Quantitative Trait Locus Analysis of Stalk Strength in Four Maize Populations

rots in maize. High yielding cultivars, increased plant densities, and improvements in soil fertility are generally Stalk lodging in maize (Zea mays L.) causes yield losses estimated accepted to have also contributed to increased stalk to range from 5 to 20% annually worldwide. Selection for rind penetrometer resistance (RPR) has proven useful in enhancing germplasm lodging. for stalk strength, and therefore improving stalk lodging resistance. Stalk lodging counts are unreliable as a measure of We conducted quantitative trait locus (QTL) analysis for RPR in stalk lodging resistance because the expression of stalk four F2:3 populations. The populations were constructed by means of lodging is affected by diseases, insects, and wind. Data combinations of MoSCSSS-High (selection for high RPR), MoSCSSSsummarized from the national white food corn perforLow (selection for low RPR), MoSQB-Low (selection for low stalk mance trials for the years 1986 to 2000 indicate that crushing strength), inbred line Mo47, and inbred line B73. Individuals visual counts of percentages of stalk lodging have coeffiin each population were genotyped for simple sequence repeat (SSR) cients of variation (CVs) in the range of 22 to 150% with or restriction fragment length polymorphism (RFLP) markers, and an average of 82% (L.L. Darrah, unpublished data). data were collected for RPR over multiple locations and replications. Several methods have been devised to measure stalk Means combined over environments were used as trait data for composite interval mapping by QTL Cartographer. Eight, 10, eight, and strength to improve stalk lodging resistance. Zuber and nine single-effect QTL and four, two, zero, and five epistatic interacGrogan (1961) developed a stalk crushing strength tions were detected for RPR in the four populations. Multilocus mod(SCS) technique whereby a 5.1-cm dried section of stalk els, including the single-effect QTL and epistatic interactions, accounted from the second or third internode above the ground for 33.4, 44.7, 48.4, and 58.7% of the total phenotypic variation. These was crushed vertically with a hydraulic press. The force data clearly indicate the complex nature of stalk strength. One chrorequired to “pop” the rind was significantly negatively mosomal region contained a QTL from all four populations, while correlated with stalk lodging in multiple studies (Zuber two QTL were in common among three of the four populations and and Grogan, 1961; Thompson, 1963). The CVs for SCS five QTL were in common between two populations. Candidate genes ranged from 8 to 35%. However, because of the destructhat overlap QTL confidence intervals include those involved in lignin tive nature of sampling by SCS, an alternative method synthesis, the phenylpropanoid pathway, and the timing of vegetative phase change. of evaluating stalk strength was desired. More emphasis was placed on rind strength because studies indicated that the rind contributed 50 to 80% of the stalk strength (Zuber et al., 1980). Sibale et al. (1992) described use S lodging resistance continues to be an imporof a modified electronic rind penetrometer to measure tant aspect of plant standability in maize. Stalk lodgstalk strength and found a highly significant correlation ing is breakage of the stalk at or below the ear, which between SCS and rind penetrometer resistance (RPR) may result in loss of the ear at harvest. Stalk lodging can with a CV of 10.5% for RPR. More importantly, RPR be caused by both biotic and abiotic factors including was significantly and negatively correlated with stalk pathogens, insects, and wind. Gibberella zeae (Schwein.) lodging (Chesang-Chumo, 1993; McDevitt, 1999; Spiess, (anamorph: Fusarium graminearum Schwabe), F. moni1995; Jampatong, 1999). liforme (Sheld.), and Diplodia zeae (Schwein.) are all Little is known about the genetic nature of stalk lodgfungal pathogens that cause stalk rot, thus reducing the ing resistance and RPR. Previous studies have investistrength of the stalk and increasing susceptibility to gated the genetics of stalk strength at a broad level and lodging (Smith and White, 1988). Insect pests that infound that multiple genic regions were involved in RPR crease stalk lodging by tunneling in the USA include the (Heredia-Diaz et al., 1996; Lee et al., 1996). These studEuropean corn borer (ECB) (Ostrinia nubilalis Hübner) ies, however, are too limited to identify the biochemical and the Southwestern corn borer (Diatraea grandiosella and physiological pathways underlying in stalk strength Dyar) (Mihm, 1985). The increased use of reduced tillor to provide a basis for marker-assisted selection. The age has likely contributed to increased incidence of stalk present study is first attempt to explore known candiS.A. Flint-Garcia, Genetics Department, North Carolina State Unidate genes that might be associated with RPR. When versity, Gardner Hall, Raleigh, NC 27695; C. Jampatong, National Corn and Sorghum Research Center, Kasetsart Univ., Klangdong, Abbreviations: CV, coefficient of variation; ECB, European corn Pakchong, Nakhonratchasima 30320, Thailand; L.L. Darrah and M.D. borer; LOD, log-odds ratio; MoSCSSS-High1, MoSCSSS(H24-High McMullen, USDA-ARS Plant Genetics Research Unit and DepartRind Penetrometer)C10S1; MoSCSSS-High2, MoSCSSS(H24-High ment of Agronomy, University of Missouri-Columbia, Curtis Hall, Rind Penetrometer)C10S2-1; MoSCSSS-High3, MoSCSSS(H24-High Columbia, MO 65211. Mention of a trademark or proprietary product Rind Penetrometer)C10S2-2; MoSCSSS-Low, MoSCSSS(H25-Low does not constitute a guarantee, warranty, or recommendation of the Rind Penetrometer)C11; MoSQB-Low, MoSQB(S10)C6; PCR, polyproduct by the USDA or the University of Missouri, and does not merase chain reaction; QTL, quantitative trait locus; R2, percent of imply its approval to the exclusion of others that may be more suitable. phenotypic variation explained; RFLP, restriction fragment length Received 13 Nov. 2001. *Corresponding author (DarrahL@missouri. polymorphism; RCBD, randomized complete block; RPR, rind peneedu). trometer resistance; SCS, stalk crushing strength; SSR, simple sequence repeat. Published in Crop Sci. 43:13–22 (2003).