Three - year variations in NR quality among different Hevea brasiliensis clones planted in Yunnan, China

The quality and performance of natural rubber (NR) are influenced by multiple factors, such as rubber tree clones, climatic conditions, soil nutrients, harvesting practices, and tree age. From May to November during 2022–2024, a systematic investigation was conducted on six major Hevea brasiliensis clones cultivated in Yunnan, China, covering seasonal variations in physicochemical properties, molecular weight, and mechanical and vulcanization performance. The results demonstrated that the dry rubber content (DRC) of all clones peaked in July and declined until November. Nitrogen content differed significantly among clones, being significantly higher in Reyan73397 and significantly lower in Yunyan77–2, showing an overall upward trend from May to November. Moreover, Yunyan77–2 exhibited higher Mooney viscosity (Mv), initial plasticity (P₀), and weight-average molecular weight (Mw), whereas Reyan73397 displayed lower values. Reyan73397 exhibited a higher plasticity retention index (PRI), while PR 107 had a lower value. However, PR107 showed superior tensile and tear strengths and a lower time to reach 90 % of maximum torque (T₉₀). Statistical analysis of many indicators revealed significant inter-clonal differences, confirming that both genetic background and seasonal environment jointly determine NR quality. Yunyan77–2 demonstrated enhanced physicochemical characteristics and higher molecular weight, whereas PR 107 excelled in mechanical and vulcanization properties. Overall, this three-year study provides comprehensive reference data for breeding improved rubber tree clones and advancing high-performance NR processing. • A systematic study on the properties of NR of six main planting clones in Yunnan, China was carried out. • The research content includes physicochemical properties, molecular weight, mechanical properties and vulcanization properties over 3 years. • Using statistical methods for analysis, there were statistical differences in the properties of natural rubber in 6 strains. • The physical-mechanical properties of NR were better in May and November, and the processing performance was better in November. • The PR107 and Yunyan77–2 can be preferred as raw materials for high-quality natural rubber.