Timothy L. Setter

Desiccation of leaves after de-submergence is one cause for intolerance to complete submergence of the rice cultivar IR 42

This paper presents evidence that severe water deficits, following de-submergence after flash flooding of rice, contribute to submergence intolerance of IR 42, a rice cultivar that rapidly elongates during submergence. In glasshouse experiments, 13-day-old rice seedlings were completely submerged for 3–5 days. The main experiments were with IR 42, a cultivar intolerant to transient complete submergence. During submergence the 3rd leaf expanded, and after 5 days submergence its sheath was 4-fold longer than in non-submerged seedlings. After de-submergence, this leaf rapidly desiccated, its water potential dropped below –2 MPa, while the stomatal conductance was very low. Excision experiments showed the water deficits after de-submergence were due mainly to a large reduction in the hydraulic conductivity in the leaf sheath. The water deficits are an important cause in the sequence of events rather than a mere result of injury: when plants were de-submerged at 100% rather than at 50% RH, water potentials remained high. However, when, after another 5 days, these plants were transferred to 50% RH, the 3rd leaf rapidly desiccated, indicating little repair of the lesion causing the low hydraulic conductivity.

Number of tillers in wheat is an easily measurable index of genotype tolerance to saline waterlogged soils: evidence from 10 large-scale field trials in India

Abstract. Over 100 wheat varieties and breeding lines from India and Australia were screened in alkaline and waterlogged soils in 10 environments over two years at one drained location and two naturally waterlogged locations in India. Mean trial grain yield was reduced up to 70% in the environments where genotypes were waterlogged for up to 15 days at the vegetative stage in alkaline soil relative to plants in drained soils. Agronomic traits (plant height, tiller number, 1000-grain weight) of genotypes were also reduced under waterlogging. At one waterlogged site, up to 68% of the genetic diversity for predicted grain yields under waterlogging could be accounted for by number of tillers (r2 = 0.41–0.68 in 2011 and 2010, respectively) and positive correlations also occurred at the second site (r2 = 0.19–0.35). However, there was no correlation between grain yields across varieties under waterlogging in any trials at the two waterlogged locations. This may have occurred because waterlogged sites differed up to 4-fold in soil salinity. When salinity was accounted for, there was a good correlation across all environments (r2 = 0.73). A physiological basis for the relationship between tillering and waterlogging tolerance is proposed, associated with crown root development. Results are compared with findings in Australia in acidic soils, and they highlight major opportunities for wheat improvement by selection for numbers of tillers when crops are waterlogged during vegetative growth.