Photothermal responses of Oryza sativa and O. glaberrima varieties and interspecific progenies from West Africa

Rice is an increasingly important cereal in West Africa, where it is grown in a wide range of hydrological conditions in high rainfall, humid forest to low rainfall, savanna agro-ecological zones. In order to identify cultivars that are well adapted to these diverse environments, and the traits that are needed in new cultivars to ensure adaptation, the effects of photoperiod and temperature on duration from emergence to flowering (f) need to be quantified. The objectives of this study were: to phenotype duration to flowering of a diverse set of rice cultivars representing types grown in West Africa using data from carefully selected photothermal controlled environments (CEs); to examine how basic vegetative phase (BVP) and photoperiod-sensitivity varied among the different species and ecotypes; and to assess the usefulness of this simplified approach for characterising genotypes and lines for plant breeding and association and functional genomics. Twenty-two genotypes of rice representing the diversity found in West Africa, and including Oryza sativa indica and japonica, Oryza glaberrima and O. sativa×O. glaberrima progenies, were grown in a controlled environment (CE) under flooded (lowland) and free-drained (upland) hydrologies at 11 and 13 h photoperiods combined with mean temperatures of 22 and 28 °C. A simple model describing f in terms of a BVP, photoperiod-sensitive phase (PSP) and post-PSP was used to analyse variation in f. Hydrology had no effect on f but did affect plant height in some genotypes. Flowering occurred earliest in the 11 h photoperiod regimes (between 41 and 87 days after emergence (DAE)) and latest at 13 h/22°C (between 68 and >150 days). The earliest genotypes to flower were all O. glaberrima and these all had a very short BVP (mean 276°C days: Tb=10°C) but were strongly photoperiod-sensitive (mean PSP 364°C days h-1). In contrast traditional O. sativa japonica cultivars were all late flowering due to a long BVP (mean 1006°C days) and strong photoperiod-sensitivity (mean 342°C days h-1). Improved japonicas, indicas and O. sativa×O. glaberrima progenies all had shorter BVPs (447-662°C days) than traditional japonicas. Photoperiod-sensitivity was also less in the progenies and improved japonicas (about 200°C days h-1). There were good correlations between values for BVP and PSP estimated in CE and the field (r=0.86 and 0.68, respectively). We conclude that diverse genotypes can be successfully phenotyped for f using a simple model and three or four carefully chosen photoperiod and temperature regimes in a CE facility. © 2003 Elsevier Science B.V. All rights reserved