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ARS Home » Southeast Area » Tifton, Georgia » Crop Genetics and Breeding Research » Research » Publications at this Location » Publication #345680

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

Location: Crop Genetics and Breeding Research

Title: Multiple insect resistance in 50 commercial corn hybrids, 2016

Author
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: 11/15/2016
Publication Date: 11/30/2016
Citation: Ni, X., Toews, M.D., Buntin, G.D. 2016. Multiple insect resistance in 50 commercial corn hybrids, 2016. In: J.D. Gassett, D. Dunn, A.E. Coy, H. Jordan, Jr., and J.L. Day (eds.). Georgia 2016 Corn Performance Tests, Georgia Agricultural Experiment Stations, Annual Publication. 101-8 pp. 34-37.

Interpretive Summary: NOT REQUIRED

Technical Abstract: Commercial corn hybrids were screened for ear- and kernel-feeding insect resistance under field conditions at Tifton, GA. Nine hybrids were rated Very Good (VG), the highest rating for multiple insect resistance in 2016 (see following table). Thirteen were Good (G), 19 were Fair (F), and 13 were Poor (P). Three hybrids included a blend of 80% transgenic and 20% non-transgenic seeds, known as refuge in a bag (RIB). In cotton growing area and all of Georgia, RIB products are required to have a 20% Non-Bt structured refuge. Four hybrids were developed utilizing YHR traits (also known as Optimum® Intrasect™), 9 hybrids have Genuity VT Double PRO (VT2P) traits, and 2 hybrids have VT Triple PRO (VT3P) traits. 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 or VT3P traits contain a stack of two or three Bt genes. VT2P hybrids targeted foliar- and ear-feeding lepidopteran pests, while VT3P hybrids have an additional Bt gene for rootworms. Overall insect damage on corn ears was high in the 2016 trial. The six types of ear- and/or kernel-feeding insects in the order of damage severity were: corn earworm and fall armyworm, stink bugs, sap beetles, pink scavenger caterpillar, and maize weevil. Corn earworm and fall armyworm damage was combined because the damage on corn cob is difficult to separate. Feeding penetration by these caterpillar pests of natural infestations in corn ears was between 0.2 and 3.5 cm, which was greater than the damage observed in 2015 (0.1-2.1 cm). Multiple species of sap beetles were recorded in 2016. Stink bug damage in 2016 was relatively low, ranging from 0.02 to 1.32% of the kernels per ear, which was similar to what observed in 2015, 0.1 to 1.4%. So was sap beetle damage 0.2-2.4% in 2016 and 0.3-2% in 2015, as well as pink scavenger caterpillar damage <1% in 2016, and 0-1% in 2015. Maize weevil infestation at harvest with 18% kernel moisture was also rarely observed in 2016. The high level of cob damage by corn earworm and fall armyworm might have been influenced by both planting time and weather conditions in 2016. In addition, flowering time of all entries were similar (between 51 and 57 days after planting), irrespective of categorization of Short (S) or Medium (M) maturity as shown in the table. The relatively early flowering observed in 2016, which is similar to what we observed in 2015, could be the result of relatively late planting date (April 21st in 2016) in combination with high temperature during the first 54 day after planting (that is, from April 21st to June 15th). In 2016, 796 degree days were recorded between April 21st and June 15th (using 60°F as base temperature), and a similar number (788 degree days) were recorded during the same period of time in 2015. Because husk tightness and husk 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 3.4 and 4, which were all considered medium for husk tightness. Husk extension ranged between 0.1 and 5.3 cm, and was negatively correlated to worm penetration and percentage of sap beetle-damaged kernels in corn ears, but not to husk tightness. Multiple insect resistance was categorized in four groups according to the insect damage ratings on corn cobs and kernels; they are very good (VG), good (G), fair (F), and poor (P). VG represents the least amount of insect damage, while P represents the greatest amount of insect damage. The rankings of the 50 hybrids for multiple insect resistance in the table was based on the results of the principal component analysis using corn husk extension and tightness along