Rosalind Deaker

Phosphorus Adsorption in Some Australian Soils and Influence of Bacteria on the Desorption of Phosphorus

Abstract Seven Australian soil samples were collected from different locations (Camden, Griffith, Narrabri, Rutherglen, Wagga Wagga, Wee Waa (Ivanhoe), and Yanco) to measure their phosphorus (P) adsorption rates. Soils were collected from the top 0–15 cm, and P was added at 0, 100, 200, 300, 400, and 500 µg P g−1 soil. Results indicated that P adsorption increased significantly with increasing levels of added P. In subsequent studies, soils from Griffith and Narrabri and two bacteria Pantoea spp. known as FA001 and FA010 were tested for P mobilization at 100 µg P g−1 soil concentration. The rate of P mobilization [P extracted by 0.01 M calcium chloride (CaCl2)] in the Narrabri soil showed significant differences between treatments, but with and without bacteria, this was not the case for the Griffith soil. In Narrabri soil, the highest extractable P (0.492 µg g−1) was obtained with the treatment containing the strain FA001 after bacterial lysis with trichloromethane (CHCl3), and the lowest P (0.236 µg g−1) was measured in the treatment without bacterial amendment and without CHCl3 treatment, indicating the P‐mobilizing ability of the strain FA001. It was found that the minimum P‐adsorption capacities (revealed from the Langmuir and Temkin adsorption isotherms) of the Narrabri and the Griffith soils are 357 and 500 µg g−1, respectively; the buffering capacities of the Narrabri and the Griffith soil are 71.7 and 93.7 µg g−1, respectively. These findings indicate that soils with high P adsorption and buffering capacities are less likely to respond to the P‐mobilizing bacteria. Therefore, the application of the Langmuir and Temkin adsorption isotherms for estimating soil P‐adsorption and buffering capacities can be used to predict the potential usefulness of biofertilizer application.

Some factors that contribute to poor survival of rhizobia on preinoculated legume seed

Abstract. Preinoculation of seed is a convenient alternative method to inoculating seed on-farm. With preinoculation, a range of plant-growth and protection agents, polymer adhesives, colour pigments or dyes, and powder materials may be incorporated into an inoculant adhesive-slurry prior to seed coating. However, our recent point-of-sale surveys support findings of previous studies that survival of rhizobia on preinoculated seed is variable and can be poor. We focussed our research, both in the laboratory and at commercial facilities, on some of the factors that may contribute to poor survival of rhizobia on preinoculated seed. We found that rhizobial survival was affected by water quality; filtration improved cell survival but was not equal to distilled water. We also found that polymers affected cell survival differently for each rhizobial strain, and that slowing the desiccation rate reduced the cell rate of decline. Although fewer in cell number, older inoculant afforded more protection for survival of rhizobial cells. There is a need to test each ingredient and stage in the seed-coating process for compatibility to determine the best practices to promote rhizobial survival on seed. Failure to act on these factors prolongs the status quo of the findings from recent retail surveys.

EFFECTS OF A MULTISTRAIN BIOFERTILIZER AND PHOSPHORUS RATES ON NUTRITION AND GRAIN YIELD OF PADDY RICE ON A SANDY SOIL IN SOUTHERN VIETNAM

Field experiments during two successive rainy seasons were conducted in southern Vietnam to evaluate the effects of a commercial inoculant biofertilizer (‘BioGro’) and fused magnesium phosphate (FMP) fertilizer on yield and nitrogen (N) and phosphorus (P) nutrition of rice. Inoculation with BioGro containing a pseudomonad, two bacilli and a soil yeast significantly increased grain yield in the second season and straw yield in both seasons by 3–5%. The FMP fertilizer significantly increased grain yield from 1.72–2.33 t ha−1 to 2.99–3.58 t ha−1 along with total N and P accumulation at all rates in both cropping seasons. In the first season the difference in grain yield between BioGro treated and untreated plots was marginal but in the second season BioGro out-yielded the control at all the rates of added P. Overall, BioGro application did not compensate for low P fertilizer application to the same extent previously demonstrated for low N fertilizer applications.

Physiological Changes in Rhizobia after Growth in Peat Extract May Be Related to Improved Desiccation Tolerance

ABSTRACT Improved survival of peat-cultured rhizobia compared to survival of liquid-cultured cells has been attributed to cellular adaptations during solid-state fermentation in moist peat. We have observed improved desiccation tolerance of Rhizobium leguminosarum bv. trifolii TA1 and Bradyrhizobium japonicum CB1809 after aerobic growth in water extracts of peat. Survival of TA1 grown in crude peat extract was 18-fold greater than that of cells grown in a defined liquid medium but was diminished when cells were grown in different-sized colloidal fractions of peat extract. Survival of CB1809 was generally better when grown in crude peat extract than in the control but was not statistically significant (P > 0.05) and was strongly dependent on peat extract concentration. Accumulation of intracellular trehalose by both TA1 and CB1809 was higher after growth in peat extract than in the defined medium control. Cells grown in water extracts of peat exhibit morphological changes similar to those observed after growth in moist peat. Electron microscopy revealed thickened plasma membranes, with an electron-dense material occupying the periplasmic space in both TA1 and CB1809. Growth in peat extract also resulted in changes to polypeptide expression in both strains, and peptide analysis by liquid chromatography-mass spectrometry indicated increased expression of stress response proteins. Our results suggest that increased capacity for desiccation tolerance in rhizobia is multifactorial, involving the accumulation of trehalose together with increased expression of proteins involved in protection of the cell envelope, repair of DNA damage, oxidative stress responses, and maintenance of stability and integrity of proteins.

Response of lettuce seedlings fertilized with fish effluent to Azospirillum brasilense inoculation

The continuous use of agrochemical inputs in modern agriculture for better crop productivity has resulted in unexpected environmental impact. This issue has raised public interest in exploring environmental friendly sustainable practices. In this study, three strains of Azospirillum brasilense (Sp7, Sp7-S and Sp245) were evaluated for their impacts on the growth of lettuce seedlings grown with fish effluent (FE) as a source of nutrients. Lettuce seeds were inoculated with these strains before sowing and at transplanting, and grown under greenhouse condition with natural light. Despite the existing indigenous microflora and low level of nutrients in the FE, the A. brasilense strains survived at populations ranging from 5 to 6 cfu g− 1 of roots and altered important agronomic traits, which led to growth enhancement. In particular, inoculated seedlings showed significant increase in the number of leaves, seedling height and root length. Chlorophyll and protein content were also improved, but only with Sp7 strain. However, the expression of pathogenesis-related protein, i.e., peroxidase, and level of endogenous indole-3-acetic acid increased by more than 50% in response to inoculation with the strains. Azospirillum inoculation also showed little or no adverse impact on the FE bacterial community indicating that it can be incorporated into a system that uses FE as a nutrient source, e.g., aquaponics. Thus, A. brasilense could be a valuable agent to help maximize the usefulness of FE or wastewater from freshwater aquaculture to further support plant growth.

Germination Characteristics of Cucumber Influenced by Plant Growth–promoting Rhizobacteria

ABSTRACT Plant growth–promoting rhizobacteria (PGPR) represent a wide genera of rhizospheric bacteria that, when introduced in association with the host plant at optimum concentration, can enhance plant growth. Experiments were conducted to determine the germination response of cucumber (Cucumis sativus L.) to PGPR inoculation. Seed were inoculated with strains of Azospirillum brasilense Sp7, Sp7-S, and Sp245, Herbaspirillum seropedicea, and Burkholderia phytofirmans PsJNT. Germination was increased by up to 9% by strains of A. brasilense Sp7 and Sp245 and H. seropedicea. All PGPR strains consistently enhanced the germination vigor index; plants produced longer and heavier roots. These PGPR benefit cucumber germination.

Early Seedling Growth Response of Lettuce, Tomato and Cucumber to Azospirillum brasilense Inoculated by Soaking and Drenching

Mangmang J.S., Deaker R., Rogers G. (2015): Early seedling growth response of lettuce, tomato and cucumber to Azospirillum brasilense inoculated by soaking and drenching . Hort. Sci. (Prague), 42: 37–46. This study evaluated the effects of three A. brasilense strains (i.e. Sp7, Sp7-S and Sp245) on the early seedling growth of lettuce, tomato and cucumber. Seeds were inoculated by soaking and drenching before and after sowing, respectively. Results show that inoculation effect varied greatly with plant species, inoculation methods and PGPR strains which could be dependent on inoculum concentration and IAA (indole-3-acetic acid) production. Generally, the magnitude of inoculation impact on the early growth of vegetables was more pronounced with Sp7-S, followed by Sp245 and Sp7. In particular, Sp7-S and Sp245 strongly enhanced root and shoot growth, germination value and vigour of tomato when inoculated by soaking. Sp245 increased the level of endogenous plant IAA of cucumber and lettuce. Despite the diverse crop responses to inoculation methods, soaking appeared to be a better technique, and majority of the strains demonstrated more consistent beneficial effects on tomato.

Improved Potential for Nitrogen Fixation in Azospirillum brasilense Sp7-S Associated with Wheat nifH Expression as a Function of Oxygen Pressure

The use of a nifH-lacZ fusion as an indicator of nitrogen fixing conditions is investigated in relation to two strains of Azospirillum brasilense with contrasting patterns of colonization on wheat roots. The degree of expression of nifH-lacZ of Azospirillum brasilense could be manipulated by controlling the oxygen pressure. A strong correlation between nitrogenase activity and nifH expression was found in pure cultures, nifH expression was maximal at 0.5% oxygen in pure cultures of both the wild type Sp7 and spontaneous mutant Sp7-S. Differentiation of the maximal expression was observed when the two strains were in association with para-nodulated wheat, resulting in greater expression by Sp7-S over a broader range of external oxygen concentrations than by Sp7. This result was observed when expressed as activity per mg of plant protein as well as per bacterium. An increase in nifH expression was also noted with para-nodulated (2,4-D treated) wheat inoculated with Sp7-S when compared with untreated wheat. No significant difference was found between treated and untreated wheat inoculated with Sp7. The results indicate that the majority of the Azospirillum brasilense Sp7-S cells occupy a more protected niche when in association with wheat roots, resulting in conditions that support a greater potential for nitrogen fixation as judged by nifH expression.

Prospects for facilitated evolution of effective N2-fixing associations with cereals: comparative performance of Azospirillum brasilense Sp7-S with various free-living diazotrophs in para-nodulated wheat

By analogy with N2-fixing sugar cane, achieving an effective N2-fixing association between cereals and diazotrophs may require an endophytic mode of colonization, allowing better protection from oxygen and improved access to carbon substrates. Using nif A-lacZ as a genetic marker on a broad host-range plasmid pVK100, inserted into a range of free-living and associative N2-fixing organisms, it has been possible to define their mode of colonization of the roots of wheat seedlings in addition to measuring the associated rates of nitrogen fixation. Of these bacterial strains, only Herbaspirillum seropedicae, Azorhizobium caulinodans and a mutant strain of Azospirillum brasilense (Sp7-S) displayed significant endophytic colonization of 2,4-D-treated wheat seedlings. By contrast, Acetobacter diazotrophicus, Azotobacter vinelandii, Derxia gummosa and other Azospirillum strains colonized at the rhizoplane. This chapter discusses these modes of colonization and the probable need for a stepwise process of facilitated evolution of selected diazatrophs and plants before an effective association can be achieved.

The Production and Potential of Biofertilizers to Improve Crop Yields

Extensive interactions of plant roots with soil microorganisms affect plant nutrition either directly by influencing mineral nutrient availability or indirectly through enhanced uptake efficiency via plant root growth promotion. Beneficial microbial interactions with roots may be either endophytic or associative and can be symbiotic, mutualistic, or incidental in nature. The increased understanding of the role of root – or rhizosphere –associated with microbes in the nutrition and/or yield of agricultural crops in particular has resulted in promotion of their use in agricultural production as alternatives or supplements to mineral or organic fertilizers. Despite this, there is an obvious lack of market penetration of microbial inoculants. This review specifically focuses on microbial inoculants, collectively termed biofertilizers, used to improve nutrition and yields of grain, legume, oil, tuber, and other crops. A vast number of commercial biofertilizers are available worldwide; however, the quality and efficacy of many of them are not proven or tested. In the absence of efficacious biofertilizers of good and consistent quality, the dependence on the use of mineral fertilizers is not likely to decrease. Thus the availability of high-quality biofertilizers must be priority particularly in countries where crop plant production plays a key role in the economy and food security.