Stalk Lodging Research Articles

Random Mating before Selfing in Maize BC Populations

In maize (Zea mays L.) inbred development programs, F2 and BC1 populations between two inbreds are usually not random-mated before selfing. Previous results suggest random mating is not useful in F2 populations. A one-locus model, however, suggests random mating increases the genetic variance by 50% in a BC1 population without affecting the population means. The objective of this study was to determine the effect of random mating on the testcross means and variances of BC1 populations. Random-mated and nonrandom-mated backcross populations were developed for two genetic backgrounds, Iowa Stiff Stalk Synthetic (BSSS) and non-BSSS. Testcrosses of these four populations were evaluated at five locations in Minnesota and Wisconsin in 2002. For grain yield, grain moisture, plant height, ear height, root lodging, and stalk lodging, the differences between testcross means of random-mated and nonrandom-mated populations were not significant (P = 0.05), as expected. Testcross variances tended to increase with random mating for most traits in the two genetic backgrounds, but none of these differences was significant. Testcross means of the best 10% families did not differ significantly between random-mated and nonrandom-mated populations. Overall, the results indicated that random mating before selfing in BC1 populations is not useful in applied breeding programs.

Within‐Row Plant Spacing Variability Does Not Affect Corn Yield

Nonuniform plant spacing within the row in corn (Zea mays L.) may reduce grain yield. To investigate the response of corn to plant spacing variability, experiments were conducted at two locations in south‐central Ontario during 2000 and 2001. Six plant spacing treatments, 6.7 to 16.2 cm in standard deviations (SD), were established by planting Roundup Ready corn with increasing proportions of conventional corn seeds and then removing the conventional corn using glyphosate before three‐leaf stage. Using SD as well as short gap, long gap, double, and cluster as an index of plant spacing variability, effects of plant spacing variability on corn growth and grain yield were investigated. Averaged across locations and years, grain yield was not significantly affected by plant spacing variability. Plant spacing variability also had no significant effect on leaf number, plant height, leaf area index, and harvest index. There were no correlations between plant spacing variability and stalk lodging and barren or double ears. The lack of strong correlations among plant growth, grain yield, and plant spacing variability indicates that spacing uniformity within the range used in this study is not a significant factor in determining grain yield under commercial conditions and common plant densities used in Ontario.

Comparison of local and exotic maize varieties for stalk lodging components in a desert climate

A 2-year study on the influence of certain plant morphological traits as well as the chemical composition of the stalk on lodging in exotic and local maize groups was done at Sultan Qaboos University. The exotic group consisted of six varieties, while five varieties were represented in the local group. The soil type was classified as saline, the EC being 3.9–4.2 dS/m. In both maize groups, lodging was negatively correlated with grain yield, rind thickness and stalk breaking strength. Weight of 5-cm stalk section was negatively correlated with lodging in the local group but the exotic group showed no such correlation. In the exotic group, lodging was positively correlated with ear height and negatively correlated with stalk lignin and total nonstructural carbohydrate (TNC) concentration but no such correlations were represented in the local group. In a stepwise regression analysis, a four-variable model consisting of shelling percentage, stalk breaking strength, rind thickness and TNC had a coefficient of determination ( R 2) of 0.66, suggesting that 66% of the variability in lodging was due to variability in these characters acting together. Based on this result it was suggested that, in breeding for lodging resistance in maize in a desert climate, it may be worthwhile to focus on these four parameters.

Vegetable and Corn Yields in the United States, 1900-Present

-1 . The average yield for the 1990s was 7839 kg·ha -1 , 5 times the yield of the 1930s. A number of researchers have studied the basis for this increase by partitioning the contributions of improved genetics from those of improved management. Systematic studies performed by Duvick (1992) on corn hybrids grown from 1930 to 1989 in cen- tral Iowa demonstrated a linear increase in yield for the duration of this time period. An equivalent of 56% of the annual average gain in Iowa corn yields for this period was determined to be attributable to the ge net ic improvements of these hybrids (Duvick, 1984, 1992). It is clear from Duvick∑ s studies that much of the genetic change is represented by increased inputs and stress associated with high input intensive man age ment systems. Modern corn is much more resistant to drought stress associated with high population densities (30,000 plants/ha, 1930s; 80,000 plants/ha, 1980s) (Duvick, 1999). High levels of nitrogen fertilizer in creas es stalk lodging in grain crops. Modern corn is more resistant to stalk lodging than corn from the 1930s. High population den si ties also increase stalk lodging. Thus, in corn genetic changes were required for optimum use of increased inputs and higher population densities. In order to carry out comparative studies, seed of cultivars repre- senting different eras must be obtained, planted, and evaluated un der controlled conditions at a number of lo ca tion × year combinations. The experiment should include multiple production practices, re flect ing current management practices as well as older practices. Such studies have been con duct ed in a number of agronomic crops (soy bean (Glycine max L. Merrill), Specht and Williams, 1984; barley (Hordeum vulgare L.), Wycham and Rasmusson, 1983; sorghum (Sorghum bicolor L. Moench), Miller and Kebede, 1984), and in most cases large portions of the overall yield gain have been attributed to progress from plant breeding. However, Douches et al. (1996) found little influence of genetic improvement in the large increases in potato (Solanum tu- berosum L.) yields in the United States since the 1920s. Those workers found most of the gains from breeding programs during this period were associated with early maturity and improved tuber appearance. Thus, the primary reason yields increased was likely improvements in production practices.

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.

Contribution of population improvement to the development of maize lines with commercial value

The grain yield was increased by 8.2% per cycle (32.8% overall) in a population of Mindszentpusztai Yellow Dent (MYD), by 8.9% per cycle (35.6% overall) in a population of Mv Syn. I and by 4.9% per cycle (19.7% overall) in a population of Westigua when tested on the closed pedigree line HMv 124-2. Averaged over the three populations the rise in grain yield was 7.5% per cycle, giving a total of around 30% after four cycles. The grain moisture at harvest showed a slight but significant decrease, while there was no change in the percentage stalk lodging. It seems probable that this increase in grain yield was achieved not at the expense of other correlated characters, but as the result of a greater frequency of gene combinations having a positive effect on grain yield, since recurrent selection was combined with selection for multiple ears at high plant density. The hybrid performance of the improved populations was extremely good, reaching 87.9% of that of commercial hybrids. Over the last 25 years around 11,500 S1 families have been tested from a total of 115 populations (including the three discussed above) and the inbreeding of the selected families was continued until the homozygous state was reached. Despite careful selection, it has not proved possible to breed inbred lines suitable for the development of hybrids with commercial value. Further research will be required to discover the reasons for this failure.

Corn Yield Response of Bt and Near-Isolines to Plant Density

Optimum plant densities for Bacillus thuringiensis (Bt) corn (Zea mays L.) should be higher than non-transgenic corn subjected to European corn borer (ECB; Ostrinia nubilalis Hubner) damage because of the reduced potential for stalk lodging. The objectives of this research were to determine if yield differences occurred in Bt compared to near-isoline hybrids and to determine if different optimum densities exist for Bt and near-isolines. Bt hybrids were compared at target densities ranging from 20000 to 36000 plants per acre at different midAtlantic locations in 2000 and 2001. Yield increases ranged from 5 to 8% in 2000 at all locations. In contrast, Bt corn performed better than near-isolines at only one of three locations in 2001, with a 10% yield advantage. Relationships between yield of near-isolines and ECB damage were weak. Plant density affected yield at all locations in both years. Regression analysis of grain yield on plant density did not reveal a consistent hybrid response, although some evidence exists that suggests Bt hybrids are more efficient than near-isolines at producing yield as plant density increases. The inability to identify different optimum densities for Bt and near-isolines may have been due to low stalk lodging, plant density treatments that did not maximize yield in most instances, or the absence of different optimum densities.

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.

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.

Rind puncture resistance in maize: inheritance and relationship with resistance to pink stem borer attack

AbstractThe main pest of maize in north‐western Spain is the pink stem borer, Sesamia nonagrioides, and stem lodging is one of the consequences of attack. Since rind puncture resistance is related to stem lodging resistance, the objectives of this work were to estimate the genetic effects involved in the inheritance of rind puncture resistance and to determine the phenotypic correlation coefficients between rind puncture resistance and pink stem borer damage. Six generations from the crosses ‘CM109’בEP31’ and ‘CM109’בEP42’ and a 10‐inbred line diallel were evaluated in Pontevedra, Spain, in 1995 and 1996. The inheritance of rind puncture resistance had two significant components, one additive and one dominant. Non‐allelic and genotype × environment interactions were not significant. Improvement for internode rind puncture resistance to increase stem strength and stalk lodging resistance could have some positive influence on resistance to pink stem borer. However, its use as an estimator of pink stem borer resistance cannot be generalized and so must be restricted to programmes that involve materials exhibiting physical resistance to pink stem borer attack.

Response of Brazilian maize hybrids from different eras to changes in plant density

Maize ( Zea mays L.) hybrids differ in their response to plant population density. Enhancements in tolerance to crowding have been obtained around the world as the result of selecting the best yielding hybrids at dense stands over a wide testing area. However, the understanding of morpho-physiological determinants of maize endurance to the population density stress still needs improvement. This study aimed to evaluate the response of maize hybrids from different eras grown extensively in Brazil to the increase in plant sowing density and to identify agronomic traits that can account for the contrasting tolerance to high interplant competition. The trial was conducted in Lages, southern Brazil, during the growing seasons of 1999/2000 and 2000/2001. A split plot design was used. The double-cross hybrids Agroceres 12, Agroceres 303, and the single-cross hybrid Cargill 929, commercially released during the 1970s, 1980s and 1990s, respectively, were evaluated in the main plots. Four plant population densities were tested in the split plots: 25,000, 50,000, 75,000 and 100,000 plants ha −1. Maize was sown in no-tillage system, having black oat as the preceding winter crop. Canopy architecture parameters, tassel dry matter accumulation, flower synchrony, grain yield and its components were evaluated. The older hybrids Agroceres 12 and Agroceres 303 out-yielded modern-hybrid C 929 at the lowest plant population density. The increase in plant population increased barrenness, lengthened the anthesis–silking interval and decreased kernel set per ear more drastically for the older than for the modern-hybrid. Consequently, the higher the number of plants per unit area, the greater the edge between grain yield and kernel number per area of C 929 in relation to its older counterparts. Current hybrid’s better performance at supraoptimum plant population densities was favored by three sets of traits. First, by lower dry matter partition to the tassel, stimulating a more balanced allometric relationship between male and female inflorescence. Second, by a more compact canopy architecture, with shorter plants, fewer and more upright leaves, enhancing solar radiation interception. Third, by low ear insertion to plant height ratio, promoting greater resistance to stalk lodging. These traits contributed to higher grain yield and positive response to higher densities in the modern-hybrid.

Row Width and Plant Density Effects on Corn Grain Production in the Northern Corn Belt

Continued genetic improvement in the ability of hybrid corn (Zea mays L.) to withstand high plant density stress requires agronomists to periodically reassess optimal plant density and row width. Furthermore, the optimal plant density level and row width for corn grain yield may vary with location, primarily latitude, in the Corn Belt. This study was conducted to evaluate corn grain yield, harvest moisture, test weight, and stalk lodging with modern corn hybrids, as affected by row width and plant density in the northern Corn Belt. At six locations in 1998 and 1999, four hybrids differing in relative maturity, ear type, plant height, and leaf orientation were planted at row widths of 76, 56, and 38 cm and five plant density levels ranging from 56000 to 90000 plants ha−1. Plots were arranged randomly in a split‐split plot configuration. Results show that corn grain yield increased 2 and 4% and harvest moisture decreased by a factor of 2.1% when row width was narrowed from 76 cm to 56 cm and 38 cm, respectively. The highest plant density evaluated, 90000 plants ha−1, had the highest grain yield. Grain moisture decreased and grain test weight increases slightly as plant density increased. A hybrid × row width interaction was not observed indicating that hybrids that yield well in conventional 76‐cm row systems will also yield well in narrow row systems.

TopCross High‐Oil Corn Production

The TopCross grain production system is rapidly gaining popularity as the preferred method of producing high‐oil corn (Zea mays L.). A blend (TC Blend) of two types of corn is planted to produce TopCross high‐oil corn (HOC) grain. Limited information is available on the effects of the TopCross system on agronomic traits that may determine the profitability of HOC production. Field experiments and on‐farm studies were performed in 1995 to 1999 across a range of production environments in Ohio to compare the agronomic performance of TC Blends with their conventional counterparts (check hybrids). Grain yields of TC Blends averaged across experiments and on‐farm studies were 8% less than those of check hybrids. The TC Blends were as tolerant to drought conditions as the check hybrids. Stalk lodging and barrenness were comparable for TC Blends and check hybrids. Little evidence existed that kernel set in TC Blends was reduced by inadequate pollen availability due to the limited number of pollinator plants in the blend. Factors that may contribute to the differences in grain yields between TC Blends and check hybrids included lower plant populations in TC Blends at harvest, competition between the two components of the blend (TC Blend pollinators and male sterile grain parents), and the physiological cost of oil synthesis. The lower grain yield, higher grain moisture content, and lower test weight associated with TC Blends should be considered when determining TopCross HOC production costs, especially if HOC grain is being produced under contract.

Combining ability of twelve maize populations

Genetic progress depends on germplasm quality and breeding methods. Twelve maize populations and their crosses were evaluated to estimate combining ability and potential to be included as source populations in breeding programs. Plant height, point of insertion of the first ear, number of ears per plant, number of grains per ear, root and stalk lodging and grain yield were studied in two locations in Brazil, during the 1997/98 season. Genotype sum of squares was divided into general (GCA) and specific (SCA) combining ability. Results indicated the existence of genetic divergence for all traits analyzed, where additive effects were predominant. The high heterosis levels observed, mainly in Xanxerê, suggested the environmental influence on the manifestation of this genetic phenomenon. Populations revealed potential to be used in breeding programs; however, those more intensively submitted to selection could provide larger genetic progress, showing the importance of population improvement for the increment of the heterosis in maize.

Carbon Remobilization and Grain Filling in Japonica/Indica Hybrid Rice Subjected to Postanthesis Water Deficits

Continued genetic improvement in the ability of hybrid corn (Zea mays L.) to withstand high plant density stress requires agronomists to periodically reassess optimal plant density and row width. Furthermore, the optimal plant density level and row width for corn grain yield may vary with location, primarily latitude, in the Corn Belt. This study was conducted to evaluate corn grain yield, harvest moisture, test weight, and stalk lodging with modern corn hybrids, as affected by row width and plant density in the northern Corn Belt. At six locations in 1998 and 1999, four hybrids differing in relative maturity, ear type, plant height, and leaf orientation were planted at row widths of 76, 56, and 38 cm and five plant density levels ranging from 56000 to 90000 plants ha−1. Plots were arranged randomly in a split-split plot configuration. Results show that corn grain yield increased 2 and 4% and harvest moisture decreased by a factor of 2.1% when row width was narrowed from 76 cm to 56 cm and 38 cm, respectively. The highest plant density evaluated, 90000 plants ha−1, had the highest grain yield. Grain moisture decreased and grain test weight increases slightly as plant density increased. A hybrid × row width interaction was not observed indicating that hybrids that yield well in conventional 76-cm row systems will also yield well in narrow row systems.

Mapping QTLs associated with drought resistance in sorghum (Sorghum bicolor L. Moench).

Drought is a major abiotic stress factor limiting crop production. Identification of genetic factors involved in plant responses to drought stress will provide a solid foundation to improve drought resistance. Sorghum is well adapted to hot dry environments and regarded as a model for studying drought resistance among the grasses. Significant progress in genome mapping of this crop has also been made. In sorghum, rapid premature leaf death generally occurs when water is limited during the grain filling period. Premature leaf senescence, in turn, leads to charcoal rot, stalk lodging, and significant yield loss. More than 80% of commercial sorghum hybrids in the United States are grown under non-irrigated conditions and although most of them have pre-flowering drought resistance, many do not have any significant post-flowering drought resistance. Stay-green is one form of drought resistance mechanism, which gives sorghum resistance to premature senescence under soil moisture stress during the post-flowering period. Quantitative trait locus (QTL) studies with recombinant inbred lines (RILs) and near-isogenic lines (NILs) identified several genomic regions associated with resistance to pre-flowering and post-flowering drought stress. We have identified four genomic regions associated with the stay-green trait using a RIL population developed from B35 x Tx7000. These four major stay-green QTLs were consistently identified in all field trials and accounted for 53.5% of the phenotypic variance. We review the progress in mapping stay-green QTLs as a component of drought resistance in sorghum. The molecular genetic dissection of the QTLs affecting stay-green will provide further opportunities to elucidate the underlying physiological mechanisms involved in drought resistance in sorghum and other grasses.

Relationships of stay green trait in maize

Genetic variation for stay green character has been exploited in maize improvement mainly in the light of selecting high yielding rather then typical stay green genotypes. Stay green is an indicator of good plant health later in the season, reduced progressive senescence, tolerance to post-flowering drought and stalk lodging, what ensure superiority of stay green genotypes in comparison to non-stay green ones, especially in drought conditions. The objective of the study was to examine relationship of stay green trait with some vegetative characters in two genetically broad based maize populations. The most consistent correlations with stay green were established for leaf and stalk water content, which has been confirmed by path-coefficient analysis.

Conditioning effects of Striga hermonthica seed on field performance of maize

Seeds of the obligate parasite Striga hermonthica, germinate in response to stimulants in the root exudate of maize and other host crops. Under laboratory conditions, conditioning (defined as treatment with moisture) of Striga seeds for one to three weeks before exposure to germination stimulant is required for optimum germination. The objective of this study was to determine if maize performance and Striga emergence, both indices of resistance, were influenced by the interval between Striga seed infestation and maize planting, under high parasite inoculum (3000–6000 germinable seeds) as practiced in maize resistance breeding field nurseries. Four conditioning treatments were investigated: maize planted immediately after Striga seed infestation, and maize planted after one, two and three weeks after infestation. Experimental design was randomized complete block with four replications. Differences among the four conditioning treatments were not significant for maize damage score, height, stalk lodging, number of ears harvested, grain yield and number of emerged Striga plants. Thus, maize planted on the same day as Striga infestation showed similar response as maize planted one to three weeks after infestation. Using high seed inoculum, maize can be planted immediately after Striga infestation in maize breeding nurseries. Combining Striga seed infestation and maize planting into a single field operation is convenient and reduces cost of screening.

Breeding Potential of Intra‐ and Interheterotic Group Crosses in Maize

New maize (Zea mays L.) inbreds are usually developed within a heterotic group. However, breeders sometimes use commercial hybrids as a nonconventional (i.e., interheterotic group) source of new inbreds. The effects of disrupting heterotic patterns in maize, by selfing from commercial hybrids, are not well understood. My objective was to compare intra‐ and interheterotic group crosses as sources of new inbreds. The inbreds B73 and H93 represented the Iowa Stiff Stalk Synthetic (BSSS) heterotic group, whereas Mo17 and B99 represented the non‐BSSS heterotic group. I estimated testcross means and genetic variances in two intragroup F2 populations: (B73 × H93)F2 testcrossed to Mo17 × B99; and (Mo17 × B99)F2 testcrossed to B73 × H93. Likewise, I estimated testcross means and genetic variances in two intergroup F2 populations: (B73 × Mo17)F2 testcrossed to H93 × B99; and (H93 × B99)F2 testcrossed to B73 × Mo17. Testcrosses of 150 individual plants from each F2 population were evaluated at three Indiana locations in 1999. Testcross means for grain yield were 1.0 Mg ha−1 higher in the intra‐ than in the intergroup F2 populations. Grain moisture and stalk lodging testcross means were lower in the intra‐ than in the intergroup F2 populations. Testcross genetic variances (VTC) for grain yield were similar among the four populations. Favorable epistatic combinations may have been broken up in the (B73 × Mo17)F2 population. The results underscore that the success of developing new inbreds from an intergroup population largely depends on finding a suitable tester for the resulting intergroup inbreds.

Quantitative trait loci for the stay green trait in sorghum (Sorghum bicolor L. Moench): consistency across genetic backgrounds and environments

Stay green in sorghum (Sorghum bicolor L. Moench) is characterized by the plant’s ability to tolerate post-flowering drought stress, thereby delaying the premature leaf and plant death. It contributes to normal grain filling and reduces the incidence of stalk lodging and charcoal rot disease during the late stages of grain development. Breeding for improving post-flowering drought tolerance in sorghum hybrids remains an important objective of sorghum breeders. Since evaluation of the stay green response is difficult and unreliable under field conditions, due to the timing and intensity of moisture stress and large environmental interaction, progress in improving drought tolerance by conventional breeding methods has been slow. The objective of the present study was to determine the consistency of quantitative trait loci (QTLs) controlling stay green in sorghum. We re-evaluated the Recombinant Inbred Line (RIL)-mapping population from the cross B35 x Tx7000 in two locations over 2 years and compared it with earlier reports. Analysis using the combined stay green-rating means of seven environments and the expanded molecular map reconfirmed all four stay green QTLs (Stg1, Stg2, Stg3 and Stg4) that were identified earlier by Xu et al. (2000). Similarly, comparison of the stay green QTL locations with earlier reported results indicated that all four stay green QTLs showed consistency across different genetic backgrounds. Examination of the stay green QTL profiles of the best and poorest stay-green lines indicated that three stay green QTLs, Stg1, Stg2 and Stg3, appear to be important for the expression of this trait when the percent phenotypic variation, and the consistency in different backgrounds and different environments, are considered. A significant epistatic interaction involving Stg2 and a region on linkage group C was also identified for the stay green and chlorophyll content. We concluded that Stg2 is the most important QTL controlling stay green, explaining the maximum amount of phenotypic variation. This report further strengthens our view to target the Stg2 QTL region for gene discovery in order to improve the basic understanding of the stay green phenomenon, which might be helpful in manipulating this trait not only in sorghum but also in other cereal crop species.