Laimosphere


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) 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).

ources

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Magyarosy, A. C. 1973. Effect of squash mosaic virus infection on microbial populations around the hypocotyl and chloroplast structure and function. Ph.D. Dissertation, Univ. Calif., Berkeley.

Magyarosy, A., and J. G. Hancock. 1972. Microbial population of the laimosphere of squash (Cucurbita maxima) "Plant and Soil" 37:187-190.

Magyarosy, A. C., and J. G. Hancock. 1974. Association of virus-induced changes in laimosphere microflora and hypocotyl exudation with protection to Fusarium stem rot. "Phytopathology" 64:994-1000.


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