Abstract
Roots are key organs for water and nutrient acquisition and transport. Therefore, root phenes that are associated with adaptation to low phosphorus (P) environments could enhance top-soil exploration, while deeper allocation is important for acquiring water and mobile nutrients. The understanding of interactions among root phenes can help in the development of common bean (Phaseolus vulgaris L.) genotypes adapted to drought and low fertility through genetic improvement. Two experiments (pot and field) were conducted at the Agricultural Research Institute of Mozambique to assess the contribution of root phenes to common bean shoot biomass and grain yield under combined stress (drought and low P). The pot study assessed eight genotypes, with four treatments combining water regimes (drought and non-stress) and phosphorus levels (200 and 25) mg P kg−1 soil. In the field study, 24 common bean genotypes were also grown in high and low phosphorus (40 kg P ha−1 and without P application) under irrigation and limited water. The grain yield from fields under drought and P stress were correlated with the pot data on root traits. The response of root phenes to drought and phosphorus stress appeared to be related to the deep and shallow root systems, respectively. Deep rooted genotypes produced more total root biomass and high taproot lateral branching density, which resulted in high total root length under drought and low P stress, while shallow rooted genotypes had low total root biomass and less taproot lateral branching. Increased shoot biomass and grain yield under drought and low P was associated with higher mean values of taproot lateral branching density and total taproot length. Genotypes SER 125, BFS 81, FBN12111-66 and MER 22 11-28 showed a greater score of tap root branching density in the pot study with the highest grain yield in the field under low P and drought stress. Therefore, these can be recommended for use in low phosphorus and drought stress environment or serve as parents for improving phosphorus use efficiency and drought tolerance in common bean.
Highlights
Despite its importance, the yield of common bean (Phaseolus vulgaris L.) in developing nations is currently very low: only one third of what is achievable in developed nations, where high inputs are used and irrigation is available to reduce abiotic and biotic limiting factors [1,2,3,4]
Positive and significant correlations were observed among root phenes and when correlated to shoot biomass and seed yield under combined low phosphorus and drought environment (Table 3)
No previous study has explicitly explored the utility of taproot lateral length and lateral branching for plant performance under edaphic stress, results from the present study suggest that an increased taproot lateral branching and length provide benefits under multiple environments
Summary
The yield of common bean (Phaseolus vulgaris L.) in developing nations is currently very low: only one third of what is achievable in developed nations, where high inputs are used and irrigation is available to reduce abiotic and biotic limiting factors [1,2,3,4]. While shoots have an important role in utilizing water and nutrients where these are limited, the root system is strictly responsible for the acquisition of these resources [8]. The importance of roots for adaptation to nutrient and water limitations is explained by the increases in root growth compared to shoot growth under edaphic stress [8,9], and it has been demonstrated that the root system has a significant effect on bean yield under water stress [10,11]. Root phenotypes play an important role by participating in the improvement of crop yield under edaphic stress by increasing the metabolic efficiency of soil exploration and by allocating roots in soil domains where several limiting resources are mostly available [7,13]
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