Stalk Lodging Research Articles

Identifying quantitative trait loci and determining closely related stalk traits for rind penetrometer resistance in a high-oil maize population

Stalk lodging in maize causes annual yield losses between 5 and 20% worldwide. Many studies have indicated that maize stalk strength significantly negatively correlates with lodging observed in the field. Rind penetrometer resistance (RPR) measurements can be used to effectively evaluate maize stalk strength, but little is known about the genetic basis of this parameter. The objective of this study was to explore a genetic model and detect quantitative trait loci (QTL) of RPR and determine relationships between RPR and other stalk traits, especially cell wall chemical components. RPR is quantitative trait in nature, and both additive and non-additive effects may be important to consider for the improvement of RPR. Nine additive-effect QTLs covering nine chromosomes, except chromosome 5, and one pair of epistatic QTLs were detected for RPR. CeSA11 involved in cellulose synthesis and colorless2 involved in lignin synthesis were identified as possible candidate genes for RPR. Internode diameter (InD), fresh weight of internode (FreW), dry weight of internode (DryW), fresh weight and dry weight as well as cell wall components per unit volume significantly positively correlated with RPR. The internode water content (InW) significantly negatively correlated with RPR. Notably, these traits significantly correlated with RPR, and the QTLs of these traits co-localized with those of RPR. The corresponding results obtained from correlation analysis and QTL mapping suggested the presence of pleitropism or linkage between genes and indicated that these different approaches may be used for cross authentication of relationships between different traits.

Evaluation of new NS maize hybrids using biplot analysis

The study analyzed two-year results of a testing of 20 new maize hybrids from FAO MG 600 as compared to a standard. Data on the hybrids NS6683, NS6686, NS281633, and NS396432 are discussed in the paper in greater detail. In order to study grain yield, grain moisture, root and stalk lodging, and resistance to pests and diseases, field trials using a RCB design with four replicates were conducted in six locations in 2009 and five locations in 2010. The results were presented in the form of GGE biplots in order to rank hybrids relative to the standard while taking into account the genotype x environment interaction and to identify the highest-yielding genotypes in different environments. It was determined that the new NS hybrids had higher grain yield than the standard by 0.883 to 1.720 tha-1, lower grain moisture by 0.85 to 2.54%, better tolerance to root and stalk lodging, and pest and disease resistance on a par to the standard. The study identified so-called ideal locations for particular hybrids, which may be of use when determining which areas the hybrids are best suited for.

Harvest Date Influence on Dry Matter Yield and Moisture of Corn and Stover

Harvest date greatly affects the biomass yield, moisture, and quality of corn and stover. Traditionally, corn and stover have been harvested at lower moisture levels. However, corn stover and grain can be more effectively utilized as animal feed and biomass-ethanol feedstock if they are collected before in-field dry down. This study determined dry matter yield, moisture content, and quality of corn and stover before, during, and after grain maturity in central Illinois. The two-year average kernel moisture was 37.4% (w.b.) when reaching physiological maturity. At the same time, the average stover moisture was 67.7% (w.b.). The dry matter yield of grain increased rapidly until reaching grain maturity and remained relatively stable after grain maturity, with an average yield of 11.2 t ha-1 over the two-year study. For corn stover, the two-year average dry matter yield was 14.7 t ha-1 at the beginning of the study (filling stage), and it decreased to 13.2 t ha-1 at grain physiological maturity and further decreased to 11.0 t ha-1 throughout grain dry down. During grain dry down, the moldy kernel percentage increased from 2.1% to 4.1% and the stalk lodging percentage increased from 1.2% to 3.6%. The results of this study showed that early harvest of corn and stover at grain maturity has several advantages: higher dry matter yield of stover, lower moldy kernel percentage, and fewer plant lodgings.

Differences in Responding Sensitivity to Ethephon among Different Maize Genotypes

Lodging is one of the key limiting factors causing serious yield decline in maize cultivation, the plant growth regulator ethephon and its complex formulation are applied to improve quality and lodging-resistance ability of stalks, which is an effective way to prevent stalk lodging. The responses in plant-type, physiological and biochemical characteristics of maize hybrid Nongda 108, Ludan 981 and their corresponding parents Xu 178, Huang-C, Qi 319, and lx9801 varieties, were studied in field condition, with 200 mg L 1 ethephon foliage spray at jointing stage. The results showed that ethephon significantly inhibited the elongation of the first to sixth basal internodes for Nongda 108 and Ludan 981, the plant height and the ear height of Nongda 108 and Ludan 981 were significantly reduced. Ethephon remarkably increased the activities of phenylalanine ammonia lyase (PAL) and indole acetic acid oxidase (IAAO) and content of abscisic acid (ABA) in elongating internodes, and decreased contents of auxin (IAA) and gibberellin (GA4). The genetic traits were analyzed, the plant height and the ear height of Xu 178, Huang-C, Qi 319, and lx9801 were significantly reduced after ethephon treating, and the length of basal internodes was shortened significantly. The PAL and IAAO activities in elongating internodes were significantly increased after ethephon treating. The endogenous IAA content of elongating internodes was significantly decreased, ABA content was significantly increased, but GA4/ABA ratio was significantly decreased. It is indicated that the response differences to ethephon among different hybrids may be attributed to the different sensitivities of the parents lines, showing corresponding performance in plant height, ear height, PAL, IAAO activities and endogenous hormone levels.

Trends of grain yield and plant traits in Chinese maize cultivars from the 1950s to the 2000s

Retrospective analyses may provide an understanding of unexploited genetic potential and indicate possible pathways for future yield improvement. The objectives of this study were to present maize(Zea mays L.)yield trends and plant traits changes for maize cultivars from the 1950s to the 2000s in China. Trials were conducted at three locations in 2007 and 2008, and at four locations in 2009. Twenty-seven single hybrids, four double-cross hybrids, and four open-pollinated varieties, were grown at three densities at each location each year. 56% of total yield gain was contributed to breeding from 1950 to 2000. New hybrids had more resistance to compound stress. Levels of response of all hybrids to higher-yielding environments were similar, and greater than that of OPVs. All maize cultivars showed morphological changes for all characteristics tested in a volatile manner from 1950 to 2000, except for relatively stable leaf number. ASI decreased and tolerance to root lodging improved, which were enhanced at higher plant densities. There were no trends for other characteristics at higher densities. Shorter maturity, smaller plant size and more tolerance to root and stalk lodging will be required for further yield improvement. Chinese maize yield improvement can benefit from agronomic strategies at higher plant densities.

Corn Response to Harvest Date as Affected by Plant Population and Hybrid

Many corn (Zea mays L.) growers in Ohio delay harvest as a management strategy for reducing grain drying costs. However, this practice increases the risk of yield loss due to extended crop weathering. Field studies were conducted at three Ohio locations in 2002 to 2004 to determine effects of three harvest date periods, early to mid‐October (HD1), early to mid‐November (HD2), and early to mid‐December (HD3), and four plant densities (59,000; 74,000; 89,000; and 104,000 plants ha−1) on the agronomic performance of four corn hybrids differing in maturity and stalk strength. Interactions between harvest date, plant population, and hybrid indicated that decreases in grain yield and increases in stalk rot and lodging associated with harvest delays were influenced by plant population and hybrid characteristics. Significant yield losses due to delayed harvest were evident only after HD2. When harvest was delayed until HD3, yields decreased at the higher plant populations, especially at 104,000 plants ha−1. Stalk rot and lodging increased at the higher plant populations, and this effect was magnified by late harvesting. Hybrids with lower stalk strength scores exhibited greater stalk lodging and yield loss when harvest was delayed beyond HD2. Stalk rot showed a greater increase between HD1 and HD2, whereas stalk lodging generally showed a greater increase after HD2. Harvest delays after HD2 achieved little or no additional grain drying. Results of this study indicate that harvest delays should be avoided when using plant populations above 74,000 plants ha−1, especially if planting hybrids that are not highly rated for stalk strength.

Selection and Adaptation to High Plant Density in the Iowa Stiff Stalk Synthetic Maize (Zea mays L.) Population

The plant density at which maize (Zea mays L.) hybrids achieve maximum grain yield has increased throughout the hybrid era, whereas grain yield on a per plant basis has increased little. Changes in grain yield, grain moisture, test weight, and stalk and root lodging have been well characterized in comparisons of commercial hybrids representing different eras of hybrid maize production but have yet to be examined in a recurrent selection program. The objective of this experiment was to determine if direct selection for grain yield and agronomic performance in the Iowa Stiff Stalk Synthetic (BSSS) population has indirectly improved adaptation to high plant density. Material from an unselected base population, BSSS, was compared to the most advanced cycles of selection from three different recurrent selection programs at seven Iowa locations in 2008 and 2009. Populations were compared at densities of 38,300, 57,400, 77,500, and 95,700 plants ha−1. Treatments were replicated twice at each location and arranged in a split plot design. Selection produced notable improvement in adaptation to high plant density for grain yield and stalk lodging. Selection did not have large impacts on density response for root lodging, test weight, or grain moisture. Because of the improvement in density response for grain yield and stalk lodging without major negative changes in other traits, our data suggest that selection has improved adaptation to high plant density in these populations.

Tillage, Crop Rotation, and Hybrid Effects on Residue and Corn Anthracnose Occurrence in Wisconsin.

Corn anthracnose (Colletotrichum graminicola) is an important disease of field corn (Zea mays). Two phases, leaf blight and stalk rot, can reduce yield through either premature leaf senescence or reduced grain harvest due to stalk lodging. Corn residue is an important source of primary inoculum and is increased through cultural practices such as no-tillage and continuous corn cropping, which are common practices in Wisconsin. Field studies conducted at the Arlington Agricultural Research Station (ARS) and the West Madison ARS showed that the incidence and severity of anthracnose leaf blight were higher in continuous-corn crop rotations than in soybean-corn rotations (91% higher incidence, 24 to 78% higher severity). Anthracnose stalk rot was marginally affected by tillage in 2008 (P = 0.09), with higher incidence in chisel-plowed treatments. There was a positive association between spring residue cover and anthracnose leaf blight but no association was found between residue and stalk rot. No association was found between anthracnose leaf blight and stalk rot. There was a negative association between anthracnose leaf blight and yield but not between anthracnose stalk rot and yield. Managing residue levels through crop rotation would help to reduce anthracnose leaf blight but further work is needed to elucidate factors that lead to stalk lodging prior to harvest.

Testcross Response to Four Cycles of Half‐sib and S2 Recurrent Selection in the BS13 Maize (Zea mays L.) Population

ABSTRACTInbred progeny recurrent selection has been shown to be theoretically superior to several forms of noninbred‐progeny recurrent selection. However, recent improvements to theory and empirical evidence suggest that inbred‐progeny recurrent selection is not a superior method of recurrent selection. In the BS13(S) population, inbred‐progeny recurrent selection has not been effective at improving population per se performance. However, no other selection programs have been evaluated in BS13(S), so there is no basis to compare inbred‐progeny recurrent selection in BS13(S) to other methods to determine if other methods might be more effective. Four cycles of half‐sib selection with inbred line B97 as tester have been completed. The first four cycles of half‐sib selection and first four cycles of inbred‐progeny selection were testcrossed to B97 and evaluated in a replicated experiment in 2007 and 2008. Half‐sib selection improved grain yield, grain moisture, stalk lodging, root lodging, test weight, and final plant density, whereas inbred‐progeny selection did not improve any of these traits. This study adds to growing empirical literature suggesting that inbred‐progeny recurrent selection is inferior to noninbred‐progeny selection methods. A hypothesis has been put forth that pseudo‐overdominance caused by linkage disequilibrium may have limited response to inbred‐progeny recurrent selection in BS13(S) as well as other maize populations.

Combining ability of early-maturing quality protein maize inbred lines adapted to Eastern Africa

Adapted early-maturing quality protein maize (QPM) hybrids with high grain yield potential in Eastern Africa would benefit maize farmers through increased grain production and subsequently higher income but they are not widely available. Fourteen early-maturing QPM inbred lines developed from POOL15QPM-SR, were crossed using the diallel mating design. The resulting single-cross hybrids were evaluated under six well-watered, drought stress and low nitrogen conditions at six locations in Eastern Africa. The objectives were to assess the grain yield potential of early-maturing F 1 QPM hybrids, estimate the general combining ability (GCA) and specific combining ability (SCA) for grain yield and other agronomic traits and determine the relationship between grain yield and other agronomic traits of the QPM hybrids. Days to anthesis, days to silking, anthesis–silking interval, ears per plant, root and stalk lodging, ear aspect, and grain yield were measured. Variation among hybrids was significant for all traits except root lodging. The best single-cross hybrid across environments was POOL15QPMFS538-B-3-B-B × POOL15QPMFS462-B-4-B-B (5.30 t ha −1). Mean squares due to GCA were significant, whereas mean squares due to SCA were not for measured traits indicating that additive genetic effects were much more important in this set of genotypes. Inbred line POOL15QPMFS538-B-3-B-B exhibited very good GCA effects for grain yield in well-watered environments and across environments for grain yield (0.74 t ha −1). Inbred line Pool15QPMFS478-B-3-B-B had the best GCA effect for grain yield under managed drought stress (0.26 t ha −1), while inbred line POOL15QPMFS319-B-2-B-B had the best GCA effect (−1.11 days) for reduced days to anthesis across environments. The new QPM inbred lines with desirable traits could be used to improve grain yield and protein quality of maize breeding programs in Eastern Africa.

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.

Response of Bt and Near‐Isoline Corn Hybrids to Plant Density

Transgenic Bt (Bacillus thuringiensis) corn (Zea mays L.) hybrids with resistance to corn rootworm (CRW; Diabrotica spp.) or European corn borer [ECB; Ostrinia nubilalis (Hübner)] can have greater tolerance to water and nutrient stress, and thus may have higher optimum plant densities. Experiments were conducted following soybean [Glycine max (L.) Merr.] over nine site‐years in Illinois to determine whether the response to plant density for corn grain yield and net return to seed cost differ among near‐isoline hybrids with no insect resistance, Bt resistance to CRW, or Bt resistance to CRW plus ECB. Similar experiments were conducted over three site‐years in Iowa following both soybean and corn for near‐isoline hybrids with Bt resistance to ECB or ECB plus CRW. Larval CRW injury was low in Iowa and stalk lodging was minimal in all experiments. Across site‐years in Illinois and in both crop sequences in Iowa, grain yield and net return to seed cost were not affected by hybrid. Net return to seed cost within $2.50 ha−1 of the maximum occurred with densities of 76,300 to >98,600 plants ha−1 following soybean in Illinois, 87,100 to 93,400 plants ha−1 following soybean in Iowa, and 87,400 to 95,700 plants ha−1 following corn in Iowa. Yields within these optimum plant densities were 15.9, 16.1, and 15.4 Mg ha−1, respectively. When CRW and ECB are managed or are at low levels, optimum plant density is similar between hybrids with or without resistance to these pests.

Corn Response to Nitrogen Fertilizer as Affected by Planting Date and Hybrid

Producers of the eastern Corn Belt are often forced to either delay corn (Zea mays, L.) planting or replant due to unfavorable early season growing conditions. In these situations producers may decrease N rates due to decreased yield potential or switch to short season hybrids to reduce the risk of frost injury prior to maturity. Hybrids with differing yield potential may have different N requirements, but definitive research to determine the impact of hybrid selection on N response is lacking. Field experiments were conducted in Ohio during 2006 and 2007 to evaluate if corn grain yield and stalk lodging attributed to N fertilizer is affected by hybrid or planting date. This experiment evaluated two planting dates (late April/early May and early/mid-June), with subplots comparing N fertilizer rates (0, 60, 120, and 180 lb N/acre), and sub-subplots containing corn hybrids of differing maturities (104, 108, 109, and two 113 days relative maturity). In 2006, planting date did not affect the economically optimum N fertilizer rate (EONR), although late planted corn did produce lower grain yields. In 2007, late-planted corn was less responsive to N with the optimum N rate being 38 lb N/acre less than early-planted corn. Differences in N response between hybrids were noted, but optimum N rates were not markedly different.

Stacked Corn Hybrids Show Inconsistent Yield and Economic Responses in New York

Stacked (two to three transgenic traits) corn (Zea mays L.) hybrids represented 40% of U.S. corn in 2008, despite limited agronomic studies. Field‐scale studies were conducted on four farms in New York for 2 yr to evaluate the agronomics and economics of double‐stacked {glyphosate resistance and Bt (Bacillus thuringiensis) European corn borer [Ostrinia nubilalis (Hübner)] trait} hybrids when following soybean [Glycine Max (L.) Merr.], as well as triple‐stacked [additional Bt corn rootworm (Diabrotica spp.) trait] hybrids in continuous corn. Stacked hybrids vs. near‐isolines had mostly lower weed densities, root damage ratings, and stalk lodging under generally low pest and lodging conditions in both rotations. Double‐stacked hybrids vs. near‐isolines yielded similarly when following soybean, but 5.7 and 3.6% higher at two sites where lodging exceeded 11%, and similarly at two sites where lodging averaged <3% in near‐isolines in continuous corn. Triple and double‐stacked hybrids yielded similarly. Grain moisture averaged 15 g kg−1 greater in stacked hybrids vs. near‐isolines in both rotations, but similarly between double and triple‐stacked hybrids in continuous corn. Partial returns had site × hybrid trait interactions in both rotations as increased yield revenue offset increased drying costs for double‐stacked hybrids vs. near‐isolines for three site‐rotation comparisons, resulting in $45 to $89 ha−1 profit gain, but not for two‐site rotation comparisons, resulting in $47 to $71 ha−1 profit loss. If stacked hybrids with the Bt corn borer trait have higher grain moisture, growers in northern latitudes should balance potential corn borer occurrence against increased drying costs.

Effects of Silicon and Drought Stress on Tuber Yield and Leaf Biochemical Characteristics in Potato

Silicon has beneficial effects on many crops, mainly under biotic and abiotic stresses. Silicon can affect biochemical, physiological, and photosynthetic processes and, consequently, alleviates drought stress. However, the effects of Si on potato (Solanum tuberosum L.) plants under drought stress are still unknown. The objective of this study was to evaluate the effect of Si supply on some biochemical characteristics and yield of potato tubers, either exposed or not exposed to drought stress. The experiment was conducted in pots containing 50 dm3 of a Typic Acrortox soil (33% clay, 4% silt, and 63% sand). The treatments consisted of the absence or presence of Si application (0 and 284.4 mg dm−3), through soil amelioration with dolomitic lime and Ca and Mg silicate, and in the absence or presence of water deficit (−0.020 MPa and −0.050 MPa soil water potential, respectively), with eight replications. Silicon application and water deficit resulted in the greatest Si concentration in potato leaves. Proline concentrations increased under lower water availability and higher Si availability in the soil, which indicates that Si may be associated with plant osmotic adjustment. Water deficit and Si application decreased total sugars and soluble proteins concentrations in the leaves. Silicon application reduced stalk lodging and increased mean tuber weight and, consequently, tuber yield, especially in the absence of water stress.

Agronomic assessment of Bt trait and seed or soil-applied insecticides on the control of corn rootworm and yield

Corn rootworm ( Diabrotica spp.) has become the most concern and widespread insect pest of corn ( Zea mays L.) production in North America. Two field experiments were conducted to assess the agronomic and yield performance of transgenic rootworm trait, Bacillus thuringiensis (Bt) Cry3Bb, seed-coating treatment, and a soil-applied insecticide under natural corn rootworm infestation. Experiment 1 compared a conventional corn hybrid with and without insecticide (Force 3G) with its near isoline Bt hybrid from 2003 to 2005, on a clay loam soil. Experiment 2 investigated the same treatments as in Experiment 1 plus an additional seed-coated Poncho treatment on a sandy loam in 2004 and 2005. Rootworm population before the crop anthesis, root node injury and root:shoot dry weight ratio during the early grain filling stage, and stalk lodging and grain yield were determined. Our data showed that rootworm population diminished over the 3 years owing to rootworm displacement and adverse weather conditions. At the clay loam site, both Force 3G and the Bt hybrid significantly reduced the larval populations, root injury and lodging score, and increased root:shoot ratio. Over the 3 years, grain yields of the Bt hybrid were 11–66% greater than the untreated non-Bt isoline hybrid; yield of the non-Bt hybrid treated with Force 3G was also significantly greater than the same untreated non-Bt hybrid in 2 of 3 years. Despite less root node injury in the first rows of non-Bt plants adjacent to the Bt plots was observed, yield benefit of this effect remained to be proven. On sandy loam soil, the larval population was very low and there were no differences in root node injury and plant lodging among all the four treatments in either 2004 or 2005. The yield of the Bt hybrid was up to 10% greater than its non-Bt isoline hybrid treated or not with an insecticide in 1 year. Our data showed that Bt rootworm seed technology was effective to control the rootworm larvae and protected grain yield under severe infestation. Furthermore, our data suggest that some of the gain in Bt hybrid yield may be attributed to the genetic transformation as observed in sandy loam soil experiment. In all cases, corn producers should be aware of the pest history, rootworm pressure in relation to economic threshold, soil type and the expected cost-to-benefit ratio before deciding to adopt any protective measures.

Parâmetros biométricos e produtividade da cana-de-açúcar após tombamento dos colmos

Os efeitos do tombamento dos colmos à produtividade da cana-de-açúcar são do interesse de pesquisadores em diversas regiões do mundo; no Brasil, entretanto, essa pesquisa é escassa. O objetivo deste trabalho foi avaliar os efeitos causados pelo tombamento e o aparecimento de brotões em parâmetros biométricos e na produtividade de duas variedades de cana-de-açúcar. O experimento foi desenvolvido no município de Jaú (SP), no período de março de 2003 a setembro de 2004. O delineamento experimental foi o de blocos ao acaso, em fatorial com quatro tratamentos (duas variedades e dois manejos de condução da cultura) em quatro repetições. Os manejos consistiram de plantas mantidas eretas e de plantas sujeitas ao tombamento dos colmos. Avaliaram-se dados biométricos e quantificaram-se brotões aos 5, 50, 95, 140 e 185 dias após o tombamento (DAT). Os valores de comprimento e números de colmos foram aumentados pelo tombamento até 95 DAT, mas a emissão de brotões foi favorecida, com conseqüente aumento da produtividade agrícola das variedades. Esses resultados são indicativos de que a colheita de colmos deve ser realizada após 95 dias do tombamento das plantas a fim de se evitar excesso de brotões na matéria-prima.

Mapping and validation of quantitative trait loci for resistance to Cercospora zeae-maydis infection in tropical maize (Zea mays L.)

Breeding for resistance to gray leaf spot, caused by Cercospora zeae-maydis (Cz) is paramount for many maize environments, in particular under warm and humid growing conditions. In this study, we mapped and characterized quantitative trait loci (QTL) involved in the resistance of maize against Cz. We confirmed the impact of the QTL on disease severity using near-isogenic lines (NILs), and estimated their effects on three major agronomic traits using their respective near isogenic hybrids (NIHs), which we obtained by crossing the NILs with an inbred from a complementary heterotic pool. We further validated three of the four QTL that were mapped using the Multiple Interval Mapping approach and showed LOD values>2.5. NILs genotype included all combinations between favorable alleles of the two QTL located in chromosome 1 (Q1 in bin 1.05 and Q2 in bin 1.07), and the allele in chromosome 3 (Q3 in bin 3.07). Each of the three QTL separately significantly reduced the severity of Cz. However, we found an unfavorable epistatic interaction between Q1 and Q2: presence of the favorable allele at one of the QTL allele effectively nullified the effect of the favorable allele at the other. In contrast, the interaction between Q2 and Q3 was additive, promoting the reduction of the severity to a greater extent than the sum of their individual effects. When evaluating the NIH we found significant individual effects for Q1 and Q3 on gray leaf spot severity, for Q2 on stalk lodging and grain yield, and for Q3 on grain moisture and stalk lodging. We detected significant epitasis between Q1 and Q2 for grain moisture and between Q1 and Q3 for stalk lodging. These results suggest that the combination of QTL impacts the effectiveness of marker-assisted selection procedures in commercial product development programs.

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.

Genetic Correlation between Corn Performance in Organic and Conventional Production Systems

Cultivars bred under conventional production systems may not be optimum for organic production systems. Our objective was to determine if, on the basis of quantitative genetic parameters, separate corn (Zea mays L.) breeding programs are needed for organic and conventional production systems. Testcrosses of 119 intermated B73 × Mo17 recombinant inbreds were evaluated in organic and conventional systems in both Waseca and Lamberton, MN, in 2006. Differences in trait means between the two production systems were significant for grain moisture, plant height, and ear height but not significant for grain yield, root lodging, stalk lodging, and stay green. The organic system led to a smaller testcross genetic variance for grain yield and higher testcross genetic variances for all other traits. The organic system led to a lower heritability for grain yield and a higher heritability for root lodging, stay green, and ear height. Genetic correlations for performance in the two production systems were 0.84 for grain yield; greater than 0.90 for grain moisture, plant height, and ear height; and about 0.50 for root lodging and stay green. The predicted ratio between the correlated response and direct response to selection in the organic system was near 1.0 for grain yield and moisture and considerably less than 1.0 for other traits. These results suggest that high‐yielding cultivars for organic systems can be developed largely by screening conventional inbreds and hybrids for their performance under organic systems.