Tolerance of tropical common bean genotypes to manganese toxicity: Performance under different growing conditions

Manganese (Mn) toxicity is an important constraint to the production of common bean (Phaseolus vulgaris L.) in tropical and subtropical soils. Amelioration of Mn toxicity by soil modification is difficult in Andosols, and liming of acid soils is often not feasible for small farmers. Substantial genetic variation for Mn tolerance exists in bean germplasm, but is difficult to assess in field trials due to interactions with several environmental factors. The objectives of this study were to identify sources of genetic tolerance to Mn toxicity and to compare their performance using three growing conditions. Contrasting genotypes were evaluated for Mn tolerance by 1) biomass accumulation under Mn stress in solution culture, 2) biomass accumulation under Mn stress in silica sand culture, and 3) seed yield of plants grown in Mn-amended soil. Genotypes varied substantially in Mn tolerance: A-283, BAT-795, Dore de Kirundu, IPA-7419, Carioca, G-12896a, and NEP BAYO 22 were susceptible, while Argentino, BAT-271, Calima, EMP-84, H6 Mulatinho, and Pintado were more tolerant when tested in solution culture. Genotypic tolerance observed in solution culture correlated well with tolerance observed in silica sand. Some genotypes that performed very well in solution culture and in silica sand did suffer severe yield reduction in Mn-amended mineral soil. Manganese toxicity reduced shoot branching resulting in fewer seeds per plant in soil grown plants. We conclude that screening of genotypes in solution culture is useful to identify sources of tolerance to Mn toxicity, but performance of those genotypes in soil might be confounded by other edaphic stresses.