Matching crops and environments : quantifying photothermal influences on reproductive development in bambara groundnut (Vigna subterranea (L.) Verdc.)

The extent to which crops are adapted to specific environments greatly depends on how their development is affected by climatic factors. Development in bambara groundnut ( Vigna subterranea (L.) Verdc.) is known to be influenced by temperature and photoperiod. The objective of this study was to quantify the influence of these factors on reproductive development in selections from different origins.

Models relating development rates to photoperiod and temperature with linear equations were made for different bambara groundnut selections on the basis of research in semi-controlled environments. The photoperiod and temperature responses could be explained very well by the photothermal conditions in the regions where the selections were obtained. Validation of the models with the results of glasshouse and field experiments showed good to reasonable agreement between observed and predicted times to flowering and podding.

It is shown that the average photoperiod between flowering and podding determines the rate from flowering to podding, and that a gradual increase or decrease in photoperiod does not affect that rate. This means that photothermal models intended to predict bambara groundnut development in field situations with fluctuating photoperiods can be based on studies with constant photoperiods. It is also shown that growth and development in bambara groundnut are largely independent and that there are no strong direct photoperiod effects on dry matter partitioning.

The usefulness of photothermal development models for identifying suitable selections for different locations and sowing dates is demonstrated in a simulation study for Botswana. It is concluded that the influence of photoperiod and temperature on bambara groundnut development can be quantified through descriptive linear models, using data from semi-controlled environment experiments with constant temperatures and photoperiods. These quantitative models, either on their own or incorporated into a crop growth model, can be useful instruments for matching bambara groundnut genotypes and specific environments.