Microbiology and Biochemistry of PtA-Resistance/Zur Mikrobiologie und Biochemie der Peronosporaresistenz

Since 1960 the blue mould disease caused by Peronospora tabacina Adam (PtA) and which leads to considerable losses, has been occurring epidemically in tobacco grown in Europe and parts of Asia and Africa. All varieties cultivated are susceptible to this fungus, which is an inevitable tobacco parasite, and must either be protected prophylactically by weekly spraying with dithiocarbamate, which leaves residues, or be replaced by new, PtA-resistant strains based on wild forms of Nicotiana. In investigations of our own - published in 5 parts in the "Zeitschrift fuer Naturforschung" - the fundaments of a third way of combatting this disease were worked out using the very PtA-susceptible German, high-quality strains "Badischer Geudertheimer'', ''Badischer Burley E'' and "Virgin SCR''. This present paper contains, summarized, the state of this work at the end of 1971. It was observed that the PtA-resistant hybrid strains (U. S. Bel.-61 types) were also infected by PtA, but this infection was stopped by the synthesis of antibodies, and that there are reciprocal effects of the substances triggering off resistance and microorganisms. The antibodies were separated out electrophoretically, established chemically and ascertained to be nucleoproteid or nucleotides, and to be an alloxazin compound closely related to vitamin B₂. Their delivery, via the roots, to the cotyledons of the said German high-quality strains produced in them, during the 2-month observation period possible, absolute resistance to Peronospora, with no external change in the varieties. The observation results and the methods for separating the substances triggering off resistance are shown in two stages of development, and the results discussed. Within the scope of the interreaction with other microorganisms a special bacteria was discovered which made it possible to also identify the substances which trigger off PtA-resistance in the commercial Difco yeast extract, and to separate them out. After delivery of these separated substances to the cotyledons of the said German varieties, the same positive resistance-triggering results were ascertained. These substances, originating from yeast extract, were compared chromatographically with those extracted from the Bel. varieties and proved to be chemically equivalent. All these results were secured over a period of several years. A curative effect which lasted up to 48 hours after PtA infection, was established. These results with the special bacteria are given in a later stage of development. This special bacteria (Micrococcus spec.) considerably accelerated the operations, which, for technical plant protection reasons, are possible only up to 5 months a year. In a first field trial in 1971, and once Peronospora had occurred naturally, the resistance behaviour of var. ''Badischer Geudertheimer'', after a single prior treatment of the cotyledons was observed throughout the whole of the tobacco crop. The results and their scientific fundaments are discussed and their possible uses, also within the scope of pollution control, are listed