In Vitro Selection Of Dendrobium Sonia-28 Protocorm-Like Bodies Against Fusarium Proliferatum
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Date
2016-04
Authors
Dehgahi, Raheleh
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Publisher
Universiti Sains Malaysia
Abstract
Dendrobium sonia-28 is an important orchid hybrid in Malaysian flower industry for its flowering recurrence and dense inflorescences which currently facing serious production problems due to fungal diseases, especially caused by Fusarium proliferatum. To overcome this impediment, one of the strategies being pursued is by the production of new orchid mutants. In vitro mutagenesis by means of Fusarium proliferatum culture filtrate (CF), fusaric acid (FA) and gamma irradiation can be used to produce economically improved mutants. In this study, selection of Fusarium proliferatum-tolerant protocorm-like bodies (PLBs) was carried out by assessing the effects of different concentrations of CF (5-20%) and FA (0.05-0.2 mM) and various doses of gamma irradiation (10-200 Gy). Results showed that PLBs survival rate and weight were inversely related to the inoculation and irradiation doses. Additionally, PLBs death and weight reducing increased among smaller PLBs after CF and FA treatments. Results indicated that the radio sensitivity test (LD50) for the PLBs was approximately at 43 Gy. Biochemical studies indicated that there was significant reduction in total soluble protein and chlorophyll contents in the treated PLBs depending upon the time of exposure and concentrations. Conversely, there were increased in peroxidase activity in the treated PLBs with increase in time of exposure and concentration of treatments. Low doses of irradiation have a stimulating effect on total soluble protein and chlorophyll contents. Histological, scanning electron microscope (SEM) and transmission electron microscopy (TEM) analyses confirmed severe surface and cell organelles damage and stomatal closure in inoculated and irradiated PLBs. Moreover, distorted chloroplasts confirmed reducing the efficiency of chlorophyll pigments. Reductions in plantlet growth were much greater at the highest concentrations of treatments. Plantlets infected with low doses of gamma radiation had better development of shoot, root and the foliage. RAPD markers showed different banding patterns for each doses of treatments and specific bands for selected and control plantlets. Leaf-bridge bioassay results revealed that leaflets obtained from PLBs challenged with higher concentrations of treatments showed less disease symptoms after being inoculated. Therefore, there is a relationship between in vivo and in vitro resistance of Dendrobium sonia-28 to infection. Hence, in vitro selection by CF, FA and gamma radiation could be an efficient method for obtaining Dendrobium sonia-28 somaclones. Moreover, gamma irradiation administered at low to moderate doses may generate PLB mutants with superior characteristics. The ability of the Dendrobium sonia-28 to survive after infection and irradiation opens new avenues for future development of fungal resistant transgenic orchids.
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Keywords
Fusarium proliferatum