GENETIC IMPROVEMENT OF MAIZE AND PEARL MILLET FOR RESISTANCE TO INSECTS AND AFLATOXIN
Location: Crop Genetics and Breeding Research
Title: Evaluation of insect resistance among 47 commercial corn hybrids
Submitted to: Corn Performance Tests
Publication Type: Experiment Station
Publication Acceptance Date: October 8, 2008
Publication Date: November 1, 2008
Citation: Ni, X., Wilson, J.P., Scully, B.T., Buntin, G. 2008. Evaluation of insect resistance among 47 commercial corn hybrids. In: A.E. Coy, J.L. Day, and J. Gasasett (eds.), Georgia 2008 Corn Performance Tests, Research Report 717, pp. 34-37, Georgia Agricultural Experiment Stations, Athens, GA.
Interpretive Summary: not required
In 2008, 65 commercial hybrids were examined for insect resistance at Tifton, Georgia. Fifteen of the 65 hybrids were new hybrids developed using new technology (named YieldGard VecTran Triple, abbreviated as VT or VT3), which allows the stack of multiple traits for stalk protection, root protection and weed control in one transformation event. We have had a relatively dry corn growing season in 2008 which were favorable for the rapid buildup of all insect populations in the irrigated experimental plots. Seven ear-feeding insects recorded as ear and kernel-feeding insect pests. They are in the order of infestation severity: the corn earworm and the fall armyworm, the southern green and brown stink bugs, the pink scavenger caterpillar and the sap beetles, and the maize weevil. Disease surveys around flowering time showed that smut, southern rust, and southern and northern blight infections were not a concern this year for all these hybrids. All entries were planted on April 4, and harvested in the week of September 2, 2008. Plots were thinned to 20,000 plants per acre.
Total insect damage rating was based on ear-feeding insect (i.e., corn earworm and fall armyworm) damage rating and percentage of damaged kernels caused by the stink bugs, the pink scavenger caterpillar and the sap beetles, and the maize weevil. Overall insect resistance rating used five categories; they were very good (VG), good (G), fair (F), poor (P), and very poor (VP) as shown in the table on next page. While VG represents the lowest amount of insect damage, VP represents the greatest amount of insect damage. Losses to maize weevil, pink scavenger caterpillar and sap beetles were based on damage by multiple generations of these insects as the crop matures in the field. Corn earworm and fall armyworm damage was combined because the damage was hard to be separated; pink scavenger and sap beetle damage also was evaluated together. Corn earworm and fall armyworm feeding penetration in corn ears on the 65 hybrids was between 1.6 and 6.4 cm, which was higher than what we observed in 2007 (0.7 - 3.7 cm). It is worth noting that stink bug damage in 2008 (0.3-4.6% of discolored kernels) was higher than in either 2006 (0-1.5%) or 2007 (0.02-2%). Other insect damage was also higher in 2008 than in the previous two years. Pink scavenger caterpillar and sap beetle damage was 0.4-7.6% in 2008 compared to 0.1-2.6% in 2007, and 0.1-3.2% in 2006, and maize weevil damage was 0.04-3.8% in 2008, compared to 0.1-0.8% in 2007, and 0-0.6% in 2006. The most significant insect damage was still corn earworm and fall armyworm feeding on developing cobs, although increases in other insect damage were recorded. Only 2 of 15 new transgenic hybrids developed with VT or VT3 showed very good insect resistance, while 5 hybrids showed poor or very poor insect damage ratings. The findings suggested insect resistance expressions might vary among the hybrids. Timely harvest can substantially reduce losses caused by these two insects. Rankings of the 65 hybrids for their resistance to the major ear-and kernel-feeding insects (i.e., corn earworm and fall armyworm, pink scavenger caterpillar and sap beetles, maize weevil, and stink bugs) 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 the yield data in other tests for specific information.
During the damage evaluation in 2008, two physical features (i.e., husk tightness and husk extension) of corn ears were examined. 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 ranged between 3.8 and 4.6, the ratings were further categorized into three categories as loose (L), medium (M), and tight (T). Husk extension was shorter compared to previous years, ranging between 1.2 and 7.3 cm. The insect damage was not correlated to either of the husk features according to the data collected in 2008. Hybrids resistant to 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. Consult your local county agent and/or extension entomologists for additional control recommendations for a specific insect pest in your region.
Data for this report were collected by J. C. Mullis (USDA-ARS, Tifton, GA), Benjamin Berry, Justin Colbert, Cody Mauldin, and Austin Thompson (University of Georgia, Tifton, Georgia).