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Highlights • First study to show that there is a large diversity of Bradyrhizobium species associated with legumes on Christmas Island. • Naturalised rhizobia are present for the crop legumes cowpea, mungbean, peanut and lablab. • No nodules were detected on common bean, chickpea, and soybean, and hence inoculation is required for these crops. • Mimosa species are nodulated by C. alkaliphilus -like strains and C. taiwanensis. • Vertical transmission of symbiosis genes in the alpha-rhizobia but horizontal transmission within the beta-rhizobia. Abstract Given that phosphate supplies may diminish and become uneconomic to mine after 2020, there is a compelling need to develop alternative industries to support the population on Christmas Island. Former mine sites could be turned into productive agricultural land, however, large-scale commercial agriculture has never been attempted, and, given the uniqueness of the island, the diversity of rhizobia prior to introducing legumes needed evaluation. Therefore, 84 rhizobia isolates were obtained from nine different hosts, both crop and introduced legumes, located at seven sites across the island. Based on 16S rRNA and recA gene sequence analysis, the isolates grouped into 13 clades clustering within the genus Bradyrhizobium, Ensifer , Cupriavidus and Rhizobium. According to the sequences of their symbiosis genes nodC and nifH , the isolates were classified into 12 and 11 clades, respectively, and clustered closest to tropical or crop legume isolates. Moreover, the symbiosis gene phylogeny and Multi Locus Sequence Analysis gene phylogeny suggested vertical transmission in the Alpha-rhizobia but horizontal transmission within the Beta-rhizobia. Furthermore, this study provides evidence of a large diversity of endemic rhizobia associated with both crop and introduced legumes, and highlights the necessity of inoculation for common bean, chickpea and soybean on the Island. [ABSTRACT FROM AUTHOR]

Phaseolus vulgaris (common bean) was introduced to Kenya several centuries ago but the rhizobia that nodulate it in the country remain poorly characterised. To address this gap in knowledge, 178 isolates recovered from the root nodules of P. vulgaris cultivated in Kenya were genotyped stepwise by the analysis of genomic DNA fingerprints, PCR-RFLP and 16S rRNA, atpD , recA and nodC gene sequences. Results indicated that P. vulgaris in Kenya is nodulated by at least six Rhizobium genospecies, with most of the isolates belonging to Rhizobium phaseoli and a possibly novel Rhizobium species. Infrequently, isolates belonged to Rhizobium paranaense , Rhizobium leucaenae , Rhizobium sophoriradicis and Rhizobium aegyptiacum . Despite considerable core-gene heterogeneity among the isolates, only four nodC gene alleles were observed indicating conservation within this gene. Testing of the capacity of the isolates to fix nitrogen (N 2 ) in symbiosis with P. vulgaris revealed wide variations in effectiveness, with ten isolates comparable to Rhizobium tropici CIAT 899, a commercial inoculant strain for P. vulgaris . In addition to unveiling effective native rhizobial strains with potential as inoculants in Kenya, this study demonstrated that Kenyan soils harbour diverse P. vulgaris -nodulating rhizobia, some of which formed phylogenetic clusters distinct from known lineages. The native rhizobia differed by site, suggesting that field inoculation of P. vulgaris may need to be locally optimised. [ABSTRACT FROM AUTHOR]

Physiological responses to acid stress in two strains of Rhizobium leguminosarum bv trifolii of differing acid-soil tolerance were compared. Acidity affected the size and morphology of the acid-tolerant strain, WSM409, but not of the acid-sensitive strain, TA1. Acid grown cells of WSM409 and TA1 had less cell-associated Ca and Mg and more P than cells grown at pH 7.0. Potassium content was lower in acid grown cells; WSM409 was less affected by pH than that in TA1. WSM409 was more tolerant of pH shock at pH 3.5 when grown at pH 4.8 than when grown at pH 7.0. TA1 was more sensitive to pH shock when grown at pH 4.8 than when grown at pH 7.0. WSM409 shows a characteristic adaptive acid tolerance response, whereas TA1 shows an acid sensitive response. [Copyright &y& Elsevier]

Bradyrhizobium are N 2 -fixing microsymbionts of legumes with relevant applications in agricultural sustainability, and we investigated the phylogenetic relationships of conserved and symbiotic genes of 21 bradyrhizobial strains. The study included strains from Western Australia (WA), isolated from nodules of Glycine spp. the country is one genetic center for the genus and from nodules of other indigenous legumes grown in WA, and strains isolated from forage Glycine sp. grown in South Africa. The 16S rRNA phylogeny divided the strains in two superclades, of B. japonicum and B. elkanii , but with low discrimination among the species. The multilocus sequence analysis (MLSA) with four protein-coding housekeeping genes (dnaK , glnII , gyrB and recA) pointed out seven groups as putative new species, two within the B. japonicum , and five within the B. elkanii superclades. The remaining eleven strains showed higher similarity with six species, B. lupini , B. liaoningense , B. yuanmingense , B. subterraneum , B. brasilense and B. retamae. Phylogenetic analysis of the nodC symbiotic gene clustered 13 strains in three different symbiovars (sv. vignae, sv. genistearum and sv. retamae), while seven others might compose new symbiovars. The genetic profiles of the strains evaluated by BOX-PCR revealed high intra- and interspecific diversity. The results point out the high level of diversity still to be explored within the Bradyrhizobium genus, and further studies might confirm new species and symbiovars. [ABSTRACT FROM AUTHOR]

Globally, land-use transition from mining to agriculture is becoming increasingly attractive and necessary for many reasons. However, low levels of necessary plant nutrients, and high levels of heavy metals, can hamper plant growth, affecting yield, and potentially, food safety. In post-phosphate mining substrates, for example, nitrogen (N) is a key limiting nutrient, and, although legumes are planted prior to cereals, N supplementation is still necessary. We undertook two field trials on Christmas Island, Australia, to determine whether Sorghum bicolor could be grown successfully in a post-phosphate mining substrate. The first trial investigated N (urea) demand (amount of N required for adequate crop growth) for S . bicolor , and whether N addition could reduce the naturally occurring cadmium (Cd) concentrations in the crop. The second trial examined whether slow release nitrogen fertilizers (SRF) could replace urea to increase biomass and reduce Cd concentrations. Our first trial demonstrated that S . bicolor has a high N demand, with the highest biomass being recorded in the 160 kg/ha urea treatment. However, plants treated with 80, 120 and 160 kg/ha were not significantly different from one another. After 7 weeks of growth, leaf Cd concentrations were significantly lower for all urea treatments compared with the control plants. However, after 23 weeks, seed Cd concentrations did not differ across treatments. Our second trial demonstrated that the application of SRF (Macracote® and Sulsync®) and 160 kg/ha urea significantly increased biomass above the control plants. There was, however, no treatment response in terms of Cd or N concentrations in the seed at final harvest. Thus, we have shown that N is currently critical for S . bicolor , even following legume cropping, and that high biomass and a significant reduction in Cd can be attained with appropriate levels of urea. Our work has important implications for cereal growth and food safety in post-mining agriculture. [ABSTRACT FROM AUTHOR]

Industrial hemp (Cannabis sativa L.) is a crop with the potential for multiple products. However, there is a lack of information regarding the effects of some key nutrients and soil microbiology. Potassium (K) and microbes can affect plant physiology, growth, and secondary metabolite production. A glasshouse experiment in a fully controlled growth room was undertaken to assess K requirements and effects on physiology on a tropical/subtropical variety of industrial hemp, ECO-GH15, bred for Australian conditions by Ecofibre (Brisbane, QLD, Australia). Increasing rates of K of conventional fertiliser liquid applications were applied to hemp plants and compared to a slow-release form containing soil microbes (SRK) under short daylength (12.5 h), simulating a tropical environment. Application of 11, 43 and 129 ppm of conventional fast-release potassium K as potassium sulphate (K 2 SO 4), or a slow (controlled) release form (131 ppm of K), were applied to plants and their growth parameters compared. A series of physiological and growth response data was collected, including photosynthesis response to increasing active radiation (PAR or PPFD) and carbon dioxide (CO2), and cannabinoid production. Plant growth responses, such as stalk diameter, height, and shoot dry weight, increased with SRK application, while no differences were observed between the three increasing conventional K rates. The lower conventional K rate (11 ppm) resulted in increased photosynthetic activity up to 600–700 PPFD. Physiological data showed that the increasing K rate produced less efficient plants in terms of PPFD and CO 2 utilisation. Cannabinoid analysis showed an increase in cannabidiol (CBD) and cannabidivarin (CBDV) at the higher K rate, while the SRK increased the production of delta-9-tetrahydrocannabinol (THC) and similar cannabinoids. This study revealed that sustained nutrient application improved plant photosynthesis and gas exchange regulation resulting in increased plant growth and cannabinoid production under tropical conditions, and helped to better understand the role of K in plant stress and physiological efficiency. [Display omitted] • Increasing conventional application of K (K 2 SO 4) did not affect final shoot biomass. • K rate affected stomata control and net photosynthesis in industrial hemp variety. • Sustained nutrient/soil microbe application enhanced growth and cannabinoid profile. [ABSTRACT FROM AUTHOR]

Hemp (Cannabis sativa L.) has regained worldwide interest as a crop across temperate and subtropical regions. However, there is a paucity of information about the responses of hemp to environmental conditions and interactions between genotype and environment. This study compared the growth responses of a temperate hemp variety (Morphet Late) and three tropical/subtropical varieties (ECO-GH15, ECO-MC16 and ECO-YP16) to tropical daylengths (11.5 h and 12.5 h), temperatures and varying nitrogen (0, 50, 100, 150 kg ha-1 of N) rates. Three experiments under controlled environmental conditions were conducted to test the growth, and cannabinoid production responses to N. Analysis of phenological data revealed significantly different responses between varieties in terms of days to emergence, time to flowering, growth patterns and final biomass showing predominant responses to daylength or temperature depending on the variety. Two tropical/subtropical varieties (ECO-GH15, ECO-MC16) responded similarly under all conditions; the other (ECO-YP16) showed a marked response to temperature rather than daylength, although all varieties had a strong biomass response to N increase. For all varieties, except the temperate variety, the concentration of Δ9-tetrahydrocannabinol (THC), cannabidiol (CBD), and some minor cannabinoids were significantly increased by a one-hour daylength increase. This study highlights the importance of temperature, daylength, and nitrogen for growth, time to flowering, and cannabinoid concentrations of different hemp varieties grown under tropical conditions and shows the importance of selecting low THC varieties for production in tropical/subtropical environments. • Temperature is critical for flowering in tropical/subtropical hemp varieties. • One extra photoperiod hour increased cannabinoids in tropical/subtropical varieties. • Nitrogen increased final biomass under tropical conditions, depending on variety. [ABSTRACT FROM AUTHOR]

Bacteria were isolated from root-nodules collected from indigenous legumes at 38 separate locations in the Gascoyne and Pilbara regions of Western Australia. Authentication of cultures resulted in 31 being ascribed status as root-nodule bacteria based upon their nodulation of at least one of eight indigenous legume species. The authenticated isolates originated from eight legume genera from 19 sites. Isolates were characterised on the basis of their growth and physiology; 20 isolates were fast-growing and 11 were slow-growing (visible growth within 3 and 7 d, respectively). Fast-growers were isolated from Acacia, Isotropis, Lotus and Swainsona, whilst slow-growers were from Muelleranthus, Rhynchosia and Tephrosia. Indigofera produced one fast-growing isolate and seven slow-growing isolates. Three indigenous legumes (Swainsona formosa, Swainsona maccullochiana and Swainsona pterostylis) nodulated with fast-growing isolates and four species (Acacia saligna, Indigofera brevidens, Kennedia coccinea and Kennedia prorepens) nodulated with both fast- and slow-growing isolates. Swainsona kingii did not form nodules with any isolates. Fast-growing isolates were predominantly acid-sensitive, alkaline- and salt-tolerant. All slow-growing isolates grew well at pH 9.0 whilst more than half grew at pH 5.0, but all were salt-sensitive. All isolates were able to grow at 37 °C. The fast-growing isolates utilised disaccharides, whereas the slow-growing isolates did not. Symbiotic interactions of the isolates were assessed on three annual, one biennial and nine perennial exotic legume species that have agricultural use, or potential use, in southern Australia. Argyrolobium uniflorum, Chamaecytisus proliferus, Macroptilium atropurpureum, Ononis natrix, Phaseolus vulgaris and Sutherlandia microphylla nodulated with one or more of the authenticated isolates. Hedysarum coronarium, Medicago sativa, Ornithopus sativus, Ornithopus compressus, Trifolium burchellianum, Trifolium polymorphum and Trifolium uniflorum did not form nodules. Investigation of the 31 authenticated isolates by polymerase chain reaction with three primers resulted in the RPO1 primer distinguishing 20 separate banding patterns, while ERIC and PucFor primers distinguished 26 separate banding patterns. Sequencing the 16S rRNA gene for four fast- and two slow-growing isolates produced the following phylogenetic associations; WSM1701 and WSM1715 (isolated from Lotus cruentus and S. pterostylis, respectively) displayed 99% homology with Sinorhizobium meliloti, WSM1707 and WSM1721 (isolated from Sinorhizobium leeana and Indigofera sp., respectively) displayed 99% homology with Sinorhizobium terangae, WSM1704 (isolated from Tephrosia gardneri) shared 99% sequence homology with Bradyrhizobium elkanii, and WSM1743 (isolated from Indigofera sp.) displayed 99% homology with Bradyrhizobium japonicum. [Copyright &y& Elsevier]