Judul: Physiological and Molecular Analysis for Development of DNA Markers in Resistance to Basal Stem Rot Disease in Oil Palm
Abstrak: Basal stem rot (BSR) is a great disease concern in oil palm plantations. The cause of this disease is Ganoderma boninense, one of the fungi from the phylum Basidiomycota which can reduce oil palm productivity up to 40%. The higher generation planted in the oil palm plantations, the more widespread of the development of this disease in Ganoderma-infected areas. The response of oil palm resistance to BSR disease is very important to be discovered. The expression of genes involved in the resistance response is also a support in the superior plant material development for Ganoderma resistant in oil palm. The final objective of the study was to obtain molecular markers capable of selecting BSR disease-resistant plants in oil palm. The first experiment results “Differential expression of root specific genes of oil palm seedlings at early stage of Ganoderma boninense infection” showed two genes performed the highest transcript accumulation in susceptible treated with G. boninense. Ten out of the 16 genes belonged to Group I and the other six to Group. Seven out of the 16 genes were differentially expressed in the samples either with or without G. boninense inoculation. The seven genes may be associated with early infection responses to G. boninense. The second experiment results “Defense response changes in roots of oil palm (Elaeis guineensis Jacq.) seedlings after internal symptoms of Ganoderma boninense pat. infection” indicated that C01, C02, and C05 seedlings were susceptible, while the other three seedlings, C03, C07, and C08, were resistant based on Ganoderma Disease Index (GDI). Infection by G. boninense in the most susceptible seedlings C05 reduced fresh weight of roots (FW) by 9.0%, and lignin content by 10.9%. The most resistant seedlings C08 were reduced by only 8.4%, and 0.2% regarding their fresh weight and lignin content, respectively. BSR disease induced SA accumulation in the most susceptible C05 and decreased peroxidase (PRX) enzyme (EC 1.11.1.7) activities in root tissues of oil palm seedlings except C07 and C08 where PRX activities remained high in the 4 months after planting. Infection with G. boninense also increased glutathione S-transferase U19-like (EgGSTU19) gene expression in the root tissues of susceptible seedlings, while laccase-24 (EgLCC24) gene expression was associated with resistance against BSR disease. Based on the relative expression of twelve genes, two genes are categorized as receptors (EgWAKL5, EgMIK1), two genes as biosynthesis signal transduction compound (EgOPR5, EgACO1), five genes as defense responses (EgROMT, EgSOT12, EgLCC24, EgGLT3, EgGSTU19), and one gene as trans-resveratrol di-O-methyltransferase-like (EgRNaseIII) predicted related to BSR infection. While two other genes remain unknown (EgUnk1, EgUnk2). Ganoderma infection-induced SA accumulation and lignification in resistant accessions promote the seedlings root biomass. Oil palm seedlings have a synergistic physical, biochemical, and molecular defense mechanism to the BSR disease. The utilization of nucleotide-based molecular markers using EgLCC24 gene is able to detect resistant oil palm seedlings to G. boninense. The third experiment results “Genes expression analysis of EgUnk3, EgZFP2, and EgIPK2b in oil palm using Ct value correction and two relative quantification approaches” showed correlation regression obtained 0.28, -0.32, and 0.29 for delta Ct of EgUnk1, EgZFP2, and EgIPK2b, respectively.
Keyword: Ganoderma boninense, marker-assisted selection, lignification, gene expression, resistant to basal stem rot