R. A. Warren

Bio: R. A. Warren is an academic researcher from Commonwealth Scientific and Industrial Research Organisation. The author has contributed to research in topics: Rhizosphere & Microbial inoculant. The author has an hindex of 7, co-authored 8 publications receiving 490 citations.

Phosphate solubilization by Penicillium spp. closely associated with wheat roots

Abstract: In this study we found that Penicillium spp. exhibiting P-solubilizing activity are common both on and in the roots of wheat plants grown in southern Australian agricultural soils. From 2,500 segments of washed and surface-disinfested root pieces, 608 and 223 fungi were isolated on a selective medium, respectively. All isolates were screened for P solubilization on solid medium containing hydroxyapatite (HA); 47 isolates (5.7%) solubilized HA and were identified as isolates of Penicillium or its teleomorphs. These isolates were evaluated for solubilization of Idaho rock phosphate (RP) in liquid culture. Penicillium bilaiae strain RS7B-SD1 was the most effective, mobilizing 101.7 mg P l−1 after 7 days. Other effective isolates included Penicillium simplicissimum (58.8 mg P l−1), five strains of Penicillium griseofulvum (56.1–47.6 mg P l−1), Talaromyces flavus (48.6 mg P l−1) and two unidentified Penicillium spp. (50.7 and 50 mg P l−1). A newly isolated strain of Penicillium radicum (KC1-SD1) mobilized 43.3 mg P l−1. RP solubilization, biomass production and solution pH for P. bilaiae RS7B-SD1, P. radicum FRR4718 or Penicillium sp. 1 KC6-W2 was determined over time. P. bilaiae RS7B-SD1 solubilized the greatest amount of RP (112.7 mg P l−1) and had the highest RP-solubilizing activity per unit of biomass produced (up to 603.2 μg P l−1 mg biomass−1 at 7 days growth). This study has identified new isolates of Penicillium fungi with high mineral phosphate solubilizing activity. These fungi are being investigated for the ability to increase crop production on strong P-retaining soils in Australia.

Potential to improve root access to phosphorus: the role of non-symbiotic microbial inoculants in the rhizosphere

Abstract: Phosphate anions in soil solution are extremely reactive and may be rapidly immobilised in the soil through precipitation and adsorption reactions, resulting in sparingly soluble forms of phosphorus (P) that are essentially unavailable to plants. This low P-fertiliser efficiency is often offset through high application rates, which are economically and environmentally unsustainable and not an available option for organic producers. Microorganisms play a fundamental role in the biogeochemical cycling of inorganic and organic P in the rhizosphere and detritusphere. Free-living rhizosphere microbes can directly increase the availability of phosphate to plant roots via mechanisms associated with solubilisation and mineralisation of P from inorganic and organic forms of total soil P. These include releasing organic anions, H+ ions, phosphatases, and cation chelating compounds into the rhizosphere. Many soil-borne microbes also increase P availability indirectly by producing phytohormones that increase root density and function. There is increasing interest worldwide in the use of rhizosphere microorganisms as inoculants to increase P availability for agricultural production. Recent research has focussed on developing actively sporulating Penicillium fungi known to express mechanisms to enhance P mobilisation and therefore, considered to be a key component of the mycoflora involved in P cycling in soils. Penicillium species do not exhibit specific plant or soil associations and have a broad agro-ecological range, indicating their potential to be developed as inoculants for a range of plant production systems. Successful adoption of microbial inoculants requires a thorough understanding of their rhizosphere ecology, genetic stability, and the mechanisms associated with enhancing P availability in soils and plant-growth promotion. This will provide a better understanding of which inoculants to use under particular agro-ecological conditions for increased efficacy and consistent performance.

Effect of soil properties on growth promotion of wheat by Penicillium radicum

Abstract: Penicillium radicum is a phosphate-solubilising fungus with plant growth promoting (PGP) activity. The widespread agronomic use of P. radicum as an inoculant is dependent on the accurate prediction of conditions where PGP response will occur. Therefore, the effect of soil physicochemical and biotic factors on PGP of wheat by P. radicum was investigated. In the first experiment, PGP was assayed in 10 soils with differing physicochemical properties. Each soil was tested with and without treatment with hydroxyapatite—an insoluble form of calcium phosphate used to increase the level of total inorganic P available for microbial solubilisation. Inoculation of wheat with P. radicum significantly (P < 0.05) increased plant growth in 4 of the 10 soils tested. The magnitude of the PGP response varied with soil type, and ranged from 8.5% (plant height, Avon soil) to 75% (plant weight, Mingenew soil). Most soil properties had little influence on PGP, with only low soil fertility (N and/or P) identified as a strong indicator of PGP by P. radicum. When detected, PGP was strongest in acidic soil conditions, although PGP was observed in neutral and alkaline soils. Virtually no interactions were detected between addition of hydroxyapatite to the soil and P. radicum inoculation. The second experiment tested PGP in 3 soils previously found to be non-responsive to inoculation, before and after sterilisation by γ-irradiation. Soil biological factors affected PGP by P. radicum in 2 of the 3 soils tested. In these soils, removal of biological factor(s) increased (P < 0.05 and P < 0.1) PGP by P. radicum. These experiments have shown that large and significant increases in plant growth promotion can be achieved through seed inoculation with P. radicum. However, both abiotic and biotic soil properties play a critical role in determining the success of inoculation. P. radicum-stimulated PGP occurred in infertile soils, with a stronger effect in acidic soil conditions. Furthermore, soil biological factors can have an important role in regulating PGP by P. radicum.

Antibiosis functions during interactions of Trichoderma afroharzianum and Trichoderma gamsii with plant pathogenic Rhizoctonia and Pythium

Abstract: Trichoderma afroharzianum is one of the best characterized Trichoderma species, and strains have been utilized as plant disease suppressive inoculants. In contrast, Trichoderma gamsii has only recently been described, and there is limited knowledge of its disease suppressive efficacies. Comparative studies of changes in gene expression during interactions of these species with their target plant pathogens will provide fundamental information on pathogen antibiosis functions. In the present study, we used complementary DNA amplified fragment length polymorphism (cDNA-AFLP) analysis to investigate changes in transcript profiling of T. afroharzianum strain LTR-2 and T. gamsii strain Tk7a during in vitro interactions with plant pathogenic Rhizoctonia solani and Pythium irregulare. Considerable differences were resolved in the overall expression profiles of strains LTR-2 and Tk7a when challenged with either plant pathogen. In strain LTR-2, previously reported mycoparasitism-related genes such as chitinase, polyketide synthase, and non-ribosomal peptide synthetase were found to be differentially expressed. This was not so for strain Tk7a, with the only previously reported antibiosis-associated genes being small secreted cysteine-rich proteins. Although only one differentially expressed gene was common to both strains LTR-2 and Tk7a, numerous genes reportedly associated with pathogen antibiosis processes were differentially expressed in both strains, including degradative enzymes and membrane transport proteins. A number of novel potential antibiosis-related transcripts were found from strains LTR-2 and Tk7a and remain to be identified. The expression kinetics of 20 Trichoderma (10 from strain LTR-2, 10 from strain Tk7a) transcript-derived fragments (TDFs) were quantified by quantitative reverse transcription PCR (RT-qPCR) at pre- and post-mycelia contact stages of Trichoderma-prey interactions, thereby confirming differential gene expression. Collectively, this research is providing information to elucidate the antibiosis mechanisms and disease suppressive activities of T. afroharzianum and T. gamsii against soilborne fungal and oomycete plant pathogens.

Acquisition of phosphorus and nitrogen in the rhizosphere and plant growth promotion by microorganisms

Abstract: The rhizosphere is a complex environment where roots interact with physical, chemical and biological properties of soil. Structural and functional characteristics of roots contribute to rhizosphere processes and both have significant influence on the capacity of roots to acquire nutrients. Roots also interact extensively with soil microorganisms which further impact on plant nutrition either directly, by influencing nutrient availability and uptake, or indirectly through plant (root) growth promotion. In this paper, features of the rhizosphere that are important for nutrient acquisition from soil are reviewed, with specific emphasis on the characteristics of roots that influence the availability and uptake of phosphorus and nitrogen. The interaction of roots with soil microorganisms, in particular with mycorrhizal fungi and non-symbiotic plant growth promoting rhizobacteria, is also considered in relation to nutrient availability and through the mechanisms that are associated with plant growth promotion.

Phosphate solubilizing microbes: sustainable approach for managing phosphorus deficiency in agricultural soils

Abstract: Phosphorus is the second important key element after nitrogen as a mineral nutrient in terms of quantitative plant requirement. Although abundant in soils, in both organic and inorganic forms, its availability is restricted as it occurs mostly in insoluble forms. The P content in average soil is about 0.05% (w/w) but only 0.1% of the total P is available to plant because of poor solubility and its fixation in soil (Illmer and Schinner, Soil Biol Biochem 27:257-263, 1995). An adequate supply of phosphorus during early phases of plant development is important for laying down the primordia of plant reproductive parts. It plays significant role in increasing root ramification and strength thereby imparting vitality and disease resistance capacity to plant. It also helps in seed formation and in early maturation of crops like cereals and legumes. Poor availability or deficiency of phosphorus (P) markedly reduces plant size and growth. Phosphorus accounts about 0.2 - 0.8% of the plant dry weight. To satisfy crop nutritional requirements, P is usually added to soil as chemical P fertilizer, however synthesis of chemical P fertilizer is highly energy intensive processes, and has long term impacts on the environment in terms of eutrophication, soil fertilility depletion, carbon footprint. Moreover, plants can use only a small amount of this P since 75–90% of added P is precipitated by metal–cation complexes, and rapidly becomes fixed in soils. Such environmental concerns have led to the search for sustainable way of P nutrition of crops. In this regards phosphate-solubilizing microorganisms (PSM) have been seen as best eco-friendly means for P nutrition of crop. Although, several bacterial (pseudomonads and bacilli) and fungal strains (Aspergilli and Penicillium) have been identified as PSM their performance under in situ conditions is not reliable and therefore needs to be improved by using either genetically modified strains or co-inoculation techniques. This review focuses on the diversity of PSM, mechanism of P solubilization, role of various phosphatases, impact of various factors on P solubilization, the present and future scenario of their use and potential for application of this knowledge in managing a sustainable environmental system.

Bacterial endophytes: recent developments and applications

Abstract: Endophytic bacteria have been found in virtually every plant studied, where they colonize the internal tissues of their host plant and can form a range of different relationships including symbiotic, mutualistic, commensalistic and trophobiotic Most endophytes appear to originate from the rhizosphere or phyllosphere; however, some may be transmitted through the seed Endophytic bacteria can promote plant growth and yield and can act as biocontrol agents Endophytes can also be beneficial to their host by producing a range of natural products that could be harnessed for potential use in medicine, agriculture or industry In addition, it has been shown that they have the potential to remove soil contaminants by enhancing phytoremediation and may play a role in soil fertility through phosphate solubilization and nitrogen fixation There is increasing interest in developing the potential biotechnological applications of endophytes for improving phytoremediation and the sustainable production of nonfood crops for biomass and biofuel production

Soil Microorganisms Mediating Phosphorus Availability Update on Microbial Phosphorus

Abstract: Microorganisms are integral to the soil phosphorus (P) cycle and as such play an important role in mediating the availability of P to plants. Understanding the microbial contribution to plant P nutrition and opportunities for manipulating specific microorganisms to enhance P availability in soil has

Plant and microbial strategies to improve the phosphorus efficiency of agriculture

Abstract: Background Agricultural production is often limited by low phosphorus (P) availability. In developing countries, which have limited access to P fertiliser, there is a need to develop plants that are more efficient at low soil P. In fertilised and intensive systems, P-efficient plants are required to minimise inefficient use of P-inputs and to reduce potential for loss of P to the environment.