Stalk lodging in maize (Zea mays L.) causes yield losses estimated to range from 5 to 20% annually worldwide. Selection for rind penetrometer resistance (RPR) has proven useful in enhancing germplasm for stalk strength, and therefore improving stalk lodging resistance. We conducted quantitative trait locus (QTL) analysis for RPR in four F 2.3 populations. The populations were constructed by means of combinations of MoSCSSS-High (selection for high RPR), MoSCSSS-Low (selection for low RPR), MoSQB-Low (selection for low stalk crushing strength), inbred line Mo47, and inbred line B73. Individuals in each population were genotyped for simple sequence repeat (SSR) or restriction fragment length polymorphism (RFLP) markers, and data were collected for RPR over multiple locations and replications. Means combined over environments were used as trait data for composite interval mapping by QTL Cartographer. Eight, 10, eight, and nine single-effect QTL and four, two, zero, and five epistatic interactions were detected for RPR in the four populations. Multilocus models, including the single-effect QTL and epistatic interactions, accounted for 33.4, 44.7, 48.4, and 58.7% of the total phenotypic variation. These data dearly indicate the complex nature of stalk strength. One chromosomal region contained a QTL from all four populations, while two QTL were in common among three of the four populations and five QTL were in common between two populations. Candidate genes that overlap QTL confidence intervals include those involved in lignin synthesis, the phenylpropanoid pathway, and the timing of vegetative phase change.

http://web.missouri.edu/~flint-garcias/RPR_QTL.pdf

Quantitative Trait Locus Analysis of Stalk Strength in Four Maize Populations

Stalk strength is an important trait in maize (Zea mays L.). Strong stalks reduce lodging and maximize harvestable yield. Studies show rind penetrometer resistance (RPR), or the force required to pierce a stalk rind with a spike, is a valid approximation of strength. We measured RPR across 4,692 recombinant inbreds (RILs) comprising the maize nested association mapping (NAM) panel derived from crosses of diverse inbreds to the inbred, B73. An intermated B73×Mo17 family (IBM) of 196 RILs and a panel of 2,453 diverse inbreds from the North Central Regional Plant Introduction Station (NCRPIS) were also evaluated. We measured RPR in three environments. Family-nested QTL were identified by joint-linkage mapping in the NAM panel. We also performed a genome-wide association study (GWAS) and genomic best linear unbiased prediction (GBLUP) in each panel. Broad sense heritability computed on a line means basis was low for RPR. Only 8 of 26 families had a heritability above 0.20. The NCRPIS diversity panel had a heritability of 0.54. Across NAM and IBM families, 18 family-nested QTL and 141 significant GWAS associations were identified for RPR. Numerous weak associations were also found in the NCRPIS diversity panel. However, few were linked to loci involved in phenylpropanoid and cellulose synthesis or vegetative phase transition. Using an identity-by-state (IBS) relationship matrix estimated from 1.6 million single nucleotide polymorphisms (SNPs) and RPR measures from 20% of the NAM panel, genomic prediction by GBLUP explained 64±2% of variation in the remaining RILs. In the NCRPIS diversity panel, an IBS matrix estimated from 681,257 SNPs and RPR measures from 20% of the panel explained 33±3% of variation in the remaining inbreds. These results indicate the high genetic complexity of stalk strength and the potential for genomic prediction to hasten its improvement.

/pdf/the-genetic-architecture-of-maize-stalk-strength-307abhqbpx.pdf

The genetic architecture of maize stalk strength.

Effects of light intensity within the canopy on maize lodging

An incomplete understanding of stalk strength and stalk lodging impedes efforts to improve maize (Zea mays L.) production. To develop a more complete understanding of stalk strength, the current study examined the effect of stalk morphology on stalk bending strength. A detailed geometric analysis was conducted on five varieties of dent corn sown at five planting densities in two replicates at each of two locations near Greenville, IA, in 2013. Stalks were imaged using high-resolution X-ray computed tomography, and morphological features of the stalk were quantified using customized computer code. After scanning, stalks were subjected to mechanical tests to determine stalk bending strength and rind penetration resistance. The section modulus of the stalk (a morphological quantity derived from engineering beam theory) was found to be highly predictive of stalk strength, and its predictions appear to be largely unaffected by common confounding factors such as hybrid and planting density. By assuming the stalk cross section to be a hollow ellipse, the section modulus of the stalk can be estimated using measurements of stalk diameter and rind thickness (which does not require computerized tomography scanning). The elliptical section modulus is highly predictive of stalk strength, does not appear to be confounded by experimental variables, and can be obtained using a pair of calipers. Thus, it demonstrates potential as a selective breeding index to improve lodging resistance. In the current study, the elliptical section modulus predicted stalk strength with four times the accuracy of rind penetration resistance (a more common method used in breeding studies). D.J. Robertson, M. Julias, S.Y. Lee, D.D. Cook, Division of Engineering, New York Univ.–Abu Dhabi, Abu Dhabi, United Arab Emirates. Received 4 July 2016. Accepted 6 Dec. 2016. *Corresponding author (douglascook@nyu.edu). Assigned to Associate Editor John Foulkes. Abbreviations: CT, computed tomography; MOI, moment of inertia. Published in Crop Sci. 57:926–934 (2017). doi: 10.2135/cropsci2016.07.0569 © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA This is an open access article distributed under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Published February 16, 2017

M. S. Zuber

Papers

A New Technique for Measuring Stalk Strength in Corn1