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ISHS Acta Horticulturae 324: Symposium on Soil Sickness and Replant Diseases in Fruit Trees

ALLELOPATHIES AND BIOLOGICAL 'DEGRADATION IN AGRICULTURAL SOILS: AN INTRODUCTION TO THE PROBLEM OF SOIL SICKNESS AND OTHER SOIL-BORN DISEASES

Author:   F. ZUCCONI
Abstract:
THE STATE OF KNOWLEDGE. The denomination of "soil sickness" indicates, in the agricultural lexicon, a condition of progressive soil inhospitality to the frequent return of a single crop. The decline of productivity which follows is generally confined to the reiterated species, affecting less other plants, mostly if botanically unrelated.

Beyond such a broad definition, however, it is hard to find an agreement as to the nature and origin of the disease, or its differentiation from other root disorders. An unwieldy consequence is that the proposed causal agents are perplexingly many, ranging from pathogens to nematodes and from nutrient deficiencies to toxins. Such a dissention reflects a basic separation of purposes among scientists, and the uncertainty of control measures. Meanwhile fruit growers and nurserymen keep generating keen observations and practical solutions for which reasonable scientific explanations remain unavailable.

The ambiguity of the existing scientific stand reflects an inadeguate knowledge of the disease, when refering both to the complexity of its effectors and multiformity of manifestations. It also reflects the confusion of a stage in which, confronted with a progressive deterioration of soil biological fertility, we can hardly discriminate between distrophies and mineral deficiencies, or between root debasement by intoxication or pests. Meanwhile, soil degradation increases, in spite of the alleged technological development, spreading soil sickness and other soil-born diseases.

It is indeed disquieting that such difficulties have not stimulated a more interdisciplinary approach, while the field remains fragmented into separate "disciplines", each feuding over its own represantation of the disease. Unfortunately, no such representation can account for the many facets of the problem, nor is able to include (or debase) alternative hypotheses. It does not surprise, then, that even ponderous reviews (Rice 1974, Putnam and Tang 1986) remained devoided of the theoretical structure required for scrutinizing the problem, guiding a sensible inquiry, or stimulating a probative research.

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