Breeding value and utilization of host plant resistance for integrated thrips (Thysanoptera: Thripidae) management in cotton (Gossypium spp.)



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Thrips are common early-season pests in cotton systems across the U.S. Host plant resistance, as part of an integrated management strategy, could be a critical tool for reducing thrips damage to cotton in both conventional and organic systems. Also, identifying and developing viable, non-transgenic cotton genotypes for organic cotton production would be valuable for growers desiring new, high-quality cultivars for their production systems. Field and greenhouse trials were conducted in 2011-2014 at the Texas A&M AgriLife Research and Extension Center at Lubbock, and at a number of cooperators’ farms on the Texas High Plains, to evaluate twenty-two cotton genotypes for novel thrips resistance and agronomic potential for organic production. Three G. hirsutum breeding lines, 07-7-519CT, 07-7-1020CT, and 11-2-802GD, exhibited the greatest resistance to thrips damage and had the greatest overall potential for utilization in organic production. Field and greenhouse trials were also conducted in 2011-2013 to elucidate the overall breeding value of thrips resistance. Broad sense heritability ranged 41-67%, depending on the family. H2 was higher in families with a day-neutral resistant parent than those with a photoperiodic resistant parent. Observed segregation ratios fit 3:1, 13:3, and 11:5 expected resistant/susceptible ratios, depending on the family. These results indicate that thrips resistance is a simply-inherited dominant trait, likely controlled by one or two genes. Actual gain from selection ranged 2-21% per cycle of selection, depending on the selection intensity. The optimum selection intensity in these evaluations was 5%, resulting in an approximate 21% gain. Field trials were also conducted in 2013-2014 to evaluate the combination of partially-resistant advanced breeding lines with weekly spray applications of spinosad insecticide on thrips populations and subsequent damage to a cotton crop. Resistant genotypes resulted in 26-37% reductions in thrips injury over the controls. In addition, spinosad applications alone reduced thrips injury up to 37% and increased lint yield 10% in 2013. However, these results were not consistent between 2013 and 2014, as a result of low thrips populations in 2014 and minimal subsequent damage to the crop. Overall, these evaluations revealed that host plant thrips resistance varies widely in cotton and can be sufficiently captured and introgressed by plant breeders. Resistant germplasm is also an effective tool for the integrated management of thrips pests and their damage to a cotton crop.



Organic cotton, Thrips resistance, Non-transgenic, Integrated pest management, Spinosad