Responses of Nodulation and Grain Yield to Fertilization with Phosphorus (P) of Outstanding Low P Tolerant Phaseolus vulgaris L. Genotypes in Highly Acidic and Phosphorus Deficient Soils Such of Rwanda

Promoting the use of low phosphorus (P) and acidity tolerant bean genotypes in highly acidic and low P soils is a long term cost-effective strategy to increase bean production in sub-Saharan countries. Moreover, the performance of beans under the widespread soil related stresses like acidic and P deficient is not well documented. Thus, pot experiments were established in greenhouses in Rubona, Rwanda. Each pot was filled with 5 kg of highly acidic and P deficient soil collected from Nyamagabe district. The objective of the experiment was to identify superior grain yielding and nodulating bean genotypes suitable for such acidic and P deficient soils and their response to P inputs. Four low P tolerant genotypes used (G 2858, RWR 1873, RWV 1668; and RWV 1348) and 59/1-2 (local check) were subjected to three levels of P (0, 5, 10 mg kg-1) and treatments were laid in completely randomized design with 6 replications. The climbing genotype RWV 1348 had the highest grain yield (22.9 g pot-1), followed by two bush genotypes RWR 1873 and RWV 1668 with the same grain yield of 14.7 g pot-1, while the local check (climbing) and GR 2548 (climbing) had low grain yield. Nodulation efficiency was 73, 54, 50% for RWR 1873, RWV 1348 and RWV 1668 respectively. Again, the local check and GR2548 had low effective nodulation (19 and 31% respectively). The input of P at 5 mg kg-1 soil increased grain yield of RWV 1348, RWR 1873 and RWV 1668 at 17, 21, and 33% respectively. On the other hand, doubling this rate has declined the yield of all genotypes. Genotype RWV 1348, a climber, is the best outstanding low P tolerant bean genotype under the highly acidic and low P deficient soils such of Rwanda and have a slight grain yield response when P fertilizer is applied. The two-bush bean genotype RWV 1873 and RWV 1688 are also outstanding low P tolerant bean genotypes compared to a climbing local check (59/1-2) and other low P tolerant climber (G2858). The genotypes RWV 1873 and RWV 1688 grain yield response to P fertilizer application has the same pattern as of RWV 1348. They are all outstanding low P tolerant genotypes and their nodulation efficiency is not responsive at P fertilizer application.