V6 Stage Research Articles

Induction of cell wall phenolic monomers as part of direct defense response in maize to pink stem borer (Sesamia inferens Walker) and non-insect interactions

Pink stem borer (PSB) causes considerable yield losses to maize. Plant–insect interactions have significant implications for sustainable pest management. The present study demonstrated that PSB feeding, mechanical wounding, a combination of mechanical wounding and PSB regurgitation and exogenous application of methyl jasmonate have induced phenolic compound mediated defense responses both at short term (within 2 days of treatment) and long term (in 15 days of treatment) in leaf and stalk tissues of maize. The quantification of two major defense related phenolic compounds namely p-Coumaric acid (p-CA) and ferulic acid (FA) was carried out through ultra-fast liquid chromatography (UFLC) at 2 and 15 days after imposing the above treatments. The p-CA content induced in leaf tissues of maize genotypes were intrinsically higher when challenged by PSB attack at V3 and V6 stages in short- and long-term responses. Higher p-CA content was observed in stalk tissues upon wounding and regurgitation in short- and long-term responses at V3 and V6 stages. Significant accumulation of FA content was also observed in leaf tissues in response to PSB feeding at V3 stage in long-term response while at V6 stage it was observed both in short- and long-term responses. In stalk tissues, methyl jasmonate induced higher FA content in short-term response at V3 stage. However, at V6 stage PSB feeding induced FA accumulation in the short-term while, wounding and regurgitation treatment-induced defense responses in the long-term. In general, the resistant (DMRE 63, CM 500) and moderately resistant genotypes (WNZ ExoticPool) accumulated significantly higher contents of p-CA and FA content than susceptible ones (CM 202, BML 6) in most of the cases. The study indicates that phenolic mediated defense responses in maize are induced by PSB attack followed by wounding and regurgitation compared to the other induced treatments. Furthermore, the study confirmed that induced defense responses vary with plant genotype, stage of crop growth, plant tissue and short and long-term responses. The results of the study suggested that the Phenolic acids i.e. p-CA and FA may contribute to maize resistance mechanisms in the maize-PSB interaction system.

Water Use Efficiency in Popcorn (Zea mays L. var. everta): Which Physiological Traits Would Be Useful for Breeding?

To ensure genetic gains in popcorn breeding programs carried out under drought conditions knowledge about the response of morphophysiological traits of plants to water stress for the selection of key traits is required. Therefore, the objective was to evaluate popcorn inbred lines with agronomically efficient (P2 and P3) and inefficient (L61 and L63) water use and two hybrids (P2xL61 and P3xL63) derived from these contrasting parents, cultivated under two water regimes (WW watered—WW; and water-stressed—WS) in a greenhouse, replicated five times, where each experimental unit consisted of one plant in a PVC tube. Irrigation was applied until stage V6 and suspended thereafter. Individual and combined analyses of variance were performed and the genotypic correlations and relative heteroses estimated. The water use efficient inbred lines were superior in root length (RL), root dry weight (RDW), and net CO2 assimilation rate (A), which were the characteristics that differentiated the studied genotypes most clearly. High heterosis estimates were observed for RL, SDW, leaf width (LW), leaf midrib length (LL), and agronomic water use efficiency (AWUE). The existence of a synergistic association between root angle and length for the characteristics A, stomatal conductance (gs), and chlorophyll concentration (SPAD index) proved most important for the identification and phenotyping of superior genotypes. Based on the study of these characteristics, the higher AWUE of the previously selected inbred lines could be explained. The results reinforced the importance of root physiological and morphological traits to explain AWUE and the possibility of advances by exploiting heterosis, given the morphophysiological superiority of hybrids in relation to parents.

Characterization and Expression Analyses of Callose Synthase Enzyme (Cals) Family Genes in Maize (Zea mays L.).

The callose synthase enzyme genes (Cals) generally plays an important role in resisting to environmental stresses as well as in regulating the microspore development of higher plant. However till now, few researches about ZmCals genes have been reported in maize. In this study, ten ZmCals genes were identified, and they are distributed on four chromosomes in maize. All ZmCals proteins contain Glucan-synthase-domain and Fks1-domain. RNA-seq data from public databases were analyzed and the result suggested that ZmCals involved in the development of various tissues, and a strong expression presented especially in young tissue. qRT-PCR analysis shown that most of ZmCals are highly expressed in root, stem and leaf at jointing stage (V6 stage) with maize inbred line B73. Seven out of 10 ZmCals genes display higher expression during maize anther development especially from stage 6 to stage 8b, the dynamic accumulation process of callose is also observed during these period with aniline blue staining. Above results indicated multiple ZmCals may participate in the deposition of callose in maize anther. Therefore, ZmCals are necessary not only for reproductive organ but also for nutritive organ during maize growth and development. This study lays certain foundation for further investigating the roles of the callose synthase enzymes genes in maize.

Nitrogen deficiency and corn yield with delayed N application

AbstractDelaying the application of N to corn (Zea mays L.) may help to match N supply to N uptake, but may also increase the risk of yield loss if N is applied too late or N uptake is delayed. In a 3‐yr study with corn following soybean [Glycine max (L.) Merr.] (SC) and corn following corn (CC), N application was either split, with half (112 kg N ha–1) at planting and the rest at stages ranging from V3 to R3; or with the entire increment (224 kg N ha–1) applied at these stages. In SC, there was no yield loss from delaying application of the second increment of N to as late as R3, but yields declined as the full increment of N was delayed, by 5% at V9 to 34% at R3. In CC, delaying the second N increment to stage R2 or R3 lowered yield by 5% compared to application at V3, and delaying the full increment of N increasingly lowered yield, by 8% at V6 to 40% at R3. Corn able to recover leaf chlorophyll content (SPAD) following delayed N application produced full yields, and cumulative N deficiency (CND, ΔSPAD × delay expressed as modified growing degree days over periods with ΔSPAD>0, SPAD‐MGGD) was linearly correlated with yield loss. With half of the N at planting, the remainder could be delayed to R1 or later without yield loss, but without N at planting, N needed to be applied before stage V9 in SC and before stage V6 in CC in order to assure maximum yield.

Responses of Low-Cost Input Combinations on the Microbial Structure of the Maize Rhizosphere for Greenhouse Gas Mitigation and Plant Biomass Production.

The microbial composition of the rhizosphere and greenhouse gas (GHG) emissions under the most common input combinations in maize (Zea mays L.) cultivated in Brazil have not been characterized yet. In this study, we evaluated the influence of maize stover coverage (S), urea-topdressing fertilization (F), and the microbial inoculant Azospirillum brasilense (I) on soil GHG emissions and rhizosphere microbial communities during maize development. We conducted a greenhouse experiment and measured methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) fluxes from soil cultivated with maize plants under factorial combinations of the inputs and a control treatment (F, I, S, FI, FS, IS, FIS, and control). Plant biomass was evaluated, and rhizosphere soil samples were collected at V5 and V15 stages and DNA was extracted. The abundance of functional genes (mcrA, pmoA, nifH, and nosZ) was determined by quantitative PCR (qPCR) and the structure of the microbial community was assessed through 16S rRNA amplicon sequencing. Our results corroborate with previous studies which used fewer input combinations and revealed different responses for the following three inputs: F increased N2O emissions around 1 week after application; I tended to reduce CH4 and CO2 emissions, acting as a plant growth stimulator through phytohormones; S showed an increment for CO2 emissions by increasing carbon-use efficiency. IS and FIS treatments presented significant gains in biomass that could be related to Actinobacteria (19.0%) and Bacilli (10.0%) in IS, and Bacilli (9.7%) in FIS, which are the microbial taxa commonly associated with lignocellulose degradation. Comparing all factors, the IS (inoculant + maize stover) treatment was considered the best option for plant biomass production and GHG mitigation since FIS provides small gains toward the management effort of F application.

Dicamba-Tolerant Soybean Response to 2,4-D Micro-Rates at Three Growth Stages Dicamba-Tolerant Soybean Response to 2,4-D Micro-Rates at Three Growth Stages

While dicamba and 2,4-D belong to the same herbicide group, dicamba- and 2,4-D-tolerant soybeans are not cross-resistant. A study was conducted to investigate dicamba-tolerant (DT) soybean response to 2,4-D micro-rates at three growth stages. The study used a randomized complete block design with six replications and a split-plot treatment arrangement. Main plots consisted of three 2,4-D application times [second trifoliate (V2); beginning of flowering (R1); and full flowering (R2)] and subplots consisted of six 2,4-D micro-rates (1/5; 1/10; 1/50; 1/100; 1/500; and 1/1,000 of the label recommended dose of 1,120 g ae ha-1) and a check with no herbicide applied. DT soybean injury symptoms were assessed at 7, 14 and 21 days after treatment (DAT). Yield components, grain yield and yield loss were estimated. The greatest soybean injury (59%) at 21 DAT, delay in canopy closure (16.8 d), and reduction in number of branches plant-1 (52%), pods plant-1 (38%) and 100 seed weight (16%) which ultimately resulted in yield loss (78%) was caused by 1/5 of the label recommended dose of 2,4-D (214 g ae ha-1) at R1 growth stage. Based on effective dose (ED) estimates, 8.66 g ae ha-1 2,4-D caused 0.22 Mg ha-1 (5%) yield loss in DT soybean at R1 but a 1.34- and 2.11-fold higher dose of the same herbicide was required to cause equal yield loss at R2 and V2 growth stages, respectively. Similarly, the number of branches plant-1, pods plant-1 and flowers plant-1 were more sensitive to 2,4-D at R1 than V2 and R2 growth stages with the latter being the most sensitive yield component. On the other hand, 100 seed weight was 3.1- and 4.5-fold more sensitive to 2,4-D at R2 than R1 and V2 growth stages, respectively. Overall, these results showed that DT soybean is most sensitivity to 2,4-D at R1.

Low doses of glyphosate can affect the nutrient composition of common beans depending on the sowing season

Glyphosate application, even in low doses, changes the nutrient composition of crops. The objective of this research was to evaluate the effects of low doses of glyphosate and the sowing season on the macronutrient and micronutrient contents of early cycle common beans. Two experiments were conducted in the field, namely one in the winter season and one in the wet season, using the early cycle common bean cultivar IAC Imperador. The experimental design was a randomized complete block design consisting of the application of low doses of glyphosate [0.0, 1.8, 7.2, 12.0, 36.0, 54.0, and 108.0 g acid equivalent (a.e.) ha−1] in the phenological stage V4 with four replications. Environmental conditions, such as air temperature, interfered with the response of early cycle common beans to low doses of glyphosate. In the winter season, doses of 7.2 g a.e. ha−1 and 36.0 g a.e. ha−1 increased the nutrient composition in the bean leaves, whereas only the Cu content increased in the grains by the dose of 1.8 g a.e. ha−1. In the wet season, there was no increase in the nutrient composition in the bean leaves. The Cu, Zn, Mn, and Fe contents in the grains increased with from the dose of 12 g a.e. ha−1 to above the amount normally observed in common beans, thereby improving the nutritional quality of the food. Our study indicated that low doses of glyphosate alter the nutrient composition of common beans, whereas environmental conditions interfere with the response of common beans to low doses of glyphosate.

Can nutrient‐utilization efficiency be improved by reduced fertilizer supply to maize plants treated with the plant growth regulator paclobutrazol?

AbstractIn previous investigations of several maize cultivars, an improvement of the harvest index was obtained by paclobutrazol (PAC) application combined with an increase in water‐use efficiency. However, so far nutrient‐utilization efficiencies could not be enhanced when control and PAC‐treated maize plants received the same amount of fertilizers. With adjusted fertilizer supply according to the lower requirement of the smaller, PAC‐treated plants, an improvement of nutrient‐utilization efficiencies may be expected. Thus, in the present study, PAC was applied at growth stage V5 to two maize cultivars (Zea mays L. cvs. Galactus and Fabregas) grown in a container experiment. Shortly after PAC application, differential NPK fertilization was introduced in order to obtain a nutrient supply according to the requirement of control plants (100% NPK), the requirement of PAC‐treated plants (85% NPK) and a further slight decrease (78% NPK). Plant height and transpiration rates were significantly reduced due to PAC treatment with stronger effects on Galactus than on Fabregas. Pollen shed, silking and the anthesis‐silking interval (ASI) were unaffected by PAC application and fertilizer supply. Senescence of PAC‐treated plants was delayed, whereas it was accelerated with reduced fertilizer supply. The grain yield of cultivar Galactus was significantly decreased due to PAC application by 13% to 20%, and this effect was strengthened due to reduction in NPK supply. These grain yield reductions were solely caused by decreases in kernel number, which were closely linked to reductions in cob length. On the contrary, PAC treatment did not affect grain yield of Fabregas and reductions due to less NPK supply were small. Harvest index and water‐use efficiency were enhanced by PAC treatment. Plant nutrient contents were similar for control and PAC‐treated plants, but strongly related to fertilizer supply with significant decreases due to reductions in NPK application. The N‐, P‐ and K‐utilization efficiencies of both cultivars were either decreased or unaffected by PAC treatments. The key constraint for improvements of nutrient‐utilization efficiencies is grain yield reduction due to PAC. This problem should be addressed in further studies with avoidance of grain yield decreases by delayed application time combined with fine‐tuning of cultivar‐specific PAC application rates.

Critical Time for Weed Removal in Corn as Influenced by Planting Pattern and PRE Herbicides

Determining the critical time for weed removal (CTWR) is essential for the development of an integrated weed management plan. Therefore, field experiments were conducted to evaluate the effects of two planting patterns (standard and twin-row) with and without PRE-applied herbicides on CTWR in corn. Experiments were laid out in a split-plot arrangement with two main plots: (i) standard row planting (SRP) that is 70 cm wide, and (ii) twin-row planting (TRP) with 50 cm distance between each set of double rows. Each main plot was divided into two sub-plots (with and without PRE herbicides). The sub-sub-plots consisted of seven weed removal timings for PRE herbicides, and tank mixes were utilized (S-metolachlor (1.44 kg a.i. ha−1) + terbutylazine (0.75 kg a.i. ha−1)). The CTWR without PRE herbicides was similar in both the SRP and TRP systems, where it was around the V1 to V2 (16 to 19 d after emergence (DAE)) growth stages. The use of PRE-applied herbicides delayed CTWR in SRP to the V4 to V10 (25 to 58 DAE) stages and up to the V11 (60 DAE) stage in TRP. These results clearly indicate that PRE herbicides are important for protecting corn yields regardless of the planting pattern. In more meteorologically favorable seasons (sufficient heat and precipitation) in both sowing systems, corn plants produce their biological maximum with the fact that over the number of plants per unit area (SRP = 80,000 plants ha−1, TRP = 93,900 plants ha−1) provide higher yields in variants with PRE herbicides, and thus the advantage of the TRP system can be justified.

Maize resistance to Spodoptera frugiperda and its relationship to landrace variety, plant stage, and larval origin

AbstractPrevious studies have raised the hypothesis that laboratory‐reared insects may lose their ability to induce plant defenses because induction‐associated gut bacteria may be eliminated by antibiotics used in artificial diets. The present study was conducted to determine whether maize (Zea mays L., Poaceae) responses to Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) differ when field‐collected vs. laboratory‐reared insects are feeding. One fifth instar from the laboratory or field was released onto a resistant or a susceptible landrace variety at vegetative stages 4 and 6 (V4 and V6), or plants remained uninfested. Five days later, damage was estimated and sections of maize leaves were fed to forth instars in a Petri dish assay to assess the effects of previous feeding on weight gain, leaf consumption, and nutritional indices of conspecifics. Initially, field‐collected larvae caused more damage on V4, but not on V6 maize plants, than laboratory‐reared larvae. In V6 plants, the resistant variety showed less leaf damage than the susceptible variety. In a Petri dish assay, there were no differences between effects of laboratory‐reared and field‐collected larvae on the measured parameters, but larvae from both sources promoted increased susceptibility in maize plants at the V4, but not the V6 stage. This was characterized by higher weight gain and higher efficiency of conversion of ingested food (ECI) (on both maize varieties), and lower metabolic cost (MC) (on one variety) when S. frugiperda larvae fed on leaves pre‐infested with laboratory‐reared larvae compared to leaves of uninfested plants. Conversely, S. frugiperda larvae fed on leaves pre‐infested with field‐collected larvae consumed a greater amount of leaf tissue (on both varieties) compared to leaves of uninfested plants. A similar experiment with neonates showed no effects of landrace variety or previous infestation on insect weight and survival, but insects obtained a higher body weight when fed on V4 compared to V6 plants. In conclusion, S. frugiperda laboratory‐reared larvae were equally able as field‐collected larvae to induce susceptibility in V4 maize plants, and maize plants were more resistant to the pest at the V6 than at the V4 stage.

Epicotyl length in seedlings of soybean cultivars subjected to reduced inter-row spacing

The objective was to evaluate the epicotyl length of seedlings of soybean cultivars in the field, submitted to plant densification by reducing the inter-row spacing. Two field experiments were conducted in Rio Paranaíba in the state of Minas Gerais and the effect of reduced spacing (20 cm, 30 cm, 40 cm and 50 cm between rows) was evaluated. The assessment of the epicotyl length was done by using a millimeter ruler when the plants reached the V2 development stage. The experiments were conducted in a randomized block design with four repetitions. In experiment 1, the BRSMG752S cultivar was submitted to four inter-row spacings and no differences were found among them. In experiment 2, the simple factorial scheme 4 x 3 was considered, with 4 spacings and 3 cultivars, to analyze the effect of the interaction between cultivars (96R10, 97R50 and 98Y21) and spacing (20, 30, 40 and 50 cm between rows). The results of experiment 2 indicated that there was no significant effect for spacing and that the cultivars presented statistically different averages. Thus, it can be concluded that the epicotyl length of soybean seedlings, grown in the field in Rio Paranaíba in the state of Minas Gerais and evaluated at the V2 stage of development, was not influenced by the distance between the sowing lines and that the cultivar 96R10 showed the highest and 98Y21 the lowest mean epicotyl length of soybean seedlings, grown in the field in Rio Paranaíba in the state of Minas Gerais and evaluated at the V2 stage of development.

Effect of glyphosate and glufosinate on nutritional content and agronomic performance of maize possessing cp4epsps and pat transgenes

The aim of this study was to check the tolerance level of maize possessing the transgenes cp4epsps and pat, exposed to high rates of glyphosate or glufosinate. Field experiments were carried out in 2016/17 at the first growing season; and the other in the second growing season, in Palotina, state of Paraná (PR), Brazil. The design was completely randomized block with 4 replications, which were set up with variations of rates of herbicides: glyphosate (0; 2,160; 4,320; 6,480 and 8,640 g ae ha-1) (experiment 1) and glufosinate (0; 1,500; 3,000; 4,500 and 6,000 g ai ha-1) (experiment 2). The application was performed at the V4 stage. Plants were evaluated for injuries, final plant height, stem diameter, 100-grain mass, yield and content of P, K, S, Fe, Cu and Zn. The results show that there was no reduction in yield and 100-grain mass, as well as changes in nutrient contents, even with the use of high rates of glyphosate and glufosinate. This is explained by the rapid recovery of maize hybrids under favorable developmental conditions. Despite causing injuries and decreased height, application of glyphosate (up to 8,640 g ae ha-1) or glufosinate (up to 6,000 ai ha-1) did neither reduce yield and 100-grain mass nor the nutrient contents of grains. This shows the high selectivity of these herbicides. Nonetheless, crop injury and reduction in height were observed in maize plants for herbicide application. This indicates the risks of using herbicides above the rates recommended in the package insert, despite the absence of deleterious effects on yield

Assessment of nitrogen diagnosis methods in sunflower

AbstractNitrogen deficiency can severely limit sunflower (Helianthus annuus L.) grain yield and quality. Our objective was to evaluate N diagnosis methods based on: (a) pre‐plant soil nitrate‐nitrogen (NO3––N) test (PPSNT) and soil N mineralized in short‐term anaerobic incubation (Nan), (b) Greenness index (GI) and the normalized difference vegetation index (NDVI) measured at 6 (V6) and 12 (V12) leaves, and (c) grain nitrogen concentration (Nc). Seventeen experiments were carried out between 2010 and 2019 in Argentina, evaluating nine N rates (0, 30, 40, 60, 80, 90, 120, 150, and 160 kg N ha–1). The GI, NDVI, N sufficiency index and relative normalized difference vegetation index (NDVIr) were determined at V6 and V12 growth stages. On average, yield response to N was 492 kg ha–1 and Nc response was 0.25% in 9 and 11 responsive experiments, respectively. The inclusion of Nan improved the PPSNT diagnosis method. The critical N availability (PPSNT + fertilizer N) threshold was 115 kg N ha–1 for experiments with low Nan (<60 mg kg–1), and 90 kg N ha–1 for experiments with high Nan (>60 mg kg–1). The NDVIr at V12 allowed monitoring the crop N status with a 0.95 critical threshold. The Nc adequately diagnosed N deficiencies and the critical threshold was 2.26%. Also, Nc was predicted from the ratio between N availability and grain yield (R2 = .39). Our results would allow to better estimate N availability to recommend adequate N fertilizer rates for sunflower aiming to optimize grain yield and quality, and minimize the economic and environmental cost of fertilization.

Modeling of Diurnal Changing Patterns in Airborne Crop Remote Sensing Images

Airborne remote sensing technologies have been widely applied in field crop phenotyping. However, the quality of current remote sensing data suffers from significant diurnal variances. The severity of the diurnal issue has been reported in various plant phenotyping studies over the last four decades, but there are limited studies on the modeling of the diurnal changing patterns that allow people to precisely predict the level of diurnal impacts. In order to comprehensively investigate the diurnal variability, it is necessary to collect time series field images with very high sampling frequencies, which has been difficult. In 2019, Purdue agricultural (Ag) engineers deployed their first field visible to near infrared (VNIR) hyperspectral gantry platform, which is capable of repetitively imaging the same field plots every 2.5 min. A total of 8631 hyperspectral images of the same field were collected for two genotypes of corn plants from the vegetative stage V4 to the reproductive stage R1 in the 2019 growing season. The analysis of these images showed that although the diurnal variability is very significant for almost all the image-derived phenotyping features, the diurnal changes follow stable patterns. This makes it possible to predict the imaging drifts by modeling the changing patterns. This paper reports detailed diurnal changing patterns for several selected plant phenotyping features such as Normalized Difference Vegetation Index (NDVI), Relative Water Content (RWC), and single spectrum bands. For example, NDVI showed a repeatable V-shaped diurnal pattern, which linearly drops by 0.012 per hour before the highest sun angle and increases thereafter by 0.010 per hour. The different diurnal changing patterns in different nitrogen stress treatments, genotypes and leaf stages were also compared and discussed. With the modeling results of this work, Ag remote sensing users will be able to more precisely estimate the deviation/change of crop feature predictions caused by the specific imaging time of the day. This will help people to more confidently decide on the acceptable imaging time window during a day. It can also be used to calibrate/compensate the remote sensing result against the time effect.

Efficiency in nitrogen management using conventional and transgenic technology in the cultivation of maize

The objective to evaluate the maize yield components as a function of the top-dressing nitrogen partitioning in maize plants with conventional and transgenic technology. The experiment was carried out in the agricultural crops of 2012/2013 and 2013/2014, in the municipality of Tenente Portela-RS, Brazil. The experiment was set up in a randomized block design in a factorial scheme with two genetic technologies x 11 nitrogen fertilization treatments, arranged in three replications. The treatments were composed of top-dressing applications in the phenological stages V2 - two fully expanded leaves, (V2), V4 - four fully expanded leaves, (V4), V6 - six fully expanded leaves (V6) and V8 - with eight fully expanded leaves (V8) and split applications in V2+V4; V2+V6; V2+V8; V4+V6; V4+V8; V6+V8; and V2+V4+V6+V8. There was interaction between genetic technologies and levels of nitrogen fertilization in the maize crop. The highest grain yield was obtained with conventional technology because it presented plants with greater prolificacy, ear diameter and number of grains per row. Grain yield was superior with nitrogen fertilization in V4 and in nitrogen splitting in the V4 + V6, V4 + V8 and V2 + V4 + V6 + V8 stages.

Plant growth stage and leaf part to diagnose sweet corn nitrogen status using chlorophyll sensor and scanner image analysis

The application and use of image analysis to assess the plant nitrogen (N) status has gained importance especially in precision agriculture for cereal plants using aerial remote sensing or even ground-based commercial N sensors. The objective of this work was to propose the plant growth stage and leaf parts possible to be used in sweet corn plant for N diagnosis using the SPAD chlorophyll meter and a table scanner images. A field experiment was carried out at the Federal University of Viçosa. A randomized block design was used, in a 4x3x5 factorial scheme (growth stages x leaf parts x N doses), with five replications. SPAD reading and scanner images were obtained for Red, Green and Blue (RGB) were obtained using the ImageJ® software. The data were submitted to analysis of variance and Pearson's correlation analysis at a 5% probability. Reading position on the middle part of the leaf at V10 and at R1 growth stages are suitable for assessing sweet corn N status using SPAD with 51.40 and 45.09 as an optimal reference value, respectively. RGB values determined with the scanner also was suitable for assessing the N status of sweet corn. The technique does not require special expertise for its application. It is proposed table containing optimal reference values of SPAD and RGB colors in the medial part of the sweet corn leaf at V10 and R1 development stages of corn plant.

Effect of Ti treatments on growth, photosynthesis, phosphorus uptake and yield of soybean (Glycine max L.) in maize-soybean relay strip intercropping

Shade is the main growth and yield limiting factor for soybean seedlings in maize-soybean relay strip intercropping. Therefore, a field experiment was conducted to investigate the effect of titanium (Ti) foliar application on soybean under a maize-soybean relay strip intercropping system. In this study, the soybean plants were sprayed with Ti treatments (T0S = 0, T1S = 125, T2S = 250, T3S = 500 and T4S = 1000 mg L−1) under maize-soybean relay strip intercropping. The results have indicated that under intercropping environment, Ti application significantly affected the growth of the plants. The soybean plants supplied with Ti treatment (T1S) significantly improved soybean diameter and stem strength at both V5 and R5 stages. Ti application resulted in a significant increase in SPAD values in T1S (i.e. 31.69 % and 21.21 %) and T2S (i.e. 21.55 % and 22.19 %) in comparison to control at both V5 and R5 stage, respectively. Furthermore, foliar application of Ti (T1S) significantly increased photosynthetic rate by 33.15 % and 22.80 % at both V5 and R5 stages. The stomatal conductance (Gs) increased significantly in T1S (44.39 %) and T2S (31.30 %) at the V5 stage and in T1S (29.85 %) at the R5 stage, respectively in comparison to control leading to increase root and shoot biomass in both V5 and R5 stages except for treatment T4S. Analysis of stem anatomical structure, stem strength (lodging resistance), and phosphorus content revealed that foliar application of Ti not only improved the shade tolerance but also increased yield (16–17 %) of soybean under maize-soybean relay strip intercropping. Conclusively, foliar application of Ti could be helpful in mitigating the shade stress and increasing soybean yield under the strip intercropping system.

The transcriptome landscapes of citrus leaf in different developmental stages.

The temporal expression profiles of citrus leaves explain the sink-source transition of immature leaves to mature leaves and provide knowledge regarding the differential responses of mature and immature leaves to biotic stress such as citrus canker and Asian citrus psyllid (Diaphorina citri). Citrus is an important fruit crop worldwide. Different developmental stages of citrus leaves are associated with distinct features, such as differences in susceptibilities to pathogens and insects, as well as photosynthetic capacity. Here, we investigated the mechanisms underlying these distinctions by comparing the gene expression profiles of mature and immature citrus leaves. Immature (stages V3 and V4), transition (stage V5), and mature (stage V6) Citrus sinensis leaves were chosen for RNA-seq analyses. Carbohydrate biosynthesis, photosynthesis, starch biosynthesis, and disaccharide metabolic processes were enriched among the upregulated differentially expressed genes (DEGs) in the V5 and V6 stages compared with that in the V3 and V4 stages. Glucose level was found to be higher in V5 and V6 than in V3 and V4. Among the four stages, the largest number of DEGs between contiguous stages were identified between V5 and V4, consistent with a change from sink to source, as well as with the sucrose and starch quantification data. The differential expression profiles related to cell wall synthesis, secondary metabolites such as flavonoids and terpenoids, amino acid biosynthesis, and immunity between immature and mature leaves may contribute to their different responses to Asian citrus psyllid infestation. The expression data suggested that both the constitutive and induced gene expression of immunity-related genes plays important roles in the greater resistance of mature leaves against Xanthomonas citri compared with immature leaves. The gene expression profiles in the different stages can help identify stage-specific promoters for the manipulation of the expression of citrus traits according to the stage. The temporal expression profiles explain the sink-source transition of immature leaves to mature leaves and provide knowledge regarding the differential responses to biotic stress.

Crop succession and split-application of nitrogen effects on common bean yield in short no-tillage system

AbstractEvaluating the effects of crop successions in no-tillage system (NTS) is essential for the correct recommendation of agronomic practices, such as top-dressing nitrogen fertilization. The aim was to evaluate the effect of the crop succession and the splitting of top-dressing N fertilization on the agronomic performance and economic viability of common bean crop. The experiment was conducted in southeastern Brazil for two agricultural seasons in an area under NTS, using a split-plot in randomized complete block design. The plots represented three cropping successions (maize in sole crop, maize intercropped with Urochloa ruziziensis and U. ruziziensis in sole crop) and the subplots composed of ten combinations of splitting of top-dressing N, at the stages V3, V4 and R5 of the common bean crop. In relation to the single application of the N dose of 90 kg ha−1, the common bean had higher response as a function of the N splitting schemes adopted, regardless of the previous cropping succession. The cropping successions evaluated did not interfere with the seed yield of common bean as subsequent crop, even at the beginning of the establishment of NTS. To obtain higher seed yield and economic viability, the N dose of 90 kg ha−1 indicated for the crop must be split and applied among the phenological stages V3, V4 and R5.

Nitrogen inputs influence vegetative metabolism in maize engineered with a seed-specific carotenoid pathway.

Metabolomic profiling of a maize line engineered with an endosperm-specific carotenogenic pathway revealed unexpected metabolic readjustments of primary metabolism in leaves and roots. High-carotenoid (HC) maize was engineered to accumulate high levels of carotenoids in the endosperm. The metabolic interventions influenced the flux through non-target pathways in tissues that were not affected by the targeted intervention. HC maize at the vegetative stage also showed a reduced susceptibility to insect feeding. It is unknown, however, whether the metabolic history of the embryo has any impact on the metabolite composition in vegetative tissues. We, therefore, compared HC maize and its isogenic counterpart (M37W) to test the hypothesis that boosting the carotenoid content in the endosperm triggers compensatory effects in core metabolism in vegetative tissues. Specifically, we investigated whether the metabolite composition of leaves and roots at the V6 stage differs between HC and M37W, and whether N inputs further alter the core metabolism of HC compared to M37W. We found an increase in the abundance of organic acids from the tricarboxylic acid (TCA) cycle in HC even under restricted N conditions. In contrast, low levels of carotenoids and chlorophyll were measured regardless of N levels. Sugars were also significantly depleted in HC under low N. We propose a model explaining the observed genotype-dependent and input-dependent effects, in which organic acids derived from the TCA cycle accumulate during vegetative growth and contribute to the increased demand for pyruvate and/or acetyl-CoA in the endosperm and embryo. This response may in part reflect the transgenerational priming of vegetative tissues in the embryo induced by the increased demand for metabolic precursors during seed development in the previous generation.