Judul: Biochemical and Transcriptomic Analyses in Phalaenopsis Response to Soft-Rot Disease Pathogen (Dickeya dadantii)
Abstrak: Phalaenopsis orchid is one of the orchid genera with high ornamental and economic value. Soft-rot disease (SRD) is a devastating disease in Phalaenopsis orchid caused by the necrotrophic pathogens, Dickeya dadantii. Evaluations of several Phalaenopsis species for their response to D. dadantii infection reveal that P. amboinensis is the most resistant, while P. amabilis is a very susceptible species. Resistant species information related to biochemical and molecular response under pathogen infection is essential in providing resistant parents to conduct conventional and molecular breeding programs of Phalaenopsis. Resistant species can be used as the parent in cross-breeding, while the biochemical and molecular mechanism of plant resistance can be used to develop biochemical and molecular markers for selecting resistant progenies. The main purpose of the research is to identify the intraspecies variation response of P. amboinensis and P. amabilis to SRD pathogens and analyze the possible resistance mechanism through a biochemical and transcriptomic approach. The research is provided on three topics. The first topic aims to evaluate intraspecies resistant variation in the P. amboinensis and P. amabilis wild populations and identify the plants that show resistance or susceptible responses to D. dadantii consistently to be used as breeding materials and resistant mechanism study in further experiments. The second topic was aimed to study the possible role of Phenylalanine ammonia-lyase (PAL), Peroxidase (POD), salicylic acid (SA) and jasmonic acid (JA) in the susceptible or resistance response of P. amboinensis and P. amboinensis to D. dadantii infection and its potential for biochemical markers for resistance to SRD. In the third topic, transcriptomic analyses based on the RNA sequencing approach were performed in P. amboinensis as a prospective resistant parent to predict the molecular plant response to D. dadantii infection and the potential genes and molecular mechanism involved in resistant species. The research results show the intraspecies variation of P. amboinensis and P. amabilis wild populations in their response to D. dadantii infection. The responses of 47 P. amboinensis and 29 P. amabilis individuals were tested against D. dadantii using the detached leaf inoculation method. Soft-rot symptom diameter was measured at 6 to 42 hours post-inoculation (HPI) for disease assessment, including disease symptom diameter, disease severity, and resistance level to D. dadantii. Of 47 plants of P. amboinensis, 2.13% are very susceptible, 2.12% are susceptible, 4.25% are moderate resistant, and 91.49% are resistant, while in P. amabilis, 20.69% are very susceptible, 3.45% are susceptible, 13.78% are moderate susceptible, and 62.08% are resistant. SRD-resistance trait in P. amboinensis is more stable compared to the P. amabilis. The selected resistant plants of P. amboinensis and very susceptible plants of P. amabilis were used for the second and third topics of the dissertation. The second topic of the research was predicting the biochemical defense (defense-related enzymes, PAL and POD, and signal transduction hormones (SA and JA) that may be involved in Phalaenopsis resistance mechanisms to SRD pathogen. The endogenous PAL, POD, SA and JA were measured under mock and D. dadantii inoculation on P. amboinensis and P. amabilis. The results showed that PAL and POD activities were higher in P.
Keyword: orchid, resistance mechanisms, RNA sequencing, species