|REX, PAUL - Former ARS Employee|
Submitted to: Journal of Plant Studies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2015
Publication Date: 3/26/2015
Citation: Abbas, H.K., Rex, P. 2015. Presence of adhesive vesicles in the mycoherbicide Alternaria helianthi. Journal of Plant Studies. 4(2): 21-29.
Interpretive Summary: Alternaria helianthi is an effective biological fungal agent on the very important weed common cocklebur. The effectiveness of this pathogen depends on many factors such as temperature, media, formulation..etc. This fungus was found to be more effective when its spores were produced at low temperature (18 C). This study showed that the spores grown at 18 C produced sticky materials in large numbers than the spores grown at higher temperature (28 C). These sticky materials might play a significant factor in the effectiveness of this pathogen against common cocklebur and also it might play a big role in survival of this biological agents. These are very important findings and they are very useful in conducting more research for better understanding of the efficacy of this biological agent. This information is useful for other scientists working in this field of research.
Technical Abstract: Alternaria helianthi conidia have been shown to cause disease on common cocklebur. Conidia were applied to slides made hydrophobic by coating with dimethyldicholorosilane (mimics leaf surface), then rinsed and treated with FITC-Con A to stain the adhesive material. Alternaria helianthi conidia grown at 18 °C were more virulent than those grown at 28 °C, and adhered to the leaves of treated plant and produced multiple, aggressive, branched, long germ tubes in much greater numbers. The 18 °C conidia caused damage symptoms including necrotic lesions on leaves and stems, stunting and mortality to all biotypes tested of common cocklebur at the 6- to 12-leaf growth stages in greenhouse when treated with 50,000 conidia /ml. Under confocal laser scanning microscopy, the distribution of the adhesive material on the conidial surface was varied, being evenly distributed on some conidia while appearing as globules on others. Examination by transmission electron microscopy showed that virulent conidia had dense ribosomes and abundant endoplasmic reticulua indicating actively synthesizing cytoplasm. Adhesive vesicles, which appear to be the means of export of the adhesive from the cytoplasm, were often arranged along external cell walls. An osmophilic material, possibly the adhesive substance itself, was seen between the cell membrane and the cell wall. This substance may play an important role in the virulence of A. helianthi to common cocklebur and survival of this pathogen.