Photosynthesis and Latex Burst Characteristics in Different Varieties of Rubber Trees (Hevea brasiliensis) under Chilling Stress, Combing Bark Tensile Property and Chemical Component Analysis

Rubber trees (Hevea brasiliensis) serve as the primary source of natural rubber. Their native habitat is characterized by warm and humid conditions, so they are particularly sensitive to low temperatures. Under such stress, latex burst can cause severe damage to rubber trees, which is due to the uniqueness of their economically productive parts. In order to establish a correlation between young and mature rubber trees and provide a novel prospective for investigating the mechanisms of latex burst and chilling resistance in rubber trees, the chlorophyll contents, photosynthesis, and chlorophyll fluorescence parameters in four varieties of one-year-old rubber tree seedlings were analyzed under artificially simulated chilling stress. The latex burst characteristics were subsequently recorded. A comprehensive statistical analysis of the chilling-resistance rank was conducted using the membership function method and the combination weighting method. Meanwhile, chemical compositions and tensile properties of barks from two-year-old twigs of mature rubber trees were ascertained. A correlation analysis between chilling resistance, chemical compositions, and tensile properties was performed to identify any interrelationships among them. The results showed that the number and the total area of latex-burst positions in variety Reken628 seedlings were greater than those in other varieties, and the lowest number and total area of latex-burst positions were observed in variety RRIM600 and variety PR107, respectively. With the exception of variety GT1, nectar secretion was noted in all other varieties of rubber tree seedlings under chilling stress. The chilling resistance of the four varieties decreased in the following order: variety GT1 > variety RRIM600 > variety PR107 > variety Reken628. The chilling resistance was strongly (p < 0.001) negatively correlated with cellulose content and acid-insoluble lignin content, respectively. The total area of latex burst was significantly (p < 0.001) and positively correlated with holocellulose content and maximum load, respectively. Furthermore, this study also provides new insights into the mechanism of nectar secretion induced by low temperatures and its association with the chilling resistance of rubber trees.