RESISTANCE TO SCN WHAT DOES IT MEAN

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RESISTANCE TO SCN WHAT DOES IT MEAN? J. H.
Orf Department of Agronomy and Plant
Genetics University of Minnesota St. Paul, MN
55108 612-625-8275 orfxx001_at_umn.edu
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Stunting and chlorosis induced by soybean cyst
nematode infection on soybean roots
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Management of SCN

• Use resistant varieties
• Rotate with non-host crops
• Goal to reduce yield losses and reduce SCN numbers

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White to light yellow soybean cyst nematode
females on soybean roots
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The Disease

• Disease is interaction of SCN and soybean plant
• Is SCN present? --observe roots, soil samples
• How many nematodes in the field? --soil samples,
  200-500 eggs/100 cc soil-threshold level
• Population designation of the field so proper
  source of resistance can be used
• Ultimate testassess the reproductive ability of
  the SCN field population for the soybean variety
  to be planted

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Life Cycle of The Soybean Cyst Nematode
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SCN Resistance

• Resistance to SCN
• no or limited reproduction of an SCN
  population on a soybean variety
• Resistance due to several genes in the soybean
• Over 100 Plant Introductions have resistance to 1
  or more SCN populations
• Current varieties trace to a few PIs

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Levels of Resistance

• Susceptible check Lee 74 or other susceptible
• Greenhouse test
• Calculate Female Index (FI)

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Levels of Resistance (contd)

• Less than 10 FI for resistance
• Why less than 10 cutoff
• Four level scheme
• 1 9 scale

R resistant FI lt 10 MR moderately
resistant FI 10-30 MS moderately
susceptible FI 31-60 S susceptible FI gt 60
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Pioneer Hi-Bred International, Inc.
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Levels of Resistance (Contd)

• Field evaluations of reproductive ability

• Soil samples at planting-initial egg count (Pi)
• Soil samples at end of season (R6)--final egg
  count (Pf)
• Reproductive index
• Reproductive index lt 0.5 generally indicates
  resistance

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Use of Resistant Varieties (Contd)

• Use resistant source that does not allow
  reproduction (or low levels, lt10 FI) of SCN
• Most sources of resistance effective in most
  field situations in Minnesota
• Know level of resistance in variety being
  considered for planting because not all varieties
  have received all the genes from the original
  source of resistance

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Selecting SCN Resistant Varieties

• When considering an SCN resistant variety,

• find out source of resistance
• ask for data using Minnesota field populations to
  determine level of resistance (FI)
• Ask for Minnesota field data that looks at the
  reproductive index
• Data from several tests or sites

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Table 2. 2001 Minnesota SCN Variety Test
(selected varieties).
Lee 74 155 females
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Use of SCN Resistant Varieties

• Use varieties and crop rotations to manage SCN
  populations so they do not reduce soybean yields
• Ultimate test assess the reproductive ability
  of each SCN field population for the soybean
  variety or varieties to be planted

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Questions?
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Summary of Standardized Conditions
I. Sampling A. Ensure a representative sample
of the population. B. Subsample eggs after cysts
are extracted and crushed. II. Indicator
lines A. Use seed from USDA Soybean Germplasm
Collection only. B. Prepare seed for
germination in germination paper 3 days before
installing the test. C. Select seedlings for
uniformity and lack of disease symptoms just
before transplantation. D. Transplant seedlings
into pasteurized sandy loam soil (75 sand)
just before soil infestation.
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• Infestation mixture
• A. Prepare infestation mixture (eggs J2) just
  before soil infestation.
• B. Agitate infestation mixture gently before and
  during soil infestation procedure.
• C. Infest each experimental unit (soil in
  container with one seedling) with 20 eggs
  J2/cm3 soil.
• D. Do not overwater after inoculum application!
• Experimental design
• A. Use a completely randomized or randomized
  complete block arrangement.
• B. Replicate treatments at least 3 times run
  experiment twice.
• V. Environmental conditions
• A. Maintain 27 to 28 C root zone temperature.
• B. Provide 16-hour days.
• C. Water judiciously.

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VI. Data collection A. Allow test to run 28 to
30 days after soil infestation. B. Soak
experimental units to release soil from
roots. C. Dislodge females from roots with
water, on nested 20- over 60-mesh sieves. D.
Prepare suspensions of females for counting, and
enumerate under x 60 magnification. E. Extra
ct and count females on Lee 74 first. If lower
than 100 discard test and run
again. F. Calculate FI and assign HG Type
designation (Table 2). VII. Reporting
A. Report actual number of females observed on
Lee 74. B. Report FI on all indicator lines
tested in text or Table. Specify lines not
tested. If test is incomplete and add to
the HG Type designation. C. Name inbred lines
or special isolates according to Bird and
Riddle (1994).
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Stunting and chlorosis induced by soybean cyst
nematode infection on soybean roots
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