Screening Germplasm and Quantification of Components Contributing to Thrips Tolerance in Tetraploid Cotton.

Three hundred and ninety one Gossipium hirsutum and 34 G. barbadense accessions were screened for thrips tolerance under field conditions at the Upper Coastal Plain Research Station in Rocky Mount, North Carolina in 2014 and 2015. Visual damage ratings, thrips counts, and seedling dry weights were recorded at 2.5, 3.5 and 4.5 weeks after planting. Population density and thrips arrival times varied between years. Data from the three separate damage scoring dates provided a better estimate of tolerance or susceptibility than ratings from individual dates over the season. Five tolerant G. barbadense accessions and five moderately tolerant upland cotton accessions were identified from field evaluations. Tobacco thrips [Frankliniella fusca (Hinds)], followed by western flower thrips [Frankliniella occidentalis (Pergande)] were the dominant thrips species in the study. Greenhouse experiments were conducted in 2015-16 to determine if plant height, growth rate, leaf pubescence, and leaf area were significantly different in tolerant and susceptible groups of G. hirustum and G. barbadense accessions identified from the field screenings. Leaf pubescence and relative growth rate were significantly higher in tolerant accessions compared to susceptible lines in absence of thrips. There was no difference for plant height and leaf area. Results suggest thrips tolerant plants have a possible competitive advantage in faster growth and higher trichome density, which limits thrips movement.