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 com mon bean (Phaseolus vulgaris L.) in tropical and subtropical soils. Amelior ation of Mn toxicity by soil modification is difficult in Andosols, and lim ing of acid soils is often riot feasible for small farmers. Substantial gen etic variation for Mn tolerance exists in bean germplasm, but is difficult to assess in field trials due to interactions with several environmental fa ctors. The objectives of this Study were to identify sources of genetic tol erance to Mn toxicity and to compare their performance using three growing conditions. Contrasting genotypes were evaluated for Mn tolerance by 1) bio mass accumulation under Mn stress in solution culture, 2) biomass accumulat ion under Mn stress in silica sand culture, and 3) seed yield of plants gro wn in Mn-amended sail. Genotypes varied substantially in Mn tolerance: A-28 3, BAT-795, Dore de Kirundu, IPA-7419, Carioca, G-12896a, and NEP BAYO 22 w ere susceptible, while Argentino, BAT-271, Calima, EMP-84, H6 Mulatinho, an d Pintado were more tolerant when tested in solution culture. Genotypic tol erance observed in solution culture correlated well with tolerance observed in silica sand. Some genotypes that performed very well in solution cultur e and in silica sand did suffer severe yield reduction in Mn-amended minera l 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 ther ed aphic stresses.