Chemistry: molecular biology and microbiology – Micro-organism – per se ; compositions thereof; proces of... – Bacteria or actinomycetales; media therefor
Reexamination Certificate
1997-12-18
2001-08-21
Fox, David T. (Department: 1638)
Chemistry: molecular biology and microbiology
Micro-organism, per se ; compositions thereof; proces of...
Bacteria or actinomycetales; media therefor
C435S471000, C435S481000, C435S478000, C435S252340, C435S876000, C424S164100, C424S093470, C424S093200, C514S002600
Reexamination Certificate
active
06277625
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to biocontrol of plant root diseases. In particular, the invention relates to strains of fluorescent Pseudomonas species which have a biosynthetic locus which encodes for the production of the antibiotic phenazine-1-carboxylic acid stably introduced into the genome, and have biocontrol activity for control of plant root diseases, in particular, diseases caused by the soil-borne pathogen, Rhizoctonia. The invention further relates to methods of making the transgenic strains, and application thereof to control plant root diseases.
2. Description of the Art
Root diseases caused by Rhizoctonia, Pythium, and
Gaeumannomyces graminis
, cause a significant adverse impact on the production of important crops worldwide. The root disease take-all, caused by
Gaeumannomyces graminis
var.
tritici
(Ggt), Rhizoctonia root rot, caused by
Rhizoctonia solani
and
R. oryzae
, and Pythium root rot caused by any of several Pythium species, notably,
Pythium ultimum
and
P. irregulare
, are important root diseases of small grain crops, e.g., wheat, barley, triticale, and rye, worldwide.
Rhizoctonia, a member of the basidiomycotina class of fungi, causes root and stem rot on most food, fiber, and ornamental plants throughout the world, including small grain crops, turf grass, asparagus, canola, corn, sugarbeet, tomatoes, potatoes, peas, rice, beans, soybeans, strawberries, zucchini, and cotton. Root rot on small grain crops caused by Rhizoctonia occurs throughout the United States Pacific Northwest, in Australia, and South Africa, and potentially throughout the temperate regions of the world wherever small grains are grown, especially if grown with reduced or notillage (direct drilling). Rhizoctonia root rot caused by
R. solani
AG8 begins as brown cankerous lesions on the seminal and crown roots that eventually girdles and then severs the roots. Plants with roots pruned off by this disease remain stunted and eventually die without making heads. The disease tends to affect plants in patches and has given rise to other names, such as bare patch disease, purple patch, crater disease, and barley stunt disorder. Of all small grain crops, barley is especially susceptible to
R. solani
AG8
. Rhizoctonia oryzae
infects the embryos of germinating seeds, preventing germination or limiting the formation of seminal roots to only one or two when healthy seedlings produce five or six seminal roots. These two Rhizoctonia species, together with
Rhizoctonia cerealis
and possibly other Rhizoctonia species occur as different mixtures, depending on the soil, cropping systems, weed management practices, and possibly other factors not yet identified.
The soil-borne pathogen complex of Pythium spp. comprises a group of fungi that are among the most successful of all microbial colonists in agricultural soils. It is estimated that nearly all cultivated soil in the world contains spores of at least one, two, three, and even as high as ten Pythium species. Pythium, a member of the oomycetes class of fungi, like Rhizoctonia, affects virtually all food, fiber, and ornamental plants throughout the world. Examples of these plants are given above. Pythium damage to small grains begins as embryo infections and associated poor emergence or stand establishment and continues as destruction of the fine lateral rootlets and root hairs. Plants with Pythium root rot have the appearance of plants without enough fertilizer, because the disease limits the absorptive capacity of the root system through destruction of fine rootlets and root hairs. There are several species of Pythium with ability to attack cereals, either embryos of germinating seeds, root tips and fine rootlets, or all of these delicate and usually juvenile or meristematic tissues.
Widespread diseases of small grain crops and turf grass are caused by the soil-bome fungus
Gaeumannomyces graminis
(Gg), a member of the ascomycotina class of fungi, 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 probably the most important root disease of wheat and related small grains worldwide. 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 grases and has been suggested as causing crown sheath rot in rice.
The pathogens responsible for takeall and Rhizoctonia root rot survive as hyphae or mycelium in the tissues of host plants colonized through their parasitic activities. Pythium species survive in soil as thick-walled oospores or sporangia produced from nutrients robbed from the plant through parasitism. Usually, all three diseases develop simultaneously on the same plants, although one root disease may dominate.
Although Pythium species are ubiquitous in agricultural soils cropped to small grains, damage to small grains caused by Pythium species, e.g., reduction in seedling emergence and plant vigor, is greatest in soils kept wet, especially if the soils are also naturally high in clay content and with pH values below 6.0. Allowing volunteer cereals (plants that develop from seed spilled or dropped by the harvester on the soil surface) to grow in the field after harvest of one crop until only 1 or 2 days before planting the next crop, then spraying with an herbicide such as glyphosate (Round-up®, Monsanto), controls the weeds but greatly favors Pythium root rot and Rhizoctonia root rot. Planting wheat directly into the standing stubble of a previous wheat crop with soil kept moist by sprinkler irrigation or leaving the soil covered with straw favors all three root diseases.
Wheat and other cereals with root disease yield poorly and return less on investments to the grower. Plants with these root diseases also compete poorly with weeds, thereby making it necessary to spend more on herbicides to control weeds. Small grains with root diseases also leave fertilizer unused in the soil, including nitrates, which then may move by leaching below the rooting zone and eventually into ground water. Growers throughout the world continue to use some form of tillage for production of s
Cook R. James
Huang Zhengyu
Mavrodi Dmitri V.
Raaijmakers Jos M.
Thomashow Linda S.
Connor Margaret A.
Fado John D.
Fox David T.
Silverstein M. Howard
The United States of America as represented by the Secretary of
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