The production of sclerotia by Sclerotium rolfsii: II. The relationships between mycelial growth and initiation of sclerotia

Abstract

The relationship between mycelial growth and initiation of sclerotia in a single isolate of S. rolfsii Sacc. was investigated (1) in Petri dishes of different sizes, (2) in colonies (part or whole) transferred to fresh media and/or Petri dishes, and (3) in colonies having different rates of mycelial growth. Initiation appears to be regulated by the growing hyphae at the periphery of the mycelial mat. In dishes of 5, 7, 9 and 13 cm. diam. initials did not appear until the lateral extension of the mycelium was restricted. In colonies on millipore filters transferred to fresh plates where further extension of the mycelium could occur, initiation of sclerotia was suppressed. On central disks 5 cm. diam. removed from colonies at different stages of growth, initiation began earlier than on undisturbed colonies of comparable age. When the growth rate on a particular medium was altered, either by incubating at a lower temperature during the early stages or by using different inocula, there was a corresponding change in the number of initials formed. An analysis of data from seventeen experiments showed a highly significant, positive correlation between growth rate and number of initials produced. The significance of these results is discussed. It is suggested that initiation of sclerotia depends on the accumulation in the hyphae of substances which are metabolized in a different way from that involved in mycelial growth.