Rubber plant (Hevea) is one of the main crops for smallholders in Thailand and in Southeast Asia because milky latex extracted from the tree is the chief source of natural rubber. Thailand is a foremost exporter of rubber. But, currently; rubber plants are becoming vulnerable to various pathogens including bacteria1, viruses2 and especially fungi3, exclusively fungi (Rigidoporus microporus) which cause white root disease in rubber tree. It can extend in the deep into soil and infect rubber trees through root contact by excreting rhizomorphs4. In response; plants have developed defensive mechanism by producing proteins (PR-proteins) having antimicrobial role against stress and pathogens5. They have been basically divided into 17 families and the PR-1 and PR-3 are the antifungal proteins that exhibit anti fungal properties6.
It was reported that both PR-1 and PR-3 provide shield in cucumber seedlings against Fusarium oxysporum CS-20 inoculation7. Therefore, the abundances of PR-1 and PR-3 mRNA transcripts can be employed as indicators of tolerance rubber clones. Accordingly, Natthakorn, Korakot and Charassri designed an experiment to evaluate the expression levels of PR-1 and PR-3 genes in tolerant (PB5/51) and susceptible (BPM24 and RRIM600) rubber clones after R. microporus infection. In this experiment, scientists isolated the mRNA of HbPR-1b and HbPR-3 from rubber leaves. Quantitative real-time PCR was employed to compare gene expression levels of HbPR-1b and HbPR-3 among 3 rubber clones (PB5/51, BPM24 and RRIM600) after R. microporus infection at 0, 12, 24, 48, 72 and 96 hours. The relative transcript abundances between inoculated and control plants were compared by means of gene expression between time points and Tukey’s HSD test. Researchers assessed the significance of difference between time points by using probability value (p<0.05).
Natthakorn and colleagues verified the expressional variability of two PR-genes which establish tolerance against white root disease in the rubber tree. Moreover; the HbPR-1b and HbPR-3 can be differentiated between tolerant and susceptible clones and showed more transcript levels in PB5/51 as compared to others. Consequently, researchers stated that accumulations of HbPR-1b and HbPR-3 may be considered as significant criteria to determine the tolerance of new rubber clones against R. microporus.
These research findings can play a key role for early selection of rubber tree for the white root disease tolerance breeding programs. Analysis of genetic linkage among markers and recognition of the genetic locations of enviable phenotypes would further enhance the selection accuracy. Moreover; it will amplify the genetic improvement of H. brasiliensis through molecular breeding and utilization of genetic resources.
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17 November, 2019