Reproduction of M. arenaria on flue-cured tobacco homozygous for Rk1 and/or Rk2 resistance genes, and possible effects of soil temperature on resistance

Jill Pollok, Virginia Tech University 20

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Nematodes in Tobacco

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Nematodes in Tobacco

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Root-Knot Nematode Damage

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Root-Knot Nematode Damage

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Crop rotation

Nematicides

Resistant varieties

Current Control Options

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M. incognita 22%

M. arenaria 41%

M. javanica 5%

M. hapla 32%

2004 VA Nematode Survey, Flue-Cured Tobacco

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M. incognita

8%

M. arenaria

58%

M. javanica

9%

M. hapla 25%

2010 VA Nematode Survey, Flue-Cured Tobacco

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Reproduction Experiment

• Genes Rk1 and Rk2 are

responsible for root knot

resistance in tobacco

– Rk1: resistance to races 1 and 3 of

M. incognita

– Rk2: resistance mostly

uncharacterized

• Objective: Does having both

resistance genes (Rk1Rk1 and

Rk2Rk2) give more resistance in

tobacco to M. arenaria than just

one or the other?

TOBACCO ENTRY RESISTANCE GENES

Coker 371 Gold Susceptible

SC 72 Rk1Rk1

NC 95 Rk1Rk1

T-15-11 Rk2Rk2

STNCB-2-28 Rk1Rk1 Rk2Rk2

NOD 8 Rk1Rk1 Rk2Rk2

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Methods

• 6 tobacco entries

• 6 replications

• Inoculated each plant with

5,000 root-knot eggs

• 60 days after inoculation, cut

plant tops off, rinsed roots,

and collected data

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1. Gall Rating

• Weight of galled roots/total root

weight

2. # of females per gram root

• Sub-divided root system in half

by weight

• Stained ½ red with Phloxine B,

collected three 1-g samples

from stained roots, counted the

number of egg masses to

estimate females

Root-knot egg masses protruding from roots.

Methods: Data Collected

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McGawley, via Nemapix

Methods: Data Collected

3. # of eggs per gram root

• Bleach-extracted eggs from the root

surface of the other half of the root

system

• Suspended eggs in 500 ml water and

counted two 10-ml aliquots

• Averaged the counts and calculated

eggs for 500 ml/0.5 root weight to

estimate eggs/gram roots

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Host Plant Reaction: Galling

Mean data from 5 trials, each with 6 replications. Data presented are non-transformed means of 6 observations. Means followed by the same letter(s) are not significantly different according to statistical analysis of transformed [log10(x+1)] data and the Tukey-Kramer honest significant difference (HSD) test. Data were analyzed in JMP Pro 11.

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Egg masses/g root by trial

Mean data from 5 trials, each with 6 replications. Data presented are non-transformed means of 6 observations. Means followed by the same letter(s) are not significantly different according to statistical analysis of transformed [log10(x+1)] data and the Tukey-Kramer honest significant difference (HSD) test. Data were analyzed in JMP Pro 11.

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Eggs/g root by trial

Mean data from 5 trials, each with 6 replications. Data presented are non-transformed means of 6 observations. Means followed by the same letter(s) are not significantly different according to statistical analysis of transformed [log10(x+1)] data and the Tukey-Kramer honest significant difference (HSD) test. Data were analyzed in JMP Pro 11.

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Reproduction Experiment Conclusions

• Galling, egg masses per g of root, and eggs per g of root were significantly lower when entries possessed Rk1 alone versus the control.

• Combining Rk1 and Rk2 genes further reduced galling (in 1 of 5 trials), egg masses (in 4 of 5 trials), and eggs (in 3 of 5 trials). Entries containing both Rk1 and Rk2 genes exhibited the largest reduction in nematode reproduction.

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Soil Temperature Experiment

• Objective: to determine if

temperature plays a role in

resistance gene efficacy

• Previous student noted that

resistance seemed to break down

at temps above 30°C (with M.

javanica)

• Tested at 25°, 30°, and 35°C

• Inoculated with 3,000 RK eggs,

took down after 35 days

• Soil moisture was standardized

between chambers based on soil

moisture deficit in designated pot

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Host Plant Reaction: Galling

Mean data from 1 trial with 4 replications. Data presented are non-transformed means of 4 observations. Means followed by the same letter(s) are not significantly different according to

statistical analysis of transformed [log10(x+1)] data and the Tukey-Kramer honest significant difference (HSD) test. Data were analyzed in JMP Pro 11.

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Mean data from 1 trial with 4 replications. Data presented are non-transformed means of 4 observations. Means followed by the same letter(s) are not significantly

different according to statistical analysis of transformed [log10(x+1)] data and the Tukey-Kramer honest significant difference (HSD) test. Data were analyzed in JMP

Pro 11.

Egg masses/g root by temp

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Mean data from 1 trial with 4 replications. Data presented are non-transformed means of 4 observations. Means followed by the same letter(s) are not significantly different according to

statistical analysis of transformed [log10(x+1)] data and the Tukey-Kramer honest significant difference (HSD) test. Data were analyzed in JMP Pro 11.

Eggs/g root by temp

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Temp Experiment Conclusions

• At 25°C, galling, egg masses/g root, and eggs/g root followed trends

shown in previous reproduction experiments

• Plants with Rk1, or Rk1 and Rk2, almost always had significantly

fewer egg masses/g root and eggs/g root than the control and Rk2

plants at 30°C

• At 35°C there were no significant differences between any cultivars

for the number of egg masses/g root or the number of eggs/g root

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What Am I?

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Thank You

Dr. Chuck Johnson

Dr. Jon Eisenback

Dr. David Reed

VT Southern Piedmont summer help

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