Abstract:

Objective: This study aims to investigate the variation patterns of latex yield and physiology during the occurrence and development of tapping panel dryness (TPD) induced by ethephon overstimulation in rubber tree (Hevea brasiliensis), so as to provide a theoretical basis for making better use of ethephon to stimulate latex production and taking effective measures to prevent the occurrence of TPD. Method: In this study, the healthy plants of rubber tree clone 'Reyan 7-33-97' were used to induce different grades of TPD by overstimulation of tapping with ethephon, and the change patterns of latex yield and related physiological indexes of plants with different grades of TPD were compared and analyzed, including pH, lutoid bursting index, dry rubber content, total solid content, thiol content, inorganic phosphorus content, the size distribution and average size of rubber particles. Result: 1) During tapping with ethephon overstimulation, the latex yield showed a trend of rising first and then falling. The yield increased continuously by more than three fold in the early stage. However, the TPD was soon induced. With the occurrence and development of TPD, the latex yield decreased gradually and finally became lower than that of healthy plants. 2) The lutoid bursting index increased significantly with the severity of TPD, the ruptured lutoid then resulted in blockage of the laticifers. This phenomenon was directly related to the occurrence of TPD. The latex pH values of TPD plants also increased slightly, but only the pH value of grade 3 TPD plants showed a significant difference from that of healthy ones. 3) Ethephon overstimulation had a dilution effect on latex. The contents of latex dry rubber and total solid in latex of TPD plants were lower than those of healthy ones. The contents decreased gradually in grades 2-3 TPD plants, and then recovered gradually in grades 4-5 TPD plants. 4)The thiol contents were significantly increased in grades 2-3 TPD plants, but gradually decreased to nearly normal levels in grades 4-5 TPD plants. In grades 2-5 TPD plants, the inorganic phosphorus contents showed a decreasing trend, but all showed higher than the healthy plants. 5) The size distribution of latex rubber particles of healthy plants ranged from 0.09 to 2.27 μm with a single peak. With the occurrence and development of TPD, the size distribution gradually moved to the direction of small size, and the peak value also decreased. Consistent with that, the average size of rubber particles became smaller with the increase of TPD grade. The average particle sizes of grades 2-5 TPD plants were significantly lower than that of healthy ones. The average particle size of healthy plants was 0.89 μm, while that of grade 5 TPD plants was only 0.79 μm. Conclusion: Over stimulation of tapping with ethephon will result in an increase in the burst of lutoid, outflow of a large amount of thiol and inorganic phosphorus, and the decrease of rubber particles, which will lead to the damage and blockage of the laticifer system, affect the rubber biosynthesis and latex flow, and finally show the symptoms of TPD. In the production of natural rubber, ethephon stimulation should be reasonably used, avoiding excessive stimulation to induce TPD which always results in yield reduction.

Key words: Hevea brasiliensis, tapping panel dryness, physiological effect, ethephon stimulation, latex