Abstract
BackgroundStalk 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.ResultsField testing of DARLING was performed at multiple sites. Validation was based upon several 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 rigidity values attained using the DARLING apparatus are strongly correlated with bending strength measurements. Third, flexural stiffness and bending strength values obtained with DARLING are in agreement with laboratory-based stiffness and strength values for corn stalks. 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/h.ConclusionsThe 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 technology has many applications, including breeding, genetic studies on stalk strength, longitudinal studies of stalk flexural stiffness, and risk assessment of lodging propensity.
Highlights
Stalk lodging is a major problem for both farmers and plant breeders
This paper describes a portable, field-based tool called “DARLING” that replicates the failure mode of naturally lodged stalks and provides quantitative measurements of stalk bending strength and stalk flexural stiffness
Failure patterns DARLING induces failure patterns that are entirely similar to those observed in naturally lodged maize plants
Summary
DARLING has been used to perform several thousand tests on sorghum, and maize at over 15 sites. Maize plants that have not reached full maturity and that exhibit high levels of turgor pressure will often exhibit snapping failures (i.e., the stalk will snap in half ) during natural lodging events. This failure type is sometimes referred to as “green snap”. In prior research, long-span 3-point bending tests of maize stalks as described in Robertson et al [13] have demonstrated that stalk flexural rigidity is strongly correlated with stalk bending strength [15] This same correlation is observed in the data collected using DARLING (see Fig. 7). Stalk strength measurements obtained by DARLING over the course of 2 years were found to be significantly correlated with historical lodging incidence data of the same hybrids. (see Sekhon et al [16] for a full description and statistical analysis of correlations with natural lodging counts)
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