Zygotic development and endosperm dynamics in Hevea brasiliensis: Progress, challenges and emerging opportunities of in vitro pollination and fertilisation

Hevea brasiliensis is the primary source of natural rubber, a vital raw material with widespread applications across various industries. Owing to the consistent rise in demand for this strategic commodity, enhancing productivity remains as a key objective in rubber breeding. However, genetic recombination breeding in Hevea faces significant challenges, including seasonal flowering, low fertility, early fruit drop etc. These factors limit the production of sufficient full-sib families available for effective selection and thereby increase the cost and effort of artificial pollinations. Enhancing fruit/seed set is particularly important in a highly heterozygous perennial crop like Hevea . This study was aimed to investigate the fertilization and fruit set processes in Hevea brasiliensis , identify various factors contributing to low fruit set and explore the feasibility of an in vitro fertilization system to generate a higher number of desirable recombinants. The research was conducted using flowers and fruits from mature trees of clone RRII 105. Key factors such as age of the flower, methods of pollination, and culture media for fertilization and embryo formation were examined. Successful fertilization and embryo formation under in vitro conditions were demonstrated in H.brasiliensis . for the first time. Additionally, the study provides novel insights into embryo and endosperm development under both in vitro and in vivo conditions, shedding light on potential causes of low fruit set. The findings will be beneficial for breeders, in the recovery of hybrid seeds especially from difficult crosses of breeding programs. The protocol developed in this study can be utilized for the consistent and sustainable development of hybrid embryos into seedlings from different cross combinations.