Laimosphere

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: λαιμός) denotes a connecting organ (neck) while -sphere indicates a zone of influence. Topographically, the laimosphere includes the soil around any portion of subterranean plant organs other than roots where exuded nutrients (especially sugars and amino acids) stimulate microbial activities. Subterranean plant organs with a laimosphere include hypocotyls, epicotyls, stems, stolons, corms, bulbs, and leaves. Propagules of soil-borne plant pathogens, whose germination is stimulated by a plant 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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