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It is predicted that drought will be more frequent and sustained in the future, which may affect the decline of rubber tree production. Therefore, it is critical to research some of the variables related to the drought-resistance mechanism of the rubber tree. As a result, it can be used to guide the selection of new rubber drought-resistance clones. The goal of this study was to identify drought-resistance mechanisms in rubber clones from the high drought factor index (DFI) group using ecophysiological and biochemical variables. The treatments consist of two factors, namely water deficit and contrasting clones based on the DFI variable. The first factor consisted of three levels, namely normal (fraction of transpirable soil water (FTSW) > 0.75), severe water deficit (0.1 < FTSW < 0.20), and recovery condition (FTSW > 0.75 after rewatering). The second factor consisted of seven clones, namely clones G239, GT1 (low DFI), G127, SP 217, PB 260 (moderate DFI), as well as G206 and RRIM 600 (high DFI). RRIM 600 had the highest DFI among the other clones as a drought-tolerance mechanism characteristic. Furthermore, clones RRIM 600, GT1, and G127 had lower stomatal conductance and transpiration rate than drought-sensitive clone PB 260. As a result, as drought avoidance mechanisms, clones RRIM 600, GT1, and G127 consume less water than clone PB 260. These findings indicated that clone RRIM 600 was a drought-resistant clone with drought tolerance and avoidance mechanisms. [ABSTRACT FROM AUTHOR]

Climate change has an impact. Droughts will become more common in the future and as a result is the drop of rubber production. Drought tolerant rubber genotypes, may reduce drought risk, could be discovered by selection of germplasm and crossing progenies. As perennial plant, conventional rubber selection of rubber needs long time. Molecular detection such as QTL (precise and fast detection) for screening to get drought tolerant rubber genotypes is very important to be conducted. A variable widely used to screen stress tolerance genotypes is Performance Index (PI). Measurement of PI in normal, moderate, and severe drought stress enables the calculation of the Drought Factor Index (DFI). DFI as an integrative parameter for drought tolerance trait provides simple and robust method to quantify the tolerance ability of plants to withstand drought condition. This research is the first application of DFI to select drought-tolerant rubber genotypes and to identify QTLs related to DFI. This research aimed to select candidate drought-tolerant genotypes from the biparental population PB 260 × SP 217 as well as to identify QTLs related to DFI variable. One hundred and thirty-two genotypes and four control commercial clones, namely PB 260, SP 217, GT1, and RRIM 600 have been successfully screened using DFI variable. Normal, moderate, and severe drought stresses were calibrated for each plant by monitoring the fraction of transpirable soil water (FTSW). Due to the skewed distribution of DFI data that was generated in the phenotyping step, the Kruskal-Wallis non-parametric test was used to test the significance of each QTLs using MapQTL version 6 software. From this research, it can be concluded that DFI can be used as a parameter for selection of drought tolerant rubber clones. Based on DFI calculation, the top ten high DFI genotypes/clones were genotype number 34, 206, 056, 007, 205, 225, 066, 235, 109, and clone RRIM 600. Furthermore, the most significant detection of QTL for DFI variables was found in locus g5TA2155, located at 0.553 cM in LG5. It indicated that this locus contained genes controlling DFI trait. • Climate change results in prolonged dry season that impacts on the drops of rubber yield. • Drought Factor Index was calculated for one hundred and thirty-two genotypes from the PB 260 x SP 217 population • The genotypes with a high Drought Factor Index were selected as candidate drought-tolerant rubber genotypes. • Furthermore, the QTLs for Drought Factor Index were also determined. • Identification of genetic markers on genes underlying QTL enable Marker Assisted Selection for drought tolerance [ABSTRACT FROM AUTHOR]