Plant protecting and regulating compositions – Seed coated with agricultural chemicals other than fertilizers
Reexamination Certificate
2000-02-23
2003-02-25
Clardy, S. Mark (Department: 1616)
Plant protecting and regulating compositions
Seed coated with agricultural chemicals other than fertilizers
C504S117000
Reexamination Certificate
active
06524998
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of Invention
The invention relates to improvements in plants. In particular, the invention relates to improved biological compositions which are effective to increase the growth rate of seedlings and develop systemic disease immunity in plants and to control soil nematodes. The invention relates also to seeds treated with the composition and to the treated seedlings and plants.
Organic Amendments and Chitin
Naturally occurring nematode suppressiveness has been reported for several agricultural systems (Stirling et al., 1979, Kerry, 1982, Kluepfel et al., 1993,), but suppressiveness can also be induced by crop rotation with antagonistic plants such as switchgrass (
Panicum virgatum
) (Kokalis-Burelle et al., 1995) and velvetbean (
Mucuna deeringiana
) (Vargas et al., 1994) or organic amendments including pine bark (Kokalis-Burelle et al., 1994), hemicellulose (Culbreath et al., 1985), and chitin (Mankau and Das, 1969, Spiegel et al., 1986, Rodríguez-Kábana and Morgan-Jones, 1987). A major component of the suppressiveness of chitin amendments is believed to be biotic, and several reports confirm increased numbers of nematode antagonistic microorganisms associated with chitin-induced suppressive soils (Godoy et al., 1983, Rodríguez-Kábana et al., 1984). Extensive work has been done over the past years on fungi associated with chitin amendments (Godoy et al., 1983, Rodríguez-Kábana et al., 1984), while less information is available on bacterial community structure and the role of bacteria in chitin-induced suppressiveness.
Chitin, a glucosamine polysaccharide, is a structural component of some fungi, insects, various crustaceans and nematode eggs. In egg shells of tylenchoid nematodes, chitin is located between the outer vitelline layer and the inner lipid layer and may occur in association with proteins (Bird and Bird, 1991). The breakdown of this polymer by chitinases can cause premature hatching which results in fewer viable juveniles (Mercer et al., 1992). In the soil, chitinases are produced by some actinomycetes (Mitchell and Alexander, 1962), fungi (Mian et al., 1982), and bacteria (Ordentlich et al., 1988, Inbar and Chet, 1991), but chitinases are also released by many plants as part of their defense mechanism against various pathogens (Punja and Zhang, 1993) and plant-parasitic nematodes (Roberts et al., 1992). Chitinases depolymerize the chitin polymer into N-acetylglucosamine and chitobiose. Further microbial activity results in the deamination of the sugar and accumulation of ammonium ions and nitrates (Rodríguez-Kábana et al., 1983). Nematicidal concentrations of ammonia in association with a newly formed chitinolytic microflora are believed to cause nematode suppressiveness (Mian et al., 1982, Godoy et al., 1983). Benhamou et al. (1994) have shown that chitosan, the deacetylated derivative of chitin, induces systemic plant resistance against
Fusarium oxysporum
f. sp.
radicis-lycopersici
in tomato when applied as a seed treatment or soil amendment. This suggests that plant defense mechanisms might contribute to the overall nematode suppression.
Changes in one component of the microflora in a community often leads to other changes, and it was recently reported that soil amendment with 1% chitin led to alterations in the taxonomic structure of the bacterial communities of the soil, rhizosphere and endorhiza (Hallmann et al., 1998). Several bacterial species were found in chitin-amended soils and cotton rhizospheres which were not detected in non-amended soils and rhizospheres. Additionally, it was determined that chitin-amended soils selectively influenced the community structure of endophytic bacteria within cotton roots. For example,
Phyllobacterium rubiacearum
was not a common endophyte-following chitin amendment, although its populations in soil were stimulated by chitin.
Burkholderia cepacia
was the dominant endophyte-following chitin amendment but was rarely found among the endophytic community of non-amended plants. Hence, alterations in microbial community structure are associated with the control of nematodes which occurs upon soil amendment with chitin.
Plant Growth-Promoting Rhizobacteria (PGPR)
Plant-associated microorganisms have been extensively examined for their roles in natural and induced suppressiveness of soilborne diseases. Among the many groups of such organisms are root-associated bacteria, which generally represent a subset of soil bacteria. Rhizobacteria are a subset of total rhizosphere bacteria which have the capacity, upon re-introduction to seeds or vegetative plant parts (such as potato seed pieces), to colonize the developing root system in the presence of competing soil microflora. Root colonization is typically examined by quantifying bacterial populations on root surfaces; however, some rhizobacteria can also enter roots and establish at least a limited endophytic phase. Hence, root colonization may be viewed as a continuum from the rhizosphere to the rhizoplane to internal tissues of roots.
Rhizobacteria which exert a beneficial effect on the plant being colonized are termed PGPR. PGPR may benefit the host by causing plant growth promotion or biological disease control. The same strain of PGPR may cause both growth promotion and biological control. Efforts to select and apply PGPR for control of specific soilborne fungal pathogens have been reviewed (Kloepper, 1993; Glick and Bashan, 1997). Among the soilborne pathogens shown to be negatively affected by PGPR are Aphanomyces spp.,
Fusarium oxysporum, Gaeumannomyces graminis
, Phytophthora spp., Pythium spp.,
Rhizoctonia solani, Sclerotium rolfsii, Thielaviopsis basicola
, and Verticillium spp. In most of these cases, biological control results from bacterial production of metabolites which directly inhibit the pathogen, such as antibiotics, hydrogen cyanide, iron-chelating siderophores, and cell wall-degrading enzymes. Plant growth promotion by PGPR may also be an indirect mechanism of biological control, leading to a reduction in the probability of a plant contracting a disease when the growth promotion results in shortening the time that a plant is in a susceptible state, e.g. in the case where PGPR cause enhanced seedling emergence rate, thereby reducing the susceptible time for pre-emergence damping-off. An alternative mechanism for biological control by PGPR is induced systemic resistance.
Nematode Biocontrol Agents
Many recently published examples of biocontrol of nematodes by antagonists involve use of the non-culturable pathogen
Pasteuria penetrans
(reviewed in Stirling, 1991b). Populations of the pathogen often increase upon continual cropping of crops susceptible to nematodes and may contribute to soil suppressiveness to nematodes in these cases.
P. penetrans
produces resting spores which adhere to the cuticle of nematodes, where they produce a germ tube, penetrate the host, and develop an extensive colonization and digestion of the host nematode. Unfortunately, procedures to produce sufficient spores for inoculative biocontrol studies are laborious, and no practical mass cultivation systems are available (Ciancio, 1995). Nematode-trapping fungi have provided control under greenhouse conditions, however practical control in the field has not been consistently achieved. This result most likely occurs since nematode-trapping capacity of most species is not related to nematode density as would be required for economic control (Stirling, 1991a). Several reports of culturable rhizobacteria as biocontrol agents of nematodes have been published (Becker et al., 1988; Hallmann, et al., 1997; Kloepper et al., 1992; Kluepfel, et al., 1993; Martinez-Ochoa et al., 1997; Oka et al., 1993; Sikora, 1988). While some reductions in nematode damage or populations have been reported upon introduction of bacteria in these model systems, none of the studies present data showing field efficacy at levels which would provide economically practical protection.
Induced Systemic Resistance (ISR) with PGPR
Induced resistance, whereby a plant's natural
Kenney Donald S.
Kloepper Joseph W.
Rodriguez-Kabana Rodrigo
Auburn University
Clardy S. Mark
Schnader Harrison Segal & Lewis LLP
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