West Lafayette, Indiana
March 20, 2008
Purdue University researchers have identified several
soybean varieties that grow well in areas of the Midwest like
southern Indiana and are resistant to root-knot nematodes, a
plant-destroying parasite with a recently confirmed presence in
that part of the state.
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Root-knot
nematodes, recently confirmed in southern
Indiana, can cause extensive damage to soybeans,
corn and watermelon, three of the main cash
crops in that area of the Midwest. Purdue plant
pathologist Andreas Westphal and his research
team have identified several commercial
varieties of soybeans that grow well in the area
and are resistant or tolerant to this type of
nematode and also to soybean cyst nematode. In
the photo, Westphal is holding a tomato plant
infected with root-knot nematodes, evidenced by
the knobby growths on the roots. (Purdue
Agricultural Communication photo/Tom Campbell) |
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The researchers verified that
resistance in soybeans to one nematode parasite doesn't predict
how well the plant will fight off another nematode species, said
Andreas Westphal, assistant professor of plant pathology. Some
of the varieties also were resistant to soybean cyst nematode.
"We were trying to identify soybean lines that will grow in
Indiana and are root-knot nematode resistant," said Westphal,
who is senior author of the report published online in the
journal Crop Science and will be published in the March-April
print issue.
The research team recently published a paper in Plant Health
Progress that details the distribution of root-knot nematodes on
soybeans in southwestern Indiana.
"We also wanted to find varieties that are nematode-tolerant,"
Westphal said. "In other words, the nematode is present in the
soil, but the plant doesn't suffer a lot of damage."
Root-knot nematodes, including the species Meloidogyne
incognita, infect soybeans in sandy loam soil and also reproduce
on corn and the highly root-knot nematode-sensitive watermelon,
two other major cash crops in the southern part of Indiana. The
area, along with additional parts of the state, also suffers
from other nematodes, including the soybean cyst nematode
(Heterodera glycines). Root-knot nematodes are responsible for a
loss of 93,000 tons of soybeans annually in the United States.
Other than resistant and tolerant plants, available methods to
rid fields of the destructive organisms are not always practical
or economically feasible, Westphal said. For example, chemicals
that are effective against nematodes can be dangerous to the
environment, people and animals.
A major concern for farmers is that soybeans, corn and
watermelon are all susceptible to root-knot nematodes. Most
farmers in southern Indiana plant crops in a
soybean-corn-watermelon rotation. If the parasites infect the
soybeans, then the organisms will be in the soil and can damage
the subsequent crops planted in the same field.
"The availability of nematode-resistant varieties is important,
not only for soybean production, but also for the whole rotation
sequence because a resistant soybean crop will reduce the number
of nematodes in the soil," Westphal said.
The study involved planting eight soybean strains in a
commercial field near Vincennes, Ind. These were plant varieties
that already were known to grow well in soil and weather similar
to that found in southern Indiana. The field had a history of
root-knot and soybean cyst nematode infestations. Westphal and
his team also tested some of the same soybean lines in a field
in which they introduced the nematodes and in a greenhouse where
they used similar soil containing the root-knot nematodes.
Using plants known to be resistant to soybean cyst nematode, the
researchers confirmed resistance to that nematode doesn't
predict how resistant the plant will be to root-knot nematodes.
Although Indiana farmers previously were aware of the damage to
their crops from soybean cyst nematode, it was only recently
that they learned about root-knot infection of soybeans. They
now know how to identify both nematodes and how these parasites
damage crops.
Damage by plant-parasitic nematodes usually appears in patches
in fields because where nematodes are introduced determines the
infestation area. The type of soil and environmental conditions
also play a role in the parasite's survival.
Both the soybean cyst and root-knot nematode feed on roots,
robbing the plant of needed nutrients and water. The
lemon-shaped soybean cyst nematode is easy to spot on the root
because it stays on the outside. These pinhead-sized nematodes
are white, then yellow, and finally become brown as they mature.
The nematode-induced cysts are much smaller than the so-called
"nodules," which are structures induced by the beneficial
bacterium rhizobium. Rhizobium association aids the plant in
nutritional nitrogen absorption.
The root-knot nematode induces big clumps, or galls, on the root
that look a bit like a wart or a tree knot, and the deformations
are much bigger than the signs caused by the soybean cyst
nematode. The nematode galls have irregular tumorlike shapes, in
contrast to the spherical shape of nodules caused by rhizobium
association.
Next the researchers will try to determine varieties of cover
crops that are nematode-resistant. Cover crops are used over the
winter to control erosion but can provide a habitat for the
parasites. This means that larger populations of the parasites
are present when crops are planted in the spring.
"We hope that we can improve nematode suppression in the entire
crop sequence to improve the yield of the cash crops," Westphal
said.
The other authors on this paper were graduate student Greg
Kruger and postdoctoral researcher Lijuan Xing, both of the
Purdue Department of Botany and Plant Pathology, and Allen
LeRoy, Purdue Department of Agronomy soybean breeding and
genetics professional.
The Indiana Soybean Alliance; Indiana Crop Improvement
Association; AG Spectrum; Purdue departments of Botany and Plant
Pathology, and Agronomy; and the Purdue College of Agriculture
provided support for this research.
ABSTRACT
Meloidogyne incognita Resistance in Soybean under Midwest
Conditions
Greg R. Kruger, Lijuan Xing, Allen R. LeRoy, and Andreas
Westphal
Soybean cultivars of maturity groups II to IV were tested in the
greenhouse for resistance to Meloidogyne incognita (Kofoid and
White) Chitwood. Selected cultivars were tested in a field of
sandy loam soil naturally infested with M. incognita and
Heterodera glycines Ichinohe (2004) or in a silt loam soil
artificially infested with M. incognita (2005). In 2004, H444NRR
was resistant to M. incognita, but not to H. glycines; LS94-3207
and LNX97164-35-5 were resistant to both nematodes; Gateway 427,
H444NRR, LNX97164-35-5, and SB4399CT were moderately resistant
to M. incognita in greenhouse tests; HF9665-2-15 was resistant
to M. incognita but highly susceptible to H. glycines. In 2005,
LS94-3207, H444NRR, LNX97164-35-5, and Manokin were resistant to
M. incognita. In microplots with two sandy loam soils,
HF9665-2-15 exhibited tolerance to increasing inoculum levels of
M. incognita. High-yielding soybean cultivars in maturity groups
II to IV with resistance and tolerance to M. incognita were
identified. Under field conditions, resistance to the more
widespread nematode H. glycines, combined with resistance to M.
incognita, is highly desirable to reduce the risk of yield
reduction and to improve cropping sequences that include
soybean.
ABSTRACT
Distribution and Damage Caused by Root-Knot Nematodes on
Soybean in Southwest Indiana
Greg R. Kruger, Lijuan Xing, Judith B. Santini and Andreas
Westphal
The distribution of Meloidogyne spp. in southwestern Indiana was
determined in a county-wide survey in two counties and at two
farm operations with a history of Meloidogyne infestation.
Meloidogyne spp. were found within the Eolian sand deposits in
southern Knox Co. and in the northern and central parts of
Daviess Co. Meloidogyne spp. were found in approximately 80% of
production fields on the two farms south-southeast of Vincennes,
Knox Co. In addition, a transect study was conducted in a
soybean (cv. 93M90) field to quantify suspected damage from
Meloidogyne incognita. In this field, areas of varying sizes
contained stunted and chlorotic soybean plants typical of
nematode damage. In single transects through each of three
damaged areas, plant weights, nematode-induced root galling,
nematode densities, and soil chemical and physical properties
were taken at 1.5-m intervals. Multiple regression analysis was
conducted with the plant, nematode, and soil parameters
determined for each location. The amount of nematode-induced
galling had the greatest contribution (RČ = 0.40, P < 0.01) to
reduced plant top biomass in the damaged soybean areas.
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