| Carambola (Averrhoa carambola L., Oxalidaceae) is a high-biomass tree spread widely across tropical and subtropical regions of the world. It has been identified as a new Cd-accumulating species. Our previous study has shown that great differences existed among different carambola cultivars in their ability to absorb and accumulate Cd. Obviously optimization of the potential of carambola for Cd extraction depends on the choice of appropriate cultivars that combine traits such as high Cd accumulation in shoots and high biomass productivity. In the present study, firstly, field surveys were conducted to explore the Cd accumulation capacities of different carambola cultivars grown in the Guangdong Province. Secondly, hydroponic experiment was carried out in order to validate the high Cd accumulation capacities of different carambola cultivars. Thirdly, field trials were undertaken to evaluate the phytoextraction potential for Cd by different cultivars. Finally, RAPD fingerprinting was constructed to analyze the genetic similarity among cultivars of carambola. The major results obtained from the present study are presented as follows:1. The field survey consisted of 19 carambola cultivars collected through the Guangdong Province of China, encompassing 14 commercial cultivars and 5 local cultivars grown in the area. For all the cultivars, carambola accumulated Cd very efficiently. On average, the Cd BCFs of different cultivars varied 1.16-20.2, 1.22-28.2 in twigs and leaves respectively, corresponding with Dongguan Sweet and Zhongda. Actually, irrespective of cultivar, carambola planted in the field accumulated averagely significant amounts of Cd in its twig (2.04 mg kg-1) and leaf (2.65 mg kg-1).2. In the hydroponic experiment, when Cd concentrations in solutions were 5 mg/kg, all 14 cultivars of carambola could accumulate more than 100 mg kg-1 Cd in the aerial tissues under Cd stress, the maximum accumulation was up to 437 mg kg-1 in Erlin’s twig. The Cd TFs of some commercial cultivars were > 1. When Cd concentrations were 20 mg kg-1, compared with that at 5 mg kg-1, Cd exerted an insignificant inhibitory effect on the biomass accumulation per plant in all cultivars, and no effects of metal toxicity were observed in carambola seedlings after 8 weeks of exposure to Cd. Different cultivars of carambola all showed a strong Cd tolerance.3. Field trials were undertaken to evaluate the phytoextraction potential for Cd by different cultivars. The results showed that carambola stand planted densely with 2-yr-old seed-seedling grew fast in the field and had high phytoextraction efficiency for Cd. When it was grown for about 230 days, Wuchuan Sweet carambola yielded a high shoot biomass of 29.5 ton ha-1, extracted 330 g ha-1 Cd, and removed 12.8% of the total soil Cd.4. Thirteen RAPD primers that could amplify stable polymorphic products were selected from 48 random primers for the fingerprinting construction of 17 carambola cultivars and genetic similarity analysis. All the 17 cultivars could be identified by the combination of several primers. The clustering analysis showed that 17 carambola cultivars could be divided into four groups when the GSC value was 0.74, the average genetic similarity coefficence was 0.68.Our results showed that all carambola cultivars investigated were able to accumulate considerably high concentrations of Cd in various degrees, and show high capacities to tolerate Cd. Generally speaking, the accumulation capabilities of commercial cultivars appear to be greater than those of local ones. Furthermore, they show their clear superiority in adaptability, growth rate and resistance. Therefore they are more efficient in phytoextraction. |
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