Seed germination of selected Hevea brasiliensis (wild, ex A. juss.) mull. arg. (latex timber clone) and influence of fertilizer and water deficit on seedling performance

The increasing demand for high quality rubber planting material has resulted in the need for selection of clones with high quality and proper management practices. Hence, this study has been carried out with the objective to evaluate seeds germination and seedling performance towards fertilizer and water deficit. Initially, germination test was carried out with 50 seeds of six clones namely PB 260 (control), RRIM 901, RRIM 2001, RRIM 2005, RRIM 2006 and RRIM 2026. Germination percentage was determined after two weeks. After germination, seedlings were transplanted into polythene bags and growth performances were evaluated for three months. In the second study, the response of seedlings towards single fertilizer was evaluated. Locally produced urea, Agrenas was compare with imported ammonium sulphate with a treatment rate of 10 g N from Agrenas per plant (T1), 20 g N from Agrenas per plant (T2), and 10 g N from (NH4)2SO4 per plant (T3) and zero N per plant (T4). Another study on fertilizer was conducted to evaluate current fertilizer recommendation using compound fertilizer, RISDA 1. Four different rates of RISDA 1(10.7: 16.6: 9.5: 2.4) compound fertilizer were used;T1 (0 g per plant) act as control, T2 (50%, 18.75 g per plant), T3 (100%, 37.5 g per plant) and T4 (150%, 56.25 g per plant) with T3 (100%) being the rate recommended by the Rubber Industry and Smallholders Development Authority. In order to evaluate rubber tree to water stress condition, a study was carried out under rain shelter. Two new latex timber clones from Malaysian Rubber Board (MRB),RRIM 2001 and RRIM 3001 were used in this study. Five levels of treatment were used; plants watered for every two days, five days, 10 days, 15 days and everyday which acted as control. The results showed that clone PB 260 had the highest germination percentage with 72%, while seeds from clone RRIM 2005 were the lowest (48.57%). Although germination percentage was second highest, seeds from clone RRIM 2001 had the best growth performance as shown by seedling height, girth and root dry weight. This study suggested seeds from clone RRIM 2001 were the most suitable seeds to be used for rootstocks production. In the second study, it was found that urea performed as well as ammonium sulphate at the equivalent of 10 g N per plant as reflected by leaf dry weight, leaf N content, height and girth increment measurements. Most leaves of the plants in T2 were scorched and somehad abscised from the plant.All treatments, except T2, showed that the girth and height increased steadily over time. Through this study, it was found that urea performed equally well when compared to ammonium sulphate at the equivalent of 10 g N per plant. However, in terms of cost per unit nitrogen, urea is much cheaper. For another study on fertilizer, results showed that the maximum value of plant height and girth was from T4 (RISDA 150%) with the mean of 62.11 cm and 4.41 cm, respectively. The P content were not significantly different among the treatments while the K and Mg content were highest in T4 (150%) and significantly different from other treatments. Compared to nutrient critical values, T4 met the nutrient sufficiency range for rubber. The nutrient use efficiency shows decreasing efficiency with increasing rates of fertilizer. From this study, it can be concluded that the current recommended fertilizer rate were insufficient, and precise fertilizer application should be considered to optimize fertilizer use efficiency. For water deficit study, fundamental changes of plant growth and physiological responses showed that treatment with sufficient water for clone RRIM 2001 (T1) had higher values than other treatments. Photosynthesis rate was highest in well watered (T6)with mean 11.26 μmol m-2s-1, while T4, T5 and T9 were lowest with the mean 0.00 μmol m-2s-1. Stomata conductance showed significant difference between T6 with 0.16 μmol m-2s-1 compared to under stress treatments with 0.00 μmol m-2s-1. The results also showed root length increase with the increase of water stress. There was treatment failure to adapt to water stress at treatments withholding water for 15 days followed by treatments of 10 days and five days respectively. From this study, it can be concluded that Hevea brasiliensis cannot withstand water stress at nursery stage. From all these studies, it can be concluded that seed germination percentage and seedling performance was influenced by the genotype. Over dosage of fertilizer would be detrimental to the seedlings and insufficient nutrient would results in visual deficiency symptoms and affect the growth performance. Rubber seedling also cannot withstand water stress and need proper water management if planted on dry areas.

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