Project Summaries

06-878  Project Manager: P. F. O'Leary


Freddie M. Bourland and Glenn E. Studebaker, University of Arkansas; Tina G. Teague, Arkansas State University

Tarnished plant bug (TPB) (Lygus lineolaris (Palisot de Beauvois) has become the major insect pest in much of the cotton belt since boll weevils have been eradicated and worms controlled by Bt cotton. This project provides information for quantifying the level of resistance in available cotton lines (objective 1), how to effectively use partial resistance (objective 2) and how to more efficiently select for improved resistance (objective 3). Work was on all three objectives continued in 2012.

In 2012, 133 cotton lines plus susceptible Frego-bract cotton (Fg) checks were evaluated in six different tests (two state variety tests, two Regional Strain Tests, and two UA strain tests) using small plots with 12 replications at Keiser. Accumulative percentage of "dirty flowers" (flowers with damaged, discolored anthers) from five sequential sampling dates in August were determined for each line. All cultivars and strains had significantly lower % dirty flowers than the Fg checks. Significant variation in % dirty flowers was found among normal bract cotton lines in each test. By normalizing TPB damage in the variety tests by Fg check means, consistence of genotypic response to TPB over years was apparent. Over years, the lowest TPB damage was found for ST 5288B2RF, PHY 367WRF, UA222, NGX 0012B2RF, and AM 1511B2RF. UA48, DG 2430B2RF, UA1033, and PHX4339CB had the highest TPB damage. This variation between UA48 and UA222 was confirmed when data from strain tests were compared over years. Sensitivity to TPB should be considered when choosing and managing a variety.

The relative value of TPB resistance and earliness on response to TPB was evaluated in large plots at Keiser in 2012. Based on "dirty flower" data from small plots, two resistant and two susceptible varieties were evaluated in early and late-planted trials. Each set of two varieties were represented by an early and late-season maturing variety. TPB levels were high in 2012. Susceptible varieties tended to have higher populations of TPB and reached the treatment threshold of 3 TPB/5 row feet earlier than the resistant varieties. Except for one variety, late planted cotton required more insecticide treatments than early planted cotton. No trend associated with variety maturity was found. Over five years of testing, we have found that the resistant varieties (as identified by % dirty flowers in small plot tests) required approximately half as many insecticide applications for TPB when compared to susceptible varieties. Utilizing resistant varieties could potentially cut growers TPB management costs in half.

Field and laboratory trials were aimed at evaluating techniques for screening cottons with host plant resistance to TPB. The field cage and main stem cuttings techniques show promise and could be helpful in evaluating TPB resistance of new cotton germplasm. We observed differences in 3-day plant bug nymph survival between resistant and lines when bugs were exposed to field grown cotton plants. These differences were not apparent with greenhouse grown plants. These results remind us that host plant resistance is relative, and the expression of resistance often is dependent on environmental factors. Field cage tests were time and labor intensive. Use of cuttings method was easier, and much more appealing to research personnel. Use of newly hatched nymphs allowed greater separation among lines; however, use of such tiny, delicate insects required skilled and competent personnel.   Overall, we believe that these results show promise for further expanding the terminal cuttings HPR screening protocol. If the cuttings technique is confirmed, resistance of varieties and breeding lines could be compared by taking plant cuttings from existing field tests. Also, cuttings could be made from segregating populations thereby allowing breeders to directly select for resistance to TPB. Further evaluations using additional cotton lines and with standardized handling of test insects are needed.


Project Year: 2012

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