Mechanisms of adaptation of low soil phosphorus tolerant common beans to water deficit

Abstract

ABSTRACT

Water deficit due to unreliable rainwater supply and soil phosphorus deficiency are by far the most prevalent abiotic stresses limiting common bean production in sub-Saharan Africa. Intervention into these factors is increasingly through the use of tolerant varieties, as an alternative to costly input use such as irrigation and fertilisers. This study therefore, assessed the low soil P tolerant common bean genotypes of morphological and physiological responses as adaptation mechanisms to water deficit conditions in both controlled and field environments. In the controlled environment, treatments included three bean genotypes, namely AFR703-1 and AFR708 (low soil P tolerant), and K131 (check); two water levels, namely water deficit and well-watered as the control; and three levels of phosphorus (0, 6 and 16 mg P kg-1 of soil). Treatments were laid out in a completely randomised design. A field study was also carried out at two sites in central Uganda, namely the Mukono Zonal Agricultural Research and Development Institute in Mukono District considered as wellwatered environment and at Wabinyonyi in Nakasongola considered as the water deficit environment. Phosphorus was applied as triple superphosphate (TSP) at rates of 0, 12 and 32 kg P ha-1, while the two test materials used in the controlled environment were also used in the field experiment on top of JESCA, and MCM2001 genotypes. Treatments were laid out in a randomised complete block design with three replications. The adaptive mechanisms associated with water deficit and low soil P tolerance in the studied genotypes, especially the AFR genotypes; include specific leaf area (SLA), shortening of the physiological activities and root development. However, the gains achieved towards tolerance to both water deficit and low P by the test genotypes are not translated into corresponding grain yield gains.