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Annual Report: CIRAD 2007

A new model to explain photoperiodism in African sorghum

Photoperiod sensitivity is a key adaptation of annual crop species in tropical regions. By this mechanism, their growth cycle can be tailored to climatic constraints, especially rainfall. The flowering date may thus be adapted to and independent of the sowing date, thus enabling the plants to avoid water stress at the end of the cycle along with biotic constraints. A new model that accounts for this mechanism has been developed within the framework of PhD thesis research at CIRAD.

Photoperiod-sensitive sorghum varieties (generally large) have a small panicle © M. Vaksmann/Cirad

Many studies have focused on the complexity of the photoperiod sensitivity of sorghum, but none of them has given rise to the development of a single model that could explain this species’ phenological plasticity and diversity. A recent study carried out at CIRAD led to the development of an innovative model called Impatience. The underlying concept is inspired from animal behaviour science—when there is an extended wait for a “good” environmental signal, the plant gradually lowers its day length requirements to trigger flowering. This very simple model has been successfully validated for a range of genotypes.

The model has already been implemented for genetic research, in addition to agricultural and ecological applications. In genetics, a plant phenotyping method was developed using this model to parameterize the sensitivity of varieties to the genotypic photoperiod. This plant characterization approach is of interest for molecular genetics studies, via quantitative trait loci (QTLs) or marker-assisted mapping, and thus for breeding genotypes adapted to specific climatic environments. The Impatience model has also been incorporated in the SarraH plant growth simulation model for agroecological applications. The resulting tool can be implemented to identify optimal areas for varietal adaptation by matching their photoperiodic responses to rainy season duration patterns in West Africa. Moreover, it can be used to analyse the flexibility of cropping calendars according to the site and genotype, and to determine the yield potential and interannual variations.

This research has been underpinned by two complementary studies. The first aims to determine aspects of the agrobiodiversity of African sorghum varieties with respect to different environmental constraints. The second involves an analysis of crop yield build-up according to ideotypes favoured by breeding. The goal is especially to breed varieties that combine a specific photoperiod response profile and an improved harvest index so that the plants will be better adapted to climatic variations and givehigher yields.

Due to their unique growth development patterns, photoperiod-sensitive sorghum varieties (generally large-sized) have a small panicle, which results in a low harvest index and poorer yield. Different but related sorghum varieties were compared and the results revealed that photoperiodism associated with a reduction in plant size and late leaf senescence led to a better assimilate distribution, thus boosting the harvest index while also markedly increasing crop yields and their stability. Studies are under way to validate these results with a more substantial dataset. If they confirm the initial trends, the foundations could be laid for a green revolution through breeding of new highly adaptable varieties to replace photoperiod-insensitive varieties that have not fulfilled farmers’ needsin African savannah regions.

Contact

Michael Dingkuhn, E-mail
Genotype Plasticity and Crop Performance (UPR),

Partners

  • International Crop Research Institute for the Semi-Arid Tropics (ICRISAT, Mali)
  • Institut d’économie rurale (IER, Mali)

For further information

  • Dingkuhn M., Kouressy M., Vaksmann M., Clerget B., Chantereau J., 2008. A model of sorghum photoperiodism using the concept of threshold-lowering during prolonged appetence. European Journal of Agronomy, 28 : 74-89 (doi:10.1016/j.eja.2007.05.005).
  • Kouressy M., 2007. Adaptation agroécologique et potentialités des sorghos photopériodiques à paille courte au Mali. Thèse de doctorat, université Montpellier II, 161 p.
  • Kouressy M., Dingkuhn M., Vaksmann M., Clément-Vidal A., Chantereau J., 2008. Potential contribution of dwarf and leaf longevity traits to yield improvement in photoperiod sensitive sorghum. European Journal of Agronomy (doi:10.1016/j.eja.2007.07.008).
  • Kouressy M., Dingkuhn M., Vaksmann M., Heinemann A.B., 2007. Adaptation to diverse semi-arid environments of sorghum genotypes having different plant type and sensitivity to photoperiod. Agricultural and Forest Meteorology (doi:10.1016/j.agrformet.2007.09.009).