The morpho-physiological effect of drought and drought QTL analysis on Bambara Groundnut (Vigna Subterranean (L) Verdc)

Global warming threatens global food production with rising temperatures and increasing periods of drought. Bambara groundnut with its relatively high percentage of seed protein and its ability to produce some yield where other crops fail seems to fit the characteristics of an alternative crop for the future. Although Bambara groundnut is said to be drought tolerant and is more resilient than many other crops, few studies have been carried out on this crop in comparison to other crops, especially in terms of drought tolerance. The aim of the study is to evaluate the different genotypes and a segregating population under drought and perform QTL analysis of agronomic and drought related traits for the mapped populations. A field experiment was conducted at Crop for the Future Research Centre (Field Research Centre) in Malaysia from January 2016 to May 2016 to evaluate two genotypes from dry (S19-3 and DipC) and two from wet (Uniswa Red and Gresik) countries. The plants were harvested starting from 120 DAS due to rain daily starting from 110 DAS which could damage the pods. In this experiment, S19-3 recorded the highest seed yield (Irrigated=10.26g/plant, Rainfed=10.03g/plant) in both treatments as it has completed its lifecycle (>100 days) whereas the other genotypes were still in pod filling stage. Under water stressed conditions, the crops complete their lifecycle earlier which may explain the higher number of seeds in DipC and Uniswa Red under rainfed conditions (DipC: Irrigated= 3.07g/plant, Rainfed= 5.30g/plant; Uniswa Red: Irrigated= 2.89g/plant, Rainfed= 7.53g/plant). The result from this experiment gives an insight into the suitable genotypes to be considered when planting the crop in Malaysia under rainfed conditions. The second experiment was set up in a controlled environment glasshouse at the Future Crop Glasshouses, Sutton Bonington Campus, the University of Nottingham, UK. 105 F3 lines from a segregating population derived from the cross between IITA (maternal) and LunT (paternal) was evaluated in a Randomised Complete Block Design with three replicates. For the droughted plot, irrigation was terminated for five weeks at 56 DAS, after 50% flowering was observed across all the lines. Irrigation was resumed at 91 DAS and the ability of the plant to recover was observed. The total soil moisture content based on PR2 readings during the drought treatment was reduced by an average of 22.3% and the mean value for stomatal conductance reduced from 150.45 mmol m-2 s-1 at 62 DAS to 48.6 mmol m-2 s-1 at 90 DAS. When observed, the plants were wilted, and leaves were drying off indicating severe water stress. As drought was introduced at 50% flowering, the pod filling stage was affected by drought stress. Pod number, pod weight, no of seed, seed weight, and harvest index were reduced significantly in the drought treatment of the F3 population. Rewatering at 91 DAS resulted in significant increases in both stomatal conductance and SPAD readings and it continued to increase until 104 DAS. A group of 682 markers were subjected to linkage analysis. A genetic map comprised of 161 markers with an average spacing of 9.0 cM covering 1447.8 cM was constructed for the IITA x LunT F2 population for QTL analysis. Morphological and physiological differences observed within the F3 segregating population in the glasshouse experiment provided trait data for a QTL analysis. The Interval Mapping (IM) results produced a total of 23 QTLs for drought and 15 QTLs for irrigated, with 5 significant QTLs and 33 putative QTLs, associated with 14 studied traits including double-seeded pods, biomass, shelling percentage, stomatal conductance, SPAD readings, leaf width, seed length, days to podding, days to flowering, pod width, pod length, seed width, seed length, single seed weight distributed over 9 linkage groups: LG1, LG2, LG3, LG4, LG5, LG6, LG7, LG9 and LG10. Overlapping QTLs were found on LG 3, LG 4, LG 7 and LG 9. The results from this study will help to further evaluate and understand the drought responses in Bambara groundnut which could be an important for agricultural biodiversity and food security challenge