Grain legume crops, a key dietary protein source for many people, are largely intolerant to waterlogging. This is despite some grain legumes often being exposed to waterlogged soils when grown as relay sown crops – a practice of hand broadcasting legume seeds into a standing rice crop two weeks prior to rice harvest – in Bangladesh, India and Nepal. Relay sowing avoids tillage whilst maximising access to residual soil moisture by the legume crop. Excess soil moisture can however result in reduced yield and, in extreme cases, crop failure. When seeds are exposed to waterlogging during germination, they can experience very low oxygen (hypoxia) or no oxygen (anoxia) conditions that can lead to germination failure. Tolerance to waterlogging varies between and within grain legume species and the effects also vary depending on the duration of waterlogging. Despite this, information of germination responses to hypoxia amongst various grain legume crops, including lentil, faba bean , field pea and grass pea, is limited.
In their new study published in AoBP, Wiraguna et al. evaluated the tolerance of seeds of lentil, faba bean, field pea and grass pea to soil waterlogging, anoxia and hypoxia. The study comprised three experiments designed to determine whether (1) there is variation in tolerance to soil waterlogging between and within these legume crop species, (2) there is variation in tolerance of grain legume seeds to anoxia applied at imbibition and also differences in recovery ability following subsequent re-aeration; and (3) the seeds of the grain legumes differ in tolerance to hypoxia during germination.
The soil profiling of soil waterlogging showed that oxygen declined and then stabilized by the fourth day after waterlogging and oxygen was not detected at 8 mm below the soil surface. Lentil had higher seedling emergence (55 %) than the other species during soil waterlogging. However, lentil had lower seedling survival (9 %) than grass pea (28 %) during recovery following soil drainage. Grass pea seeds were more tolerant of anoxia and hypoxia than the seeds of the three other species. The findings of Wiraguna et al. demonstrate the superior waterlogging tolerance of grass pea and highlight their suitability for relay sowing systems compared with the other grain legumes in this study.
Wiraguna, E., Malik, A.I., Colmer, T.D., Erskine, W., 2021. Tolerance of four grain legume species to waterlogging, hypoxia and anoxia at germination and recovery. AoB PLANTS. https://doi.org/10.1093/aobpla/plab052