| Natural rubber is a polymer with excellent performance,and has a quality that synthetic rubber cannot match.Currently,the production method of natural rubber is extremely single,and bark tapping is the only practice in a large scale with a mature industrial chain,from which 99% of the world’s natural rubber comes.The rubber planting areas in China are in a climate with low temperatures and drought stress in winter and spring,which results in seasonal fallen leaves.If the leaves can be utilized to produce natural rubber,it will be a beneficial supplement to natural rubber production,and thus increase the yield of the rubber tree.However,there is currently a lack of systematic research on the content and characteristics of leaf-origin rubber.At the same time,the rubber tree varieties currently selected are all aimed at the yield of stem bark tapping,and there are not varieties selected based on leaf-origin rubber.This study established a breeding method of varieties with high leaf rubber content by measuring the rubber content of leaves,analyzing the correlation between leaf rubber content and bark rubber yield,and small leaf-stem rubber.The main results of this study are as follows:(1)The Soxhlet extraction method was used to determine the rubber content of leaves during various growth and developmental stages.The rubber content of stable stage leaves was significantly lower than that of other developmental stages.There was no statistically significant difference in the rubber content extracted from the leaves during the discoloration stage,light green stage,semi withered yellow,complete withered yellow,and defoliation stages,with rubber content extracted ranging from 1.20% to1.39%.(2)The rubber content in leaves of different varieties and different plants of cross IAN873 × Reyan106 was studied,and was found to depend on the genotypes of the rubber tree.(3)It was found that the leaf rubber content of different rubber tree varieties was not correlated with their bark rubber yield(R=0.1334,P>0.05),and similarily,the leaf rubber content of hybrid progenies was not correlated with the number of laticifer rows in their bark(R=0.2037,P>0.05).Due to the highly significant positive correlation between the yield of bark latex and the number of laticifer rows,it is further confirmed that the rubber content of leaves is not correlated with the yield of conventional bark latex.(4)There were significant differences in the small petiole rubber value between rubber tree varieties and hybrid offspring lines,indicating that the small petiole rubber value of rubber trees depends on genotype.There was a significant positive correlation between the small petiole rubber value and the leaf rubber content among rubber tree varieties(R=0.919,P<0.02);The small petiole rubber value of hybrid offspring lines also showed a significant positive correlation with leaf rubber content(R=0.8468,P<0.05).Therefore,small petiole rubber can be used to select rubber tree varieties(lines)with high leaf rubber content.(5)The GPC analysis showed that the molecular weight of leaf rubber was slightly higher than that of stem bark rubber.The hydrogen spectrum of nuclear magnetic resonance spectroscopy showed that the rubber extracted from leaves was a relatively pure rubber hydrocarbon,with a quality no less than that of the bark rubber,and can be used as an alternative source of natural rubber.(6)The number-proportion of different particle sizes in leaf latex and stem bark latex was similar,but the volume-proportion of small rubber particles in the former was much higher than that in the latter,while the volume proportion of large rubber particles in the former was significantly lower than that in the latter.The differences in particle size characteristics may be an important factor leading to differences in their molecular weight and other characteristics.(7)The molecular weight of small rubber particles in latex was significantly higher than that of large rubber particles.The molecular weight of various types of rubber particles in the leaf latex showed a unimodal distribution;whereas,the total rubber particles and large rubber particles of the stem bark latex showed a bimodal distribution,while the small rubber particles showed a unimodal distribution.The molecular weight of total rubber particles in leaf latex is higher than that in stem bark latex.These results indicate that the elasticity,strength,and other properties of leaf latex may be better than those of stem bark rubber... |
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