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Identification of physiological traits and QTLs associated with drought resistance in rubber (Hevea brasiliensis Mull. Arg.) using PB 260 X SP 217 population and several control clones
Dissertation Abstract:
Occurrence of dry season suppress rubber plantation productivity. Unfortunately, occurrence of drought and deficit rainfall in some regions including Indonesia is predicted to be more frequent in the future. Therefore, researches to select and to identify QTLs for drought resistant rubber clone as well as to study resistance mechanism of drought resistant rubber clone are needed to be conducted. This research had four steps: determining the best time for chlorophyll-a fluorescence observation (research topic I), selecting drought tolerant candidate clones using the DFI variable (research topic II), detecting QTLs for the DFI (drought factor index) variable (research topic Ill), and validation and physiological observation on three contrasting clones on three water deficit levels (research topic IV). The research topic I was carried out to determine the best period for measuring chlorophyll-a fluorescence, which would be used in research topic II. Furthermore, based on the DFI variable, the research topic II was done to identify drought resistant candidate clones from the PB 260 X SP 217 population. Moreover, the goal of research topic Ill was to find QTLs for the DFI variable, while the research topic IV sought to determine the physiological characteristics of three contrasted clones at three different water deficit levels. The research topic I research found that a dark adaption time of two hours after sunset was sufficient for measuring chlorophyll-a fluorescence transients in rubber leaves without the use of leaf clips. Clones RRIM 600, GT1, and SP 217 required 15 minutes of dark adaptation if measured before 7.30 a.m., whereas clone PB 260 required 60 minutes. Furthermore, the top ten drought tolerant clones were 34, 206, 056, 007, 205, 225, 066, 235, 109, and RRIM 600, according to research topic II. In addition, based on Kruskal-Wallis analysis, the most significant detection of QTL for DFI parameter was found in locus g5TA2155, which is located at 0.553 cM in LG5. The DFls resulted from research topic II and IV were identical. Clone RRIM 600, SP 217, 127, and GT1 showed lower stomatal conductance, transpiration rate, H2O content of leaf cell, and relative humidity of leaf cell compared to clone PB 260. It indicated that clone RRIM 600, SP 217, 127, and GT1 consume less water than PB 260 and used avoidance mechanism to withstand drought condition. Furthermore, clone RRIM 600 and 206 showed high DFI values. Hence, these clones used tolerance mechanism to withstand drought condition. These results indicated that clone RRIM 600 was a drought resistant clone based on drought tolerance and avoidance mechanism. Furthermore, the lowest DFI group showed the lowest POD enzyme activity.