Photosynthetic responses and tolerance to root-zone hypoxia stress of five bean cultivars (Phaseolus vulgaris L.)

Common bean (Phaseolus vulgaris L.) is very sensitive to waterlogging, which is considered a limiting factor for its production. The objective of this studywas to evaluate photosynthetic responses and tolerance to root-zone hypoxia stress of five bean cultivars (Cerinza, Bachue, Bianca, Bacata and NUA35). Bean seedlings of the five cultivars were grown in hydroponics and subjected for 14 days to two treatments (i) high oxygen availability in the root zone or (2) low oxygen availability or hypoxia stress. Results showed that all cultivars under hypoxia stress exhibited reductions in photosynthesis rate (62%-82%), stomatal conductance (73%-97%), transpiration rate (51%-92%), actual quantum yield, non-photochemical quenching, electron transport rate and in the content of chlorophylls and carotenoids. An increase in leaf electrolyte leakage was also observed, which suggests a loss in the stability of cell membranes because of hypoxia stress. The cultivars Bachue, Bianca, Cerinza and NUA35 showed an increase in proline content (300%-750%) compared to plants grown with high oxygen. The cultivar with the highest water use efficiency and the lowest loss of dry mass was Cerinza, followed by NUA35. These cultivars, Cerinza and NUA35, showed a higher tolerance to hypoxia (0.36 and 0.38) according to the waterlogging tolerance coefficient compared with the other cultivars grown with low oxygen availability. The performance of these cultivars could be attributed to the greater reduction in stomatal conductance, maintaining low rates of transpiration but without a high reduction in the CO2 intake. In this way, the tolerance in these cultivars could be associated with the greaterwater use efficiency during the conditions of hypoxia, comparedwith the other cultivars. (C) 2019 Published by Elsevier B.V. on behalf of SAAB.