Selection Improves Drought Tolerance in Tropical Maize Populations: II. Direct and Correlated Responses among Secondary Traits
1999
Chapman, S.C. | Edmeades, G.O.
Recurrent selection for drought tolerance for three to eight cycles has increased grain yield (GY) under drought at flowering by 30 to 50% in three lowland tropical maize (Zea mays L.) populations. The relationships among secondary traits as a result of this selection have not been determined, however. The objectives of this study were to measure direct and correlated changes due to selection in secondary traits by evaluating cycles of selection and appropriate check entries at five water-stressed (mean yield 2.35, range 1.01–4.48 Mg ha⁻¹) and five well-watered environments (mean yield 7.96, range 5.81–10.40 Mg ha⁻¹). Under drought, changes per cycle with recurrent S₁ selection (P < 0.05) were as follows: GY 12.6%, fertile ears per plant (EPP) 8.9%, grains per fertile ear (GPE) 6.3%, grain number per square meter 12.2%, 1000 grain weight no change, anthesis-silking interval (ASI) −22.0%, days from sowing to 50% anthesis −0.7%, plant height −2.0%, primary tassel branch number −5.9%, and senesced leaf area 2.7%. Responses under well-watered conditions were smaller but generally of the same sign. Grain yield was strongly associated with grain number per square meter in both water-stressed and well-watered environments (r = 0. 96; r = 0.87; P < 0.001) Grain yield, EPP, and GPE were strongly correlated with ASI across entries under drought (r = −0.89, −0.93, −0.90; P < 0.001), though not when water was plentiful. The use of managed stress environments that consistently reveal genetic variation for these traits at specific times during crop development is endorsed for selection purposes.
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