Beneficial microorganism survival on seed, roots and in rhizosphere soil following application to seed during drum priming
Introduction
Direct-seeded crops such as carrots and onions can suffer from poor crop establishment due to uneven seed germination in the field. This can lead to variable plant spacing and lack of uniformity, and may have a negative impact on yield and marketability of the crop. In order to improve seedling establishment, seeds can be primed before planting (Rowse, 1996b, Halmer, 2004). This procedure involves the controlled addition of water to a seed batch to start the physiological germination process, but before the radicle emerges from the seed coat the procedure is stopped and seed is dried back to a low moisture content. Seed can then be stored or planted straight away. Priming ensures that the entire seed batch is at the same point in the germination process, so that once the seed is planted there is a rapid and more uniform emergence, particularly under cold or wet conditions (McQuilken et al., 1998, Halmer, 2004). Various priming techniques exist, including osmopriming or hydropriming (Caseiro et al., 2004), solid-matrix priming (Taylor et al., 1988), steeping priming (Halmer, 2004) and drum priming (Rowse, 1996a, Caseiro et al., 2004). The latter two are used commercially in the UK.
Primed seed can subsequently be pelletted or film-coated with pesticides, according to normal commercial practices. However, due to environmental concerns, there is an ongoing need to reduce the use of pesticides in agriculture and horticulture, and alternatives to chemicals are being sought to improve crop establishment and health. One option is the use of beneficial microorganisms or biocontrol agents applied to seed or roots, which may promote plant growth or provide disease control through a variety of mechanisms, including production of plant hormones, antibiotics or enzymes; induced systemic resistance; direct parasitism of plant pathogens or deleterious microorganisms; or competition with pathogens for space or nutrients (Whipps, 2001, Zahir et al., 2004). In particular, the application of beneficial microorganisms to seed is a niche that can be exploited commercially to reduce the use of seed-applied pesticides and, importantly, microbiological seed treatments also can be used by organic growers.
Applying beneficial microorganisms to seed during the priming process is commercially realistic, as microorganism suspensions can easily be incorporated into the water used for seed priming. Previous work has shown that selected fungal and bacterial isolates could survive and proliferate on carrot and parsnip seed during drum priming (Wright et al., 2003a). However, not all seed-type/microorganism combinations were successful, and applied fungal isolates could not be recovered from leek seed after priming (Wright et al., 2003a). Another crop that is primed is onion (Caseiro et al., 2004, Halmer, 2004), but no work has been done on the potential for applying beneficial microorganisms to onion seed during drum priming.
Successful application of selected microorganisms to seed in a commercially viable way is only the first step towards using beneficial microorganisms to improve crop health. It is equally important that the microorganisms remain viable and can colonise the developing roots and rhizosphere in order to continue improving plant growth and to potentially control disease. Seed-applied microorganisms have the potential to become established in the rhizosphere of plants, as they may transfer onto the developing root as it emerges from the seed (Harman, 1991). Much work has been done on applying microorganisms to seed using various techniques, including the use of suspensions, slurries, powders, peat carriers, or encapsulation in alginate (Fravel et al., 1998, McQuilken et al., 1998, Walker et al., 2004). However, the survival and establishment in the root zone of beneficial microorganisms applied to seed during drum priming has not been studied previously.
In order to investigate the possibility of delivering beneficial microorganisms to the root zone by application to seed during priming, work was carried out with two main aims: firstly to investigate the survival of four selected beneficial microorganisms on onion and carrot seed during drum priming, using a laboratory-scale system. These microorganisms were all known for their biocontrol or plant growth promoting (PGP) properties. The second aim was to conduct glasshouse experiments to determine whether the seed-applied microorganisms could subsequently become established on the roots and in the rhizosphere of onion and carrot, in three contrasting soil-types.
Section snippets
Microorganism storage and preparation
Four beneficial microorganisms were selected for use in this study, based on their known biocontrol or PGP properties, or availability within a commercial product. Pseudomonas chlororaphis MA342 is the active ingredient in Cedomon®, targeting cereal pathogens (Johnsson et al., 1998), and was obtained from Dr. M. Hökeberg, BioAgri, Uppsala, Sweden; Pseudomonas fluorescens CHA0 has activity against a wide range of soil-borne pathogens (Maurhofer et al., 1994) and was obtained from Prof G. Défago,
Onion seed
The two fungal isolates both dropped in number at the end of the hydration phase following application to onion seed at 7 log10 cfu g−1 dry seed (Fig. 1). This high initial inoculum was required to achieve the final target of at least 5 log10 cfu g−1 dry seed after drying back, as an overall decline in numbers occurred during the priming process. However, at the end of the incubation phase, microorganisms were always recovered in higher numbers than those found at the end of the hydration phase.
Discussion
Seed priming is used to improve emergence of direct-seeded crops, particularly under wet or cold conditions (Halmer, 2004). Previous work has shown that combining priming with the application of beneficial microorganisms can improve crop establishment and several methods have been used to achieve this (Harman and Taylor, 1988, Callan et al., 1990, Jensen et al., 2004). These have generally involved first coating the seed with a microorganism suspension, and then priming the seed using a variety
Acknowledgments
We acknowledge funding from the Horticulture LINK programme, Elsoms Seeds Ltd., Germains Technology Group UK, the Horticultural Development Council, and the Department for Environment, Food and Rural Affairs. We also thank Andrew Mead for help with the experimental designs and statistical analyses, and Dr. Emma Coventry for critically reviewing earlier drafts of the manuscript.
References (43)
- et al.
Bacterial survival in soil: effects of clays and protozoa
Soil Biology and Biochemistry
(1993) Seed treatments for biological control of plant disease
Crop Protection
(1991)The analysis of onion and garlic
Journal of Chromatography A
(2006)- et al.
GUS and GFP transformation of the biocontrol strain Clonostachys rosea IK726 and the use of these marker genes in ecological studies
Mycological Research
(2002) - et al.
Soil inoculation with the biocontrol agent Clonostachys rosea and the mycorrhizal fungus Glomus intraradices results in mutual inhibition, plant growth promotion and alteration of soil microbial communities
Soil Biology and Biochemistry
(2006) - et al.
SMP: solid matrix priming of seeds
Scientia Horticulturae
(1988) The potential of mycoparasites for biological control of plant diseases
Annual Review of Phytopathology
(1990)- et al.
An adapted selective medium for the quantitative isolation of Trichoderma species
Plant Pathology
(1993) - et al.
Root colonization by inoculated plant growth-promoting rhizobacteria
Biocontrol Science and Technology
(2001) Protozoa and plant growth: The microbial loop in soil revisited
New Phytologist
(2004)
Rhizodeposition and microbial populations
Bio-priming seed treatment for biological control of Pythium ultimum preemergence damping-off in sh2 sweet corn
Plant Disease
Field performance of sweet corn seed bio-primed and coated with Pseudomonas fluorescens AB254
HortScience
Comparison of three priming techniques for onion seed lots differing in initial seed quality
Seed Science and Technology
Polypropylene straw ampoules for the storage of microorganisms in liquid nitrogen
Journal of Microbiological Methods
Formulation of microorganisms to control plant diseases
Spatial colonization patterns and interaction of bacteria on inoculated sugar beet seed
Phytopathology
Methods to improve seed performance in the field
Myths and dogmas of biocontrol: changes in perceptions derived from research on Trichoderma harzianum T-22
Plant Disease
Improved seedling performance by integration of biological control agents at favourable pH levels with solid matrix priming
Phytopathology
Combining effective strains of Trichoderma harzianum and solid matrix priming to improve biological seed treatments
Plant Disease
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