largest source of variation, accounting for 51 to 91% of the total variation. Variability among replicate cultures and results of repeat experiments were generally also significant. The effect of square-to-square variability on the precision of spore yield measurement was minimized by counting a moderate number (ca. 30) of squares per culture. Culture-to-culture variability limited the practical precision of spore production measurements to a 95% confidence interval of approximately the mean +/- 25%. We provide guidelines for determining the number of replicate cultures required to attain this or other degrees of precision. Particle counter-derived spore counts and counts based on spore weights were much less variable than were hemacytometer counts, but they did not improve spore production estimates very much because of culture-to-culture variability. Results obtained by both of these methods differed from those obtained with a hemacytometer; particle counter measurements required a correction for spore pairs, while the relationship between spore weights and spore counts changed as the cultures aged.

Autoradiographic studies of ethylenediurea distribution in woody plants.

Carbon-14-labelled ethylenediurea (EDU), synthesised from diethylenetriamine and (14)C-urea, was stem-injected into 2-year-old seedlings of sugar maple, white ash, flowering dogwood and flowering crabapple. At time intervals ranging from 1 h to 42 days after treatment, macroautoradiographs of leaf, stem and root tissue were made to determine relative distribution patterns of labelled chemical. Translocation of (14)C-EDU was very rapid and predominantly acropetal, especially after the first few hours. Maximum quantities of (14)C were found in leaf tissue approximately 7-10 days following injection, after which the intensity of the labelled chemical declined over the remainder of the study (42 days). Distribution patterns of (14)C-EDU were correlated with observed levels of protection afforded most plants when the chemical is injected 7 days before fumigation with ozone.