Location: Tropical Crops and Germplasm ResearchTitle: Use of scanning electron microscopy in the speciation of Gliocephalotrichum spp. in rambutan (Nephelium lappaceum L.) Author
Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 4/2/2012
Publication Date: 11/1/2012
Citation: Latoni-Brailowsky, E., Serrato-Diaz, L., Rivera-Vargas, L., Goenaga, R.J. 2012. Use of scanning electron microscopy in the speciation of Gliocephalotrichum spp. in rambutan (Nephelium lappaceum L.). Phytopathology. 102:S6.3. Interpretive Summary:
Technical Abstract: Rambutan is a tropical tree fruit crop native to Malaysia. Worldwide, fruit rot is a limiting factor for fruit quality. In 2011, fruit rot was observed on rambutan at the USDA-ARS Tropical Agricultural Station in Mayaguez, Puerto Rico, and was attributed to Gliocephalotrichum spp. Light microscopy (LM) and molecular characterization are tools to differentiate Gliocephalotrichum spp. The use of scanning electron microscopy (SEM) has been a successful tool to differentiate powdery mildews at species level. To test the potential of SEM to speciate Gliocephalotrichum spp., two pathogenic species, G. bulbilium (Gb) and G. simplex (Gs), and a saprophytic G. bacillisporum (Gba), were grown on rambutan spintem (fruit hair-like appendage) tissue (Gb and Gs) and onto carnation leaf agar (Gba). Plant tissue was prefixed in 3% gluteraldehyde and 0.1 M potassium phosphate buffer, (pH =7.2) for 24 h at 8°C. Samples were dehydrated with ethanol, followed by critical point drying. Detailed SEM observations of stipes under penicilli, basal conidiophore cells, conidiophore stalks, and patterns of the surfaces of conidia and chlamydospores were obtained. From the base to mid-section of the stalk, verrucose-like patterns were observed on Gb, but smooth patterns on Gba and Gs. Conidial surface of Gb were ornamented with undulated fibrillar patterns, whereas conidia of Gba and Gs were smooth. Conidia of Gs were slightly curved at one end but conidia of Gb and Gba were straight. Chlamydospores of Gs were solid and smooth but bulbilloid aggregates of Gb were porous. Emergence of the conidiophores and mycelia on plant tissue suggest differences in infection processes among species. Conidiophores of Gb and Gba emerge through the stomata but conidiophores of Gs ruptured epidermal spintems cells. SEM has the potential to be used as a characterization tool for species of Gliocephalotrichum on rambutan and other crops.