Drug – bio-affecting and body treating compositions – Whole live micro-organism – cell – or virus containing – Bacteria or actinomycetales
Reexamination Certificate
1999-09-14
2002-09-10
Saucier, Sandra E. (Department: 1657)
Drug, bio-affecting and body treating compositions
Whole live micro-organism, cell, or virus containing
Bacteria or actinomycetales
C435S252340, C435S253300, C435S876000
Reexamination Certificate
active
06447770
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to biocontrol of diseases caused by the soil-borne fungus
Gaeumannomyces graminis
. In particular, the invention relates to strains of fluorescent Pseudomonas species (spp.) which have unique root-colonizing ability for small grain crops and biocontrol activity for diseases caused by
Gaeumannomyces graminis
in small grain crops and take-all patch in turf grass. The invention further relates to isolation and identification of the unique strains, and application thereof to control plant diseases caused by
Gaeumannomyces graminis.
2. Description of the Art
Widespread diseases of small grain crops and turf grass are caused by the soil-borne fungus
Gaeumannomyces graminis
(
Gg
), and result in significant economic losses due to reductions in crop yield. Take-all, a disease caused by
Gaeumannomyces graminis
var.
tritici
(
Ggt
) occurs in all wheat-growing regions of the world and is the most important root disease of wheat. Symptoms of wheat take-all include dark longitudinal lesions on roots; in severe cases, the entire root may become blackened with disease with the fungus migrating to the crown of the wheat plant (where the crown roots originate) and the tillers (stems). Severely infected wheat plants are identified in the field by their white heads which result when infection of the crown by the fungus cuts off water transport to upper plant parts causing the plant to die prematurely. Yield losses can be considerable up to 50% of the potential wheat yield. There are no resistant wheat cultivars and registered fungicides perform inconsistently. Further, growers are being increasingly challenged to grow wheat with minimum or no tillage to reduce soil erosion. These practices increase the severity of take-all and other root diseases. Although wheat is particularly susceptible to the take-all fungus, many other Gramineae such as barley, rye, and triticale can also be infected.
Traditionally, take-all has been controlled by a combination of crop rotation and tillage, practices which reduce the inoculum potential of the pathogen. However, because long rotations are often not economically feasible and tillage contributes to soil erosion, the trend in cereal production is toward less tillage and two or three wheat crops before a break. Both of these practices exacerbate take-all. There is no known source of genetic resistance in wheat against take-all, and methods of chemical control are limited. The need for agriculture to become more sustainable and less dependent on chemical pesticides has necessitated the development of alternative approaches to control take-all and other soil-borne diseases.
Other
Gg
fungi, for example,
Gaeumannomyces graminis
var.
avenae
(
Gga
) infects oats and grasses and have been identified as causing take-all patch in turf grasses such as bent grass.
Gaeumannomyces graminis
var.
graminis
(
Ggg
) infects some grasses and has been suggested as causing crown sheath rot in rice.
All agricultural soils show some degree of antagonism to
Ggt
and other soil-borne pathogens. This has been referred to as “general suppression” (N. Gerlagh,
Netherlands Journal of Plant Pathology
74:(Suppl. 2) 1-97 (1968) or “general antagonism” (D. Hornby,
Annual Review of Phytopathology
, Annual Reviews Inc. Palo Alto, Calif. (1983), pp. 65-85). General antagonism results from the overall microbial activity in a soil. In addition, a “specific” suppression (biological control) of
Ggt
(known as take-all decline) develops in certain circumstances which is superimposed over “general suppression” and which results in a nearly complete control of take-all. Take-all decline (TAD) is a natural biological control of take-all, defined as the spontaneous reduction in disease and the increase in yield with extended monoculture of
Ggt
-susceptible small grain crops such as wheat and barley. TAD was first observed more than 50 years ago and is now recognized as a worldwide phenomenon. The similarity of TAD throughout the world is remarkable in view of the broad range of soil types, climates, and agronomic conditions under which wheat, barley, and other small grains are cultivated. Field studies have clearly indicated that the development of TAD follows a consistent pattern everywhere, requiring the continuous cultivation of a small grain and the presence of the take-all pathogen. Factors such as soil type and previous cropping history only seem to modulate the extent and speed of development of TAD. Despite the fact that take-all eventually declines, most growers abandon monculture prematurely because interim losses can be considerable. Once established, however, TAD permits a recovery in yield and persists as long as monoculture continues. Practical exploitation of TAD offers the potential as a natural biological control of take-all. However, to do this, the responsible mechanism(s) for TAD would need to be identified and applied. However, research to date has been mostly descriptive and no particular occurrence of TAD is yet fully understood. A similar decline of take-all patch caused by
Gga
occurs in established turf.
TAD has been extensively studied in an attempt to determine the mechanisms responsible for natural take-all suppression. The most common theories put forward to explain this phenomenon include changes in the microbiological status of the soil, build up of antagonistic bacteria, changes in the pathogenicity and population of the fungus, and presence of protective fungi (D. Hornby in “Take-All Decline: A Theorists's Paradise,”
Soil
-
borne Plant Pathogens
, Ed. B. Schippers and W. Gams, Academic Press, New York (1979), pp. 133-156 and D. Hornby,
Annual Review of Phytopathology
, Annual Reviews Inc., Palo Alto, Calif. (1983), pp. 65-85). Homby reviewed these explanations and concluded that no single mechanism could explain TAD worldwide, and this view has been universally accepted by those working in the field of disease suppressive soils.
The most widely held explanation for TAD is based on microbial interactions between the take-all pathogen and specific antagonistic root-associated microorganisms (R. J. Cook and A. D. Rovira,
Soil Biology and Biochemistry
8: 269-273 (1976)). Several types of evidence support a role for microbial antagonism in the suppression of
Ggt
. For example, suppressiveness can be transferred by incorporation of a small amount (1-10% w/w) of a TAD (suppressive) soil into a take-all conducive soil. Furthermore, the suppressiveness of a TAD soil is eliminated by pasteurization of the soil with moist heat (60° C., 30 min.), by soil fumigation with methyl bromide or by growing crops which are non-hosts of the pathogen.
Studies of the microbial antagonism involved in TAD have focused on attempts to identify specific
Ggt
-antagonistic microorganisms and to transfer these organisms to soil to reproduce suppression. A wide variety of microorganisms have been tested given the prevailing idea that the specific strains responsible differ among TAD soils. Cook and Rovira, 1976, supra, originally hypothesized that among the antagonistic microorganisms the fluorescent Pseudomonas spp. have a key role in TAD. U.S. Pat. No. 4,456,684 describes Pseudomonas strains which suppress diseases caused by take-all and other
Gg
fungi and methods for selection and application of the strains.
Many of the most effective strains produced the antibiotic 2,4-diacetylphloroglucinol (Phl) (C. Keel et al.,
Applied and Environmental Microbiology
62:552-563 (1996)). Phl is a phenolic metabolite with activity against a variety of bacteria, viruses, and fungi, including the take-all pathogen (reviewed in L. S. Thomashow and D. M. Weller, In: G. Stacey and N. T. Keen (eds.)
Plant
-
microbe Interactions
, Vol. I, Chapman & Hall, Ltd. London, pp. 187-236 (1996)). J. M. Raaijmakers et al. (
Applied and Environmental Microbiology
63:881-887 (1997)) report that Phl-producing fluorescent Pseudomonas spp. were present on roots of wheat grown in three TAD soils from Washington S
Cook R. James
Raaijmakers Jos M.
Thomashow Linda S.
Weller David M.
Afremova Vera
Connor Margaret A.
Fado John D.
Saucier Sandra E.
Silverstein M. Howard
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