Cytology of the Asexual Stages of the Australian Brown Rot Fungus Monilinia fructicola (Wint.) Honey

Abstract

The value of the HCl-Giemsa technique in the study of fungal cytology has again been demonstrated. Using this technique the cytology of the asexual stage of Monilinia fructicola has been studied with the following results.
Nuclear division in the homocaryon is synchonous for all nuclei within a cell. Division appears to proceed by mitosis, the haploid chromosome number being four.
The range of numbers of nuclei throughout the mycelium has been investigated. Mature conidia contain an average of 6.6 nuclei with a distribution from 4 to 10. Upon germination initially 2 to 3 nuclei move into the germ tube. The remainder divide synchronously within 24 hours incubation and about half of these subsequently move into the germ tube. Hyphal cells are generally multinucleate with a distribution of 1 to 40 nuclei per cell. Lateral branches are generally multinucleate when delimited by a septum. Hyphal tips and conidiophores are generally multinucleate. Young conidia initially receive 2 to 3 nuclei each and may receive more subsequently by the movement of nuclei from conidium to conidium in older parts of the chain.
The movement of nuclei into germ tubes, into lateral branches, along anastomoses, into young conidia and through septal pores has been observed.
This study has shown that the asexual stage of Monilinia fructicola has virtually every conceivable mechanical process for the production and maintenance, coupled with the possible dissociation, of a heterocaryon.
The question of differential rates of nuclear division within a heterocaryotic mycelium is at present only a theoretical possibility. However, the presence of multinucleate cells; nuclear movement through septal pores, through anastomoses and between conidia; multinucleate lateral branches and hyphal tips and multinucleate conidiophores and conidia, provides for Monilinia fructicola a system of great potential flexibility in adaptation to the environment.