Progress in evaluating converted cotton race stocks for resistance to whiteflies and aphids

1
Progress in evaluating converted cotton race
stocks for resistance to whiteflies and aphids

• Mary M. Toothaker
• Dr. Marvin Harris
• Dr. C. Wayne Smith
• Texas AM University

2
Why is this necessary?

• With the eradication of the boll weevil,
  secondary pests such as whiteflies and aphids
  have become important pests
• Honeydew from excessive whitefly and aphid
  populations affect ginning and reduce quality of
  the fiber

• Feeding by excessive populations of aphids and
  whiteflies can decrease nutrient availability

(Photo Richard Sequeira)
3

• Aphids and whiteflies are also known vectors of
  many plant viruses
• Aphids becoming an increasing problem with use of
  Bt cotton
• Aphid populations have been shown to be higher in
  Bt fields than non-Bt fields, probably because of
  a decreased use of insecticides

Cotton Leaf Crumple Virus, transmitted by Bemisia
tabaci
4
Selecting for Resistance

• Research done in 2003 - 2004 confirmed that 6
  cotton race stocks (CRS) out of a selection of
  116 photoperiod-insensitive race stocks showed
  resistance to whitefly

• TX0154
• TX0156
• TX0188

• TX0195
• TX0221
• TX0242

5
Selecting for Resistance

• TX0154 and TX0156 were shown to be significantly
  lower in percent survival
• TX0188, TX0195, TX0221, TX0242 were shown to be
  significantly longer in developmental time

6
Selecting for Resistance

• Goal Do plants within one CRS show variability
  in resistance characteristics compared to a known
  susceptible
• Selection criteria - whitefly survival and
  developmental time Which is better?

7
Selecting for Resistance - Whitefly

• 4 plants of each CRS, 3 leaves per plant
• Excised leaf technique
• Ten adult whiteflies were placed and contained on
  each leaf

8
Selecting for Resistance - Whitefly

• Whiteflies removed after 24 hours and clip cages
  placed on same area
• Number of eggs laid were counted and recorded
• Nymphs allowed to hatch and develop for 14 days
• After 14 days, the number of each instar was
  counted every 24 hours until all had completed
  development or died
• Mean number of days to adulthood and percent
  mortality were calculated for each plant within
  each race stock

9
(No Transcript)
10
(No Transcript)
11
Current Research

• 20 whole plants (6-8 leaf stage) of each CRS and
  a susceptible control (DP or PSC355)
• Three cages per plant
• 7-8 adult whiteflies per cage

12
Results
13
Results
14
Results
15
Discussion

• Mortality appears to be the better selection
  criteria
• Much more variation within each CRS in percent
  mortality than the controls using excised leaf
  technique
• Days to adulthood appear to be slightly higher in
  the test groups than the controls

16
Breeding

• By using whole plants, individual plant
  selections (IPS) can be made within each CRS
  using this selection criteria

17
Other Projects

• Use water-sensitive paper to measure honeydew
  production
• Quantify amount of honeydew produced per acre
  over time
• Could determine aphid numbers in a field by
  measuring the honeydew produced

in conjunction with USDA
18
Proof of Concept
Honeydew production by pecan aphid on a known
susceptible variety of pecan
Honeydew production on a suspected resistant
variety of pecan
19
Acknowledgements

• Cotton, Inc.
• Texas AM University Department of Entomology
• Alexandra Gomezplata
• Jessica Honaker
• Robert Puckett
• Allen Dean
• Sarah Skrivanek
• Texas AM University Plant Growth Facilities
• Roger Horn
• Texas AM University Department of Soil Crop
  Sciences
• Kasi Clay
• Dawn Deno
• USDA-ARS-SPARC
• Dr. Juan Lopez
• Dr. Dan Martin