Mining Genes from Tropical Maize Germplasm To Improve Drought Tolerance and Corn Earworm Resistance

1
Mining Genes from Tropical Maize Germplasm To
Improve Drought Tolerance and Corn Earworm
Resistance  Wenwei Xu1 and Mike Blanco2 1
Agricultural Research and Extension Center, Texas
AM University, Route 3, Box 219, Lubbock, TX
79403, USA 2 USDA-ARS/Plant Introduction, G212
Agronomy Hall, Iowa State University, Ames, IA
50011, USA

• Introduction
• Drought and corn earworm (Helicoverpa zea) cause
  severe yield losses in maize in the world. Corn
  earworm (CEW) feeding also increases mycotoxin
  production (Edmeades et al., 1992 McMillian et
  al., 1987 Wiseman and Morrison, 1981).
  Improving drought tolerance and host-plant
  resistance is crucial to minimizing yield
  reduction, grain quality loss and irrigation
  costs.
• Tropical maize germplasm offers a vast and
  diverse gene pool, yet, it has not been widely
  used in the U.S. (Goodman, 1985). More emphasis
  in breeding tropical germplasm is evident in the
  Germplasm Enhancement of Maize (GEM) project, a
  cooperative effort among the U.S. Department of
  Agriculture, U.S. universities, and seed
  industry. Its goal is to widen the diversity of
  U.S. maize germplasm base through introgression
  of exotic germplasm (Pollak and Salhuana, 1999).
• Objective
• To identify new sources of drought tolerance and
  CEW resistance from GEM germplasm.
• Materials and Methods
• Three check hybrids and 71 GEM breeding crosses
  with 25-50 tropical background were used.
  Plants were grown in Lubbock, TX under irrigated
  and two drought conditions in the same field in
  two years.

Table 3. Days to pollinating (DTP), CEW
penetration (CEW), yield under well-irrigation
(Yield 1) and drought conditions (Yield 2), and
stay green ratings (SG) of top 15
crosses. Entry DTP CEW Yield 1 Yield 2
SG days cm kg/ha kg/ha 1-5 ANTIG03N12 7
4 4.8 9573 3591 2.9 UR11002N0308b 71 6.7
8686 4309 3.9 AR16026N12 70 8.0 8202
4445 3.8 ANTIG01N16 77 5.4 9177
3694 3.6 BG070404D27 83 4.0 8226
2075 2.6 PRICGP3N1218 74 8.0 9202
2893 2.8 CUBA84D27 82 5.0 8721
1569 2.3 CUBA164D27 82 5.7 8509
2196 2.5 ANTIG03N1216 73 7.2 8432
3852 3.8 CH05015N1204 69 9.4 8026
3744 3.8 PRICGP3N1211c 73 6.9 8303
3379 3.6 BR51501N11a 76 4.6 7489
2782 3.0 BR51403N16 78 6.2 8821
2288 3.0 BR51675N0620 71 9.1 8013
3837 3.7 GUAD05N06 75 6.3 7631
3238 3.7 B73xMo17 (ck1) 73 9.3 5597
2542 4.3 P34K77 (ck2) 69 6.4 8806
4025 4.1 P3223 (ck3) 76 6.3 10684
4988 3.2 Test Mean 73 7.5 6713
2632 3.5 LSD 0.05 3 2.0 2105
1019 0.5 Conclusion Under three water regimes,
15 GEM breeding crosses exhibited good yield
potential, earworm resistance, stay green rating,
grain mold resistance, long ear, early maturity,
tall plant, upright leaves, or good husk coverage
or a combination of these characters. The best
cross was ANTIG03N12. Acknowledgements Financial
support from the Texas Corn Producers Board, the
High Plains Underground Water District No.1, and
USDA-ARS GEM project is appreciated.
Table 2. Correlation among days to pollinating
(DTP), plant height (PHT), stay green rating
(SG), corn earworm penetrating (CEW), ear length
(EARL), percent of molded grains (Mold) and yield
under well-irrigated condition. PHT
CEW EARL Mold Yield  DTP
0.78 -0.53 0.14 -0.35 0.02 PHT
-0.53 0.44 -0.46 0.29  CEW 0.06
0.68 -0.48 EARL -0.27
0.48 Yield and Stay Green under Severe Drought
Stress Conditions Drought increased barren
plants, induced early onset of plant senescence,
and reduced grain yield. Several GEM crosses
were similar to checks in yield but significantly
better in stay green trait. Table 3 shows top 15
breeding crosses based on insect resistance,
yield, maturity, and drought tolerance. ANT
IG03N12 yielded well under three water regimes
and had good CEW resistance, low grain mold, good
stay green trait, upright leaves, and tight
husk. References Edmeades, G.O., et al., 1992.
Proc. 47th Ann. Corn and Sorg. Ind. Res. Conf.
ASTA, Washington. Goodman, M.J. 1985. Iowa State
J. of Res. 59497-527. McMillian, W.W., et al.,
1987. J. Entomol. Sci. 22307-310. Pollak, L. and
W. Salhuana. 1999. Ann. Corn and Sorg. Industry
Res. Conf. 53143-158. Wiseman, B.R. and W.P.
Morrison. 1981. Agric. Rev. Man. ARM-S U.S. Dep.
Agric. Res. Serv. Res. South. Res., 18 pp. Xu,
W., L. Pollak, and E.D. Bynum. 2003. Crop Prot.
22859-864.

• Each test used a randomized complete block
  design with three replications. Seeds were sown
  on 18 April 2002. Plot size 4.6 m x 1 m single
  row.
• All tests were irrigated before emergence to
  ensure good germination and stand establishment.
• Water was supplied by a subsurface
  drip-irrigation system. Drought was imposed at
  tasseling stage.
• Three water regimes
• Water regimes Total water (mm/ha)
• Well-irrigation 1029
• Drought stress 1 326
• Drought stress 2 439
• Rainfall
• January to August 218 mm
• Planting to mature 174 mm.
• Stay green rating was scored
• on a 1 to 5 scale with 1 100
• green leaf areas and 5 0
• green leaf area. It was scored
• three times as the stay green trait progressed.
• After maturity, 10 primary ears
• per plot were collected from
• consecutive plants. Ear