Response of maize (Zea mays L.) to post-emergence applications of topramezone

Topramezone is a new herbicide for post-emergence control of broadleaf and grass weeds in maize. Two field experiments were conducted in northern Greece in 2008 and 2009 to determine the response of grain maize to topramezone applied with the adjuvant DASH at 2–4, 4–6 and 6–8 maize leaf stage. In both years, plant height, cob number and yield were not differently affected with the use of herbicide at these growth stages, indicating no difference in selectivity and a similar response of maize to the three post-emergence applications of topramezone. Slight injury symptoms of leaf bleaching were observed in the second year, however, they were transient with no lasting injury on maize growth.     

Control of volunteer cereals with post-emergence herbicides in maize (Zea mays L.)

Volunteer winter cereals are found sporadically in maize (Zea mays L.) fields across southern Ontario. Seven field trials were conducted over a two-year period (2006 and 2007) at four locations to determine the efficacy of five acetolactate synthase (ALS)-inhibiting herbicides for the control of volunteer cereals applied at two post-emergence application timings (2–4 and 4–7 maize leaf tips). The volunteer cereals were a hard red winter wheat (Triticum aestivum L.) (‘Hyland AC Morley’), soft red winter wheat (‘Pioneer 25R47’), soft white winter wheat (‘Pioneer 25W41’), and a autumn rye (Secale cereale L.) (‘FR’) cultivar. Volunteer cereal competition in maize resulted in a yield reduction of up to 44%. Foramsulfuron, nicosulfuron, nicosulfuron/rimsulfuron provided greater than 70% control of the volunteer cereals at 56 days after treatment (DAT), while primisulfuron and rimsulfuron provided greater than 60% control. Volunteer cereal control with early and late application was greater than 82 and 61%, respectively. Hard red winter wheat was the most sensitive to the ALS-inhibiting herbicides with control of 84–93%. Soft red and soft white winter wheat cultivars were intermediate in sensitivity with control of 76–87%, while autumn rye was the least sensitive with control of at 56–71% control at 56 DAT. Maize yields were improved when volunteer cereals were controlled with the use of herbicides compared to the weedy control, but were lower than the weed-free control. Early herbicide application resulted in improved control of volunteer cereals and higher maize yield.     

Variability of grain productivity and energy profile of maize (Zea mays L.) genotypes

The goal of the present work was to test if there is genetic variability between precocious and superprecocious cycle maize genotypes in terms of grain productivity and energy profile. Data from two separate experiments were used. An experiment was conducted with 36 precocious cycle genotypes and another experiment was conducted with 22 superprecocious cycle genotypes. The following variables were measured: grain productivity (PROD), ethereal extract (EE), starch (ST), amylose (AML), and nitrogen-corrected apparent metabolizable energy (AMEn). For all variables, basic statistics and analysis of variance was performed. For each experiment, the genotypic correlation matrix was calculated and the multicollinearity was evaluated. Then, the Mahalanobis generalized distance matrix was calculated, the clustering of the genotypes was performed and the averages of the groups formed were compared, separately for each experiment. There was genetic divergence between precocious genotypes, as well as between superprecocious genotypes, especially in terms of grain PROD, EE concentration, and AML concentration. Groups of more productive genotypes presented lower EE and higher AML grain concentrations. The results of the present study indicated that it is possible to plan crossings between groups of genotypes in terms of PROD, EE and AML, with the goal of maximizing heterosis.     

Yield and quality losses caused by common rust (Puccinia sorghi Schw.) in sweet corn (Zea mays) hybrids

Yield and quality of fresh ears were measured in field plots of selected hybrids of sweet corn (Zea mays L.) that were affected by rust (Puccinia sorghi Schw.) or were nearly rust-free (mancozeb-sprayed). In 1978, 28 hybrids were tested. Losses in total yield ranged from zero in the more resistant entries to nearly 50% in more susceptible entries. In 1979, three cultivars were planted. Yield losses of these cultivars were similar in ranking order to those in 1978, although the loss was greater in late-planted plots because of the greater final severity of the disease. Losses in total yield in late-planted sweet corn were 18%, 26% and 49% for cv. Sugarloaf (most resistant), cv. Jubilee (intermediate) and cv. Style Pak (most susceptible), respectively.     

Ranking of partial resistance to common rust (Puccinia sorghi Schr.) in 30 sweet corn (Zea mays) hybrids

Thirty sweet corn (Zea mays) hybrids were evaluated for resistance to rust (Puccinia sorghi Schr.) for 3 years in an artificially inoculated field plot at St Paul, Minnesota. On the basis of visual determinations of rust severity, these cultivars were ranked according to level of resistance. All of them allowed at least some rust to develop, but the degree of final rust severity varied considerably. Correlation coefficients between the rust severity scores recorded for the hybrids in all three pairs of years were 0·68 (1978–1979), 0·79 (1978–1980) and 0·86 (1979–1980). Spearman's rank correlation coefficients were 0·76, 0·89 and 0·82, respectively, for the same comparisons.     

Guidelines for in-season nitrogen application for maize (Zea mays L.) based on soil and terrain properties

Nitrogen (N) fertilizers are often applied to maize (Zea mays L.) in excess of economically optimal rates because of the uncertainty of dealing with seasonal and spatial variability. A better understanding of the relationships among field, apparent soil electrical conductivity (EC_a), elevation, slope and seasonal characteristics is therefore essential for performing optimal variable-rate N applications. This study focused on responses during the exponential growth phase, when it is critical that N supply be not limited. Measurements at high spatial resolution allowed to understand the effects of the relationships among N, EC_a, elevation, slope and season on future yield formation. The study was conducted over three years (2005-2007). Mid-season growth responses to applied N were greatest where EC_a levels were high and elevation was low in 2005 and 2007, but not in 2006. Areas with slope ≥1 degree were also more responsive to N rates. Overall best mid-season growth was found in areas of low EC_a, high Elevation and low Slope. However, the best responses to in-season N fertilization were found in areas with opposite properties (high EC_a, low Elevation and high Slope). Indeed, relatively high rates of in-season N were needed to enhance crop growth in areas of high EC_a, low Elevation and high Slope, which are characteristic of unfavourable growth conditions. In counterpart, lower N rates were sufficient for optimal growth in soils at low EC_a high Elevation and low Slope. Also, despite the fact that conditions of high soil variability were specifically selected for the study, the effects and interactions reported for soil NO₃-N content were small. The interaction of EC_a with early seasonal precipitation is likely a key relationship to consider in variable-rate N application: low-lying areas with fine soil texture showed the greatest dependence on weather for optimal N rates. Indeed, the relationships among factors influencing the response to in-season N fertilization were stronger when seasonal conditions were particularly favourable to maize growth. These results are fundamental to the establishment of in-season application rules for spatially variable N algorithms.     

Association between line per se and hybrid performance under excessive soil moisture stress in tropical maize (Zea mays L.)

Excessive moisture (EM) stress during the summer–rainy season is one of the major production constraints for maize (Zea mays L.) in large areas of South and South-East Asia. A key question in breeding for tolerance to excessive moisture is the extent to which the performance of maize hybrids can be predicted on the basis of per se performance of inbred lines under excessive moisture. We attempted to identify the relationship between morpho-physiological traits and grain yield measured on inbred parents and their single cross progenies under EM stress. Responses of various morpho-physiological traits, except days to 50% anthesis, differ significantly under normal versus EM stress. Superiority of hybrid progenies over parental inbred lines increased under EM stress, suggesting that hybrids were comparatively more tolerant to EM stress than inbred progenies. Across moisture regimes, all morpho-physiological traits of hybrids, except lodging and root porosity under normal moisture, were found to be positively and significantly correlated with mid-parent traits. Our data suggest that per se performance of lines was a relatively more important factor in determining hybrid performance under EM stress, while under optimum soil moisture conditions mid-parent heterosis was relatively more important than per se performance of mid-parent. Phenotypic correlation between hybrid and mid-parent yields showed a strong relationship under EM stress (r = 0.66^**). The relationship was statistically significant under normal moisture as well, though it was comparatively weak (r = 0.41^*). Our findings suggest that performance of hybrid progenies under excessive moisture can be predicted and improved to some extent on the basis of their inbred parents that have been systematically selected and improved for EM stress.     

Protein quality and endosperm modification of quality protein maize (Zea mays L.) under two contrasting soil nitrogen environments

Quality protein maize (QPM) breeding involves the combined use of the opaque-2 (o2) gene and the genetic modifiers of the o2 locus to develop cultivars with modified kernel endosperm, and increased concentrations of lysine and tryptophan. This study was designed to assess grain yield performance, endosperm modification, and protein quality and quantity under two contrasting soil nitrogen environments. A 15-parent diallel cross was evaluated under one low nitrogen stress and one optimal nitrogen environment each at Harare (Zimbabwe) and Bako (Ethiopia). Most QPM hybrids showed higher protein quality levels than the best non-QPM check under both conditions. Protein concentration tended to vary across nitrogen levels, but not endosperm type. Significant differences were found for the test of main effect (nitrogen-level) for endosperm modification and tryptophan concentration. This indicated that QPM maintains quality even under low soil nitrogen, a widespread condition in Africa. General combining ability (GCA) mean squares were highly significant for most protein quality traits for each environment and across environments whereas specific combining ability (SCA) mean squares were not significant in most cases. This indicated that additive gene effects were primarily responsible for variation of most traits evaluated and hence progeny performance can adequately be predicted on the basis of parental performance. Inbred lines P2, P4 and P12 had desirable GCA effects for endosperm modification while P1 and P3 had the best GCA for tryptophan concentration in grain. The current study suggests that hybrids with desirable endosperm modification, protein quality and stable performance under low nitrogen stress and optimal conditions can be produced with careful selection.     

Calibrating the leaf colour chart for need based fertilizer nitrogen management in different maize (Zea mays L.) genotypes

Large field to field variability restricts efficient fertilizer N management when broad based blanket recommendations are used in maize (Zea mays L.). To achieve higher yields and to avoid nitrogen (N) deficiency risks, many farmers apply fertilizer N in excess of crop requirement in maize. Field experiments were conducted for five years (2005–2009) to establish and evaluate threshold leaf colour to guide in-season need based fertilizer N topdressings in four maize genotypes. Colour (of the first top maize leaf with fully exposed collar) as measured by comparison with different shades of green colour on a leaf colour chart (LCC) and maize grain yield was significantly correlated. The Cate–Nelson plot of chlorophyll (SPAD) meter/leaf colour chart values against relative grain yield of 0.93 for the experiments conducted during first two years indicated that LCC shade 5 during vegetative growth stages and LCC shade 5.5 at silking stage (R1) can guide crop demand driven N applications in maize. Evaluation of the established threshold leaf greenness during the next three years revealed that fertilizer N management using LCC 5 starting from six-leaf (V6) stage to before R1 stage resulted in improved agronomic and N recovery efficiency in different maize genotypes. There was no response to fertilizer N application at R1 stage. The study revealed that in maize, fertilizer N can be more efficiently managed by applying fertilizer N dose based on leaf colour as measured by LCC than blanket recommendation.     

Genotypic variation for root traits of maize (Zea mays L.) from the Purhepecha Plateau under contrasting phosphorus availability

Phosphorus (P) deficiency is a major constraint for maize production in many low-input agroecosystems. This study was conducted to evaluate genotypic variation in both root (root architecture and morphology, including root hairs) and plant growth traits associated with the adaptation of maize landraces to a P-deficient Andisol in two locations in the Central Mexican highlands. Two hundred and forty-two accessions from the Purhepecha Plateau, Michoacan were grown in Ponzomaran with low (23 kg P₂O₅ ha⁻¹) and high (97 kg P₂O₅ ha⁻¹) P fertilization under rain-fed field conditions, and subsequently a subset of 50 contrasting accessions were planted in the succeeding crop cycle in Bonilla. Accessions differed greatly in plant growth, root morphology and P efficiency defined as growth with suboptimal P availability. The accessions were divided into 3 categories of P efficiency using principal component and cluster analyses, and 4 categories according to the retained principal component and their relative weight for each genotype in combination with growth or yield potential. The distribution of accessions among three phosphorus efficiency classes was stable across locations. Phosphorus-efficient accessions had greater biomass, root to shoot ratio, nodal rooting, nodal root laterals, and nodal root hair density and length of nodal root main axis, and first-order laterals under P deficiency. Biomass allocation to roots, as quantified by the allometric partitioning coefficient (K) was not altered by P availability in the efficient accessions, but inefficient accessions had a lower K under low P conditions. Accessions with enhanced nodal rooting and laterals had greater growth under low P. Dense root hairs on nodal root main axes and first-order laterals conferred a marked benefit under low P, as evidenced by increased plant biomass. Late maturity improved growth and yield under low P. These results indicate that landraces of the Central Mexican highlands exhibit variation for several root traits that may be useful for genetic improvement of P efficiency in maize.     

Conversion into bioethanol of insect (Sitophilus zeamais Motschulsky), mold (Aspergillus flavus Link) and sprout-damaged maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench)

The bioconversion into ethanol of insect (Sitophilus zeamais), mold (Aspergillus flavus) and sprout-damaged maize and sorghum was investigated. Kernel test weight losses due to insect damage in maize were almost twice compared to sorghum (18.6 vs. 10.7%). All damaged kernels lost some of the starch and increased soluble sugars, ash and crude fiber. The mold-damaged sorghum contained approximately five times more FAN compared to the control. The sprout-damaged kernels contained the highest amounts of reducing sugars prior (11 g/L) to and at the end (146.5 g/L) of liquefaction with α-amylase. Ethanol yields based on the already damaged grain indicated that sprout-damaged kernels yielded similar amounts compared to sound kernels (381.1 vs. 382.6 L/ton and 376.6 vs. 374.8 L/ton of sorghum or maize respectively). The insect-damaged maize and sorghum have reduced ethanol yields compared with the controls (29 and 23% respectively), and this negative result was mainly due to dry matter losses during the inadequate storage. Despite differences in ethanol yield, all treatments have similar conversion efficiencies (76.1–89.9%) indicating the robustness of yeast facing biotic-damaged feedstocks. This research demonstrates that the use of already damaged insect, mold or sprouted kernels is feasible and a good alternative for biorefineries.     

The usefulness of iron bioavailability as a target trait for breeding maize (Zea mays L.) with enhanced nutritional value

Iron (Fe) deficiency is the most widespread nutritional problem, affecting as many as half of the world's population. Only a small fraction (2-15%) of Fe from plant sources is typically bioavailable, that is, available for absorption and nutritionally useful for humans. This study evaluated Fe concentration and bioavailability for three diverse sets of 12, 14 and 16 maize hybrids grown in two- or three-location trials to assess the feasibility of selecting for Fe bioavailability in breeding programs. Bioavailability of Fe, assessed using the in vitro digestion/Caco-2 cell model, varied significantly among hybrids in two of the three trials. Location effects were larger than location by genotype interaction effects, additive but not non-additive gene action was significant, and heritability estimates were mostly between 0.55 and 0.65 for Fe bioavailability estimators. Bioavailability of Fe was not associated with Fe concentration in grain or with grain yield. Negative correlation of Fe bioavailability with zinc concentration in grain for one of the three hybrid trials, and positive correlation with provitamin A concentrations in one trial were indicative of inhibitor and enhancer effects on Fe bioavailability, respectively. Although use of the Caco-2 cell model is promising, particularly because it integrates the whole meal, or food matrix effect on Fe bioavailability, the complex nature of the assay and moderate heritability of bioavailability estimators make it most suitable as an intermediate selection tool, following high throughput selection for molecular markers of Fe bioavailability, currently in development by other researchers, and preceding validation and efficacy trials with animal and human models.     

Weed control and yield response to mesotrione in maize (Zea mays)

Mesotrione has recently been registered for weed control in maize in Ontario, Canada; however, there is still little information on the doses required to provide 90% control for the complete spectrum of broadleaved weeds that the product controls. Our objective was to determine mesotrione doses that would provide at least 90% control of four economically important weeds, without impacting final maize yield by more than 5% in comparison to a weed-free control. Sixteen field trials were conducted at six Ontario locations in 1999–2001 to evaluate the effectiveness of mesotrione at doses ranging from 9 to 280 g ai ha⁻¹. The doses required to reduce weed biomass by at least 90% (I₉₀) varied with location and year, and for common lambsquarters and velvetleaf differed by application timing. For lambsquarters, the estimated doses required ranged from 10 to 1984 g ai ha⁻¹ for preemergence applications and 15–38 g ai ha⁻¹ for postemergence applications. Doses of 45 and 19–243 g ai ha⁻¹ were required to effectively reduce the biomass of redroot pigweed. Velvetleaf was effectively controlled preemergence with 288 g ai ha⁻¹ and postemergence with 31 g ai ha⁻¹ of mesotrione. Final maize yield was only reduced by more than 5% of a weed-free control when a dose of less than 35 g ai ha⁻¹ of mesotrione was applied. These results show that biologically effective weed control with reduced doses of mesotrione is possible depending on the spectrum of broadleaved weed species present in the field.     

Popcorn (Zea mays L. var. everta) yield and yield components as influenced by the timing of broadcast flaming

Farmers are interested in producing popcorn under organic production systems and propane flaming could be a significant component of an integrated weed management program. The objective of this study was to collect baseline information on popcorn tolerance to broadcast flaming as influenced by propane dose and crop growth stage at the time of flaming. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, NE in 2008 and 2009 using five propane doses (0, 13, 24, 44 and 85 kg ha⁻¹) applied at the 2-leaf, 5-leaf and 7-leaf growth stages. Propane was applied using a custom-built research flamer driven at a constant speed of 6.4 km h⁻¹. Crop response to propane dose was described by log-logistic models on the basis of visual estimates of crop injury, yield components (plants m⁻², ears plant⁻¹, kernels cob⁻¹ and 100-kernel weight) and grain yield. Popcorn response to flaming was influenced by the crop growth stage and propane dose. Based on various parameters evaluated, popcorn flamed at the 5-leaf showed the highest tolerance while the 2-leaf was the most susceptible stage. The maximum yield reductions were 45%, 9% and 16% for the 2-leaf, 5-leaf and 7-leaf stages, respectively. In addition, propane doses that resulted in a 5% yield loss were 23 kg ha⁻¹ for the 2-leaf and 7-leaf and 30 kg ha⁻¹ for the 5-leaf stage. Flaming has a potential to be used effectively in organic popcorn production if properly used.     

Distribution of phytic acid and mineral elements in three indica rice (Oryza sativa L.) cultivars

Three indica rice cultivars with different grain shapes were selected to determine the milling characteristics and distribution of phytic acid (PA) and six mineral elements including magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), zinc (Zn), and selenium (Se). Milling characteristics were quite different among the rice cultivars with different physical dimensions. Similar milling times did not necessarily result in the same degree of milling (DOM) for different rice cultivars. The concentrations of phytic acid and minerals decreased with an increased DOM. These results also showed that phytic acid and minerals except for Zn and Se were not evenly distributed and highly concentrated in the outer layer (0% < DOM < 15%) of the rice kernel. In contrast, Zn and Se seem to be relatively evenly distributed in the grain. Optimum DOM of about 14% was detected for Zhenong 7 (long and slender grain); 10% was found for Zhenong 60 (medium-grain) and 9% for Zhenong 34 (short and round grain). The information generated in this experiment could be useful to optimize milling procedures for maximum removal of phytic acid, minimum mineral losses and weight loss in indica rice cultivars with different grain shapes.     

Stalk strength and reaction to infection by Macrophomina phaseolina of brown midrib maize (Zea mays) and sorghum (Sorghum bicolor)

Reduced lignin concentration in brown mid-rib mutants in both maize and sorghum have resulted in improved dry matter digestibility, increased milk yield and higher energy in lactating cows. However, the mutations were not widely deployed due to concern that reduced lignin concentration might increase vulnerability to lodging and stalk rot incidence. The objective of this study was to determine the effects of the mutations on stalk strength and stalk rot resistance in both sorghum and maize. Six brown midrib (bmr) sorghum, four brown midrib (bm) maize, and their normal isolines were evaluated for stalk strength and stalk rot disease reaction at two locations in four replications. Three randomly selected plants in each plot were inoculated with Macrophomina phaseolina at 14 d after flowering by using the toothpick inoculation technique. On 28 d after inoculation, the plants were rated for disease severity by measuring the length of necrotic lesions in the stalks. Stalk strength was determined from another three random plants in each plot by using a rind penetrometer. The mutations had no effect on stalk rot disease severity in either sorghum or maize though stalks strength was markedly affected by the mutations in both species. While maize bm entries broke easily in response to mild mechanical stress, bmr sorghums did not exhibit sign of stalk collapse in all backgrounds. The result suggests that the bmr genes in both maize and sorghum can be deployed without incurring losses to stalk rot disease.     

Timing and propane dose of broadcast flaming to control weed population influenced yield of sweet maize (Zea mays L. var. rugosa)

Farmers are interested to produce sweet maize under organic production systems and propane flaming could be a potential alternative tool for weed control in organic sweet maize production. Therefore, the objective of this study was to investigate the response of sweet maize to broadcast flaming as influenced by propane dose and crop growth stage. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, NE in 2008 and 2009 using five propane doses applied at three different growth stages of V2 (2-leaf), V5 (5-leaf) and V7 (7-leaf). The propane doses were 0, 13, 24, 44 and 85 kg ha⁻¹. The response of sweet maize to propane flaming was evaluated in terms of visual crop injury, effects on plant height, yield components (plants m⁻², tillers plant⁻¹, number of ears plant⁻¹, cob length and number of seeds cob⁻¹) and fresh marketable yield. The response of different growth stages of sweet maize to propane doses was described by log-logistic models. Based on most parameters tested, V7 was the most tolerant while V2 was the least tolerant stage for broadcast flaming. The maximum yield reductions with the highest propane dose of 85 kg ha⁻¹ were 22%, 12% and 6% for V2, V5 and V7 stages, respectively. Furthermore, a 5% yield reduction was evident with 23, 25 and 36 kg ha⁻¹ of propane for V2, V5 and V7 growth stages, respectively, suggesting that plants flamed at V7 stage can tolerate higher dose of propane for the same yield reduction compared to the other growth stages. We believe that flaming has a potential to be used effectively in organic sweet maize production if properly used.     

Weed control and sweet maize (Zea mays L.) yield as affected by pyroxasulfone dose

Pyroxasulfone is a new herbicide being considered for registration in sweet maize in Canada; however, there is still little information on the doses required to provide 90% control of annual grass and broadleaved weeds found in southwestern Ontario. The objective of this study was to determine pyroxasulfone doses that would provide at least 90% control of several economically important weeds, without impacting final sweet maize yield by more than 5% in comparison to a weed-free control. Six field trials were conducted over a two-year period (2007 and 2008) at three Ontario locations to evaluate the effectiveness of pyroxasulfone at doses ranging from 31.25 to 1000 g a.i. ha⁻¹. The doses required to reduce weed biomass by at least 90% (I₉₀) varied by weed species. Doses of 93, 499, and 111 g a.i. ha⁻¹ were required to reduce the biomass by 90% of redroot pigweed, common lambsquarters and green foxtail, respectively. There was greater than 95% control of velvetleaf, large crabgrass and barnyardgrass with 31.25 g a.i. ha⁻¹, the lowest dose tested. Sweet maize yield could not be consistently maintained within 5% of the weed-free control. There are several factors that may have contributed to the reduced yield, including soil texture effects, competition as a result of poor common lambsquarters control, and hybrid sensitivity. These results show that biologically effective weed control with pyroxasulfone may be achieved at lower than proposed doses for several weed species; it remains unclear if this is economically sustainable due to the potential impacts on yield.     

Kernel amino acid composition and protein content of introgression lines from Zea mays ssp. mexicana into cultivated maize

Development of high yield maize germplasm with satisfying nutritional quality has been a major objective for maize breeders. Introgression lines from hybrids between Zea mays ssp. mexicana, a close wild relative of cultivated maize, and elite maize inbred line Ye515 were obtained. Ear-related traits of the lines showed wide range of variation compared to the maize parent. Kernel protein contents in the progeny lines ranged from 7.89% to 12.44%. Considerable variability of protein fractions and amino acid composition of mature endosperms was observed. Protein contents for some lines such as SD00362, SD00312 and SD00259 were significantly higher than that of Ye515, and Lys and some other essential amino acids were conspicuously improved. It was concluded that introgression from Z. mays ssp. mexicana into a maize background had great effects on protein content and composition, and that desirable inbred lines with enhanced protein contents and improved nutritional value were produced via alien introgression.