| Summary: | Five experiments were conducted to investigate the effect of drought and high temperature stress on the growth and development of bambara groundnut (Vigna subterranea (L.) Verdc). Three glasshouse experiments were conducted at the University of Nottingham, Sutton Bonington Campus, UK, and two field experiments were conducted at the Botswana College of Agriculture, Gaborone, Botswana. In the glasshouse experiments, two landraces were grown, S19-3 (from hot, dry environment/ Namibia) and Uniswa Red (from cool, wet environment/ Swaziland) under two different temperatures, 33±5 oC and 23±5 oC. In the first experiment (2006), soil moisture was non-limiting. In the second experiment (2007) drought was imposed at pod filling stage (77 DAS). In the third experiment (2008), the same two landraces were grown under the same temperatures, but the drought was imposed at flowering (30 DAS). In the first field experiment, two landraces were grown under three sowing dates and two water regimes; rain fed and drought. The two landraces were Dip C (from hot, dry environment/ Botswana) and Uniswa Red. Drought was imposed approximately at pod filling (63 DAS). In the second field experiment, the same landraces were grown under the same sowing dates and water regimes with drought imposed at 30 DAS. Canopy development and growth were affected by temperature and water stress. In the glasshouse experiments, Uniswa Red always gave the highest leaf number at the high temperature and S19-3 had the lowest at the low temperature. Leaf number decreased with drought, it reached over 100 in the full irrigation treatment, and less than 100 in late season drought treatment and a maximum of 60 in the early season drought treatment. Crops grown under high temperature always had higher leaf area index and total dry matter. The highest yield (306 gm-2) was produced by S19-3 at 33°C in 2007 and the lowest (31.1 g m-2) by Uniswa Red at 33°C in 2008. Comparison of regressions showed no significant difference in water use efficiency (WUE) between treatments in 2007. However, there were significant differences in 2008 when S19-3 (1.80 g kg-1) had a greater WUE than Uniswa-Red (1.09 g kg-1) at the high temperature, but both landraces had similar WUE at the low temperature (S19-3 2.28 g kg-1, Uniswa Red 2.23 g kg-1). This indicates that, despite being from a hot, dry environment, S19-3 performs well at the low temperature, and this is supported by data from 2007 when S19-3 maintained the highest soil moisture content and the lowest evapotranspiration at the low temperature. For the field experiments, where the temperature decreased with delay in sowing, there was a reduction in development, growth and yield. The effect of sowing date on leaf number was significant in both field experiments. In the first field experiment, the four treatments mean of leaf number of leaves declined from 62 per plant in the first sowing date (D1) to 52 leaves per plant in the third sowing date (D3) and 46 leaves per plant in the fifth sowing date (D5) and it was 64, 52, and 37 for D1, D3, and D5 respectively in the second field experiment. WUE decreased with delay in sowing from average of 1.9 g kg-1 in D1 to average of 0.45 g kg-1 in D5. The landraces varied in their response to temperature and drought stress with respect to growth, development and resource capture and conversion. The landraces used different mechanisms to resist drought and temperature stress, that include high leaf water content, reduction in leaf area to reduce transpiration surface and avoidance through faster growth rate.
|
|---|
