Assessing damage by second-generation southwestern corn borer and sugarcane borer and development of sources of resistance in tropical and subtropical maize
1997
Kumar, H. | Mihm, J.A.
In 1992, having achieved adequate levels of resistance to first-generation (whorl stage attack) Diatraea spp. borers, Population 391 was formed to attempt to identify sources of resistance to second-generation (post anthesis stage) attack The ultimate objective is to develop complete cycle (planting to harvest) resistance to the two most important stem borer species that attack maize in the American subtropical and tropical growing areas. Plants were infested at anthesis +/- 1 week with Sugarcane borer (SCB), Diatraea saccharalis Fabricius, at Poza Rica (ClMMYT's tropical lowland station) or Southwestern Corn Borer (SWCB), Diatraea grandiosella Dyar, at Tlaltizapan (ClMMYT's subtropical station) in the ear zone (Ear leaf, one leaf above and below the ear) with 60-65 larvae larvae per plant. Selection was carried out over the next three cycles using one or several criteria (ear damage, sheath damage, stalk damage - indicated by the number of internodes tunneled) and compared and correlated with data from sub-samples rated for sheath and husk damage. For SCB in tropical environments, there was a marked and obvious preference for the larvae to attack the developing ears. The correlations between sheath damage and stalk damage were not significant, but those between ear damage and stalk damage were significant. However, the relationships were highly genotype specific. For SWCB, in subtropical environments, damage directly to the ears, sheath and husks was not so striking, so selection was based on stalk damage. The best lines were recombined at S3 levels, and the second cycle of S1 recurrent selection has begun, while the elite fraction is now available as S4 lines for further testing. Our data show sufficient variability to forest all concluding that there is a single best method to select for multiple species, second-generation resistance in tropical maize.
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