IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

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17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Tuesday 29 November 2011 Concurrent Session 7 – Field Applications III 1600 - 1720 Authors: Amanda Bonython 1,2 , Ross Ballard 1,2 , Nigel Charman 1,2 & Andrew Craig 1,2 1 South Australian Research and Development Institute, GPO Box 397, Adelaide, SA, 5001, Australia. 2 Cooperative Research Centre for Future Farm Industries. Crawley, WA, 6009. Presentation Title: Improved nodulation of regenerating messina plants Presentation Time: 1640 – 1700 Messina (Melilotus siculus syn. M. messanensis) is a promising annual pasture legume for areas affected by dryland salinity. Sinorhizobium medicae strain, WSM1115, was used during initial species evaluation. Prompt nodulation occurred in year of sowing but nodulation failure was commonplace in regenerating pastures. Strain WSM1115 failed to persist in the saline soils over summer. Alternative strains of rhizobia and agronomic practices were evaluated to improve nodulation. Six agronomic treatments and two inoculation treatments were applied in a factorial design. Messina seed was inoculated with either a mixture of experimental strains (SRDI554, WSM4118 and WSM4194) or WSM1115. Agronomic treatments were applied to modify the soil micro-environment and improve rhizobial persistence. They comprised sowing a perennial companion species, either Cichorium intybus or Puccinellia ciliata; incorporating soil additives at sowing, gypsum (2.5 t/ha) or clay (75t/ha); applying an organic mulch over the summer months, or applying a soil containing medic rhizobia prior to regeneration. Plots were sown in 2008 at two trial sites near Keith, South Australia. The soils were alkaline sands with summer soil surface salinity levels of 14.6 ECe dS/m (Site 1) and 5.3 ECe dS/m (Site 2). The sites were free of medic rhizobia prior to sowing. In 2008, all treatments had >97% plants nodulated. In 2009, ten regenerating plants from each plot were sampled and percentage nodulation and nodule score per plant determined (Score 0=0 nodules; 1=1-4 nodules; 2=5-9 nodules; 3=10-14 nodules, 4=15-19 nodules, 5=20-29 nodules, 6=30+ nodules). At Site 1 (more saline) plant nodulation and nodule score increased from 35% and 0.6 (WSM1115 treatment) to 95% and 3.0 (strain mixture treatment). At Site 2, most regenerating plants in the WSM1115 treatment were nodulated (80%), but had few nodules (score 1.6). Nodule score increased to 3.9 in the strain mixture treatment. At both sites, the application of soil containing medic rhizobia resulted in levels of nodulation approaching the strain mixture treatment. Other agronomic treatments were less effective. The mixture of rhizobia strains improved the nodulation of regenerating messina plants compared to WSM1115. Strain of rhizobia influenced messina nodulation more than the agronomic treatments. 54 2011
17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Tuesday 29 November 2011 Concurrent Session 7 – Field Applications III 1600 – 1720 Authors: Keletso Mohale 1 , Alphonsus Belane 1 , Flora Pule-Meulenburg 2 and Felix D Dakora 3 1 Department of Crop Sciences, Tshwane University of Technology, 175 Nelson Mandela Drive, Private Bag X680, Pretoria 0001, South Africa 2 Department of Biotechnology and Food Technology, Tshwane University of Technology, 175 Nelson Mandela Drive, Private Bag X680, Pretoria 0001, South Africa 3 Department of Chemistry, Tshwane University of Technology, 175 Nelson Mandela Drive, Private Bag X680, Pretoria 0001, South Africa Presentation Title: Symbiotic functioning and rhizobial biodiversity of Bambara groundnut (Vigna subterranean L.Verdc) grown in farmers‟ field in South Africa Presentation Time: 1700 – 1720 Although Bambara groundnut (Vigna subterranea L.Verdc) is an important food legume in Africa, little is known about its symbiotic N nutrition. This study assessed N2 fixation in Bambara groundnut plants grown in 26 farmers‟ fields, and characterized their bacterial symbionts isolated from root nodules. Isotopic analysis showed that N derived from fixation in Bambara groundnut varied from 55% to 97%. Actual amounts of N-fixed also varied for different farms and villages, and ranged from 3.7 to 212.7 kg N.ha -1 . Bacterial isolates from root nodules showed phenotypic differences in growth rate, colony appearance, shape, and texture. Following Koch‟s postulate, 19 slow-growers and 31 fast-growers were tested for their nodule-forming ability on Bambara groundnut. The bacterial isolates showed marked differences in their ability to elicit nodule formation and promote plant growth in Bambara groundnut. However four slow-growers and five fast-growers formed ineffective nodules on Bambara groundnut. Analysis of data from 16S rDNA sequencing showed that Bambara groundnut isolates formed three distinct clades, one with Bradyrhizobium liaoningense, another with Burkholderia tuberum CIP 108238, while the third clade clustered with Rhizobium sp. CCNNYC119 (in a sub-clade) and Mesorhizobium sp. W39 (in another sub-clade). Taken together, the data revealed that Bambara groundnut depends on N2 fixation for its N nutrition and is nodulated by diverse microsymbionts that belong to both alpha and beta-proteobacteria. 55 2011
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