Large variation in carbon isotope composition of bulk leaf material of rubber trees from a germplasm collection: An opportunity for improving water use efficiency in breeding programs

The rubber tree (Hevea brasiliensis) is an important economic crop, particularly in Thailand. As the plantations extend to new and drier areas, iriformation on physiological parameters such as water use efficiency (WUE) is required to help breeding for adapted genotypes. Carbon isotope composition of bulk leaf (~13C) can be used as an indicator of intrinsic water use efficiency (WUE) of plants. A prerequisite step is to analyse the genetic variability of o13C. We compared the carbon isotope composition of bulk rubber tree leaf (~13C) in rainy and dry seasons in a collection of 49 wild genotypes of rubber in Northern Thailand. There were large ~13C variations among the genotypes at all seasons. ~13C ranged between -33.3%0 to -30.0%0 in rainy season and -33.1%0 to -29.9%0 in dry season. ~13C was rather stable with a good correlation between rainy and dry season. In rainy season, there was a positive significant correlation between ~13C, leaf mass per area (LMA) and leaf nitrogen per area (N ). The average ~13C was significantly different between two genetic clusters previously identified in this population. The large genetic variability of ~13C in wild rubber population is promisingfor breeding genotypes using less water. (Résumé d'auteur