Alternative fruiting pathways in Phycomyces

Developmental distinctions between giant and dwarf fruiting bodies of Phycomyces blakesleeanus (Burgeff) were studied by means of size measurements and growth analyses. Histograms of fruiting body lengths showed a bimodal distribution, with peaks around 0.3 millimeter (dwarfs) and 30 millimeters (giants). Individual cultures contain both giants and dwarfs. Differences between giants and dwarfs appear in the first phase of development; the apex of the giant is tapered, whereas the dwarf apex is dome-shaped. Probable cytological distinctions at this stage are cited in discussion. The dwarfs terminate enlargement upon expansion of the sporangium, thus lacking the subsequent phase of rapid elongation (stage IV) that contributes 90% of the length in the case of giants. It was concluded that P. blakesleeanus maintains two developmental patterns for asexual fruiting, with dwarfs and giants differing radically in growth regulation.