Identification of Diachea leucopodia on Strawberry from Greenhouse in Korea

Abstract

We have detected the slime mold, Diachea leucopodia (GNU06-10) in a strawberry greenhouse located in Sancheong-gun, Gyeongnam. Typical fruiting bodies had developed gregariously on the strawberry leaves, petioles, and plant debris on ground soil habitat, and also surprisingly on plastic pipes and a vinyl covering. Field samples were examined via stereomicroscopy, light microscopy, and SEM for the determination of morphological characteristics. Dark-brown to black spores formed gregariously within the stipitate cylindrical sporangium, and were covered by an iridescent peridium, which may be intact at maturity, or may have disintegrated. The upper portion of the peridium generally breaks up to expose the spores, whereas the lower portion was usually persistent. The results of energy dispersive X-ray spectrometer (EDS) analysis showed that lime was present in the stalk and columella but absent from the spores, capillitium, and peridium. The above characteristics confirm its taxonomic position in the genus Diachea. However, this genus is intermediate in character between the Physarales and Stemonitales of the Myxogastromycetidae. Hence, this genus had been classified as a member of the Stemonitales until the mid-1970's, on the basis of its iridescent peridium and noncalcareous capillitial system, similar to Comatricha of the Stemonitaceae. By way of contrast, emphasis on morphological characteristics, most notably the calcareous stalk and typical columella, places Diachea within the order Physarales. The presence of a phaneroplasmodium during the trophic stage and lime deposition in its sporophores, as was confirmed in this work, supported the inclusion of Diachea in the Physarales, and the noncalcareous capillitial system verified its identification as a member of the Didymiaceae. Further characteristics of the species D. leucopodia include the following: phaneroplasmodium, spore globose 7.5 µm in diameter, very minutely roughened; sporangia 500 µm × 1mm, more or less cylindrical, gregarious, stalked 1.2mm; stalk and columella white.

Keywords: Diachea leucopodia; Digital mapping; Energy dispersive X-ray spectrometry; Slime mold; Strawberry.

Fig. 1

Fruiting bodies and other morphological features of Diachea leucopodia associated with the strawberry plant. A, mature sporophores pedicellate sporangia, which is elongated, cylindrical on strawberry plant and also on plastic pipes; B, weed, leaf lesions affected by colonized sporophores and also on debris on ground soil, and interior surface of vinyl coverings; C, Scanning electron micrographs of partly dehisced membranous peridium showing portion of columella and capillitia of Diachea leucopodia; D, In vitro cultivation of Diachea leucopodia. a, spore germination (light microscopy); b, phaneroplasmodium (digital camera); c, phaneroplasmodium (stereomicroscopy); d, Primordia with expanded apices of sporocarps (stereomicroscopy).

Fig. 2

EDS spectra of element deposition for spore against stalk or spore against carbon ribbon. Portion of SEM view shown as a tetragon was subjected to EDS analysis (SPs) and EDS digital Ca mapping (SPm). SPs-1 shows the EDS spectrum for spores adsorbed on a carbon ribbon. LE, Longitudinal extrusion of membrane wrinkled and folded up due to desiccation.

Fig. 3

EDS spectra of element deposition for peridium (PE), capillitial thread (CA), columella (CO), stalk (ST) and hypothallus (HY) (left column). Portions of SEM view shown as tetragons were subjected to EDS analysis (middle column) and the whole view was X-ray mapped for Ca deposition correspondingly (PEm, CAm, COm, and HYm) with the exception of STm, for which only the tetragon portion was mapped (right column). LE, refer to the footnote of Fig. 2.