Field-based mechanical phenotyping of cereal crops to assess lodging resistance

Abstract

Plant mechanical failure, also known as lodging, is the cause of significant and unpredictable yield losses in cereal crops. Lodging occurs in two distinct failure modes-stalk lodging and root lodging. Despite the prevalence and detrimental impact of lodging on crop yields, there is little consensus on how to phenotype plants in the field for lodging resistance and thus breed for mechanically resilient plants. This review provides an overview of field-based mechanical testing approaches to assess stalk and root lodging resistance. These approaches are placed in the context of future perspectives. Best practices and recommendations for acquiring field-based mechanical phenotypes of plants are also presented.

Keywords: anchorage; bending; lodging; phenotyping; rind penetration; root; stalk.

Figure 1

Failure patterns of cereal stalks. Natural failure patterns of cereal stalks vary by the crop type and age of the plant. (A) In small grains, the most common failure mechanism is buckling at the lower internodes. (B) However, in barley and oats, buckling of middle internodes or as high as the peduncle have been reported. (C) In contrast, for large grains, such as maize, mid‐season failure occurs in a green (or brittle) snapping pattern, with failure at the stem nodes. (D) For late‐season maize lodging, failure is defined by Brazier buckling of stem internodes, close to the node.

Figure 2

Failure patterns of cereal roots. Experimental evidence suggests that cereal crop roots act as tethers in tension or compression. During root lodging, these tethers may fail through (A) roots pulling out of the soil and/or (B) roots breaking in either tension (on the side where force is applied) or compression (on the side away from where the force is applied).

Figure 3

Devices for measuring stalk bending strength. (A) Berry’s device was developed to study winter wheat stalk lodging and consists of a hand‐held force meter with a load cell attached to a push bar that measures the resistance force required to push over multiple plants. (B) An updated version of this device, called the Stalker, was developed for small grains (wheat, oat, and barley). The Stalker reduced the weight of Berry’s device and introduced some automation, i.e., the device is pushed forward until a preset 45°, and then the force‐rotation data are continuously recorded until the test is ended by the operator. (C) Guo’s device features a hand‐held two‐component circuit block system and measures the forces required to bend maize stalks across a set of discrete angles. One component, a controller module, contains a strain sensor, single‐axis angle sensor, microcontroller, power supply module, a signal acquisition circuit, and a radio frequency transceiver. The second component consists of another radio frequency transceiver and single‐axis sensor. The two components are connected by a rigid belt, and the controller is pulled to discrete angles (represented as F₁ and F₂) to measure the maximum equivalent force (F_eq), which is used to assess stalk lodging resistance. (D) DARLING was developed to assess stalk biomechanics in larger cereal crops and more closely recreate natural failure patterns during stalk lodging. DARLING consists of a vertical support with a control box and digital display mounted at the top, a horizontal footplate attached by a hinge at the base, and an adjustable‐height load cell attached to the vertical support. Plants can be non‐destructively bent within the linear‐elastic range of the material to obtain flexural stiffness or displaced until failure; the maximum applied bending strength is then recorded.

Figure 4

Devices for measuring root anchorage. (A) Dourleijn’s device measures vertical root pulling resistance in maize. The device uses an electric‐powered motor and pulley system to pull the plants out of the soil at a constant rate. (B) Fouéré’s device measures horizontal root pushing force in maize and consists of a main frame, handle, adjustable force sensor, angle sensor, a two‐pronged steel fork with anchoring nails, and a control head with an electronic display and keys. This device uses a force sensor to transmit an angular pushing force to the stalk; an electronic control system then automatically records the resistance force. (C) Sposaro’s device, which was originally developed for sunflower and later applied to maize to improve upon root pulling/pushing resistance devices, better replicates the failure mode of root lodging. With this device, a push bar is attached to the plant stem, while a base protractor and an offset pulley system are used to pull the plant over. Root failure moment (Rfm) can then be calculated. (D) For smaller crops (e.g., canola, wheat, rice), a commercially available prostrate testing device can been used. The device attaches to an adjustable mounted plate attached to the plant. Plants are displaced to a 45° angle, and the pushing resistance is then recorded.