Abstract:

Objective: In this paper, the physiological characteristics of latex flow in young rubber trees of different varieties under the various tapping systems were studied, in order to lay the theoretical foundation for elaborating the mechanism of latex flow and provide a guidance for planning rational tapping system to different varieties in natural rubber production. Method: The 6-year-old healthy virgin rubber trees of 4 varieties, PR107, RY8-79, Tjir1 and RY7-33-97, were selected, and the intensive tapping with S/2 d/2 (tapping line length of ? stem circumference and one tapping every two days) and subsequent stimulation with 1% ethrel were applied. The rubber particle size, and conventional physiological parameters of latex flow, such as the dry rubber content (DRC), latex volume, duration of latex flow, initial velocity and plugging index, were investigated, and further the effects of different tapping times were compared. Result: 1) The rubber particle size of different varieties was different obviously. In the virgin tree, the order of rubber particle size was RY8-79 >PR107 > RY7-33-97 > Tjir1. During the intensive tapping, the rubber particle size of different varieties increased firstly then decreased with the increase in tapping times, and the rubber particle size of RY8-79 and Tjir1 changed faster than that of PR107 and RY7-33-97. After the eighth intensive tapping, the rubber particle size decreased to below 0.80 μm usually, which was significantly lower than the largest size (P<0.05). During the ethrel stimulation, rubber particle size generally showed a downward trend and remained at a low level. 2) In the virgin tree, the order of DRC was RY7-33-97>RY8-79 >PR107 >Tjir1. Under the intensive tapping, DRC of RY8-79 and Ry7-33-97 dropped faster than that of PR107 and Tjir1. During the ethrel treatment, DRC of PR107 showed a slight downward trend, but that of RY8-79, Ry7-33-97 and Tjir1 dropped obviously, especially for RY7-33-97. 3) Under the intensive tapping condition, the change rule of duration of latex flow was highly consistent with latex volume, and for these two parameters, RY8-79 was obviously higher than that of PR107, RY7-33-97 and Tjir1. After the ethrel treatment, the duration of latex flow and latex volume of all varieties were significantly increased (P<0.05), especially for PR107 and Tjir1. 4) The initial velocity of latex flow of RY8-79 and RY7-33-97 was obviously higher than that of PR107 and Tjir1 under intensive tapping condition, and etherl significantly reduced the initial velocity of all varieties. 5) The plugging index of RY8-79 was the lowest, while that of RY7-33-97 was the highest amongst the four varieties. Ethrel stimulation obviously reduced the plugging index. 6) Under the intensive tapping condition, the thiol content of RY8-79 was the highest, followed by PR107 and RY7-33-97, Tjir1 was the lowest. In about 48 h after ethrel stimulation, the thiols content of the four varieties generally decreased. Conclusion: The effects of latex flow induced by intensive tapping and ethrel stimulation are different among various varieties. The parameters of rubber particle size and DRC related with yield usually are difficult to recover to the healthy level under intensive tapping and ethrel overstimulation. Compared with other parameters, rubber particle size and DRC are less affected by the surrounding environment and can be used as references to evaluate the overflow. When the rubber particle size drops below 0.80 μm, it always indicates that the tapping intensity should be reduced. The varieties with fluent latex flow and high yield under natural conditions are usually intolerable to the intensive tapping and ethrel overstimulation, thus the varieties of RY8-79 and RY7-33-97 as main cultivars should avoid the application of ethrel while PR107 is fit to stimulate. Using young rubber tree as materials, combined with intensive tapping and ethrel stimulation, can be used as one of the methods for quickly screening the resistance of different varieties to tapping and ethrel stimulation in early breeding, and also provide a basis for the formulation of different variety tapping systems for rubber production.

Key words: rubber tree, intensive tapping, ethrel, rubber particle, latex flow