Morpho-anatomical adaptations to waterlogging by germplasm accessions in a tropical forage grass

Juan Andrés Cardoso,Diana Noguera,Juan De La Cruz Jiménez,Joisse Rincón,Idupulapati M Rao

doi:10.1093/aobpla/plt047

Abstract

Soil waterlogging reduces gas exchange between the soil and the atmosphere, leading to oxygen deprivation in the rhizosphere. Brachiaria spp. are the most widely sown forage grasses in tropical America. Among commercial Brachiaria grasses, B. humidicola shows superior tolerance to waterlogged soils based on maintenance of growth and reduced leaf chlorophyll loss and senescence. However, little is known about the underlying traits of waterlogging tolerance in B. humidicola or their intraspecific variation. For this purpose, an outdoor study was conducted using 12 germplasm accessions of B. humidicola that were grown in soil cylinders under drained or waterlogged soil conditions for 21 days. Dry mass production and morpho-anatomical responses (aerenchyma in shoots and roots, root diameter, proportional area of stele in roots, number of nodal and lateral roots, and length of the longest root) were determined. All accessions showed shorter roots and reduced root dry mass under waterlogged soil conditions. All accessions showed aerenchyma in shoots and roots under drained conditions but were further increased under waterlogging. All accessions showed a reduction in the proportional area of stele of roots in response to waterlogging. The accession (CIAT 26570) that showed a higher proportion of aerenchyma in shoots and roots and an increased number of nodal roots (with higher diameter and a reduction in the number of lateral roots) showed longer roots, less reduction in root dry mass and increased shoot growth under waterlogged conditions. We conclude that superior growth of one accession (CIAT 26570) under waterlogged soil conditions is probably a result of morpho-anatomical traits acting together to enhance root aeration and shoot ventilation. Further research is needed to test the ability to recover from waterlogging in B. humidicola accessions.

Highlights

Soil waterlogging occurs when soil is saturated with water
We report differences in dry mass production and morpho-anatomical responses of shoots and nodal roots under drained or waterlogged soil conditions
Leaf production increased in all accessions when grown under drained or waterlogged soil conditions (P, 0.05), but Center for Tropical Agriculture (CIAT) 6013 produced more leaves than the rest of the accessions tested (Table 1)

Summary

Introduction

Soil waterlogging (or flooding of the soil) occurs when soil is saturated with water. Apart from this, plants may display other adaptive strategies that might act together to improve root aeration and oxygen consumption within the root These include increased root diameter (Armstrong 1979; Visser et al 1997, 2000; Aguilar et al 2008), fewer lateral roots developing from the main root axis (Armstrong et al 1983; Sorrell et al 2000; Aguilar et al 2003) and narrower stele (Armstrong 1979; Armstrong and Beckett 1987; Armstrong et al 2000; McDonald et al 2002; Colmer 2003). To provide a continuum of gas ventilation between shoots and roots, aerenchyma is commonly present in shoots of plants that are well adapted to waterlogging (e.g. wetland species; Jackson and Armstrong 1999)

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Results

Discussion

Conclusion