Genetic Relationship of Stalk Strength and Ear Height in Maize

creased by 22.5% over five cycles of selection for high RPR in MoSCSSS. The correlation between RPR and The rind penetrometer is an effective tool for measuring stalk EH is of interest in terms of direct vs. indirect selection strength in an effort to improve maize (Zea mays L.) germplasm for stalk lodging resistance. However, previous studies have indicated a for stalk strength. That is, to what extent does selection significant negative correlation between rind penetrometer resistance for high RPR increase stalk strength per se, or does (RPR) and ear height (EH). The correlation between RPR and EH decreasing EH result in increased stalk strength? is of interest in understanding response to selection for RPR. Has Little research has been conducted to investigate the selection for high RPR resulted primarily in increased stalk strength nature of QTL for correlated traits. Paterson et al. per se and coincidentally lower ear heights, or has selection for high (1991) found a chromosomal region affecting both mass RPR resulted in lower ear heights and subsequently higher stalk per fruit and soluble solids in tomato (Lycopersicon strength? The objective of this study was to determine the genetic esculentum Mill). This region contained the Self-pruning relationship between RPR and the correlated trait EH. To accomplish Protein (sp) locus which was shown to affect both traits. this goal, three F2:3 populations were used to characterize and compare Schön et al. (1993) adjusted tunnel length (TL), a meaquantitative trait loci (QTL) for RPR, EH, and RPR adjusted for EH (RadjE). The original QTL analysis of RPR detected a total of sure of European corn borer (ECB, Ostrinia nubilalis 26 QTL across populations. Adjusting RPR for EH caused 11 of the Hübner) damage, for plant height (PH). They found that original RPR QTL to lose their significance. However, the majority, four of the seven original TL QTL remained significant. 15 of 26, of the original RPR QTL remained significant as QTL for One of the three QTL that lost significance after adRadjE. Because EH clearly had an effect on RPR, adjusting RPR justing for PH overlapped a PH QTL. The authors deterfor EH likely resulted in more accurate descriptions of QTL for stalk mined that that particular QTL was not responsible for strength per se. We have demonstrated that QTL analysis can be used a physiological mechanism for resistance to ECB, but to separate the effects of correlated traits from the genetic effects of rather, was limiting TL since PH determines the total the trait of interest, and recommend determining which correlated length of tunnels possible. traits may influence measurement of the main trait before initiating Several statistical programs have been developed to a QTL experiment. map QTL for multiple traits. In the multiple trait analysis method proposed by Jiang and Zeng (1995), multiple traits are mapped simultaneously, taking advantage of S lodging resistance is an important aspect of the correlation between traits by considering the correplant standability in maize. Stalk lodging is breaklated trait data as repeated measurements of a single age at or below the ear, which may result in loss of the trait. In doing this, parameter estimation is improved ear at harvest. Several methods have been devised to and statistical power is increased. Because it was our measure stalk strength as a means of improving stalk goal to reduce correlated trait effects on QTL detection lodging resistance. Sibale et al. (1992) described use of a to obtain a truer genetic description of the trait of intermodified electronic rind penetrometer to measure stalk est, RPR, we decided analyze correlated traits in a way strength. Rind penetrometer resistance (RPR) was negnearly opposite of the method of Jiang and Zeng. We atively correlated with stalk lodging (Chesang-Chumo, adjusted RPR means for differences in EH by using 1993; McDevitt 1999; Spiess, 1995; Jampatong, 1999). analysis of covariance procedures (Steele and Torrie, Recurrent S0 plant selection for RPR has been effective 1960, p. 305). in separating the synthetic population MoSCSSS into The objective of this study was to determine the getwo distinct subpopulations (Alsirt, 1993). The rind pennetic relationship between RPR and the correlated trait etrometer, therefore, is a valuable tool for measuring EH. This was accomplished by utilizing QTL analysis stalk strength. to characterize and compare QTL for RPR, EH, and Thompson (1964) found that lower internodes had RPR after adjusting for EH. greater stalk strength than higher internodes. ChesangChumo (1993) reported that ear height (EH) was deMATERIALS AND METHODS S.A. Flint-Garcia, Genetics Department, North Carolina State UniPopulation Development versity, Gardner Hall, Raleigh, NC 27695; L.L. Darrah and M.D. Recurrent S0 plant selection for increased and decreased McMullen, USDA-ARS Plant Genetics Research Unit and DepartRPR within the synthetic MoSCSSS (USDA-ARS and Mo. ment of Agronomy, University of Missouri-Columbia, Curtis Hall, Columbia, MO 65211. Mention of a trademark or proprietary proAbbreviations: ECB, European corn borer; EH, ear height; LOD, duct does not constitute a guarantee, warranty, or recommendation log-odds ratio; MoSCSSS-High, MoSCSSS(H24-HRP)C10; MoSCSSSof the product by the USDA or the University of Missouri, and does Low, MoSCSSS(H25-LRP)C11; MoSQB-Low, MoSQB(S10)C6; PH, not imply its approval to the exclusion of others that may be more plant height; QTL, quantitative trait locus; R2, percent of phenotypic suitable. Received 13 Nov. 2001. *Corresponding author (DarrahL@ variation explained; RadjE, rind penetrometer resistance adjusted for missouri.edu) ear height; RPR, rind penetrometer resistance; SSR, simple sequence repeat; TL, tunnel length. Published in Crop Sci. 43:23–31 (2003).