1. Response of Cowpea and Common Bean to Low P and Drought: Traits and Yields
ABSTRACT: Drought and low soil fertility are the major abiotic constraints to crop productivity and climate change models predict more intense environmental stresses in the semi-arid tropics.
To address these major challenges, collaborative research was conducted by IITA, CIAT and Pennsylvania State University. Cowpea and bean germplasms were phenotyped under low P and drought conditions in both greenhouse and field environments. We observed differences in their yield, shoot and root traits that are associated with adaptation to individual and combined abiotic stresses. Elite materials with traits of interest were found that could be useful in breeding programs with the aim of improving productivity of grain legumes in the face of multiple abiotic stresses.
INTRODUCTION: Cowpea and bean are important legumes cultivated by small-scale farmers in tropical regions where they face severe abiotic stresses (e.g. drought and low P). High-throughput plant phenotyping and breeding for improved high yields can be a low-input approach to enhancing the resilience of agriculture in the tropics. Significant efforts were made to breed for superior varieties and sources of tolerance to individual stresses have been reported in both species1,2. However, there is little experience with response to multiple stresses that are occurring simultaneously and causing even greater yield losses in farmers’ fields. Developing lines with multiple stress tolerance is a challenge. The main objectives were to test cowpea and common bean germplasms under both greenhouse and field conditions for their genetic variations in (i) shoot water-use related traits, (ii) growth and yield responses to low P and drought, and (iii) root system architecture (shovelomics).
RESULTS:
- Cowpea lines with shallow root system (top) & with steep root system (bottom) are the most promising for tolerance to low P and drought, respectively (Top table) .
- Plant growth and yield increase with P supply. IT89KD-288, IT97K , Danila & Iron-Bean are among the most low-P tolerant and P-use efficient cowpea lines (Bottom Fig.).
- Carioca, BFS 112 and BFS 55 had the highest grain yield under both low and high P (Top Fig. A).
- BFS 95 and 143 had the highest canopy P uptake (CPU, kg ha-1) while SER 16 and ALB 91 had the highest P-use efficiency (PUE, g g-1) under low P & moderate drought. (Top Fig. B).
- BFS 35 was the most adapted to both drought and low P and it was also superior in root hair density (RHD, visual score: 1 poor, 9 high) and root hair length (RHL, mm) (Bottom Table).
MATERIALS AND METHODS:
- Mini-core collections of cowpea were gravimetrically evaluated in pot trials in 2014/2015 at IITA-Kano to assess their genetic variation in transpiration rate (TR) and canopy temperature depression (CTD) as two key water saving traits for adaptation to terminal drought. Fifty cowpea breeding lines were tested in 2014/2015 at IITA-Ibadan in Fashola (Bray-II P: µg g-1) to evaluate their growth and yield responses to P (0 and 30 Kg P ha-1) and in 2015 at Willcox, AZ-USA for their variation in root system architecture for adaptation to low P and drought stresses.
- Thirty common bean genotypes were evaluated in 2014 in an alpha lattice design with 3 Replications at Darien-Colombia (Bray-II P: µg g-1) under 0 and 40 kg P ha-1 and deficient rainfall (157 mm) conditions. Canopy P uptake (CPU, kg ha-1), P use efficiency (PUE, g g-1), grain yield (kg ha-1), root hair density (RHD) and length (RHL) were measured. Common bean genotypes including local checks selected for yield and grain quality under 0 and 40 kg P ha-1 conditions were yield tested for drought tolerance in two field sites in Nicaragua in 2015.
Genotypic variation in plant TR (Top Fig.) and CTD (Bottom Fig.) under high VPD and WW conditions in cowpea: Lines low TR and CTD are mostly adapted to terminal drought as they save more water in the soil profile to guaranty pod and grain filling.
DISCUSSION:
- Bean lines BFS 81, 85 and 140 almost doubled grain yields of the local elite check INTA Rojo without and with 40 kg P ha-1 supply under moderate (150 mm) and severe (87 mm) drought in Nicaragia (two filed sites).
- These results validate the potential for improving productivity of grain legumes in the face of multiple stresses. We need to extend the phenotyping efforts to a wide range of germplasm including wild relatives for identification of additional sources of tolerance to abiotic and biotic stresses.
REFERENCES:
1. Beebe S.E., Rao I.M., Blair M.W.,A costa-Gallegos J.A., Phenotyping common beans for adaptation to drought. Front. Physiol. 4: 1-20.
2. Belko N., Cisse N., Zombre G., Thiaw S., Muranaka S., Diop N.N., Ehlers J.D., Selection for post-flowering drought resistance in short and medium duration cowpeas using stress tolerance indices. Crop Sci. 54_25-33.
Leveraging legumes to combat poverty, hunger, malnutrition and environmental degradation
Nouhoun Belko1*, Kanako Suzuki2, Jimmy Burridge3, Noel Duarte4, Jaumer Ricaurte5, Idupulapati Rao5, Jonathan Lynch3, Christian Fatokun2, Ousmane Boukar1, Stephen Beebe5
1IITA Kano Station, Nigeria; 2IITA-HQ Ibadan, Nigeria; 3Penn State University, USA;
4INTA, Nicaragua; 5CIAT Cali, Colombia.