[Effect of plant residues on the parasitic activity of soilborne pathogens and the saprophytic microflora of the soil. III. Influence of rye and rape grown as winter catch crop on the incidence of Cercosporella herpotrichoides Fron (author's transl)].

In a five-years field trial, the influence of two winter catchcrops, rye and rape, upon the incidence of Cercosporella herpotrichoides has been studied. The winter catch-crops had been repeated three times, followed either by stubble-crop or without in fall of the fourth year. The variants (blocks) had been completed by two variants without catch-crop, either carefully cultivated or overgrown with weeds. Each of the four blocks had been divided three times to be grown with three different crop sequences containing 80%, 60% (with the insusceptible corn), or 40% haulm fruit, respectively. Each of the 12 variants had been divided into two parts by continuous fallow stripe, one part being artificially infested with the pathogen in the beginning (1st winter wheat). In the 2nd, 3rd, and 4th year, only spring crops were grown, followed by winter wheat in the 5th year. The final exploration resulted in a medium to heavy degree of infection, being significantly higher in the 80% cereal crop sequence than in the 60% and 40% sequences. Concerning the catch-crops, infection in the rye variants was equal or significantly lower than in the carefully cultivated variants without catch-crop. On the other hand, infection of the rape variants had become significantly higher than that of the catch-crop-free ones, about as heavily as in the weed-infested variants. From fall 1966 to summer 1969, the development of the saprophytic soil microflora and several other edaphic parameters had been investigated. Remarkable differences in intensity of disintegration have been observed under the influence of the main crops, cereals or potatoes, respectively, but no differences could be stated resulting from the matter of disintegration--residues of rye or rape--, which might interpret the contrasting effects on the pathogen. Too, no indication for antagonistic activity of bacteria or actinomycetes has been noted. The results are compared with known facts of Cercosporella and of other soil borne pathogens. The difference in biology of Cercosporella on the one hand, and of root infecting fungi on the other hand seems to be most important to explain the results obtained.