The Microflora of the Rhizosphere of Tomato Plants in Relation to Soil Sterilization

Abstract

Sterilization brings about significant changes in the physical and chemical, as well as biological properties of soil which thus becomes a different and often more favourable medium for microbial activity. In an investigation of a root rot of greenhouse tomatoes marked differences in numbers of fungi, bacteria, and actinomycetes were noted in both soils and rhizospheres as a result of sterilization with steam, chloropicrin, and formaldehyde. Roots invariably supported much higher numbers of the three groups of organisms studied, thus displaying the common "rhizosphere effect". Numbers of bacteria were considerably greater on infected than on healthy roots.Qualitative differences in fungi and bacteria were also noted in both soils and rhizospheres. Of particular interest was the tendency for bacteria with simple food requirements and those stimulated by amino acids to predominate in the rhizosphere, and for those with more complex nutritional needs to predominate in soils apart from the roots.It is suggested that such nutritional investigations of rhizospheres may be useful in studies on the physiological activity of plant roots.

Residue Reviews / Rückstands-Berichte

“…The fungi as a group are usually more readily killed by soil fumigants and fungi eides than are some baeterial types (DOMSCH 1959, MUNNECKE and FERGUSON 1960, WAKSMAN and STARKEY 1923. Following treatment, they may inerease in numbers shortly after the baeteria and attain higher numbers than in the original soil (KATZNELSON and RICHARDSON 1943) or they may remain at low numbers for relatively long periods of time (MARTIN et al 1957, MOLLISON 1953. WARCUP (1951) observed that 18 months after treatment of a field soil with formalin the numbers of fungi were stilliower than in untreated soi!.…”

“…Following formalin treatment, Penicillium and Plectonaemella spp. became (KATZNELSON and RICHARDSON 1943). SMITH (1939) noted that chloropicrin fumigation often increased the relative numbers of Trichoderma in the soi!.…”

Rhizosphere fungi of five plants in Egypt

“…terreus and A. niger. It is well established that the microbial population of the soil in the rhizosphere differs both quantitatively and qualitatively from that of non-rhizosphere soil (TIMONIN 1941, KATZNELSON and RICHARDSON 1943, KATZNELSON 1946, STARKEY 1948, CLARE 1949, PETERSON 1958, LOCHHEAD 1959, YOUSSEF and MANKARIOUS 1968, EL-DOHLOB 1972, ABDEL-FATTAH 1973.…”

Microbiology of Soil

“…Timonin (194) ingeniously grew aseptic flax plants in solution and noted that the incidence of pathogenic fungi was lowered and that of the saprophytic increased by the "rhizosphere effect" of the resistant variety. Katznelson & Richardson (195) sterilized soil by steam, chloropicrin, and formaldehyde and then made analyses of tomato roots. The same "rhizosphere effect" was found under those conditions.…”