Multiple insect resistance in 51 commercial corn hybrids, 2021

Authors: Ni, Xinzhi; TOEWS, MICHAEL - University Of Georgia; BUNTIN, G. DAVID - University Of Georgia

Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: 1/3/2022
Publication Date: N/A
Citation: N/A

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 51 transgenic Bt hybrids were included in this year’s trial; 15 hybrids were rated Very Good (VG), the highest rating for multiple insect resistance in 2021; 11 were Good (G); 14 were Fair (F), and 11 were Poor (P) as shown in Table 1. Five hybrids were developed utilizing SmartStax™ technology (abbreviated as SS or STX in the name of the hybrids); 2 hybrids have YHR traits (also known as Optimum® Intrasect™); 16 hybrids have VT2P trait; 1 hybrid with Trecepta Technology (abbreviated as TRC), and one hybrid has 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 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 (denoted for Genuity Viptera Double PRO®) trait that contains a stack of two Bt genes, which target foliar- and ear-feeding lepidopteran pests. TRC (denoted for Trecepta Technology) was built on the proven VT Double PRO® Technology, gives extra control against corn borers and other above ground pests. Flowering time of all entries was between 61 and 65 days after planting. In comparison to 2019 (54-60 days after planting), the late flowering in 2021 reflected the relatively cool and wet weather conditions before pollination at the Tifton location. Because no trial was performed in 2020 due to the pandemic of COVID-19, the data from 2018 and 2019 were used for comparison. Overall insect damage on corn ears in 2021 was relatively low when compared to the observed damage in 2018 and 2019. The six types of ear- and/or kernel-feeding insects in order of damage severity were: corn earworm and fall armyworm, stink bugs, the pink scavenger caterpillar, maize weevil, and sap beetles. Corn earworm and fall armyworm damage was measuring by the length (cm) of feeding damage penetrated 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 2.2 cm per ear, which was much less than the damage observed in 2019 (0-4.1 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. Because of kernel feeding insect damage was low, maize weevil, stink bug, sap beetle, and pink scavenger caterpillar damage was combined, which was ranged between 0.35-5.25% of the damaged kernels in 2021. The data related to insect damage were subjected to the principal component analysis using percentage of damaged kernels and three traits related to corn earworm and fall armyworm damage, that is, husk tightness and extension, and pest penetration on corn cobs. During the field season of 2021, corn rootworm and corn borer damage was not detected at the Tifton trial. 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 lo