Stalk Lodging: A Portable Device for Phenotyping Stalk Bending Strength of Maize and Sorghum

Abstract

Background: Stalk lodging (breakage of plant stems prior to harvest) is a major problem for both farmers and plant breeders. A limiting factor in addressing this problem is the lack of a reliable method for phenotyping stalk strength. Previous methods of phenotyping stalk strength induce failure patterns different from those observed in natural lodging events. This paper describes a new device for field-based phenotyping of stalk strength called "DARLING" (Device for Assessing Resistance to Lodging IN Grains). The DARLING apparatus consists of a vertical arm which is connected to a horizontal footplate by a hinge. The operator places the device next to a stalk, aligns the stalk with a force sensor, steps on the footplate, and then pushes the vertical arm forward until the stalk breaks. Force and rotation are continuously recorded during the test and these quantities are used to calculate two quantities: stalk flexural stiffness and stalk bending strength.Results: Field testing of DARLING was performed at multiple sites. Validation was based upon three factors. First, the device induces the characteristic "crease" or Brazier buckling failure patterns observed in naturally lodged stalks. Second, in agreement with prior research, flexural stiffness values attained using the DARLING apparatus are strongly correlated with bending strength measurements. Finally, a paired specimen experimental design was used to determine that the flexural data obtained with DARLING is in agreement with laboratory-based flexural testing results of the same specimens. DARLING was also deployed in the field to assess phenotyping throughput (# of stalks phenotyped per hour). Over approximately 5000 tests, the average testing rate was found to be 210 stalks/hour. Conclusions:The DARLING apparatus provides a quantitative assessment of stalk strength in a field setting. It induces the same failure patterns observed in natural lodging events. DARLING can also be used to perform non-destructive flexural tests. This new technology has many applications, including breeding, genetic studies on stalk strength, longitudinal studies of stalk flexural stiffness, and risk assessment of lodging propensity.

Stalk Bending Strength is Strongly Associated with Maize Stalk Lodging Incidence Across Multiple Environments

“…1). The force applied to the stalk induces a bending moment in the stalk similar to the bending moment created by wind loading and creates a failure pattern that is consistent with natural lodging Cook et al, 2019).…”

“…Based on the joint model, stalk bending strength measurements produced by DARLING emerged as the most important predictive phenotype of stalk lodging incidence. Given that phenotyping with DARLING can be accomplished rapidly in the field (Cook et al, 2019), this approach may be easily incorporated in breeding programs. The historical lack of an economical and quantitative phenotyping method is responsible for a dearth of information on the genes and genetic elements controlling stalk strength and lodging resistance.…”

“…Stalk bending strength measurements taken on field-grown plants by the novel DARLING apparatus (Cook et al, 2019) emerged as the most important predictive phenotype of stalk lodging incidence. Data also supports the effectiveness of rind puncture resistance as a phenotyping strategy, though this approach lacks the specificity of stalk bending strength measurements.…”

“…Stalk bending strength was measured using the newly developed Device for Assessing Resistance to Lodging IN Grains (DARLING). A detailed description and proper usage of DARLING and the type of data collected has been published recently (Cook et al, 2019). Briefly, the DARLING apparatus consists of a vertical arm and a footplate.…”

“…To address issues that circumvent adoption of stalk strength as a predictive phenotype for stalk lodging incidence, a novel field-based platform for assessing stalk bending strength of maize stalks in vivo was developed. The novel device, known as DARLING (Device for Assessing Resistance to Lodging IN Grains), measures stalk bending strength in field-grown plants by simulating the loading conditions and failure patterns of naturally lodged plants (Cook et al, 2019). Stalk bending strength data acquired from the device are strongly correlated with lab-based measurements of stalk bending strength and stalk flexural stiffness (Cook et al, 2019).…”