Germplasm Screening and Dissecting Growth Components Contributing to Thrips Tolerance in Cotton

G. hirsutum and G. barbadense accessions were screened for thrips tolerance under field conditions in North Carolina. Visual damage score, thrips count, and dry weight was recoded at 2.5, 3.5 and 4.5 weeks after planting. Intensity and time of arrival for thrips varied over the years. A higher thrips pressure was recorded during 2^nd year compared to first year of screening. Data from three scoring dates was strongly correlated and provided a better estimate of tolerance/susceptibility. Positive correlation was observed between damage score and total thrips count over years. However, dry weight and number of thrips were found to be negatively correlated. Overall, Pima accessions had lower leaf damage and higher dry weight than G. hirsutum lines. Tobacco thirps (Frankliniella fusca (Hinds)), followed by Western flower thrips (Frankliniella occidentalis) were dominant thrips species in the study. Three greenhouse studies on selected tolerant and suceptible lines indicated that plant height, biomass production, and leaf area are not associated with thrips tolerance.