GENETIC IMPROVEMENT OF MAIZE AND PEARL MILLET FOR RESISTANCE TO INSECTS AND AFLATOXIN
Location: Crop Genetics and Breeding Research
Title: Resistance to multiple ear-feeding insects in 59 commercial corn hybrids - 2010
Submitted to: Corn Performance Tests
Publication Type: Experiment Station
Publication Acceptance Date: October 28, 2010
Publication Date: December 1, 2010
Citation: Ni, X., Buntin, G., Wilson, J.P. 2010. Insect Screening Results: Resistance to multiple ear-feeding insects in 59 commercial corn hybrids - 2010. In: Coy, A. E., Day, J. L., and Gassett, J., editors. Georgia 2010 Corn Performance Tests, Georgia Agricultural Experiment Stations, Annual Publication 101-2, Athens, GA.
Interpretive Summary: not required
Twelve of the 59 hybrids examined in 2010 (as indicated in the following table) have been developed utilizing YieldGard VecTran Triple technology (abbreviated as VT3 or VT3P). The hybrids with VT3 only contain the YieldGard-corn borer gene, while the hybrids with VT3PRO contain a stack of YGCB and the new Cry2A gene. In addition, 22 have transgenic weed-control (RR=Roundup ready), and 6 have glyphosate tolerance (GT) gene.
Five ear- and/or kernel-feeding insects and their damage were recorded in 2010. They are in the order of infestation severity: sap beetles, corn earworm and fall armyworm, the brown stink bug, and pink scavenger caterpillar. Multiple species of sap beetles and stink bugs were also recorded in 2010. In addition, maize weevil infestation was very low on these entries at harvest with 18% kernel moisture in 2010. Disease surveys around flowering time showed minimal smut, southern rust, and southern and northern blight infections. Very few ears with ear rot were recorded this year.
The combined insect damage rating reflected cob damage by the corn earworm and the fall armyworm, as well as kernel damage by the sap beetles, the stink bugs, and the pink scavenger caterpillar. Multiple insect resistance was categorized in five groups according to the insect damage ratings on corn cobs and kernels; they are very good (VG), good (G), fair (F), poor (P), and very poor (VP). VG represents the lowest amount of insect damage, while VP represents the greatest amount of insect damage. Losses to pink scavenger caterpillar and sap beetles were based on damage by possibly multiple generations of these insects as the crop matures in the field. Corn earworm and fall armyworm damage was combined because the damage was difficult to separate, as was damage by sap beetles and pink scavenger caterpillars. Corn earworm and fall armyworm feeding penetration in corn ears on the 59 hybrids was between 0.1 and 3.2 cm, which was lower than what we observed in 2009 (0.7 - 3.5 cm). Stink bug damage in 2010 (0.05-2.9% discolored kernels) was lower than that in 2009 (0.5-5.6%) and 2008 (0.3-4.6%), but higher than that in 2007 (0.02-2%), and 2006 (0-1.5%). Sap beetle damage ranged from 0.2-2.8% in 2010. Very low maize weevil infestation at harvest with 18% kernel moisture this year confirmed that timely harvest at maturity could be an effective management tool to reduce maize weevil infestation. The most important insects were the corn earworm and the fall armyworm, which caused the greatest kernel loss among all ear-feeding insects examined. Combined rankings of the 59 hybrids for their resistance to the major ear-feeding insects are given in the following table. The lettered ratings in the table refer only to relative resistance to insects and are not indicative of yield. Please refer to other reports for yield data.
Husk tightness and husk extension of ears were also examined in 2010. Husk tightness was assigned using a scale of 1 to 5, in which 1 = very loose and 5 = very tight. Because average rating for husk tightness was between 2.5 and 4.4, only loose (L), medium (M), and tight (T) ratings are given in the table. Husk extension was between 0 and 8.1 cm. Corn earworm damage was negatively correlated to husk tightness and husk extension in 2010. Some of the transgenic corn hybrids showed poor overall insect resistance ratings with multiple insect damage ratings (such as, corn earworm, stink bugs, and sap beetles), which could be caused by the fact that transgenic events in these hybrids only confer resistance to one species but not to all species of the ear-feeding insects.
The 17 hybrids resistant to ear-feeding insects are highly recommended for planting and are presently the most economical means, especially in late plantings, for the reduction of ear-feeding insect damage and for reduction for aflatoxin contamination. Consult with your county agent and/or extension entomologists for additional control recommendations for a specific pest in your area.
All entries were planted at the UGA Lang-Rigdon Farm on April 7, 2010 and harvested on July 29, 2010 at kernel moisture of 18%. Plots were thinned to 20,000 plants per acre. Plots were maintained and data were collected by Penny Tapp (USDA-ARS, Tifton, GA), and Blake Edore, Kimberly Goodman, Breanna Coursey, and Johnothan Roberts (University of Georgia, Tifton, Georgia).