Plant husbandry – Coated or impregnated seed – method or apparatus
Patent
1995-06-05
1997-12-16
Robinson, Douglas W.
Plant husbandry
Coated or impregnated seed, method or apparatus
47 58, 71 6, 71 7, 424 933, 424 9347, 424 9348, 4352521, 4352522, 4352524, 4352533, A01C 106, C12N 104, C05F 1108
Patent
active
056971869
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the use of microorganisms to enhance crop productivity and, more specifically, to the use of flocculated forms of bacteria, particularly Azospirillum, Rhizobium, or a combination thereof, as crop inoculants and delivery systems for other agriculturally beneficial microorganisms.
BACKGROUND OF THE INVENTION
Many microorganisms are known to exert beneficial effects on plant growth. Among these are the well-known nitrogen-fixing Rhizobium species, which are symbionts of leguminous species. Azospirillum species, which are free-living nitrogen-fixing bacteria associated with the roots of grasses, are also now recognized for their plant growth-promoting qualities.
It has been shown that Azospirillum can be induced to transform from vegetative cells to desiccation-resistant encysting forms under limiting cultural conditions (i.e., culture media providing the minimal amount of nutrients required for growth). This transformation is accompanied by the overproduction of exocellular polymers that cause aggregation and extensive flocculation of the cells in culture. Sadasivan et al., J. Bact., 163:716-23 (1985).
Rhizobium species have also been observed to flocculate in culture medium and in association with roots. Napoli et al., App. Microbiol., 30:123-31 (1975); Deinema et al., Arch. Mikrobiol., 78:42-57 (1971). Unlike Azospirillum, flocculation dynamics of Rhizobium heretofore have not been studied. No distinctions have been made between microscopic aggregates and the massive aggregation of cells characteristic of Azospirillum cultured under specified conditions (e.g., suitable carbon source, low nitrogen content and high C:N ratio).
Inoculation of seeds or soil with beneficial microorganisms for crop improvement has been practiced for a number of years. However, variable and inconsistent results have often been obtained due to loss of inoculant viability or variability of dosage due to changes in inoculant viability. Okon et al., CRC Crit. Rev. Biotechnology, 6:61-85 (1987).
One of the most commonly used carriers for commercial inoculants of agriculturally beneficial microorganisms is peat. For Rhibozium and Azospirillum species, bacteria are cultured in fermentors to reach high population levels (i.e., .about.10.sup.9 cells/ml), then added to pre-sterilized peat. The inoculum thereafter may be applied to seeds (by preparing a slurry containing the peat/bacteria mixture and gums or sugars to improve adhesion), by applying directly to soil (e.g., by dripping peat suspensions into planting furrows) or by mixing with other planting media. Okon et al., supra. Each of these delivery methods suffers from inconsistent dosage due to loss of viability under varied seed storage or field condition. Okon et al., supra.
Several other formulations of crop inoculants have been proposed in an attempt to overcome problems with loss of viability and inconsistent dosage. These methods involve entrapment of living cells in various biopolymers, such as polyacrylamide (Dommergues et al., Appl. Environ. Microbiol., 37:779-81, 1979), xanthan and carob gums (Mugnier et al., Appl. Environ. Microbiol., 50:108-114, 1985) and alginate (Bashan, Appl. Environ. Microbiol., 51:1089-98, 1986; Fages, Appl. Microbiol. Biotechnol., 32:473-78, 1990).
Although entrapment of microorganisms in biopolymers increases the concentration and stability of inoculants, the production of such inoculants often involves multiple steps and requires specialized equipment. For example, one method of preparing alginate beads carrying Azospirillum involves the following steps: (1) growing Azospirillum in nutrient broth; (2) adding sodium alginate, along with various other ingredients, to the culture broth containing the Azospirillum cells; (3) extruding the mixture under pressure through 1 mm plastic nozzles, the resulting drops being projected into a 6 g/l CaCl.sub.2 solution to form alginate beads containing entrapped bacteria; (4) removing the CaCl.sub.2 solution; and (5) dehydrating the beads by air-drying, freeze-
REFERENCES:
patent: 4583320 (1986-04-01), Redenbaugh
Bleakley et al. Floc formation by Azospirillum lipoferum grown on poly-B-hydroxybutyrate. Applied Environmental Microbiology vol. 54, pp. 2986-2995 1988.
Okon. Azospirillum as a potential inoculant for agiriculture. Trends in Biotechnology. vol. 3, pp. 223-228 1985.
Bashan, J., Applied and Environmental Microbiology 51:1089-1098, 1986.
Deinema, M. et al., Arch. Mikrobiol. 78:42-57, 1971.
Fages, J., in Azospirillum/Plant Associations, Yaacov Okon, ed. CRC Press 1994, ch.6.
Lamm, R.B., et al., Can. J. Micro. 27:1320-1325, 1981.
Mugnier, J., et al., Appl. and Environ. Micro 50:108-114, 1985.
Napoli, C., et al., Appl. and Environ. Micro. 30:123-131, 1975.
Okon, Y., et al., Microbial Inoculants as Crop-Yield Enhancers, in CRC Critical Reviews in Biotechnology, Boca Raton, FL, CRC Press, 1987 pp. 61-85.
Sadasivan, L., et al., J. Bact. 163:716-723, 1985.
Stormo, K., et al., Appl. and Environ. Micro. 58:727-730, 1992.
Arunakumari Alahari
Neyra Carlos A.
Olubayi Olubayi
Kimball Melissa L.
Robinson Douglas W.
Rutgers The State University of New Jersey
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