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Possible Replicative Forms of a Mycoplasmalike Organism and their Location in Aster Yellows Diseased Nicotiana and Aster. J. F. Worley, Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 60:284-292. Accepted for publication 9 September 1969. DOI: 10.1094/Phyto-60-284.

Mycoplasmalike bodies were observed in phloem cells of tobacco (Nicotiana rustica) and aster (Callistephus chinensis) plants suffering from aster yellows. Most cells containing the mycoplasmalike bodies were sieve elements devoid of recognizable plant organelles, but bodies were occasionally seen in elements containing apparently intact mitochondria, plastids, or degenerate nuclei. The bodies were rarely observed in parenchyma cells adjacent to mature sieve elements. Pleomorphism was evidenced by a wide variety of sizes, shapes, electron densities, and arrangements. The bodies were bounded by a clearly defined membrane with no evidence of a second membrane or cell wall. Single spherical bodies varied in diam from 75 to 600 mµ; the long dimension of the elongated forms attained lengths of 1 µ. Structures suggesting chains, binary fission, budding, and filamentous growth may represent stages in the life cycle of the organism in its plant host.