Photoperiod sensitivity of local millet and sorghum varieties in West Africa

Photoperiod has a strong impact on the development of local millet and sorghum varieties which are two of the most important staple food crops for millions of people in West Africa. Therefore, a better understanding of the response to photoperiod is needed in order to improve production and ultimately increase yield. Several studies have demonstrated the importance of the adaptive capability of local varieties, especially in coping with environmental stress conditions. The objective of this study was to determine the photoperiod sensitivity (PS) characteristics of the most common local varieties of millet and sorghum in Burkina Faso, West Africa. Planting date experiments consisting of 5 or 6 planting dates with complementary irrigation and fertilizer to avoid water and nitrogen stress effect on phenology were conducted at the experiment station of Di in northwestern Burkina Faso during the rainy seasons of 2003, 2004, 2006 and 2007. The study included 7 millet and 11 sorghum varieties from the three main agroecological zones in Burkina Faso to determine their sensitivity to photoperiod. In addition to the various key phenological parameters, panicle initiation date was measured in 2007. Therefore, thermal time from emergence to PI and photoperiod at PI could be experimentally determined. After evaluation of the relation between the PI stage and the other stages that could easily be observed, thermal time from emergence to flag leaf expansion was used to determine the date of panicle initiation (PI) as well as the photoperiod at PI for the experiments conducted from 2003 to 2006. Then, a graphical analysis was conducted to define the critical threshold photoperiod and photoperiod sensitivity for each variety. For both millet and sorghum, the photoperiod sensitivity ranged from 142 to 6184 growing degree days (GDD h−1) per hour of photoperiod extension. The critical photoperiod (Pc) ranged from a daylength of 13.00 to 13.35 h. Although these experiments were only conducted at one location, this study showed that photoperiod response is not only related to latitude, but depends also on the capability of lowlands to maintain soil moisture. There was a positive correlation between the critical photoperiod (Pc) and the latitude of origin of the local varieties and a negative correlation between photoperiod sensitivity and the latitude of origin. Further work will include the implementation of these results in crop simulation models for yield forecasting and the determination of crop management alternatives for millet and sorghum in West Africa