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SOIL CONDITIONS AND THE TAKE‐ALL DISEASE OF WHEAT
Author(s) -
GARRETT S. D.
Publication year - 1936
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1936.tb06120.x
Subject(s) - mycelium , fungus , biology , hypha , soil water , aeration , carbon dioxide , rhizoctonia , botany , agronomy , ecology , rhizoctonia solani
SUMMARY Ophiobolus gramini‐s can spread through the soil only along the roots of its host plants. A distinction can thus be made between two phases in the activity of the fungus, a parasitic or ascendant phase, in which the fungus is actively increasing on the roots, and a pseudo‐saprophytic or declining phase, in which the fungus is merely persisting in dead host tissue. In the declining phase, the disappearance of the fungus from the soil must be hastened by the action of the soil saprophytes in actually decomposing its mycelium. Certain soil conditions, which at one time increase the activity of the fungus on the roots of its host, may at another time hasten the disappearance of the resting mycelium from a fallow soil. The rate of growth of Ophiobolus graminis along the roots of wheat seedlings has been found to vary widely with soil conditions, and growth may even be inhibited altogether. The best growth of all is made in sand; growth in soil increases both with improvement in aeration, and with rise in p H value; it is thus best in light and open soils, and in alkaline soils. In the case of neutral and alkaline soils, growth may be improved by steaming. A hypothesis has been put forward whereby the rate of growth of the fungus along the roots is related to the concentration of carbon dioxide in the microclimate of the root zone, along which the fungal hyphae are growing. Carbon dioxide is produced by the respiration of the host root, the hyphae of Ophiobolus, and the soil microflora; variation in the concentration of carbon dioxide in the root zone will depend on the rate of diffusion of the gas away from the root. This will be most rapid, on the one hand, in light and open soils favouring rapid physical diffusion, and, on the other, in alkaline soils, which can act chemically as carbon dioxide acceptors. These are just the soil conditions which make for most rapid growth of the fungus along the roots. Growth of Ophiobolus graminis along the roots is also most rapid under just those soil conditions known to favour the occurrence of the take‐all disease in the field, viz. loose and open soils, soils of light texture, and alkaline soils. This well‐established action of soil conditions upon the prevalence of the disease in the field is thus considered to operate directly through the fungus, rather than indirectly through the resistance, yet to be demonstrated, of the host plant.