Exploiting Plant Functional Diversity in Durum Wheat???Lentil Relay Intercropping to Stabilize Crop Yields under Contrasting Climatic Conditions

Relay intercropping is considered a valuable agroecological practice to increase and stabilize crop yields while ensuring the provision of several ecosystem services as well as sustainability and resilience to changing climatic conditions. However, farmers are still reluctant in the use of intercropping practices since there is a huge knowledge gap regarding the time of sowing, sowing ratio, crop stand density, and cultivar choice. In this study, we carried out a 3-year field experiment in Central Italy to assess the effect of relay intercropping on the agronomic performance and competitiveness of winter durum wheat (Triticum durum Desf. cv. Minosse) and spring lentil (Lens culinaris Medik. cv. Elsa) under a low-input management system, comparing different crop stand types (monocrop vs. intercrop) and target plant densities (350 plants m2—full dose vs. 116 plants m2—1/3 dose). The results revealed that intercropping increased grain yield compared to monocropping: significantly (p < 0.0001) against both monocrops in 2021 and non-significantly against durum wheat in 2019 and 2020. Yield advantage in both intercropping systems ranged between 164 and 648%. Durum wheat competitiveness was stronger in 2019 and 2021, while lentil was the most competitive component in 2020. Intercropping favored P accumulation in durum wheat shoots. There was no difference in grain yield of both crops between the highly- and lowly-dense system in 2020 and 2021. Both intercropping strategies were as effective as mechanical hoeing in controlling weeds and proved beneficial in stabilizing lentil productivity. Further economic analysis capturing the additional costs incurred in intercropping and mechanical weeding would highlight the magnitude of profitability of these systems

Smart use of microbial-rich vermicomposting to enhance tripartite plant-microbe-soil interactions

Vermicomposting is a natural process that utilizes earthworms and associated microbiome to transform organic wastes into vermicompost by-products that are rich in beneficial microorganisms and nutrients such as carbon, phosphorus, nitrogen, magnesium, and calcium. Liquid vermicompost extract (LVE), a derivative of the vermicomposting process, has recently gained interest among scientists and organic farmers due to their potential ability to enhance tripartite plant-microbe-soil interactions that would lead to improved plant and root growth, soil health and overall crop yield productivity. To investigate the short-term effect of LVE on soil mycorrhizal inoculum potential (MIP) and plant-mycobiome interactions, a field trial was carried out at CiRAA E. Avanzi, San Piero a Grado, Pisa, Italy. The effect of LVE and its associated microbial and chemical components on soil MIP and AMF root colonization was evaluated on five summer crops, i.e. chickpea (Cicer arietinum L.), berseem clover (Trifolium alexandrinum L.), lentil (Lens culinaris L.), soybean (Glycine max L. Merrill), and sunflower (Helianthus annuus L.). The test plants were grown with or without the application of LVE in a split-plot trial with five replicates. Freshly made LVE from vermicomposting of wheat straws mixed with horse manure was screened for microbial properties using the Illumina Miseq sequencing platform. Seed inoculation with LVE was done before planting while field inoculation was done at the stem-elongation stage. Un-inoculated seeds and plots were used as controls. Soil MIP was assessed before planting and after harvesting, while AMF root colonization was evaluated at the mid-flowering stage of each crop. The bacterial 16S and fungal ITS sequence analyses showed a high bacteria and fungal abundance and taxonomic alpha diversity present in the LVE. The most dominant taxa included Mucor, Citrobacter, Pseudomonas, Arcobacter, Azomonas and Clostridium. These microbes are commonly found in agricultural soil and are linked to the hydrolysis of complex organic matter, nutrient recycling, production of growth-promoting factors and siderophores, while others are known to produce peptide antimycotics and antibiotics that protect plants against pathogenic soil microorganisms. The soil MIP significantly (p < 0.0001) differed between the two soil sampling times (before planting and after harvesting). It was evident that both seed and field inoculation with LVE significantly enhanced the soil MIP and this could benefit the next crop under rotation. AMF root colonization varied significantly across the crop species (p < 0.0001) and LVE treatment (p = 0.006). Highly nodulated lentils and berseem clover roots recorded significantly higher AMF root colonization than all the other crops. LVE inoculation had an overall positive effect on AMF root colonization with an average increase of 6.2% compared to the un-inoculated crops. These short-term results indicate that there could be a positive effect of the LVE inoculation on the soil MIP and AMF root colonization of our test crops, which could be attributed to the beneficial additive effects of the LVE that enhanced the tripartite plant-microbe-soil interactions

Genetic and phenotypic diversity of microsymbionts nodulating promiscuous soybeans from different agro-climatic conditions

Abstract Background Global food supply is highly dependent on field crop production that is currently severely threatened by changing climate, poor soil quality, abiotic, and biotic stresses. For instance, one of the major challenges to sustainable crop production in most developing countries is limited nitrogen in the soil. Symbiotic nitrogen fixation of legumes such as soybean (Glycine max (L.) Merril) with rhizobia plays a crucial role in supplying nitrogen sufficient to maintain good crop productivity. Characterization of indigenous bradyrhizobia is a prerequisite in the selection and development of effective bioinoculants. In view of this, bradyrhizobia were isolated from soybean nodules in four agro-climatic zones of eastern Kenya (Embu Upper Midland Zone, Embu Lower Midland Zone, Tharaka Upper Midland Zone, and Tharaka Lower Midland Zone) using two soybean varieties (SB8 and SB126). The isolates were characterized using biochemical, morphological, and genotypic approaches. DNA fingerprinting was carried out using 16S rRNA gene and restricted by enzymes HaeIII, Msp1, and EcoRI.  Results Thirty-eight (38) bradyrhizobia isolates obtained from the trapping experiments were placed into nine groups based on their morphological and biochemical characteristics. Most (77%) of the isolates had characteristics of fast-grower bradyrhizobia while 23% were slow-growers. Restriction digest revealed significant (p < 0.015) variation within populations and not among the agro-climatic zones based on analysis of molecular variance. Principal coordinate analysis demonstrated sympatric speciation of indigenous bradyrhizobia isolates. Embu Upper Midland Zone bradyrhizobia isolates had the highest polymorphic loci (80%) and highest genetic diversity estimates (H’ = 0.419) compared to other agro-climatic zones. Conclusion The high diversity of bradyrhizobia isolates depicts a valuable genetic resource for selecting more effective and competitive strains to improve promiscuous soybean production at a low cost through biological nitrogen fixation

Potential for legume-cereal relay intercropping in enhancing plant-soil-AMF interactions and yield

The effect of relay intercropping between winter durum wheat sown at 33% and 100% densities and lentils on soil mycorrhizal inoculation potential (MIP), crop yield, and land equivalent ratio (LER) under a low input management system was investigated. The relay intercropping system significantly (P=0.017) influenced soil MIP. A clear trend and a higher soil MIP increase was recorded in the relayed system compared to the sole cropping system. At harvest, no significant (P=0.067) difference in lentil grain yield was observed between the sole and intercropped lentils, but a slight reduction in wheat grain yield: -17% and -14% in intercropped wheat at 33% and 100% density respectively. However, wheat yield reduction could be compensated by the high-valued lentil harvest, which averaged 1.24 and 0.77 t ha-1 for 33% and 100% density respectively. LER values for both relay systems were &gt;1 indicating a yield advantage of the relay system in durum wheat-lentil production

Genetic Characterization and Diversity of Rhizobium Isolated From Root Nodules of Mid-Altitude Climbing Bean (Phaseolus vulgaris L.) Varieties

The increasing interest in the use of rhizobia as biofertilizers in smallholder agricultural farming systems of the Sub-Saharan Africa has prompted the identification of a large number of tropical rhizobia strains and led to studies on their diversity. Inoculants containing diverse strains of rhizobia have been developed for use as biofertilizers to promote soil fertility and symbiotic nitrogen fixation in legumes. In spite of this success, there is paucity of data on rhizobia diversity and genetic variation associated with the newly released and improved mid-altitude climbing (MAC) bean lines (Phaseolus vulgaris L.). In this study, 41 rhizobia isolates were obtained from the root nodules of MAC 13 and MAC 64 climbing beans grown in upper and lower midland agro-ecological zones of Eastern Kenya. Eastern Kenya was chosen because of its high production potential of diverse common bean cultivars. The rhizobia isolates were characterized phenotypically on the basis of colony morphology, growth and biochemical features. Rhizobia diversity from the different regions of Eastern Kenya was determined based on the amplified ribosomal DNA restriction analysis (ARDRA) of PCR amplified 16S rRNA genes using Msp I, EcoR I, and Hae III restriction enzymes. Notably, native rhizobia isolates were morphologically diverse and grouped into nine different morphotypes. Correspondingly, the analysis of molecular variance based on restriction digestion of 16S rRNA genes showed that the largest proportion of significant (p &lt; 0.05) genetic variation was distributed within the rhizobia population (97.5%) than among rhizobia populations (1.5%) in the four agro-ecological zones. The high degree of morphological and genotypic diversity of rhizobia within Eastern Kenya shows that the region harbors novel rhizobia strains worth exploiting to obtain strains efficient in biological nitrogen fixation with P. vulgaris L. Genetic sequence analysis of the isolates and testing for their symbiotic properties should be carried out to ascertain their identity and functionality in diverse environments