After soil fertility, drought is the major abiotic stress limiting maize production in the tropics, and is the most important source of variation in yield over time. Eight cycles of recurrent full-sib (FS) selection or up to four cycles of recurrent S1 selection were practiced on one early-maturing and three late-maturing maize populations adapted to the tropical lowlands. By controlling irrigation in an otherwise dry season, drought stress was applied at flowering and during grain filling. Well-watered nurseries were used to ensure that yield potential was maintained. Selection was for an index of traits that sought to: increase grain yield, reduce anthesis-silking interval (ASI), reduce barrenness, delay senescence, reduce tassel size and increase leaf angle while leaving male flowering date unaltered. Traits related to yield and flowering behavior received the greatest weighting. Gains ranged from 80-108 (mean 94) kg ha-1 yr-1 under FS selection, and from 73-144 (mean 111) kg ha-1 yr-1 under Sl recurrent selection, when selections were evaluated at a yield level of 1.5-2.4 t ha-1 (annual gains >5%). Under well-watered conditions (5.6-8.0 t ha-1), gains were from 38-108 (mean 73) kg ha-1 yr-1 from FS and from 27-89 (mean 59) kg ha-1 yr-1 from S1 selection. Yield increases were associated strongly with reduced ASI, reduced barrenness and increased harvest index; mildly with delayed leaf senescence and reduced tassel size; and not at all with changes in leaf angle. Biomass production under all conditions and plant water status under drought were unaffected by selection. Reductions in ASI were associated with faster ear growth rates, suggesting an increased partitioning of assimilates to the growing ear. Floret number has declined with selection, but in one population mean floret size at 50% anthesis doubled. This was associated with a marked increase in floret survival under stress. We conclude that it is possible through selection to increase grain yields under severe drought stress (mean yield of 2 t ha-1) by 25-40%, while at the same time increasing yield potential by around 5-10%. The key to success is carefully managed drought stress coinciding with flowering and the choice of elite germplasm, followed by selection for grain yield, ears per plant, ASI, staygreen and a constant anthesis date. Acknowledgement: Parts of the contents of this paper have been presented in various forms elsewhere (Edmeades et al., 1992, 1993, 1997a, b).

Research and Partnership Program

English

9802|AGRIS 9702|anterior|R97-98PROCE|FINAL9798

Jose Juan Caballero

INT1888

CIMMYT Publications Collection