The laimosphere is the microbiologically enriched zone of soil that surrounds below-ground portions of plant stems; the laimosphere is analogous to the rhizosphere and spermosphere. The combining form laim- from laimos (Greek) denotes a connecting organ (neck) while -sphere indicates a zone of influence. Topographically, the "laimosphere" includes the soil around any portion of plant shoots other than roots where hypocotyl exudates influence microbial activities. Subterranean plant organs within a laimosphere include hypocotyls, epicotyls, stems, stolons, corms, bulbs, and leaves. Propagules of soil-borne plant pathogens, whose germination is stimulated by a plant and exudates in the laimosphere, can initiate hypocotyl and stem rots leading to "damping-off". Pathogens commonly found to cause such diseases are species of "Fusarium", "Phoma", "Phytopthora", "Pythium", "Rhizoctonia" and "Sclerotinia".

Fig. 1. A diagram denoting the location of the "laimosphere, rhizosphere," and "spermosphere" of the subterranean organs of a plant ("Plant and Soil" 37:187-190, 1972).

Fig. 2. Chlamydospores of "Fusarium solani f. sp. cucurbitae" forming in the laimosphere of a squash hypocotyl, Magyarosy 1973.

Fig. 3 & 4. Early lesion development in the epidermis of a squash hypocotyl caused by "Fusarium" solani stained with tetrazolium salt, Magyarosy 1973.

Fig. 5. Diagram of hypocotyl stem rot leading to "damping-off" caused by "Rhizoctonia solani" (Univ.Calif. Agr. Exp. Sta. Service Manual 23, 1957).


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