Journal of Economic Entomology Advance Access published October 16, 2015 Journal of Economic Entomology, 2015, 1–7 doi: 10.1093/jee/tov275 Plant Resistance Research article Cotton Square Morphology Offers New Insights into Host Plant Resistance to Cotton Fleahopper (Hemiptera: Miridae) in Upland Cotton Laura Ann McLoud,1,2 Steven Hague,1 Allen Knutson,3 C. Wayne Smith,1 and Michael Brewer4 1Department of Soil and Crop Sciences, Texas A&M University, 370 Olsen Blvd., TAMU 2474, College Station, TX 77843, ([email protected]; [email protected]; [email protected]; [email protected]; [email protected]) 2Corresponding author, e-mail: [email protected], 3Department of Entomology, Texas A&M AgriLife Research and Extension Center, 17360 Coit Rd., Dallas, TX 75252 and 4Department of Entomology, Texas A&M AgriLife Research and Extension Center, 10345 Hwy 44, Corpus Christi, TX 78406. Received 22 May 2015; Accepted 24 August 2015 Abstract Cotton fleahopper, Pseudatomoscelis seriatus (Reuter) (Hemiptera: Miridae), is a piercing–sucking pest of cot- ton (Gossypium hirsutum L.) that feeds preferentially on developing flower buds, called squares. Heavy infesta- tions cause yield reductions that result from abscission of squares damaged by the cotton fleahopper feeding. Antixenosis, or nonpreference, has been reported as a mechanism of host plant resistance in cotton to cotton fleahopper. Square structure, particularly the placement of the reproductive tissues, and stylet penetration were investigated as factors that influence resistance to cotton fleahopper in cotton lines derived from crosses with Pilose, a cultigen of upland cotton resistant to cotton fleahopper, and backcrossed with high-yielding, suscepti- ble lines. Ovary depth varied among the lines tested and was found to be a heritable trait that affected the ability of a fleahopper’s feeding stylets to penetrate the reproductive tissues in the square and might influence prefer- ence. Behavioral assays suggested antixenosis as a mechanism of host plant resistance, and the trait conferring antixenosis was found to be heritable. Results suggest ovary depth plays a role in conferring resistance to cot- ton fleahopper and is an exploitable trait in resistance breeding. Key words Pseudatomoscelis seriatus, cotton fleahopper, Gossypium hirsutum Host plant resistance is defined as the phenomenon by which plants cotton grown in the United States is genetically modified (U.S. under the same environmental conditions experience different levels of Department of Agriculture [USDA] 2014), but the cotton fleahop- injury from insect herbivory (Painter 1958); plants with comparatively per, Pseudatomoscelis seriatus (Reuter), a piercing–sucking pest, is little damage are often termed resistant, and those with comparatively not managed by genetically modified cotton. Identifying, character- more damage are often termed susceptible. Host plant resistance can izing, and exploiting host plant resistance traits may lead to the de- be described using three terms: tolerance, antixenosis, and antibiosis. velopment of cultivars with increased resistance to cotton Briefly, tolerance is a plant’s ability to survive under and sufficiently re- fleahopper and mitigate yield losses and costs associated with con- cover from insect infestation to be able to produce biomass and repro- trolling this insect. duce; antixenosis, or nonpreference, is the aversion of the insect to Cotton fleahopper is an early season pest of upland cotton, and feeding on or even selecting the plant as a potential host; and antibiosis damage usually is most severe in the central and southern portions describes a fitness cost for the insect feeding on the plant (Painter of the U.S. Cotton Belt, particularly in the dryland production sys- 1958, Reese et al. 1994, Strauss and Agrawal 1999). tems of Texas (Ring et al. 1993), where cotton cultivars have an The use of host plant resistance to control cotton insect pests has early maturity habit and begin squaring around the time of senes- been most successful in breeding early maturing varieties which es- cence of the cotton fleahoppers’ weedy spring hosts. The insect feeds cape late season insect pests; this approach is an important part of primarily on developing cotton flower buds, or squares, early in de- integrated pest management systems in cotton, Gossypium spp., in velopment, when the squares are of pinhead (1–2 mm in diameter) the United States (Jenkins and Wilson 1996). Presently, pest insect or match-head (2–3 mm in diameter) sizes (Knutson et al. 2013) and control in upland cotton (Gossypium hirsutum L.) is accompanied contain high concentrations of amino acids essential to insect by planting genetically modified cultivars. Currently, 96% of all growth and development (Showler 2009). Size of cotton squares is VC The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: [email protected] 1 2 Journal of Economic Entomology, 2015, Vol. 0, No. 0 also known to influence feeding preference and female fecundity in Table 1. Line identifications, pedigrees, and designations (donor boll weevil (Anthonomus grandis grandis Boheman; Showler 2005). parent [DP], recurrent parent [RP], or backcross [BC1F3]) of parental Feeding injury by cotton fleahopper causes abscission of squares and lines and backcross progeny thus delayed maturity of the crop. Line ID Pedigree Designation Martin et al. (1988) conjectured that polygalacturonase in the fleahopper’s saliva, which aids in the digestion of pectins in the mid- TAM07V-45 96WD-22/02Q-42 RP dle lamella, may be responsible for the plant tissue lesion character- TAM06WE-14 DPL491/96WD-22//AP9257/96WD-22 RP istic of cotton fleahopper feeding (Miles 1972). Bell et al. (2007) 13-6 Pilose/Deltapine50 DP reported that cotton fleahopper can vector plant pathogens during 15-2 Pilose/Deltapine50 DP 18-1 Pilose/Deltapine50 DP feeding, and these pathogens, if delivered into the developing ovary, 18-3 Pilose/Deltapine50 DP can result in ovary tissue necrosis characteristic of squares shed after 20-1 Pilose/Deltapine50 DP being fed on by cotton fleahopper. Previous studies, emphasizing the 20-2 Pilose/Deltapine50 DP role of leaf pubescence in conferring resistance, report degrees of re- 12511 TAM06WE-14 //TAM06WE-14 /15-2 BC1F3 sistance to cotton fleahopper among cultivars and cultigens evalu- 12522 TAM06WE-14 //TAM06WE-14 /13-6 BC1F3 ated in field studies (Lukefahr 1970, Walker et al. 1974) and in field 12524 TAM06WE-14 //TAM06WE-14 /18-1 BC1F3 and cage studies (Knutson et al. 2013, McLoud et al. 2015). 12525 TAM06WE-14 //TAM06WE-14 /18-3 BC1F3 McLoud et al. (2015) evaluated the role of Pilose (PI 528521), a 12547 TAM07V-45//TAM07V-45/13-6 BC1F3 densely pubescent cultigen, in conferring resistance to cotton flea- 12548 TAM07V-45//TAM07V-45/15-2 BC1F3 hopper. While the pilose phenotype was found to have a high level 12550 TAM07V-45//TAM07V-45/18-1 BC1F3 12552 TAM07V-45//TAM07V-45/20-2 BC F of resistance, measured as reduced number of damaged squares, 1 3 12553 TAM07V-45//TAM07V-45/18-3 BC F McLoud et al. (2015) also reported resistance in plants with smooth 1 3 12554 TAM06WE-14 //TAM06WE-14 /20-1 BC1F3 and hairy pubescent phenotypes, suggesting resistance can be sepa- 12555 TAM06WE-14 //TAM06WE-14 /20-2 BC1F3 rated from the pilose trait and that alternative host plant mecha- nisms are responsible for resistance. In this study, we build on the hypothesis that resistance is not de- Cotton Fleahoppers pendent on the pilose trait. The purpose of this study was to examine Cotton fleahoppers were reared according the methods of Breene the role of square morphology, specifically the structure and placement et al. (1989) and Gaylor and Sterling (1975). Woolly croton, Croton of the developing ovary, in influencing resistance of upland cotton to capitatus Michaux, stems were collected in burlap sacks at College cotton fleahopper. Additionally, the heritability of this host plant resis- Station in January of 2012–2014. Stems were stored for long term in tance trait and its potential as a tool for breeders is also discussed. a cold storage seed room (15C and ca. 50% relative humidity [RH]). As needed, stems were removed from the sacks, broken into Materials and Methods smaller pieces, and placed in 4.73-liter plastic buckets, the openings of which were covered with plastic mesh and secured with rubber Germplasm bands. The buckets were filled with water for 20 min, drained, and Cotton fleahopper-resistant germplasm was obtained from the placed in an incubator at 27.0 6 1C and a photoperiod of 12:12 Texas A&M AgriLife Research Cotton Improvement Lab (CIL) in (L:D) h. After a week of soaking in this manner every other day, the College Station, TX, and from Allen Knutson at the Texas A&M buckets were checked for hatched nymphs by inverting and shaking AgriLife Research Center in Dallas, TX (McLoud et al. 2015). Eight over a black counter top. Nymphs were collected with an aspirator parental lines and 11 BC1F3 lines were derived from this plant mate- and transferred to plastic containers (710 ml) covered with organza rial (McLoud et al. 2015) and were evaluated (Table 1). Two high- and lined with a Kimwipe (Kimberly-Clark, Irving, TX) and placed yielding breeding lines were selected as parents from the CIL: in the incubator. Adults and nymphs were fed store-bought, USDA- TAM07V-45 (‘TAMCOT 22’/02Q-42), a line with glabrous leaves certified organic green beans purchased from a local grocery store. and stems, and TAM06WE-14 (‘DP 491’/TAMCOT 22//AP9257/ Green beans were replaced every other day and as needed. TAMCOT 22), a line with relatively hairy stems and leaves. TAMCOT 22 (Thaxton et al. 2005, PI 635877) was developed and released by Texas A&M AgriLife in 2005; DP 491 (PVP Behavioral Assays 200100159, PI 618609) is a high-quality cultivar released in 2004; Behavioral assays were conducted with parental and backcross lines 02Q-42 is an unreleased breeding line of Texas A&M AgriLife (Table 1).