EVALUATION OF BEAN GERMPLASM FOR LOW PHOSPHORUS TOLERANCE ON TROPICAL SOILS

Bean genotypes from two gene pools were compared for their adaptability to low phosphorus tropical soils in order to evaluate the existing germplasm for low phosphorus tolerance and supply new genetic resources for breeding. The results indicated a significant genotypic variation of low phosphorus tolerance in the tested germplasm. Under low phosphorus conditions, the largeseeded genotypes from the Andean gene pool outperformed the small-seeded genotypes from the Mesoamerican gene pool both in vegetative growth and phosphorus uptake at early stage and in grain yield at harvest. The relative performance of different genotypes are similar on the two tropical soils, implying that there was no obvious soil specificity for beans in response to low phosphorus availability. Under high phosphorus conditions, however, the grain yield of the Andean genotypes was lower than that of the Mesoamerican genotypes. The Andean genotypes would not be readily utilized for their low yield potential in spite of their demonstrated ability of low phosphorus tolerance. Therefore, it is necessary to identify the morphological and physio-biochemical indices of low phosphorus tolerance and understand their genetic control, so that this trait can be incorporated into an ideal genotype. This will be an effective approach of breeding beans for low phosphorus in the future.