COMPARATIVE GROWTH PERFORMANCE AND ACTIVITY OF DEFENSE RELATED ENZYMES AND GENE EXPRESSION IN RUBBER CLONES AGAINST RIGIDOPORUS MICROPORUS INFECTION

Rigidoporus microporus is the causal agent of rubber white root disease (WRD). Control of this is commonly carried out by chemical treatment. The use of tolerant rootstocks may present an effective method to lessen its impact. The screening of rubber rootstocks for tolerance of WRD was investigated by both defense-related enzymes and gene expression, and assessment of disease symptoms.Two recommended clones in Thailand (RRIT251 and RRIT408) and RRIM623 (Malaysian clone) were screened and compared with susceptible clones (RRIM600 and BPM24) and tolerant clone (PB5/51) by inoculating young rubber seedling with R. microporus. The expression of PRs and PAL were analyzed at 0, 1, 3, 5, and 7 days post inoculation (dpi) along with the defense-related enzyme activities. Based on observed transcriptional level of PRs and PAL genes, CHI, PAL, and POD enzyme activities, and also evidence from WRD symptom assessment in the field, we concluded that PB 5/51 had the best tolerance with the lowest disease incidence, high PAL and POD enzyme activities, with the next best being RRIM 623 and RRIT 251, respectively. Meanwhile, BPM 24, RRIM 600, and RRIT 408 clones are moderately susceptible to WRD. The study introduces new possibilities for the control of WRD using alternative rubber rootstock clones.