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 A&M 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

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