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a ENSA, 2 Place Viala, 34060 MONTPELLIER Cedex, France
b CIMMYT, P.O. Box 6-641, 06600 Mexico D.F., Mexico
c 52A Williams Street, Cambridge, New Zealand
* Corresponding author (pmonneveux{at}yahoo.fr)
The objectives of this study were to evaluate direct and correlated responses to recurrent selection for drought tolerance in two CIMMYT maize (Zea mays L.) source germplasm populations, DTP1 and DTP2, adapted to the lowland and mid-altitude tropics. Selection was primarily based on grain yield, ears per plant, anthesis-silking interval, and leaf senescence under drought. Cycles C0, C3, and C6 of DTP1 and C0, C3, C5 and C9 of DTP2 were evaluated under drought, low N, and optimal conditions. In both populations, significant yield gains were observed under drought conditions, associated with a significant increase in numbers of ears per plant and grains per ear, and significant reductions in anthesis-silking interval, ovule number and abortion rate during grain filling. Abortion rate was positively correlated with the number of ovules at silking and with anthesis-silking interval. In DTP1, recurrent selection under drought was associated with a derease of tassel and stem dry weight and with an increase of ear dry weight and harvest index. This study confirms the effectiveness of recurrent selection under drought as a means of improving tropical maize source populations for performance under water deficits and to a lesser extent under low N. The primary mechanism underlying these changes appears to be improved partitioning of assimilates to the ear at flowering, at the expense of tassel and stem growth.
Abbreviations: ASI, anthesis-silking interval C, carbon CIMMYT, Centro Internacional de Mejoramiento de Maíz y Trigo DA, days to anthesis DS, days to silking DTP-W, drought tolerant population-white DTP-Y, drought tolerant population yellow DTP1, drought tolerant population 1 DTP2, drought tolerant population 2 N, nitrogen PAR, photosynthetically active radiation PH, plant height.
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