Stalk Lodging Resistance Research Articles

In situ evaluation of stalk lodging resistance for different maize (Zea mays L.) cultivars using a mobile wind machine

BackgroundStalk lodging is an impediment to improving profitability and production efficiency in maize. Lodging resistance, a comprehensive indicator to appraise genotypes, requires both characterization of mechanical properties in laboratory and investigation of lodging percentage in field. However, in situ characterization of maize lodging resistance still remains poor. The aim of this study was to develop an indicator, named cumulative lodging index (CLI), based on lodging percentages at different wind speeds for evaluating lodging resistance for different maize cultivars, and to evaluate the accuracy and reliability of this method.ResultsDifferent cultivars showed different patterns of lodging percentage along with wind speeds. The failure wind speed (FWS) for maize ranged between 16 and 30 m s−1 across cultivars. The CLI differed between maize cultivars and showed favorable reliability (i.e. nRMSE of 5.38%). Mechanical properties of the third internode did not vary significantly between cultivars. Significant differences in the reduction index (RI) of wind speed sheltered by maize canopy were found between cultivars.ConclusionOur findings implied that mobile wind machine is powerful in reproducing wind disaster that induce crop lodging. The newly-built CLI was demonstrated to be a more robust indicator than mechanical properties, FWS, and RI when evaluating lodging resistance in terms of both reliability and resolution. This study offers a new perspective for evaluating in situ lodging resistance of crops, and provides technical support for accurate identification of lodging-resistant phenotypic traits.

Dual Application of Ethephon and DCPTA Increases Maize Yield and Stalk Strength

Core Ideas Combined treatment with ethephon and DCPTA enhanced stalk mechanical strength of maize. Combined treatment with ethephon and DCPTA improved the post‐anthesis dry matter accumulation of maize. Combined treatment with ethephon and DCPTA improved the grain yield of maize. The combination of ethephon (2‐chloroethyl phosphonic acid, ETH) and 2‐diethylaminoethyl‐3,4‐dichlorophenylether (DCPTA) has been used in maize (Zea mays L.) production in Northeast China, but limited information is available on the effectiveness of ETH+DCPTA. In this study, field experiments were conducted with two maize hybrids, ZhengDan 958 (‘ZD958’) and DongNong 254 (‘DN254’), which were planted at a density of 75,000 plants ha−1, to study the influence of ETH, DCPTA, and ETH+DCPTA on stalk quality (rind penetration strength [RPS], stalk bending strength [SBS], dry weight per unit, cross‐sectional area, and rind thickness), photosynthetic characteristics, bleeding sap, dry matter accumulation (DMA), and yield. Ethephon significantly reduced the lodging rate, plant height, ear height, and center of gravity of both maize hybrids and increased the RPS, SBS, dry weight per unit, cross‐sectional area, and thickness over the 2 yr. Ethephon also significantly decreased the leaf area index (LAI), chlorophyll content (SPAD value), net photosynthetic rate (Pn) and bleeding sap levels and accelerated leaf senescence, which ultimately decreased the yields. Although the application of DCPTA tended to increase the LAI, Pn, and bleeding sap levels and delayed leaf senescence, the plant height, ear height and the center of gravity also increased markedly, resulting in poorer stalk lodging resistance and higher lodging rate. Greater green leaf area, photosynthetic ability and bleeding sap levels and delayed leaf senescence in response to ETH+DCPTA mainly contributed to the increased postanthesis DMA. Thus, the application of ETH+DCPTA could provide a stable method for increasing the maize grain yield.

Classification of Corn Stalk Lodging Resistance Using Equivalent Forces Combined with SVD Algorithm

Corn stalk lodging, which involves the breakage of the stalk below the ear following either bad weather, insect infestation or stormy rain, usually leads to harvest loss, increased harvesting time and higher drying costs. The objective of this study was to develop a method that can classify corn stalk lodging resistance. This method, which employed the maximum equivalent force exerted on a corn stalk, corresponding stalk agronomic traits, and the singular value decomposition (SVD) algorithm, showed that the five corn varieties with different stalk lodging resistance from two planting densities of 60,000 plants/ha and 75,000 plants/ha can be effectively classified. A customized device was designed to measure the equivalent forces. Three factors, including the planting density, the stalk diameter, and the maximum equivalent force with comprehensive contributions of −0.4603, 0.4196 and 0.4068, which are related to principal components, play an important role in the classification of corn stalk lodging resistance. The results showed that the corn stalk lodging resistance decreased with increase in planting density; however, with the increase in stalk diameter and maximum equivalent force, the lodging resistance significantly increased. Corn breeders can develop higher lodging resistance-based corn varieties by using this approach.

Application of paclobutrazol: a strategy for inducing lodging resistance of wheat through mediation of plant height, stem physical strength, and lignin biosynthesis.

Lodging is a major constraint contributing to poor grain yield and quality of wheat (Triticum aestivum L.) worldwide. The use of plant growth regulators is becoming a foremost agro-chemical approach for minimizing the risk of lodging in cereal crops. The present study was conducted to examine the effects of the paclobutrazol application on culm physical strength, lignin content, and lodging resistance of wheat. Wheat seeds were soaked in paclobutrazol at the concentrations of 0 (CK, as control), 200 (PB1), 300 (PB2), and 400 (PB3) mgL-1. Our results showed that paclobutrazol resulted in a dose-dependent decrease of plant height, internode length, and center of gravity height. Paclobutrazol treatments evidently increased the culm diameter, culm filling degree, and wall thickness of basal internodes, resulting in greater stalk-breaking strength and lodging resistance index (CLRI), where their maximum values were obtained with PB1 treatment. In addition, the activities of lignin-related enzymes were improved by paclobutrazol, particularly at low concentration, which increased the lignin accumulation of the basal internodes of wheat, subsequently improving the capability of stalk lodging resistance. Moreover, the correlation analysis revealed significant correlations between stem diameter, culm filling degree, and lignin with stalk bending strength and CLRI. The paclobutrazol concentration ≥ 300mgL-1 (PB2 and PB3 treatments) showed inhibitive effects on various culm morphological traits. These results suggest that not only the plant height, but also the lignin contents and physical strength of internodes are closely related with the lodging resistance of wheat, and reduction in plant height along with improved culm morphological characteristics and higher lignin accumulation in basal internodes could effectively relieve the risk of lodging.

A Non-Destructive and Direction-Insensitive Method Using a Strain Sensor and Two Single Axis Angle Sensors for Evaluating Corn Stalk Lodging Resistance.

Corn stalk lodging is caused by different factors, including severe wind storms, stalk cannibalization, and stalk rots, and it leads to yield loss. Determining how to rapidly evaluate corn lodging resistance will assist scientists in the field of crop breeding to understand the contributing factors in managing the moisture, chemical fertilizer, and weather conditions for corn growing. This study proposes a non-destructive and direction-insensitive method, using a strain sensor and two single axis angle sensors to measure the corn stalk lodging resistance in the field. An equivalent force whose direction is perpendicular to the stalk is utilized to evaluate the corn lodging properties when a pull force is applied on the corn stalk. A novel measurement device is designed to obtain the equivalent force with the coefficient of variation (CV) of 4.85%. Five corn varieties with two different planting densities are arranged to conduct the experiment using the novel measurement device. The experimental results show that the maximum equivalent force could reach up to 44 N. A strong relationship with the square of the correlation coefficient of 0.88 was obtained between the maximum equivalent forces and the corn field’s stalk lodging rates. Moreover, the stalk lodging angles corresponding to the different pull forces over a measurement time of 20 s shift monotonically along the equivalent forces. Thus, the non-destructive and direction-insensitive method is an excellent tool for rapid analysis of stalk lodging resistance in corn, providing critical information on in-situ lodging dynamics.

Multi-Locus Genome-Wide Association Study Reveals the Genetic Architecture of Stalk Lodging Resistance-Related Traits in Maize.

Stalk lodging resistance, which is mainly measured by stem diameter (SD), stalk bending strength (SBS), and rind penetrometer resistance (RPR) in maize, seriously affects the yield and quality of maize (Zea mays L.). To dissect its genetic architecture, in this study multi-locus genome-wide association studies for stalk lodging resistance-related traits were conducted in a population of 257 inbred lines, with tropical, subtropical, and temperate backgrounds, genotyped with 48,193 high-quality single nucleotide polymorphisms. The analyses of phenotypic variations for the above traits in three environments showed high broad-sense heritability (0.679, 0.720, and 0.854, respectively). In total, 423 significant Quantitative Trait Nucleotides (QTNs) were identified by mrMLM, FASTmrEMMA, ISIS EM-BLASSO, and pLARmEB methods to be associated with the above traits. Among these QTNs, 29, 34, and 48 were commonly detected by multiple methods or across multiple environments to be related to SD, SBS, and RPR, respectively. The superior allele analyses in 30 elite lines showed that only eight lines contained more than 50% of the superior alleles, indicating that stalk lodging resistance can be improved by the integration of more superior alleles. Among sixty-three candidate genes of the consistently expressed QTNs, GRMZM5G856734 and GRMZM2G116885, encoding membrane steroid-binding protein 1 and cyclin-dependent kinase inhibitor 1, respectively, possibly inhibit cell elongation and division, which regulates lodging resistance. Our results provide the further understanding of the genetic foundation of maize lodging resistance.

Study on Maize Stalk Lodging Resistance in Cyclic Cross Selection

Stalk lodging resistance is a particularly important trait on maize, especially in terms of mechanized harvesting of the crop. Stalk lodging represents a major problem of corn with yield losses. Because of this reason, it takes a special attention on the breeding process. The purpose of this research was the study of maize stalk lodging resistance before the harvest time and finding the best breeding lines for this type of resistance. We used 7 breeding lines (TE 229, TE 202B, TA 452, TE 330A, TD 364, TE 317 and TE 335) as maternal lines and another 3 (TD 268, TC 385A and TC 399) as testers. Lines were tested in 2011 and 2012, in compared cultures with 24 variants, where 21 of them were the experimental hybrids between tested lines and testers and the other 3 werethe control hybrids Turda 201, Turda Favorit and PR39D81. Variance analysis was performed according to the classical model of a two-factor system. Genic effects were calculated after 2nd North Carolina model. Regarding the results, the highest percentage of unbroken plants was on TD 268 tester (80.7%) and the lowest on TD 364 tested line (70.2%). Tested lines that was noted for the general combining ability of lodging resistance were TA 452 and TE 335. Crossings that marked high values for non-additive effects were TA 452 x TC 385A, TE 202B x TC 399 and TE 202B x TD 268. Effects values for general combining ability were between -4.72% and +4.49% on tested lines, -1.68% and +5.78% on testers; effects values for specific combining ability were between -11.25% and +7.58%. Regarding the tested lines was noted TA 452 inbred line and regarding the testers was noted TD 268 inbred line. On this issue, we can state that in the selection process of maize hybrids must be chosen only those hybrid combinations with stalk-lodging resistance because of the similar contribution of additive and non-additive genic effects to resistant genotypes.

Response of Maize Grown Under High Plant Density; Performance, Issues and Management - A Critical Review

Modern cropping is based on relatively high plant density. The improved grain yield per unit area of modern maize (Zea mays L.) hybrids is due to the increased optimum plant population rather than the improved grain yield per plant. High plant density has been widely used to enhance grain yield in maize. Subsequently we review the effect of planting density on physiology, phenology, morphology, nitrogen use efficiency, water use efficiency grain yield information in maize crop. At higher plant populations reduced grain yield also results from the increased pollento- silking interval and the following barrenness. However, it may lead to higher risk lodging hence causing significant yield loss of the crop. Future insights are morphological and physiological basis controlling barren and stalk lodging resistance. How root traits, and anatomy of sheath and stem of maize plants correspond to high plant population and a further study on the physiological and biological basis of organ development that may govern the mechanisms of high plant density would be essential for future research.

Ploidy effect and genetic architecture exploration of stalk traits using DH and its corresponding haploid populations in maize

BackgroundDoubled haploid (DH) lines produced via in vivo haploid induction have become indispensable in maize research and practical breeding, so it is important to understand traits characteristics in DH and its corresponding haploids which derived from each DH lines. In this study, a DH population derived from Zheng58 × Chang7-2 and a haploid population, were developed, genotyped and evaluated to investigate genetic architecture of eight stalk traits, especially rind penetrometer resistance (RPR) and in vitro dry matter digestion (IVDMD), which affecting maize stalk lodging-resistance and feeding values, respectively.ResultsPhenotypic correlation coefficients ranged from 0.38 to 0.69 between the two populations for eight stalk traits. Heritability values of all stalk traits ranged from 0.49 to 0.81 in the DH population, and 0.58 to 0.89 in the haploid population. Quantitative trait loci (QTL) mapping study showed that a total of 47 QTL for all traits accounting for genetic variations ranging from 1.6 to 36.5 % were detected in two populations. One or more QTL sharing common region for each trait were detected between two different ploidy populations. Potential candidate genes predicated from the four QTL support intervals for RPR and IVDMD were indirectly or directly involved with cellulose and lignin biosynthesis, which participated in cell wall formation. The increased expression levels of lignin and cellulose synthesis key genes in the haploid situation illustrated that dosage compensation may account for genome dosage effect in our study.ConclusionsThe current investigation extended understanding about the genetic basis of stalk traits and correlations between DH and its haploid populations, which showed consistence and difference between them in phenotype, QTL characters, and gene expression. The higher heritabilities and partly higher QTL detection power were presented in haploid population than in DH population. All of which described above could lay a preliminary foundation for genetic architecture study with haploid population and may benefit selection in haploid-stage to reduce cost in DH breeding.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0742-3) contains supplementary material, which is available to authorized users.

Genetic architecture of rind penetrometer resistance in two maize recombinant inbred line populations.

BackgroundMaize (Zea Mays L.) is one of the most important cereal crops worldwide and provides food for billions of people. Stalk lodging can greatly undermine the standability of maize plants and therefore decrease crop yields. Rind penetrometer resistance is an effective and reliable method for evaluating maize stalk strength, which is highly correlated with stalk lodging resistance. In this study, two recombinant inbred line populations were constructed from crosses between the H127R and Chang7-2 lines, and between the B73 and By804 lines. We genotyped these two populations and their parents using 3,072 single nucleotide polymorphism markers and performed phenotypic assessment of rind penetrometer resistance in multiple environments to dissect the genetic architecture of rind penetrometer resistance in maize.ResultsBased on two linkage maps of 1,397.1 and 1,600.4 cM with average interval of 1.7 and 2.1 cM between adjacent makers, respectively, seven quantitative trait loci (QTL) for rind penetrometer resistance were detected in the two recombinant inbred line populations. These QTL were distributed in seven genomic regions, and each accounted for 4.4–18.9% of the rind penetrometer resistance variation. The QTL with the largest effect on rind penetrometer resistance, qRPR3-1, was located on chromosome 3 with the flanking markers PZE-103123325 and SYN23245. This locus was further narrowed down to a 3.1-Mb interval by haplotype analysis using high-density markers in the target region. Within this interval, four genes associated with the biosynthesis of cell wall components were considered as potential candidate genes for the rind penetrometer resistance effect.ConclusionsThe inheritance of rind penetrometer resistance is rather complex. A few large-effect quantitative trait loci, together with a several minor-effect QTL, contributed to the phenotypic variation in rind penetrometer resistance in the two recombinant inbred line populations that were examined. A potential approach for improving stalk strength and crop yields in commercial maize lines may be to introgress favorable alleles of the locus that was found to have the largest effect on rind penetrometer resistance (qRPR3-1).

English

  Trials were carried out using five composite maize varieties in a Striga lutea (Lour) endemic soil of Temidire-Eruwa, Oyo State, Nigeria, in 2004 and 2005. The composite maize varieties were tested under varied fertilizer types, nitrogen (N) concentrations and artificial striga infestation. The objective was to test these striga resistant maize varieties for yield and agronomic performance under the above conditions. The result showed that, variety and year of evaluation differed significantly (P<0.01) for almost all agronomic characters such as plant stand, days to anthesis (silking and tasselling), plant and ear heights as well as root and stalk lodging resistance at both 100 and 200 kgN/ha. Variety x year interaction were also significantly different (P<0.01) for all agronomic characters except root lodging and husk tip cover. Fertilizer type differed only for days to silking, plant height and plant aspect, while year x nitrogen source and variety x nitrogen source was highly significant (P<0.01) for field weight. Plant stands were generally better in 2004 than 2005 for all varieties except Acr 97syn-W and DMR-LSR-W. The composite maize varieties were able to tolerate high N-concentration except DMR-LSR-Y which do not utilize excess nitrogen above 100 kgN/ha. Use of striga resistant maize varieties concomitantly with nitrogen fertilizer is recommended for farmers in S. lutea endemic ecology, for higher grain yield.   Key words: Composite maize, fertilizer type, nitrogen (N) concentrations, striga resistance, yield.

QTL mapping of stalk bending strength in a recombinant inbred line maize population

Stalk bending strength (SBS) is a reliable indicator for evaluating stalk lodging resistance of maize plants. Based on biomechanical considerations, the maximum load exerted to breaking (F max), the breaking moment (M max) and critical stress (σ max) are three important parameters to characterize SBS. We investigated the genetic architecture of SBS by phenotyping F max, M max and σ max of the fourth internode of maize plants in a population of 216 recombinant inbred lines derived from the cross B73×Ce03005 evaluated in four environments. Heritability of F max, M max and σ max was 0.81, 0.79 and 0.75, respectively. F max and σ max were positively correlated with several other stalk characters. By using a linkage map with 129 SSR markers, we detected two, three and two quantitative trait loci (QTL) explaining 22.4, 26.1 and 17.2% of the genotypic variance for F max, M max and σ max, respectively. The QTL for F max, M max and σ max located in adjacent bins 5.02 and 5.03 as well as in bin 10.04 for F max were detected with high frequencies in cross-validation. As our QTL mapping results suggested a complex polygenic inheritance for SBS-related traits, we also evaluated the prediction accuracy of two genomic prediction methods (GBLUP and BayesB). In general, we found that both explained considerably higher proportions of the genetic variance than the values obtained in QTL mapping with cross-validation. Nevertheless, the identified QTL regions could be used as a starting point for fine mapping and gene cloning.

Effect of N supply on stalk quality in maize hybrids

The identification of maize nitrogen (N) response for stalk quality is valuable in stalk breeding improvement, stalk lodging resistance and for use in bioenergy. This study analyzed the effect of two N levels and estimated quantitative genetic parameters for stalk quality in summer maize in the north China plain (NCP). Thirty hybrids were sampled and tested from three to four geographic locations under high nitrogen (HN) (225 kg N ha −1) and low nitrogen (LN) (0 kg N ha −1) during 2006–2008. Compared to HN level, stalk crude protein (CP) was significantly reduced (22.06%) under LN level. Ether extract (EE), ash content (AC), in vitro dry matter digestion (IVDMD) and lignin content (LC) were lower under LN level. Cellulose content (CC), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were increased with a reduction in N, however N did not significantly affect EE, ADF and LC. An increase in NDF and ADF content under low vs. high N level was mainly attributed to a reduction in CC. ADF and NDF exhibited positive correlation and both showed a positive correlation with CC but a negative correlation with LC, IVDMD and CP. Negative correlations between IVDMD and CC, IVDMD and LC, and CP and CC were also detected. The interaction variance of genotype × year × location ( σ 2 GYL ) for each N level, with the exception of σ 2 GYL for CC under HN, was significant and most stalk quality traits were evaluated in different locations and years. The estimates of genetic variance ( σ 2 G ) and heritability ( h 2) were greater under HN, with the exception of LC and EE. The interaction of genotype × nitrogen ( σ 2 GN ) for CP was more important than σ 2 G . The genotypic correlation coefficients ( r G ) for performance in different stalk quality traits between HN and LN were significant. However, it was necessary to evaluate both HN and LN for IVDMD. For other stalk quality traits, breeding maize under HN levels may serve to develop hybrids well adapted to high and/or low N level. The response to N trend was similar between high oil and normal maize hybrids.

BRS 1002: nova cultivar de milho para o Sul do Brasil

O híbrido de milho BRS 1002 é um híbrido simples, de ciclo precoce, desenvolvido pela Embrapa Trigo, em Passo Fundo, RS. Apresenta excelente sanidade foliar associada à alta produtividade, ótima estabilidade de produção, porte médio, arquitetura ereta, resistência ao acamamento e quebramento, além de ótimo empalhamento. BRS 1002 é indicado para a época normal de semeadura nos estados do Rio Grande do Sul, Santa Catarina e Sul do Paraná.

Diallel Analyses of Agronomic Traits Using Chinese and U.S. Maize Germplasm

Added genetic diversity among commercial maize (Zea mays L) hybrids may further increase yields and safeguard against vulnerability. Introducing exotic germplasm into breeding programs would increase the genetic base from which elite commercial inbreds are derived. Ten populations of maize, created from Chinese and/or U.S. inbreds or strains, were evaluated by Griffing's diallel analysis for combining ability of grain yield, stalk lodging, ear height, flowering time, and European corn borer (ECB; Ostrinia nubilalis Hübner) resistance to estimate their potential as sources of exotic germplasm for U.S. breeding programs. Grain yield general combining ability was largest for the population Mo17 Syn.(H14)C5, a synthetic improved by half‐sib selection using US13 as a tester. Grain yield specific combining ability was largest in the cross Chinese Mix 2 × Mo17 Syn.(H14)C5. Chinese Mix 2 × Mo17 Syn.(H14)C5 had more stalk lodging than the B73 × Mo17 and Pioneer Brand 3394 checks. Because of the high yield potential and other moderate‐to‐good agronomic traits of the cross combination, Chinese Mix 2 was selected as the best population for selection. Its large specific combining ability effect with Lancaster type material, which is commonly known in breeding programs, shows potential for further improvement. No native ECB resistance in Chinese germplasm was detected (two environments in 1 yr) compared with the resistant check Pioneer Brand 3184.

Response to long-term selection in early maturing maize synthetic varieties

Long-term continuous selection is essential for germplasm improvement. However, choice of germplasm for long-term genetic improvement might limit the success of germplasm enhancement programs. The objective of this research was to report the response to long-term selection in early maturing North Dakota (ND) synthetic varieties. We wanted to determine whether the performance of three ND maize synthetic varieties was improved by long-term mass selection (M) and if the performance of one of them was improved by long-term modified ear-to-row (MER) selection. The evaluation of long-term selection response was performed at two plant densities. An experiment in a randomized complete block design with split-plot arrangement was used to evaluate NDSM(M), NDSAB(M), NDSCD(M), and NDSAB(MER) under 75,000 and 42,500 plants per hectare across seven environments. Long-term mass selection for grain yield and stalk lodging resistance in NDSM(M), NDSAB(M), and NDSCD(M) was not successful, since there were no significant changes in grain yield or stalk lodging in these populations at either low or high densities. On the other hand, long-term modified ear-to-row selection was effective for grain yield improvement in NDSAB(MER). Grain yield increased non-linearly from 3.9 Mg ha−1 in cycle 0 to 5.0 Mg ha−1 in cycle 12 at a rate of 2.5% per cycle. Interaction between plant density and genotype was not detected even though selection was performed at relatively low densities (20,000 plants ha−1 for mass selection and 50,000 plants ha−1 for ear-to-row selection). The confirmation of a lack of interaction between plant density and genotype suggests that selection at low plant densities might still be able to provide high-density stress resistance through density-independent genotypes, allowing progeny testing across multiple locations with better accuracy and fewer resources. Selection methods that emphasize both additive and dominance effects such as full-sib recurrent selection are recommended to maximize genetic improvement of advanced population cycles of early maturing synthetics.

Divergent Selection for Rind Penetrometer Resistance and Its Effects on European Corn Borer Damage and Stalk Traits in Corn

Corn (Zea mays L.) grain yield is affected by a number of factors, including stalk lodging and pests such as the European corn borer (Ostrinia nubilalis Hübner; ECB). European corn borers contribute to stalk lodging and also cause a direct grain yield reduction through physiological effects that decrease the plant's ability to produce and translocate photosynthates. Although much progress has been made in improving standability, stalk lodging remains a major problem, and breeding for stalk lodging resistance continues to be important, especially if it also plays a role in ECB resistance. Missouri Second Cycle Stiff Stalk Synthetic (MoSCSSS) was selected for stalk strength by using a rind penetrometer. Twelve cycles of bidirectional selection have been completed, which has resulted in increased and decreased stalk strength in the high and low directions of selection, respectively. Selected cycles were evaluated for grain yield, stalk lodging, rind penetrometer resistance, first‐ and second‐generation ECB damage, leaf penetrometer resistance at the whorl stage and anthesis, and stalk traits including crude fiber, cellulose, lignin, and silica. Evaluation showed a decrease in grain yield in both directions of selection. Selection for high rind penetrometer resistance was effective at providing resistance to second‐generation ECB damage as well as resistance to stalk lodging. Leaf penetrometer resistance was higher in the high direction of selection at whorl stage, but reversed by anthesis where the low direction of selection had higher leaf penetrometer resistance. Crude fiber, cellulose, and lignin increased in the high direction of selection, but silica decreased in the high direction of selection. Significant correlations between the stalk traits analyzed demonstrated that stalk composition was important in providing rind penetrometer resistance, stalk lodging resistance, and second‐generation ECB resistance.

Phenotypic versus marker-assisted selection for stalk strength and second-generation European corn borer resistance in maize.

Maize ( Zea mays L.) stalk lodging is breakage of the stalk at or below the ear, which may result in loss of the ear at harvest. Stalk lodging is often intensified by the stalk tunneling action of the second-generation of the European corn borer (2-ECB) [Ostrinia nubilalis (Hübner)]. Rind penetrometer resistance (RPR) has been used to measure stalk strength and improve stalk lodging resistance, and quantitative trait loci (QTL) have been identified for both RPR and 2-ECB damage. Phenotypic recurrent selection (PS) increases the frequency of favorable alleles over cycles of selection. Several studies have indicated that marker-assisted selection (MAS) is also a potentially valuable selection tool. The objective of this study was to compare the efficiency of PS versus MAS for RPR and 2-ECB. Marker-assisted selection for high and low RPR was effective in the three populations studied. Phenotypic selection for both high and low RPR was more effective than MAS in two of the populations. However, in a third population, MAS for high RPR using QTL effects from the same population was more effective than PS, and using QTL effects from a separate population was just as effective as PS. Marker-assisted selection for resistance and susceptibility to 2-ECB using QTL effects from the same population was effective in increasing susceptibility, but not in increasing resistance. Marker-assisted selection using QTL effects from a separate population was effective in both directions of selection. Thus, MAS was effective in selecting for both resistance and susceptibility to 2-ECB. These results demonstrated that MAS can be an effective selection tool for both RPR and 2-ECB resistance. These results also validate the locations and effects of QTL for RPR and 2-ECB resistance identified in earlier studies.

Genetic Relationship of Stalk Strength and Ear Height in Maize

The rind penetrometer is an effective tool for measuring stalk strength in an effort to improve maize (Zea mays L.) germplasm for stalk lodging resistance. However, previous studies have indicated a significant negative correlation between rind penetrometer resistance (RPR) and ear height (EH). The correlation between RPR and EH is of interest in understanding response to selection for RPR. Has selection for high RPR resulted primarily in increased stalk strength per se and coincidentally lower ear heights, or has selection for high RPR resulted in lower ear heights and subsequently higher stalk strength? The objective of this study was to determine the genetic relationship between RPR and the correlated trait EH. To accomplish this goal, three F 2:3 populations were used to characterize and compare quantitative trait loci (QTL) for RPR, EH, and RPR adjusted for EH (RadjE). The original QTL analysis of RPR detected a total of 26 QTL across populations. Adjusting RPR for EH caused 11 of the original RPR QTL to lose their significance. However, the majority, 15 of 26, of the original RPR QTL remained significant as QTL for RadjE. Because EH clearly had an effect on RPR, adjusting RPR for EH likely resulted in more accurate descriptions of QTL for stalk strength per se. We have demonstrated that QTL analysis can be used to separate the effects of correlated traits from the genetic effects of the trait of interest, and recommend determining which correlated traits may influence measurement of the main trait before initiating a QTL experiment.

Quantitative Trait Locus Analysis of Stalk Strength in Four Maize Populations

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.