Phenotyping for waterlogging tolerance in crops: current trends and future prospects

Abstract

Yield losses to waterlogging are expected to become an increasingly costly and frequent issue in some regions of the world. Despite the extensive work that has been carried out examining the molecular and physiological responses to waterlogging, phenotyping for waterlogging tolerance has proven difficult. This difficulty is largely due to the high variability of waterlogging conditions such as duration, temperature, soil type, and growth stage of the crop. In this review, we highlight use of phenotyping to assess and improve waterlogging tolerance in temperate crop species. We start by outlining the experimental methods that have been utilized to impose waterlogging stress, ranging from highly controlled conditions of hydroponic systems to large-scale screenings in the field. We also describe the phenotyping traits used to assess tolerance ranging from survival rates and visual scoring to precise photosynthetic measurements. Finally, we present an overview of the challenges faced in attempting to improve waterlogging tolerance, the trade-offs associated with phenotyping in controlled conditions, limitations of classic phenotyping methods, and future trends using plant-imaging methods. If effectively utilized to increase crop resilience to changing climates, crop phenotyping has a major role to play in global food security.

Keywords: Abiotic stress; breeding; flooding; phenotyping; plant imaging; waterlogging.

Fig. 1.

Physiology of waterlogging in a plant. On the left, a barley plant under non-waterlogging conditions in well oxygenated soil. On the right, a barley plant under waterlogging stress in anoxic soil, showing a list of common physiological responses to waterlogging. Barley is used as a hypothetical example, yet these physiological responses are common to other crops experiencing waterlogging. Elements of the figure were created using Biorender.com.

Fig. 2.

Segmentation of barley plants imaged using a photon system instruments (PSI) imaging suite. (A) Two barley plants (one waterlogged and one control) imaged with a RGB sensor, Sony IMX253LQR-C with a resolution of 4112 × 3006 pixels. (B) Image after application of a colour segmentation method to remove the unwanted noise of the image.

Fig. 3.

Summary of waterlogging setup systems and phenotyping imaging methods used to evaluate waterlogging stress. (A) Comparison of different waterlogging methods, traits evaluated, advantages, and challenges associated with hydroponics, waterlogging within individual pots, pots within tanks, and waterlogging in field conditions. (B) Comparison of different imaging targets (single plant shoot, single plant root, and plot level canopy) and associated advantages and challenges of each approach using imaging sensors. Figure adapted from (Negrão and Julkowska, 2020). Elements of the figure were created using Biorender.com.