Traditional handling of plant genetic resources condenses most aspects of adaptation to climatic variability in subsistence agriculture and is known to contribute fundamentally to the development of sound production systems (WMO 2003). It is today slated for intense, conflicting questioning at the nexus of agricultural intensification processes, intervention policies and advances in biotechnology - before development and growth of agricultural income allow for a wider spectrum of response farming options. In continental West Africa, photoperiod (PP) sensitivity is required to best fit crop cycle to the probable duration of the season and is one example of the critical ingredients of environmental adaptation. It allows for grouped flowering at the end of the rainy season for a wide range of planting dates (Traoré et al. 2000) and is present in staple cereals (Mahalakshmi and Bidinger 1985) and other crops (Brink et al. 2000) with some of the highest recorded sensitivity levels worldwide. It helps minimize grain mold, insect and bird damage that affect early maturing varieties, and avoid incomplete grain filling, a problem for late maturing varieties faced with water shortage at the end of season (Cochemé and Franquin 1967; Curtis 1968; Kassam and Andrews 1975). Tillering is yet another example of unique adaptation trait, controlling the partitioning of biomass across plant organs.
It is tempting to make a parallel between contrasting levels of climate predictability and apparently marked differences in PP sensitivities observed between crops of West Africa and Southern Africa. It could be hypothesized that higher predictability of the length of growing period (LGP) in Southern Africa would favor the selection of a number of fixed maturity groups, best suited to the expected duration of the cropping season. Conversely, uncertainty associated with LGP in continental West Africa would logically tend to eliminate PP-insensitive material. Further investigation will show whether landrace PP sensitivity can be trusted as a good indicator of climate unpredictability.
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