Screening of rubber rootstocks for the white root disease tolerance with defense-related genes and enzymes

Abstract

The aims of this study were to determine the gene expression of three PR protein genes (PRIA, PR3 and PR5), PAL gene, the defense-related enzyme activities such as chitinase (CHI), peroxidase (POD) and phenylalanine ammnia lyase (PAL), and to screen cultivated rubber rootstocks for white root disease tolerance. The screening of rubber rootstocks tolerance with the white root disease caused by R. microporus was investigated by both defense-related genes and defense-related enzymes as well, and the disease assessment symptoms. The six cultivated rubber seedlings collected from different area in Southern Thailand were used in this experiment. The expression of PRs and PAL genes were analysed at 0, 1, 3, 5, and 7 days post inoculation (dpi) as well as the defense-related enzyme activities. The disease symptom was monthly observed since 3 to 9 months post inoculation. The transcript level of PRla, PR3, and PR5 genes were generally induced in tolerant rubber clones, but the pattern of the transcriptional change was different among those six cultivated rubbers when inoculated with R. microporus. Among those parameters studied expression level of PRs and PAL genes, CHI, PAL and POD enzyme activities are proven as evidence of the white root disease symptom assessment in the field, we concluded that RRIM 600 was moderate susceptible clone to white root disease as shown high disease index (37.8%) and low of percent of survival seedlings (88.9%) followed by RRIT 408 and BPM 24. PB 5/51 was the most tolerance one with the low disease incidence, high PAL and POD enzyme activities, followed by RRIM 623.