[show abstract][hide abstract] ABSTRACT: Background and AimsThe large monophyletic genus Mimosa comprises approx. 500 species, most of which are native to the New World, with Central Brazil being the main centre of radiation. All Brazilian Mimosa spp. so far examined are nodulated by rhizobia in the betaproteobacterial genus Burkholderia. Approximately 10 Mya, transoceanic dispersal resulted in the Indian subcontinent hosting up to six endemic Mimosa spp. The nodulation ability and rhizobial symbionts of two of these, M. hamata and M. himalayana, both from north-west India, are here examined, and compared with those of M. pudica, an invasive species.Methods
Nodules were collected from several locations, and examined by light and electron microscopy. Rhizobia isolated from them were characterized in terms of their abilities to nodulate the three Mimosa hosts. The molecular phylogenetic relationships of the rhizobia were determined by analysis of 16S rRNA, nifH and nodA gene sequences.Key ResultsBoth native Indian Mimosa spp. nodulated effectively in their respective rhizosphere soils. Based on 16S rRNA, nifH and nodA sequences, their symbionts were identified as belonging to the alphaproteobacterial genus Ensifer, and were closest to the 'Old World' Ensifer saheli, E. kostiensis and E. arboris. In contrast, the invasive M. pudica was predominantly nodulated by Betaproteobacteria in the genera Cupriavidus and Burkholderia. All rhizobial strains tested effectively nodulated their original hosts, but the symbionts of the native species could not nodulate M. pudica.Conclusions
The native Mimosa spp. in India are not nodulated by the Burkholderia symbionts of their South American relatives, but by a unique group of alpha-rhizobial microsymbionts that are closely related to the 'local' Old World Ensifer symbionts of other mimosoid legumes in north-west India. They appear not to share symbionts with the invasive M. pudica, symbionts of which are mostly beta-rhizobial.
[show abstract][hide abstract] ABSTRACT: Aims: To survey the occurrence of nodulated legumes in the arid and semi-arid areas of Western Rajasthan and to characterize their associated symbiotic bacteria.
Methods: Herbaceous annual species were excavated whole, while tree species were studied as seedlings in the field or as trap plants in pot experiments. Nodules were examined by microscopy to confirm their effectiveness and to determine their internal structure. Bacteria isolated from the nodules were authenticated on their original hosts and were identified on the basis of 16S rRNA sequencing. Phylogenetic trees were inferred using the neighbour-joining method.
Results: We studied 35 of more than 50 species of native legume reported from these areas. Legumes are drought escaping (annual species), drought tolerant perennials or trees possessing deep root systems and other adaptations to arid conditions. Nodulation was recorded in all members of the Papilionoideae and Mimosoideae, but only one species of Caesalpinioideae. Internal structure of nodules varied within these groups, especially with respect to the presence or absence of uninfected cells in the infected region. Full 16S rRNA gene sequencing revealed that the nodules harboured a range of nodulating bacteria belonging to the genera Sinorhizobium, Rhizobium and Bradyrhizobium, within which they formed separate sub clades.
Conclusions: This study extends the range of legumes known to grow and nodulate in semi-arid regions, and provides information about their endosymbionts.
[show abstract][hide abstract] ABSTRACT: Aloe vera Linn. (Syn. Aloe barbadensis Mill; Gwar-patha in Hindi) belongs to family Liliaceae. The plant, for its medicinal properties, has commercial value. Some of the genotypes of Aloe vera are consumed as a vegetable and processed to make curry and other edible products. We report here on the development of an efficient method for rapid clonal propagation by shoot proliferation from axillary meristem(s) of selected germplasm of Aloe vera. Explants were pretreated with 0.1% aqueous solution of both streptomycin and bavistin separately, each for 15 min. These were surface sterilized with 0.1% aqueous solution of mercuric chloride (HgCl2) for 4–5 min and washed several times with autoclaved water. These were kept in a chilled, sterile antioxidant (200.0 mg L−1 of ascorbic acid, 50.0 mg L−1 of citric acid, and 25.0 mg L−1 of polyvinylpyrrolidone; PVP) solution and cultured on semi-solid Murashige and Skoog's (MS) medium. The bud explants produced multiple (10.3 ± 0.675/explant) shoots on MS medium containing 13.32 μM of 6-Benzylaminopurine (BAP) and 100.0 mg L−1 of ascorbic acid, 50.0 mg L−1 each of citric acid and PVP, with 25.0 mg L−1 each of arginine and adenine sulphate as additives. The shoots were further multiplied by (a) repeated transfer to fresh MS medium with additives + 13.32 μM BAP, and (b) subculturing on MS medium with a lower (4.44 μM) concentration of BAP. On MS medium containing 4.44 μM of BAP and additives, a maximum number (27.8 ± 0.63) of shoots were produced. In liquid MS medium with 4.44 μM of BAP, the rate of shoot multiplication increased and the vigor of the shoots improved. One hundred percent of the cloned shoots rooted under in vitro conditions on hormone-free half-strength MS salts containing 200.0 mg L−1 of activated charcoal at 32 ± 2°C. The cloned shoots treated with 2.46 mM of indole-3-butyric acid (IBA) or 2.473 mM of β-naphthoxyacetic acid (NOA) for 5 min rooted under ex vitro conditions in the greenhouse. The rooted plants were hardened in the greenhouse and stored under an agro-net house. The cloned plants were transferred under different field conditions at various sites in Western Rajasthan. These plants grew normally. The higher rate of shoot multiplication and easier approach of direct rooting and hardening make this method superior to the methods previously reported on cloning/tissue culture of Aloe species. From a single shoot bud, approximately 5000 plants can be produced within 180 days.
Journal of Sustainable Forestry 12/2009; 28(8):935-950.
[show abstract][hide abstract] ABSTRACT: Western Rajasthan is arid and hot region of Indian Thar Desert. Plants and microbes thrive in this region are regularly subjected to hardship in the form of high thermal load, high irradiance, low precipitation (50-200mm annual) and saline and degraded soil and exhibit genetic diversity. Thus native legumes and associated rhizobia of extreme environment of Thar Desert are important genetic bio-resources and need characterization and conservation. After first time surveying and finding more than 30 native legumes species with in 12 genera belonging to all the three subfamily of Leguminosae attempt were made to isolate rhizobia from these native legumes. Rhizobia were isolated from excavated nodules of 22 species including 6 species of Indigofera, 7 species of Tephrosia, 2 species of Crotalaria, 1 species each of Chamaecrista, Prosopis, Acacia, Mimosa, Sesbania, Rhynchosia and Alysicarpus.
Fast growing (colony appeared in 1-2 days), high acid and EPS producer rhizobia were isolated from 5 species of Indigofera (I.cordifolia, I.hochestettri, I.linnaei, I.linifolia and I.tinctoria)and one species of Rhynchosia (R.minima). These rhizobia also exhibited high NaCl tolerance (8-9%) as compared to other isolated rhizobia. Medium fast growing (2-3 days), medium acid and EPS producing rhizobia were isolated from Acacia jacquemontii, Mimosa hamata, Crotalaria medicagenia, Tephrosia villosa, T.walchii and Chamaecrista pumila. These rhizobia exhibited NaCl tolerance up to 2-3%. Slow growing (colony appeared after 5 days), low acid and EPS producing rhizobia were isolated from Alycicarpus vaginalis, Sesbania bipinosa, Prosopis cineraria and Tephrosia purpuria. These rhizobia were found growing at 1% NaCl only except rhizobia of Prosopis cineraria that can tolerate NaCl up to 8%. Very slow growing rhizobia (colony appeared after 10 days), alkali producing and with no EPS were isolated from Crotalaria burhia, Tephrosia laptostachya, T.subtriflora, T.uniflora and Indigofera oblongifolia. These rhizobia were extremely low NaCl tolerance (<1%). Fast growing rhizobia from Indigofera and Rhynchosia were also found growin at 40-42ºC as compared to medium fast growing rhizobia (35ºC). Isolated rhizobia were found infective to their natural host in case of Indigofera, Alysicarpus and Acacia jacquemontii. Authentication test for other rhizobia have not tested so far. All the rhizobia were isolated from excavated nodules on YEMA, YEMA-BTB and YEMA-CR at 28ºC. NaCl tolerance was seen on YEM broath. The methods and experimental planning were based on Somasegran and Hoben (1994). The results of present investigation will be discussed in relation to rhizobial diversity in arid regions of Indian Thar Desert.