Abstract
The brown seaweed (Sargassum polycystum C. Agardh-Sargassaceae) extract was examined for its bioelicitor properties in the rubber tree seedling (Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg. - Euphorbiaceae) and its application to reduce the leaf fall disease caused by Phytophthora palmivora (Edwin John) Butler, 1917 (Peronosporaceae). The major purpose of this study was to apply this seaweed extract (SWE) to improve the disease resistance in rubber tree seedling compared to a chemical fungicide (1% metalaxyl). After foliar spraying of SWE solution, two antioxidant enzymes, catalase (CAT) and peroxidase (POD) and systemic acquired resistance (SAR)-triggered enzyme, β-1,3-glucanase (GLU), were analyzed. Both secondary metabolites, a phytoalexin scopoletin (Scp) and a signaling molecule salicylic acid (SA) were measured by high performance liquid chromatography (HPLC). Both SWE- and metalaxyl-treated plants had a close disease index (DI)-score which were 16.90 ± 1.93 and 15.54 ± 1.25, respectively, while the positive control sprayed with P. palmivora showed DI-score of 29.27 ± 1.89 which was much higher than those treated with SWE or fungicide. CAT, POD, and GLU were increased in rubber tree leaves treated with SWE solution. Furthermore, Scp and SA were significantly increased in SWE-treated leaves. Enhanced systemic acquired resistance induction, 2.09 folds of SA accumulation, was observed in the distal area comparing to the local area of SWE application. In conclusion, the positive effects of SWE elicitation from these studies revealed that SWE could be used as an alternative biocontrol agent for foliar spraying to enhance the defense responses in rubber tree seedling against P. palmivora.
Highlights
The Para rubber tree (Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg.—Euphorbiaceae.) is an economic plant as it is an important source of natural latex
The objective of this study was to elucidate the efficiency of seaweed extract (SWE) for controlling abnormal leaf fall disease caused by P. palmivora in rubber tree seedlings comparing to a commercial fungicide and to determine the biochemical changes in the rubber tree seedlings, such as the activities of defense enzymes including catalase (CAT), peroxidase (POD), and β-1,3-glucanase (GLU), accumulations of secondary metabolites (scopoletin (Scp) and salicylic acid (SA)), and systemic acquired resistance (SAR) induction following the foliar application of this SWE
The absorption band at 1252 cm-1 was due to the presence of sulfated ester groups (S = O) (Figure 1C), which is a characteristic component in fucoidan [23]
Summary
The Para rubber tree (Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg.—Euphorbiaceae.) is an economic plant as it is an important source of natural latex. Ex A.Juss.) Müll.Arg.—Euphorbiaceae.) is an economic plant as it is an important source of natural latex. It is commonly cultivated in tropical and sub-tropical areas [1], including Thailand. During periods of prolonged wet weather and high humidity conditions persisting for several days facilitate one of the most frequent diseases which is abnormal leaf fall (ALF) caused by various Phytophthora species. The impacts of this disease on rubber. One option to prevent disease is to encourage plant immunity without any genetic modification, such as induced resistance, might be more acceptable. Understanding the physiology and biochemistry of defense responses in plants may lead researchers to find an alternative way to protect the plant from its pathogen
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