A study of problems in the life-cycle of Puccinia malvacearum, from monosporidial inoculations, and cultures made under controlled conditions

Abstract

The work began with an endeavour to find a technique for inoculating the host plants of the Uredineae with single sporidia of their specific rust, with precision and certainty. This has been achieved, and single sporidia have been isolated by means of the microdissection apparatus of Dr. Chambers. The most favourable conditions for sporidial infection were then determined, and cultures kept under controlled conditions.The rust used was Puccinia malvacearum, chosen because its teleutospores germinate immediately they are ripe so that a constant supply is available over a long period. This facilitated preliminary experimentation. Results show that this fungus is homothallic: a single sporidium being sufficient to cause infection, and the production of teleutospores. This was to be expected since there is no pycnidium or aecidium in the life cycle. The method of Inoculation has universal application for the rusts and it is hoped to demonstrate this at once in a long cycled form. Reviewing the literature on Puccinia malvacearum several problems in the life-cycle were found to be as yet unsolved. A study of the complete life history by means of examination of infections of known age, made under controlled conditions, has helped to elucidate these points. Infected plants in the field have also been under observation day by day throughout the winter, to solve the problem of hibernation. The results from these experiments show that there is a retardation in the cycle consequent on the less frequent occurrence of suitable conditions for germination and infection, but new infections do occur whenever these favourable conditions prevail.