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Subject: Soil Science × End date: 2016 × Start date: 2016 × Type: Thesis ×
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    ThesisItemOpen Access
    Bioremediation of iron toxicity in lowland rice ecosystem of Assam
    (AAU, 2016) Tamuly, Danish; Das, K. N.
    Two sets of experiment viz., pot (2012-13) and field (2013-14) was carried out to find bioremediation potential to ameliorate iron toxicity in lowland rice ecosystem of Assam. Rice crop was cultivated in Yoshida medium (hydroponic culture) developed specifically for rice. The experimental set up consisted of 6 boxes containing 60 PVC cut pipes each. Two check cultivars namely Mahsuri (sensitive) and Padumoni (tolerant) were tried along with eight test cultivars namely Ranjit, Moniram, Kushal, Pankaj, Luit, Basundhara, Jaymoti and Bahadur. Two weeks old seedlings from sand cultured nursery beds were transplanted into the PVC pipes fixed with half-split foam plugs in such a way that only root was in direct contact with the Yoshida solution. Liquid paraffin oil (low density) was added to each PVC pipe to maintain a 3 mm layer for checking oxidation process. Three bacterial inoculations viz., Control, PSB5w and PSB25w along with four iron levels, 0, 500, 1000 and 1500 mg Fe L-1 were tried in different combinations. Sampling at maximum tillering stage of crop revealed leaf scoring ranging from 0.0 to 4.9 with a mean of 0.3 to 3.7. The highest mean scoring of 3.7 was observed at 1500 mg Fe L-1, which was followed by 1000, 500 and 0 mg Fe L-1 with 2.9, 1.4 and 0.3 scoring respectively. The least scoring of 1.2 was observed in PSB5w followed by PSB25w (2.0) and PSB0 (3.1) inoculated cultivars. Among the rice cultivars the leaf scoring was in the order Mahsuri (1.4) < Joymoti (1.6) < Moniram (1.7) < Prafulla (1.9) < Podumoni (2.0) < Ranjit (2.2) < Luit (2.2) < Kushal (2.3) < Basundhara (2.4). Increasing levels of iron from 0 to 1500 mg Fe L-1 was found to significantly reduce the yield attributing traits of cultivars viz., root length (8.0 to 7.0 cm) and shoot length (22.4 to 17.6 cm). Similar reduction was also observed with N, P and K content in both leaf and stem i.e. leaf N (2.42-0.97%), stem N (1.55-0.90%), leaf P (0.220-0.041%), stem P (0.271-0.039%), leaf K (0.473-0.069%) and stem K (1.420-0.208%). The Fe content in different plant parts viz., leaf, stem and root was found to significantly increase with increased Fe-level. Mean root Fe-plaque was found to significantly increase from 0.19 (Fe0) to 0.94 (Fe1500) mg Fe g-1 root. PSB x Fe-level had significant effect on agronomic growth traits viz., root length and number of leaves and on N, P and K content in both leaf and stem. Both leaf and stem N content was found to be significantly higher with cultivars inoculated with PSB5w. However, P and K content in both stem and leaf were found to be higher in PSB25w inoculated cultivars. PSB5w inoculated cultivars recorded significantly lower leaf Fe, stem Fe and root Fe than control and PSB25w. Significantly, higher root Fe plaque was found in cultivars inoculated with PSB5w than PSB25w and control. Negative and significant correlation exist between scoring with root length, shoot length, number of leaves, leaf N%, stem N%, leaf P%, stem P%, leaf K% and stem K%. However, positive and significant correlation was observed between scoring with leaf Fe, stem Fe, root Fe and Fe plaque. Subsequent validation of results of pot experiment was carried out in the ICR Farm, AAU, Jorhat. Six rice cultivars viz., Mahsuri, Moniram, Joymoti, Prafulla, Podumoni and Ranjit in increasing order of scoring were selected. Following this, the strain PSB5w which showed least scoring was also selected with the highest iron level of 1500 mg Fe L-1. PSB5w inoculated cultivar showed significantly higher root length (21.50 cm), leaf N (2.20%), leaf P (0.313%), stem P (0.277%) and leaf K (0.804%) than non inoculated cultivars. Except for Moniram, all other cultivars showed significantly lower leaf and stem iron content. Significant difference in grain yield was observed with inoculated (1730.70 kg ha-1) and non-inoculated (1644.30 kg ha-1) cultivars. Relatively higher grain yield was achieved in PSB5w inoculated cultivars Mahsuri (2000 kg ha-1) and Prafulla (1850 kg ha-1) as compared to control. Thus the Bacillus sp. PSB5w with suitable carrier material can be used as a bioremediation tool for chronically Fe-toxic lowland rice ecosystem in Assam. Further, a stress encountering bio-package consisting of seedling root dip treatment in PSB5w especially for rice cultivars Mahsuri and Prafulla may be advocated for Fe toxicity affected low land rice ecosystem from the present investigation.