MICROBIOLOGICAL DIFFERENCES BETWEEN LIMED AND UNLIMED SOILS AND THEIRRELATIONSHIP WITH CAVITY SPOT DISEASE OF CARROTS (DAUCUS-CAROTA L) CAUSED BY PYTHIUM-COLORATUM IN WESTERN-AUSTRALIA
Ka. Eltarabily et al., MICROBIOLOGICAL DIFFERENCES BETWEEN LIMED AND UNLIMED SOILS AND THEIRRELATIONSHIP WITH CAVITY SPOT DISEASE OF CARROTS (DAUCUS-CAROTA L) CAUSED BY PYTHIUM-COLORATUM IN WESTERN-AUSTRALIA, Plant and soil, 183(2), 1996, pp. 279-290
Application of lime (4000 kg ha(-1)) to a soil used for commercial car
rot production (pH 6.9) significantly (p < 0.05) reduced the incidence
of cavity spot disease of carrots compared to unlimed soil (pH 5.1).
It significantly (p < 0.0 I) increased soil microbial activity as meas
ured by the hydrolysis of fluorescein diacetate and arginine ammonific
ation. The application of lime resulted in a significant (P < 0.01) in
crease in the total numbers of colony forming units (cfu) of aerobic b
acteria, fluorescent pseudomonads, Gram negative bacteria, actinomycet
es and a significant (P < 0.01) decrease in the cfu of filamentous fun
gi and yeasts compared to unlimed soil. Liming also increased the cfu
of non-streptomycete actinomycetes rarely reported in similar studies.
These non-streptomycete actinomycetes were estimated and isolated usi
ng polyvalent Streptomyces phages and the dry heat technique to reduce
the dominance of streptomycetes on isolation plates. The non streptom
ycete actinomycetes isolated included species of Actinoplanes, Micromo
nospora, Streptoverticillium, Nocardia, Rhodococcus, Microbispora, Act
inomadura, Dactylosporangium and Streptosporangium. The numbers of act
inomycetes antagonistic to Pythium coloratum, a causal agent of cavity
spot disease of carrots increased in soil amended with lime. Applicat
ion of lime also reduced the isolation frequency of P coloratum from a
symptomatic carrot roots grown in soil artificially infested with the
pathogen, 3, 4 and 5 weeks after sowing.