Soil inoculum identity and rate jointly steer microbiomes and plant communities in the field

The importance of soil inoculation to engineer soil microbiomes and ultimately entire ecosystems is becoming widely acknowledged. Inoculation with soil from different ecosystems can induce directional changes in soil and plant communities and promote the restoration of degraded ecosystems. However, it is unknown how such inoculations influence the soil microbiome, how much inoculum is needed, and whether inocula collected from similar ecosystems will steer the microbiome in different directions. We conducted a three-year soil inoculation field experiment at a degraded grassland and used two different soil inocula both from grasslands with three inoculation rates. Our results show that inoculation with soil that originates from different donor grasslands steers the soil microbiome as well as the plant communities at the inoculated site which was a degraded grassland into different directions and that these effects were stronger with increasing amount of soil used to inoculate. Inoculation with upland meadow soil introduced more keystone genera and resulted in more complex biotic networks in the soil than inoculation with meadow steppe soil. Our experiment highlights that soil inoculation can steer soil microbiomes in the field and that the direction and speed of development depend on the origin and the amount of soil inoculum used.

Pathogenicity, Host Range and Influence of Temperature, Humidity and pH Levels on the Growth of Fusarium oxysporum f.sp. lentis

Background: Lentil is a vital nutritional source of protein in several parts of the world including India. The crop is susceptible to wilt which is a devastating soil-borne disease induced by the fungus Fusarium oxysporum f. sp. lentis. Insight of the potential threat Fusarium wilt can pose to lentils, a present study done on pathogenicity, host range and influence of temperature, humidity and pH levels on the growth of F. oxysporum f. sp. lentis.Methods: Ten isolates FOL-01 to FOL-10 of F. oxysporum f. sp. lentis (Fol) were isolated from wilted lentil plants that collected from different major lentil growing parts of Rajasthan. During 2017-18 a pathogenicity test was tested in pot house condition by seed and soil inoculation techniques for all isolates and epidomological factors evaluated in vitro conditions.Result: Results indicated that the Fol isolates represent a single race but differ in their aggressiveness on the susceptible cultivar L9-12. Pathogenicity test revealed clearly that Fol was associated with wilt symptoms and were pathogenic to lentil plants. A maximum percent disease incidence of 70.00 was showed by isolate FOL-02 in soil inoculation technique. In the morphological and cultural characterization, all the ten isolates showed various character in conidial frequency, colony color and growth pattern. Twenty plant species were tested to know the host range of Fol, out of these lentil, chickpea and pea show positive reaction with the pathogen. The influence of temperature, relative humidity and pH on the growth and sporulation of Fol was studied under in vitro conditions. Maximum mycelial growth and sporulation of the Fol were observed at 30°C, 6.0 pH and 60% relative humidity.

Vertical movement of A. brasilense Sp7 and strain Cd in soil under different inoculation regimes

<p><em>Azospirillum brasilense</em> Sp7 and <em>Azospirillum brasilense </em>Cd are two plant growth-promoting bacteria (PGPB). Traditional inoculation methods with PGPB are seed inoculation, seedling root inoculation and soil inoculation. Although these methods are simple to use, they are limited to apply at a specific plant growth stage. Therefore, PGPB inoculation by drip irrigation has been suggested as a means to deliver PGPB directly to the root zone during the plant growth stages. To quantify the intrinsic transport characteristics of two <em>A. brasilense</em> strains following point source inoculation, the properties of <em>A. brasilense</em> Sp7 and <em>A. brasilense</em> Cd (e.g., cell size, hydrophobicity, and zeta potential) and the adsorption characteristics on fine sand were measured. The transport and fate of the two strains were examined under transient water flow conditions with three soil inoculation regimes: (i) surface irrigation (ii) subsurface irrigation and (iii) soil premixing. The water content, bromide, and bacteria distribution in the soil profile were measured after 2 and 48 hours. The measured data were described using the attachment/detachment model using the Hydrus 2/3D code. The result showed that even though <em>A. brasilense</em> Sp7 and Cd exhibit similar hydrophilicity and zeta potential their adsorption and/or straining in the soil profile were differed. <em>A. brasilense</em> Cd has a smaller cell size, less adsorption and less straining than <em>A. brasilense</em> Sp7, thus its vertical movement is deeper. However, both strains accumulated at the vicinity of the water source. The results of this study will be presented and the pros and cons of three inoculation regimes<strong> </strong>will be discussed.</p>

Development of a new in vivo protocol through soil inoculation to investigate sugar beet resistance towards Ditylenchus dipsaci penetration

Summary The stem nematode, Ditylenchus dipsaci, causes severe damage in sugar beet. To date, nematode inoculation through the leaf axil has been used as the standard method to investigate D. dipsaci interaction with sugar beet under in vivo conditions. To get as close as possible to field conditions, we established a new screening mechanism to perform soil inoculation. The most suitable inoculation time point, inoculum level and positioning on sugar beet, as well as rearing process on carrots, were determined. At a 15:8°C day:night temperature regime, penetration rates of D. dipsaci were at maximum following soil inoculation at plant emergence. Up to 115 nematodes penetrated sugar beet seedlings 22 days post-planting with an inoculum level of 1000 nematodes into the soil at plant emergence. Ditylenchus dipsaci penetration rate was higher in plants with soil inoculation than with inoculation on to the leaf axil. High soil moisture increased nematode migration into seedlings when D. dipsaci inoculation was carried out in four holes 1 cm from the plant base. Rearing the nematodes for 35 days at 20°C on carrot discs resulted in an infective inoculum containing up to 50% eggs. We recommend a soil inoculation of 1000 freshly extracted nematodes per pot at plant emergence. The nematode suspension has to be previously reared for 35 days on carrot discs to obtain active D. dipsaci inoculum. This system will allow for the selection of suitable sugar beet genotypes that suppress nematode penetration, in support of breeding for resistance against D. dipsaci.

The Effect Of Norms Of Mineral Fertilizers And Nitragin Used In Repeat Crop Bean On The Agrochemical And Microbiological Properties Of Soil

It was found that inoculation with nitrogen and application of mineral fertilizers before sowing the seeds of bean crops grown as a secondary crop after winter wheat affected the agrochemical and microbiological properties of the soil. Inoculation of bean seeds with nitrogen before sowing and application of mineral fertilizers in different doses provided an increase in the amount of humus in the topsoil (0-30 cm) layer by 0.021-0.034% compared to the initial values, and the total nitrogen content by 0.006-0.009%. It was found that the increase in the number of mineral fertilizers in the background inoculated with nitrogen before sowing the seeds of beans grown as a secondary crop led to an increase in the number of ammonifiers, oligonitrophils, micromycetes, and actinomycetes compared to the control option.

Inoculation of Ensifer fredii strain LP2/20 immobilized in agar results in growth promotion and alteration of bacterial community structure of Chinese kale planted soil

In our former research, we succeeded in using agar, alginate, and perlite as immobilization materials to maintain long-term survival of the inoculant, Ensifer fredii LP2/20, in a controlled glasshouse. Therefore the information on the establishment and activity of the inoculant to promote plant growth under field conditions, the effects of the inoculant on the soil microbial communities and specific microbial taxa, and the association between the inoculant and soil elements merit further studies. Here, we found that agar was the most suitable material that supported the establishment of the inoculant under field conditions. RNA-based analysis showed that E. fredii LP2/20 immobilized in agar was still metabolically active at day 50 after being introduced into soil. Inoculation of E. fredii LP2/20 immobilized in agar conferred the highest plant dry weight (up to 89.94%) and all plant elements including total N (9.55%), P (17.94%), K (68.42%), Ca (39.77%), Mg (30.76%), Fe (29.85%), and Zn (22.44%). Inoculation of E. fredii LP2/20 immobilized in agar increased soil chemicals including soil organic matter (99.02%), total N (272.48%), P (31.75%), K (52.74%), Fe (51.06%), and Zn (63.10%). High-throughput next-generation sequencing of bacterial 16S rRNA amplicons showed that the Proteobacteria, Acidobacteria, Bacteroidetes, and Firmicutes were dominant phyla in Chinese kale field soil. Inoculation of E. fredii LP2/20 significantly affected the soil bacterial community structure by decreasing total bacterial richness and diversity. The numbers of alpha- and gamma-Proteobacteria were significantly increased while the number of delta-Proteobacteria was significantly decreased due to E. fredii LP2/20 establishment. Soil total P, K, and Ca and soil pH were the important factors that shaped the soil bacterial community composition.