Quantitative Gene Expression Analysis of Selected Genes to Screen Drought Tolerance of Selected Hevea Clones

Expansion of rubber (Hevea brasiliensis) cultivation to non-traditional areas in Sri Lanka is necessary due to the increase of global demand of natural rubber and limitation of available land in traditional rubber growing areas. To overcome the negative impact of drought stress, which experience in non-traditional rubber growing areas, plants alter their gene expression as an inherent respond strategy. In traditional rubber growing areas, during the period of February to March is considered as wintering period where recorded higher temperature, low rainfall and lower relative humidity (RH%) comparing to the   cropping months of October to December. Therefore, wintering period is more over similar to an environmental condition prevailing in non-traditional areas. Stable clones during wintering period can be expected that having more ability to survive in dry areas too. Therefore, this experiment was conducted to select more stress tolerant clones for non-traditional areas and to evaluate the level of drought responsible genes (Catalase (CAT), ascorbate peroxidase (APX) and Glutathione peroxidase (GPX)) expression of selected Hevea clones under wintering stress compared to the cropping months. Quantitative gene expression during wintering period compared to the wintering period was carried out using Bio-Rad thermal cycler. The Livack method was used to calculate fold difference between control and treatment plants. Then paired t-test was done using minitab 17 software. According to the results, all the genes were significantly up regulated in the clone RRISL Centennial 3 during the wintering period and second highest yield dropped percentage (55%) was recorded in this clone. However, HbAPX and HbCAT gene expressions were significantly upregulated while HbGPX gene expression was significantly downregulated in the clone RRISL 203 and highest yield dropped percentage (56%) during wintering period was recorded in this clone. In contrast the clone RRISL 2006, HbAPX and HbCAT gene expressions were significantly down regulated and upregulation of HbGPX gene expression was not significantly at the P≤0.05 level. This results were different from the expression pattern of other two clones and the clone RRISL 2006 showed lowest yield dropped as around 23% during the wintering period. Leaf falling of this clone also delayed compared to the other clones and might be having more drought tolerant ability than the clones RRISL 203 and RRISL Centennial 3. Therefore, this may be some other genes responsible for the situation and should be studied to confirm the results. According to those results, the clones RRISL 203 and RRISL Centennial 3 can be considered as stress susceptible clones compared to RRISL 2006, which can be considered as stress tolerance clone.