Breeding Value of Host Plant Thrips Resistance for Reduced-Input Cotton Systems.

Thrips (Thysanoptera: Thripidae) management is an important component of cotton production on the Texas High Plains, especially with the loss of systemic aldicarb as an insecticide.  As a result, host plant thrips resistance can be a valuable tool for mitigating thrips injury to cotton seedlings in reduced-input and organic production systems.  However, an understanding of the breeding value of such resistance is key for utilizing resistance in cultivar development.  Field and greenhouse trials were conducted in 2012-2014 to estimate broad sense heritability (H²) and actual gain from selection (G­_s) of thrips resistance in cotton.  In 2013-2014, five families, derived from interspecific crosses, were evaluated in greenhouse trials to estimate H² of thrips resistance.  Individual parent and F₂ plants were planted and assessed for thrips damage at 4-5 true leaves, using a visual rating scale.  H² values ranged 35-77%, depending on the family.  F₂ and F₃ populations, resulting from another interspecific cross, were evaluated at the field level in 2012 and 2013, respectively, to estimate actual gain per cycle of selection.  Thrips damage was again assessed on individual plants in each generation, utilizing a visual rating scale (F₃ progeny row ratings consisted of the mean of individual plant ratings in each row).  A 5% selection intensity resulted in an approximate 22% gain per cycle of selection; 1% selection intensity resulted in a 51% gain.  Additional field evaluations of advanced breeding lines selected for thrips resistance revealed improvement of up to 37% over a commercial standard in 2013.  These results indicate that host plant thrips resistance has moderately high heritability and significant genetic improvement can be achieved through visual selection, depending on selection intensity in a given cycle.  Resistant cotton cultivars could aid in mitigating thrips damage to a cotton crop in the absence of systemic insecticides.