Multi-purpose cowpea inoculation for improved yields in small holder farms in Kenya

Introduction In Kenya, cowpea is the most important pulse crop in the dry lands of Eastern and Coastal regions where it is commonly inter cropped with maize and sorghum. The poor yields obtained in small holder farms in Kenya (150 kg ha-1) can in part be attributed to the use of poor yielding varieties, low soil fertility (mainly N and P deficiency) low presence of effective indigenous rhizobia and high occurrence of highly competitive but inefficient indigenous rhizobia strains. Biological nitrogen fixation (BNF) through exploitation of the rhizobia-legume symbiosis and use of inoculants coupled with soil amendments such as Phosphorus offers in part a means to improve cowpea yield, nutrition and soil fertility

Breeding for symbioses – Mycorrhizae as a case study

Plant associated soil microbes are known to play an important role in the expression and stability of certain plant traits such as nutrient use efficiency and disease resistance. Arbuscular mycorrhizal fungi (AMF) form one of the primary mutualistic plant-microbe symbioses. Besides known benefits such as improved nutrient mobilisation (mainly phosphorus and zinc) and tolerance against abiotic stresses (mainly drought), an increasing number of studies highlight a significant role of AMF in the mediation of disease resistances and priming mechanisms. Individual reports have shown enhanced levels of defence-related compounds (such as glucanases, chitinases and phenolics) in mycorrhizal plants, and there is first evidence of certain phytohormone pathways (in particular jasmonate signalling) to be involved in mycorrhiza-mediated disease resistance. The level of mycorrhisation (formation of mycorrhizae on the roots) and mycorrhizal responsiveness (response to AMF) can vary widely between plant species and also among genotypes within the same species, indicating a genetic basis for the regulation of this symbiosis. Genotypic differences in mycorrhizal responsiveness have been observed in various crops and quantitative trait loci (QTL) that govern plant growth responses to AMF have been reported for maize, barley and onion. However, little is known about the heritability of mycorrhiza-mediated disease resistance. Mycorrhizal responsiveness (when based on biomass) is negatively correlated with available soil P content. Breeding under high P conditions might therefore indirectly select for poor AMF hosts. We hypothesise that a reduced mycorrhizal dependency also affects other benefits elicited by AMF such as disease resistance. We therefore pledge to include factors other than biomass to estimate mycorrhizal responsiveness (i.e. disease resistance, PUE and drought tolerance) to obtain a more comprehensive differentiation of the plant-AMF interaction. The authors also propose to complement mycorrhizal responsiveness with an additional measure called mycorrhizal efficiency since mycorrhization and mycorrhizal responsiveness on their own might not indicate an optimum cost-benefit ratio of this symbiosis. We will present initial results on genotypic variation in mycorrhization, mycorrhizal responsiveness and mycorrhizal efficiency of SNP-genotyped accessions of pea (Pisum sativum L.). Eventually, these SNP-genotyped accessions can be used to identify QTL that govern mycorrhiza-mediated disease resistance and exploit genotypic differences, e.g., via marker-assisted selection. Another research project has been initiated to investigate the role of flavonoids in defence mechanisms of pea and their possible function in microbe-mediated disease resistance. Variation in microbial composition has been attributed to a differential exudation of compounds that stimulate or suppress particular members/groups of the microbial community. The complex group of flavonoids has been shown to play a signalling and/or direct role in plant defence mechanisms, but also to influence the interaction with symbionts including mycorrhizal fungi (and also plant-symbiotic rhizobia). Overall, current and future research activities of our group aim to better understand and make use of plant-microbe interactions in plant breeding for an improved expression and stability of important plant traits

Traits related to differences in function among three arbuscular mycorrhizal fungi

Diversity in phosphorus (P) acquisition strategies was assessed among three species of arbuscular mycorrhizal fungi (AMF) isolated from a single field in Switzerland. Medicago truncatula was used as a test plant. It was grown in a compartmented system with root and root-free zones separated by a fine mesh. Dual radioisotope labeling (32P and 33P) was employed in the root-free zone as follows: 33P labeling determined hyphal P uptake from different distances from roots over the entire growth period, whereas 32P labeling investigated hyphal P uptake close to the roots over the 48 hours immediately prior to harvest. Glomus intraradices, Glomus claroideum and Gigaspora margarita were able to take up and deliver P to the plants from maximal distances of 10, 6 and 1cm from the roots, respectively. Glomus intraradices most rapidly colonized the available substrate and transported significant amounts of P towards the roots, but provided the same growth benefit as compared to Glomus claroideum, whose mycelium was less efficient in soil exploration and in P uptake and delivery to the roots. These differences are probably related to different carbon requirements by these different Glomus species. Gigaspora margarita provided low P benefits to the plants and formed dense mycelium networks close to the roots where P was probably transiently immobilized. Numerical modeling identified possible mechanisms underlying the observed differences in patterns of mycelium growth. High external hyphal production at the root-fungus interface together with rapid hyphal turnover were pointed out as important factors governing hyphal network development by Gigaspora, whereas nonlinearity in apical branching and hyphal anastomoses were key features for G. intraradices and G. claroideum, respectivel

Symbiont identity matters: carbon and phosphorus fluxes between Medicago truncatula and different arbuscular mycorrhizal fungi

Many studies have scrutinized the nutritional benefits of arbuscular mycorrhizal associations to their host plants, while the carbon (C) balance of the symbiosis has often been neglected. Here, we present quantification of both the C costs and the phosphorus (P) uptake benefits of mycorrhizal association between barrel medic (Medicago truncatula) and three arbuscular mycorrhizal fungal species, namely Glomus intraradices, Glomus claroideum, and Gigaspora margarita. Plant growth, P uptake and C allocation were assessed 7 weeks after sowing by comparing inoculated plants with their non-mycorrhizal counterparts, supplemented with different amounts of P. Isotope tracing (3)(3)P and (1)(3)C) was used to quantify both the mycorrhizal benefits and the costs, respectively. G. intraradices supported greatest plant P acquisition and incurred high C costs, which lead to similar plant growth benefits as inoculation with G. claroideum, which was less efficient in supporting plant P acquisition, but also required less C. G. margarita imposed large C requirement on the host plant and provided negligible P uptake benefits. However, it did not significantly reduce plant growth due to sink strength stimulation of plant photosynthesis. A simple experimental system such as the one established here should allow quantification of mycorrhizal costs and benefits routinely on a large number of experimental units. This is necessary for rapid progress in assessment of C fluxes between the plants and different mycorrhizal fungi or fungal communities, and for understanding the dynamics between mutualism and parasitism in mycorrhizal symbioses

Symbiont identity matters: carbon and phosphorus fluxes between Medicago truncatula and different arbuscular mycorrhizal fungi

Many studies have scrutinized the nutritional benefits of arbuscular mycorrhizal associations to their host plants, while the carbon (C) balance of the symbiosis has often been neglected. Here, we present quantification of both the C costs and the phosphorus (P) uptake benefits of mycorrhizal association between barrel medic (Medicago truncatula) and three arbuscular mycorrhizal fungal species, namely Glomus intraradices, Glomus claroideum, and Gigaspora margarita. Plant growth, P uptake and C allocation were assessed 7weeks after sowing by comparing inoculated plants with their non-mycorrhizal counterparts, supplemented with different amounts of P. Isotope tracing (33P and 13C) was used to quantify both the mycorrhizal benefits and the costs, respectively. G. intraradices supported greatest plant P acquisition and incurred high C costs, which lead to similar plant growth benefits as inoculation with G. claroideum, which was less efficient in supporting plant P acquisition, but also required less C. G. margarita imposed large C requirement on the host plant and provided negligible P uptake benefits. However, it did not significantly reduce plant growth due to sink strength stimulation of plant photosynthesis. A simple experimental system such as the one established here should allow quantification of mycorrhizal costs and benefits routinely on a large number of experimental units. This is necessary for rapid progress in assessment of C fluxes between the plants and different mycorrhizal fungi or fungal communities, and for understanding the dynamics between mutualism and parasitism in mycorrhizal symbiose

Selektion der Soja und deren Symbiosepartner auf Kühletoleranz und Effizienz der biologischen Stickstoff-Fixierung

In Central Europe low temperature is limiting soybean growth and biological nitrogen fixation (BNF). The BNF efficiency was shown to increase with bradyrhizobia strains selected for their cold tolerance. Significant bradyrhizobia x soybean variety interactions were reported. Co-inoculation with arbuscular mycorrhiza fungi (AMF) may promote bradyrhizobia and improve plant phosphorus uptake. The aim of this study is to identify (i) bradyrhizobia showing improved nodulation under cool conditions, (ii) bradyrhizobia x soybean variety and (iii) bradyrhizobia x AMF interactions. In 2011 twelve bradyrhizobia inoculants were tested with three soybean (Glycine max [L.]) varieties under three temperature regimes (14/10°C, 16/12°C, 22/20 °C) in a pot trial. In 2012 the five most promising bradyrhizobia were inoculated on twenty soybean varieties and an additional trial testing co-inoculated bradyrhizobia and AMF strains was conducted. A significant bradyrhizobia x temperature interaction was found for the number of nodules per plant and the SPAD values (indirect chlorophyll measurement; p ≤ 0,001). Significant bradyrhizobia x variety interactions were observed (p ≤ 0,01). The present results show that the selection of cold tolerant inoculants is as important as adapted soybean varieties. The efficiency of single bradyrhizobia x soybean variety combinations depends on the temperature regime

Long-term organic matter application reduces cadmium but not zinc concentrations in wheat

Wheat is a staple food crop and a major source of both the essential micronutrient zinc (Zn) and the toxic heavy metal cadmium (Cd) for humans. Since Zn and Cd are chemically similar, increasing Zn concentrations in wheat grains (biofortification), while preventing Cd accumulation, is an agronomic challenge. We used two Swiss agricultural long-term field trials, the “Dynamic-Organic-Conventional System Comparison Trial” (DOK) and the “Zurich Organic Fertilization Experiment” (ZOFE), to investigate the impact of long-term organic, mineral and combined fertilizer inputs on total and phytoavailable concentrations of soil Zn and Cd and their accumulation in winter wheat ( L.). “Diffusive gradients in thin films” (DGT) and diethylene-triaminepentaacetic acid (DTPA) extraction were used as proxies for plant available soil metals. Compared to unfertilized controls, long-term organic fertilization with composted manure or green waste compost led to higher soil organic carbon, cation exchange capacity and pH, while DGT-available Zn and Cd concentrations were reduced. The DGT method was a strong predictor of shoot and grain Cd, but not Zn concentrations. Shoot and grain Zn concentrations correlated with DTPA-extractable and total soil Zn concentrations in the ZOFE, but not the DOK trial. Long-term compost fertilization led to lower accumulation of Cd in wheat grains, but did not affect grain Zn. Therefore, Zn/Cd ratios in the grains increased. High Zn and Cd inputs with organic fertilizers and high Cd inputs with phosphate fertilizers led to positive Zn and Cd mass balances when taking into account atmospheric deposition and fertilizer inputs. On the other hand, mineral fertilization led to the depletion of soil Zn due to higher yields and thus higher Zn exports than under organic management. The study supports the use of organic fertilizers for reducing Cd concentrations of wheat grains in the long-term, given that the quality of the fertilizers is guaranteed

Green manure and long-term fertilization effects on available soil zinc and cadmium and their accumulation by wheat (Triticum aestivum L.)

Zinc (Zn) deficiency in humans due to imbalanced diets is a global nutritional problem. It is especially widespread in populations of low-income countries depending on cereals as staple food. Grain Zn concentrations are particularly low in cereals grown on soils with low phytoavailable Zn concentrations. . Plant Zn uptake depends on soil properties such as pH, calcium carbonate, iron and manganese oxides, total Zn and organic matter content (OM). Soil pH, total Zn and OM can be influenced on farms with limited access to mineral fertilizers through organic matter management practises. In this study, we investigated to what extent green manure application could increase soil Zn availability and wheat grain Zn concentrations (biofortification) on soil with different long-term fertilizer management

Einsatz von Protein- und Metabolit-Profiling-Methoden zur Unterscheidung von ökologischem und konventionellem Weizen

The interest in methods to proof organic food authenticity increases with the steadily rising popularity of food labelled organic. Profiling techniques enable the detection of a wide range of substances in biological samples. Together with bioinformatics tools these techniques are useful for biomarker searching, e. g. in plant extracts. Metabolomic and proteomic profiling techniques were used to screen organic and conventional wheat, originating from the DOK field trial in Switzerland. Up to 11 wheat varieties from three harvest years were analysed. We were able to detect a number of metabolites and proteins with significant differences between samples of conventional and organic grown wheat of the variety “Runal”. Results viewed across all 11 varieties indicated a higher influence of both the variety and the seasonal effects than the cultivation form. Nevertheless, PCA performed on metabolite data for the individual varieties and for individual growing seasons revealed a clustering according to the cultivation forms. Further research is necessary to assess, whether these methods can be applied to distinguish organic and conventional wheat from agricultural practice

Application of Mycorrhiza and Soil from a Permaculture System Improved Phosphorus Acquisition in Naranjilla

Naranjilla (Solanum quitoense) is a perennial shrub plant mainly cultivated in Ecuador, Colombia, and Central America where it represents an important cash crop. Current cultivation practices not only cause deforestation and large-scale soil degradation but also make plants highly susceptible to pests and diseases. The use of arbuscular mycorrhizal fungi (AMF) can offer a possibility to overcome these problems. AMF can act beneficially in various ways, for example by improving plant nutrition and growth, water relations, soil structure and stability and protection against biotic and abiotic stresses. In this study, the impact of AMF inoculation on growth and nutrition parameters of naranjilla has been assessed. For inoculation three European reference AMF strains (Rhizoglomus irregulare, Claroideoglomus claroideum, and Cetraspora helvetica) and soils originating from three differently managed naranjilla plantations in Ecuador (conventional, organic, and permaculture) have been used. This allowed for a comparison of the performance of exotic AMF strains (reference strains) versus native consortia contained in the three soils used as inocula. To study fungal communities present in the three soils, trap cultures have been established using naranjilla as host plant. The community structures of AMF and other fungi inhabiting the roots of trap cultured naranjilla were assessed using next generation sequencing (NGS) methods. The growth response experiment has shown that two of the three reference AMF strains, a mixture of the three and soil from a permaculture site led to significantly better acquisition of phosphorus (up to 104%) compared to uninoculated controls. These results suggest that the use of AMF strains and local soils as inoculants represent a valid approach to improve nutrient uptake efficiency of naranjilla and consequently to reduce inputs of mineral fertilizers in the cultivation process. Improved phosphorus acquisition after inoculation with permaculture soil might have been caused by a higher abundance of AMF and the presence of Piriformospora indica as revealed by NGS. A higher frequency of AMF and enhanced root colonization rates in the trap cultures supplemented with permaculture soil highlight the importance of diverse agricultural systems for soil quality and crop production