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ARS Home » Southeast Area » Tifton, Georgia » Crop Genetics and Breeding Research » Research » Publications at this Location » Publication #372956

Research Project: Genetic Improvement of Maize and Sorghum for Resistance to Biotic and Abiotic Stresses

Location: Crop Genetics and Breeding Research

Title: Insect screening results: Multiple insect resistance in 68 commercial corn hybrids, 2019

item Ni, Xinzhi
item TOEWS, MICHAEL - University Of Georgia
item BUNTIN, G. DAVID - University Of Georgia

Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: 10/28/2019
Publication Date: 3/4/2020
Citation: Ni, X., Toews, M.D., Buntin, G. 2020. Insect screening results: Multiple insect resistance in 68 commercial corn hybrids, 2019. In: D.J. Mailhot, D. Dunn, and H. Jordan Jr. (eds), Georgia 2019 Corn, Sorghum Grain and Silage, and Summer Annual Forages Performance Tests. Georgia Agricultural Experiment Station, Annual Publication. 101-11, pp. 26-30.

Interpretive Summary: not required

Technical Abstract: Commercial corn hybrids were screened for ear- and kernel-feeding insect resistance under field conditions at Tifton, GA, and the results are summarized in the following table. A total of 68 transgenic Bt hybrids were included in this year’s trial. While 27 hybrids belonged to mid- to full- season categories, the majority (41) were short-season hybrids. Of all hybrids tested, 18 were rated Very Good (VG), the highest rating for multiple insect resistance in 2019; 11 were Good (G); 22 were Fair (F); and 17 were Poor (P). One hybrid (A648-54STX) was developed utilizing SmartStax™ technology; two hybrids have YHR traits (also known as Optimum® Intrasect™); 16 hybrids have Genuity VT Double PRO (VT2P) traits; and four hybrids have the VT2P trait with refuge in bag (RIB). RIB hybrids are a blend of 95% transgenic seeds with 5% non-transgenic seeds as a strategy for management of insect resistance to Bt genes. But regulations require that in cotton-growing areas, which includes all of Georgia, all Bt corn hybrids, both pure Bt seed and the RIB products, have a 20% non-Bt seed planting as a refuge. Please see the bag tag and seed dealers for details about the Bt corn refuge requirements. SmartStax™ combined multiple transgenic technologies to control both above- and below-ground insect pests, as well as for herbicide tolerance. The Optimum® Intrasect™ insect protection traits (or YHR) include a combination of two insect protection traits – Herculex® I and YieldGard® Corn Borer, while the VT2P trait contains a stack of two Bt genes, which target foliar- and ear-feeding lepidopteran pests. Corn rootworms and corn borers were not present at Tifton during the test. Overall insect damage on corn ears in 2019 was similar to observed damage in 2017 and 2018. The six types of ear- and/or kernel-feeding insects in order of damage severity were: corn earworm and fall armyworm, stink bugs, maize weevil, the pink scavenger caterpillar, and sap beetles. Corn earworm and fall armyworm damage was determined by measuring by the length (cm) of feeding damage from the tip of the ear toward the base. Feeding penetration by natural infestation of these lepidopteran pests (from the means of the five sampled ears per plot) was between 0 and 4.1 cm per ear, which was less than the damage observed in 2018 (0-5.6 cm). Kernel-feeding insect damage was assessed by percentage (%) of damaged kernels per ear. The number of kernels per ear were estimated by multiplying the number of kernels per row by the number of rows from a representative ear for each plot. Stink bug damage at the plot level in 2019 was higher (0-8.5% or 44 kernels per ear) than observed in 2018 (0-5% or 23 kernels per ear). Kernel damage by maize weevil (0-3.3% or 23 kernels per ear) and the pink scavenger caterpillar 0-2.46% (13 kernels per ear) was also higher in 2019 than in 2018 (0-0.5% or 3 kernels per ear; and 0-1% or 6 kernels per ear, respectively). Multiple species of sap beetles were recorded in 2019. Sap beetle damaged kernels were 0-1.15% (or 7 kernels per ear), which is much less than 0-6.76% (or 40 kernels per ear) observed in 2018. Flowering time of all entries was between 54 and 60 days after planting. In comparison to the previous year (63-69 days after planting), the early flowering in 2019 reflected the relatively warm and dry weather conditions before pollination at the Tifton location. Because corn husk tightness and extension are considered important traits for ear- and kernel-feeding insect resistance, the husk features of the sampled ears were examined. Husk tightness was assigned using a scale of 1 to 5, in which 1 = very loose and 5 = very tight. Average ratings for husk tightness were between 4 and 5, which were all considered medium to tight for husk tightness rating. Husk extension ranged from 0 to 6.2 cm. Also, husk extension was negatively correlated to overall