Screening of PRSV-P Resistance and Profiling of Defensive Secondary Metabolites in Carica papaya and Interspecific Hybrid of Vasconcellea

Aims: To Screen for PRSV-P resistance in Carica papaya and interspecific hybrid of Vasconcellea (IR) and to determine the secondary metabolites difference between PRSV-P resistant and susceptible papaya using LCMS-QTOF.

Study Design: The experiment was carried out using completely randomized design (CRD).

Place and Duration of Study: MARDI Headquarters, Persiaran MARDI-UPM, 43400 Serdang, Selangor, Malaysia between January 2017 to June 2019.

Methodology: C. papaya lines L33, L90, L13 and Eksotika were germinated from seed whilst IR was imported in tissue culture from Griffith University Australia. Screening for PRSV-P resistance was carried out using completely randomized design in the glasshouse of Agrobiodiversity and Environment Research Centre, MARDI. Percentage of disease incidence and disease severity of inoculated papaya plant were evaluated weekly for eight weeks. The generated data of disease incidence and disease score were then statistically analysed using SAS 9.4 software. Secondary metabolites analysis of Carica papaya and interspecific hybrid of Vasconcellea (IR) was carried out using LCMS-QTOF in phytochemical laboratory MARDI. The accurate mass compound in the MassHunter Qualitative analysis was confirmed by hits from existing databases [Metlin - Scripps, PCDL (MassHunter Personal Compound Database and Library - Agilent Technologies)].

Results: Screening for PRSV-P resistance amongst Malaysian local lines showed a significant difference (Alpha=0.05) between line L90 [disease incidence (55%); disease score (1.2)] and the PRSV-P susceptible (Eksotika) over eight weeks observation. IR that was also significantly difference to Eksotika categorized as PRSV-P resistance. In order to profile the defense-related secondary metabolites before and after PRSV-P entry in plant, C. papaya (Eksotika) and IR were used to represent PRSV-P susceptible and PRSV-P resistant respectively. IR was used to develop partial resistance to PRSV-P in C. papaya via introgression of resistance genes in other study. Analysis of secondary metabolites using LCMS-QTOF detected anthranilic acid (AA) and para-aminobenzoic acid (pABA) in C. papaya (Eksotika) and IR at day five after inoculation. Interestingly, ϒ-aminobutyric acid (GABA) was only found in IR at rt, 1.881 min based on their accurate mass using LCMS-QTOF prior to PRSV-P inoculation.

Conclusion: Findings of this study recommended the usage of L90 in future conventional breeding with other local PRSV-P susceptible varieties such as Eksotika that has better taste and market. ϒ-aminobutyric acid (GABA) that was only found in IR was presumed to be involved in the plant defense response to PRSV-P. It potential to be developed as a resistance chemical marker could be explored in the near future.