The present invention relates to arbuscular mycorrhizal fungal preparations which can be used for improving the inoculation of plants. The inoculation of plants with mycorrhizal fungi is a useful complementation of fertilization and crop protection in agriculture, in particular in the cultivation of vegetables fruits and flowers, and in silviculture.
Arbuscular mycorrhizal fungi (AM fungi) enter an advantageous symbiosis with a multiplicity of plants. As the result of the colonization of the root cells of the plant with such fungi, a more extensive root system with better reticulate fungal penetration develops. Thus, fungal hyphae continue growing outside the normal root ball into a zone in which nutrients such as in particular phosphorus are normally not accessible to the plant. It has been shown that AM fungi bring about a significant improvement of plant growth (cf., for example, S. Gianinazzi, H. Schüepp, J. M. Barea, K. Haselwandter “Mycorrhizal technology in Agriculture”, Birkhäuser 2002; E. Sieverding “Vesicular-Arbuscular Mycorrhiza Management in Tropical Agrosystems, GTZ 1991). Despite this economically useful property AM fungal preparations have not gained major importance in agriculture, in particular the cultivation of vegetables and fruits or in silviculture. One reason can partly be attributed to the lacking availability of substantial amounts of preparations which can be applied without problems AM fungi are obligatory phytotrophs which are not capable of multiplication without host plant. Their production therefore requires a combined system. Currently AM fungal inocula, in particular Glomus sp., are prepared by culturing host plants in pots or beds on inert substrates (cf., for example H. Baltruschat et al., EP 0 183 040, 1985). Alternative production methods under meristematic in-vitro conditions (J. A. Fortin et al., U.S. Pat. No. 5,554,530, 1996) or in what are known as aeroponic systems (D. M. Sylvia et al., U.S. Pat. No. 5,096,481) are also used.
Such cultivation methods have the advantage of being simple and make possible the production of a large amount of AM fungal spores. All porous and biologically inert materials are suitable as substrates for the cultivation. A relatively coarse particle size of approximately 1 to 8 mm and pore diameters in the same order of magnitude as the spore dimensions have proven to be particularly suitable. Expanded clay, expanded slate, volcanic rocks or perlite have these properties. The use of smaller particle sizes or of less porous materials results in lower process yields.
Mycorrhizing spores are developed within the free channels of each substrate grain. Typically, AM fungal preparations are produced with approximately 100-200 infectious units per milliliter (cf. Gianinazzi, above). Depending on the particle sizes of the substrate, these units are divided to provide only 5 to 20 granules per milliliter. Despite a high number of active spores and hyphae, it thus follows that the spatial distribution around the plant roots is unsatisfactory. The efficacious and economically justifiable application of AM fungal preparations thus remains limited.
The invention aims at solving the problem of the spatially limited application of AM fungal preparations.
In accordance with the invention, a crude inoculum is first prepared by culturing AM fungi, such as Glomus sp., in particular Glomus intraradices, on porous granules as substrate, as described by Baltruschat (see above). The porous granules used for this purpose are expediently expanded clay or attapulgite or expanded slate or volcanic rock or perlite or vermiculite or a mixture of two or more of these materials. The particle size of these porous granules is expediently approximately 1 and 6 mm. Expanded clay with a particle size of 1 to 4 mm and a bulk density of approximately 250 to 300 kg/m3, in particular 270 kg/m3, has proved to be particularly expedient.
The crude inoculum contains spores, hyphae and fine root residues of the host plants. An analytical biological test as described by Sieverding (see above) reveals a probable number of infectious units of typically 300 to 600 per gram. In highly productive units, this number may even be higher than 2000. Since these units are hidden in the pores of the substrate, no isolated spores of the AM fungi, such as Glomus sp., in particular Glomus intraradices, can be observed under the microscope.
In accordance with the invention, the crude inoculum is then comminuted carefully so that the active spores are not destroyed. This can be accomplished by using a grinding process which is based on impact and not on friction. Suitable types of mills which operate by impact are, in particular, hammer mills, bladed-disk mills or jet mills. The operative parameters of the mill must be adjusted in such a way that the particle size of the ground product is in the range of approximately 100-500 μm, preferably approximately 100-250 μm. This means that, in particular, the rotational speed must be adjusted accordingly and the discharge screen must be selected accordingly. In the ground product, up to 1000 free spores or spore agglomerations per gram can be counted under the microscope.
The comminuted product which is obtained in accordance with the invention can be used directly as solid for inoculating plants with AM fungi, or else it can be standardized to a nominal activity by dilution with a customary inert material. It can also be formulated together with customary formulation auxiliaries to give a water-suspendable preparation.
The invention and its advantages are illustrated in greater detail in the examples which follow.
Comparison of Different Types of Mills, and Spore Counting
An AM fungal inoculum was prepared in expanded-clay granules with a particle size of 2-4 mm, proceeding as described by Baltruschat (see above).
The resulting mycorrhizal-containing product was ground in different mills under different conditions. The number of free spores or spore agglomerations in the mill base was determined under the microscope.
Degree of Mycorrhization of the Roots of Test Plants (Tagetes “Orangenflamme”)
Plastic plant pots (round, height 6.5 cm, diameter: 9 cm at the top, 6 cm at the bottom) were filled with a mixture of, firstly, 500 mg or 1000 mg of the product ground in accordance with Example 1 with the Pilot hammer mill No. 1, or of the crude product of Example 1, and, secondly, a substrate consisting of potting compost (Floradur-Fein) and sterilized sand in the ratio 1:1. Pots filled only with substrate (potting compost/sand) acted as the control.
Two seedling plants were pricked out into each pot. The pots were watered normally with tap water and fertilized once per week with a solution of Wuxal top N (concentration 0.05% during the first 3 weeks thereafter 0.1%).
After 10 weeks, the entire root ball was stained and evaluated under the microscope for the presence of mycorrhiza-developing hyphas, arbuscules, vesicles and spores, using a scoring key (cf. MeGonigle, T. P., Miller, M. H., Evans, D. C., Fairchild, G. L. and Swan J. A., 1990. A new method which gives an objective measure of colonization of roots by vesicular-arbuscular mycorrhizal fungi. New Phytol. 115: 495 501).
With 5 replications, the following degrees of mycorrhization resulted:
The above data show that the use of the ground product increased the degree of mycorrhization by 36% and almost 144% in comparison with the crude granules.
Number | Date | Country | Kind |
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1828/04 | Nov 2004 | CH | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CH05/00648 | 11/4/2005 | WO | 10/1/2007 |