V6 Stage Research Articles

Variability to flooding tolerance in barnyardgrass and early flooding benefits on weed management and rice grain yield

Barnyardgrass (Echinochloa crus-galli (L.) Beauv.) is one of the most problematic weed species in paddy fields. The recent large-scale evolution of herbicide resistance in this species requires the adoption of integrated methods of weed control. The present study aimed to determine the interaction of water depth, flooding irrigation onset, and pre-emergent herbicides on the control of barnyardgrass populations and to identify the variability and the putative genes involved in the regulation of flooding tolerance in this species. We identified tolerant, moderately tolerant, and flood-sensitive barnyardgrass populations through water depth-response experiments in a greenhouse. The relative expression of genes related to flooding tolerance were evaluated to confirm the flooding tolerance variability. A field experiment was conducted during the summer seasons of 2020/21 and 2021/22 to assess the interaction of the flooding onset, water depth, and pre-emergent herbicides on populations with different flood tolerances and herbicide resistance mechanisms. Water depths of 7.5 cm and 12.5 cm and plant height were selected for the diagnosis of flood tolerance. After 28 days under flooding, the 7.5 cm depth reduced plant height by an average of 26.82%. Of the 45 populations evaluated, 43 overcame the water depth of 7.5 cm, and four surpassed 12.5 cm. The relative expression of alcohol dehydrogenase 1 (ADH1), alcohol dehydrogenase 2 (ADH2), pyruvate decarboxylase (PDC1), aldehyde dehydrogenase (ALDH), and sucrose synthase 3 (SUS3) was between eight and sixteen times higher for the flood-tolerant population than for the sensitive one. In the field study, the anticipation of flooding to the two-leaves (V2) stage of rice resulted in an increase of up to 55.6% in the control of all populations evaluated compared with conventional irrigation at the four-leaves (V4) stage, including those resistant to herbicides. The grain yield was increased by approximately 11.4% with flooding onset in the V2 stage compared to the V4 stage. Barnyardgrass control and rice grain yield were not affected by water depths of 5 cm or 15 cm. The early flooding, in the V2 stage, increased rice grain yield and favored barnyardgrass control. However, variability in flood tolerance was identified in barnyardgrass populations, which may jeopardize the effect of early flooding for weed control in rice crops. The results we obtained add information on the basic knowledge of flooding tolerance in barnyardgrass and to the integrated weed management for dry direct-seeded rice.

First Report of Colletotrichum graminicola Causing Maize Anthracnose in Galicia, Northwestern Spain.

Maize (Zea mays) is one of the most important crops worldwide, and fungal diseases are responsible for major losses in food production. Anthracnose caused by Colletotrichum graminicola can infect all maize tissues, although stalk rot and seedling blight cause more significant economic damage (Munkvold and White, 2016). Anthracnose stalk rot is characterized by a distinctive external blackening of the lower stalks resulting in large black streaks, while the pith turns dark brown and has a shredded appearance. Like most stalk rots, the most obvious symptom is a sudden death of plants before grain maturity, and plant lodging. Symptoms commonly appear late in the season, suspicious maize stems of cultivar Tuy exhibiting symptoms of anthracnose stalk rot were collected from a field in Pontevedra, Galicia, Spain (Geographical coordinates: 42°23'27.1" N - 8°30'46.3" W) between June and December of 2022. Stem samples, approximately 50 mm2, were dissected and surface-disinfected for 90 seconds in 20% sodium hypochlorite (v/v) and rinsed three times in sterile distilled water. The samples were transferred to one half-strength acidified potato dextrose agar (PDA) supplemented with ampicillin (100 µg/mL) and lactic acid 90% (1.5 mL/L) and incubated for 5 days at 25 ºC (Sukno et al. 2008). Single spores were transferred to fresh PDA plates to obtain pure culture isolates. A total of six isolates were obtained, and among them, two were selected for further characterization (SP-36820-1 and SP-36820-3). Colonies grown on PDA have dark gray aerial mycelium with orange-colored spore masses. Conidia are falcate, slightly curved, tapered toward the tips, and are produced in acervuli with setae, measuring 37.65 to 24.84 x 8.02 to 4.67 µm, respectively (n = 100). These morphological characteristics are in agreement with C. graminicola previously described by Bergstrom and Nicholson (1999). Isolates were grown in potato dextrose broth (PDB) for 3 days at 25 ºC and total genomic DNA was extracted using a DNeasy Plant Mini Kit (Qiagen Inc., Valencia, CA, USA). The internal transcribed spacer region of rDNA and the manganese-type superoxide dismutase gene (SOD2) were amplified using primers ITS4/ITS5 (White et al. 1990) and SOD625/SOD507 (Fang et al. 2002) and consequently sequenced. GenBank BLAST analysis revealed that the sequences were 100% identical to strains of C. graminicola. All sequences were deposited in GenBank (see e-Xtra 1 for accession numbers). To confirm Koch's postulates, plants of a derivative of maize inbred line Mo940 (developmental stage V3) were placed horizontally in a tray for inoculation and 20 droplets (7.5 µL) of a suspension of 3 x 105 conidia per milliliter were placed on the surface of the third leaf. The trays were closed to retain moisture and incubated overnight at 23ºC. The next day, the plants were returned to a vertical position and incubated in a growth chamber at 25ºC with 80% humidity and a light cycle of 16 h of light and 8 h of dark (Vargas et al. 2012). After four days inoculated leaves presented brown elongated lesions with necrotic centers consistent with C. graminicola infection, whereas control plants remained asymptomatic. The strains reisolated from infected leaves were morphologically identical to the original isolates. To our knowledge, this is the first report of Colletotrichum graminicola causing maize anthracnose in Spain. Recently, maize anthracnose was also reported in Bosnia and Herzegovina and China (Duan et al. 2019; Cuevas-Fernández et al. 2019), suggesting the pathogen's geographic range is increasing, which may be a threat to maize cultivation in locations with optimal humid conditions for disease development.

Cereal rye residue management tactics influence interrow and intrarow weed recruitment dynamics in field corn when planting green

AbstractDelaying cover crop termination until cash crop planting (i.e., planting green) is an emerging no-till practice. Improved management recommendations are needed for optimizing weed suppression benefits while minimizing other pest, fertility, and crop management risks when planting green in corn production systems. In a 2-yr field experiment, we evaluated the interaction between cereal rye residue management tactics (standing residue, roll-crimping, roll-crimping with row cleaners) and herbicide programs (1-pass preemergence [PRE], 2-pass postemergence [POST]) when planting green on weed recruitment spatial patterns and corn performance compared to standard termination (14 d preplant [DPP]) and ryelage harvest (14 DPP) practices. In a 2-yr on-farm experiment, we evaluated corn performance in response to the same residue management tactics. Cereal rye biomass production varied significantly across years in on-station experiments, with average (4.9 Mg ha−1) and anomalous (9.9 Mg ha−1) levels observed in 2020 and 2021, respectively. In 2020, planting green with an integrated roll-crimper/row cleaner system resulted in greater intrarow weed density compared with planting green into standing cereal rye. Interrow weed density was lower when roll-crimping was employed compared to early termination (14 DPP). Planting green into standing cereal rye resulted in greater mean corn height (V5 stage) compared to other treatments, but corn population and yield did not differ. In 2021, few differences in weed recruitment patterns were observed, but corn population and yield were significantly lower in planting green treatments compared to early termination. In both years, late-season weed biomass was lower in two-pass POST programs compared to one-pass PRE programs. On-farm trials showed that planting green into standing residue increases corn height and can reduce corn populations, which may lead to reduce yields. Our results suggest that management recommendations for optimizing herbicide application timing should consider intrarow and interrow weed recruitment dynamics associated with residue management tactics needed to optimize corn performance.

Soybean Tolerance to ultra-low doses of dicamba: Hormesis or not

The widespread use of dicamba across the soybean growing regions of the United States resulted in increased off-target movement of this herbicide to susceptible vegetations. There are speculations that a drift of sublethal (ultra-low) doses of dicamba can enhance soybean growth and yield through a phenomenon called hormesis. Field studies were conducted during 2018 and 2019 to determine whether soybean growth and yield can be enhanced with ultra-low doses (0.0112–56 g ae ha−1) of dicamba, applied at three growth stages (V2, R1 and R2). There was no evidence that the ultra-low doses of dicamba (0.0112–56 g ae ha−1) increased any of the observed parameters, irrespective of the application timing. Doses of 0.56 g ae ha−1 and lower did not have a negative impact on plant dry matter, height and grain yield, even if causing visible symptomology. The estimated effective doses for 50% reduction in various growth parameters and yield (ED50) indicate that soybean is more sensitive at the R1 compared to the V2 or R2 stages. The estimated visual injury threshold that caused 5% yield loss were 53, 36 and 21% for V2, R1 and R2 stage of dicamba exposure, respectively. The proposed “No Observed Adverse Effect Level” (NOAEL), which is a safe exposure threshold, ranged from 0.0003 to 0.033 g ae ha−1. However, efforts should be made to avoid dicamba drift to susceptible soybean as there is no evidence of enhanced growth and yield with the ultra-low doses.

Can foliar application of zinc increased growth, physiology, and yield in snap beans?

This study aimed to verify the effects of leaf application of zinc (Zn) on the growth, physiology, yield, and biofortification of snap beans. The experiment was carried out in a greenhouse, in a completely randomized design, with five doses of zinc (0, 100, 200, 300, and 400 mg L−1). The leaf application of zinc was carried out at the vegetative stage V3 (third leaves). Biometric, physiological, and yield evaluations occurred at stages R5 (flowering) and R8 (harvest). The chlorophyll of plants with zinc is 36% higher with the application of 400 mg L−1 in R8. Foliar fertilization reduced the transpiration around 41%; and it increased the temperature and photosynthetic rate at 5.2% and 16.2%, respectively. The zinc concentration increases up resulted in an increase of 85 and 942% of zinc accumulation in the snap bean plant at the R5 stage. The 100 mg L−1 dose increased crop yield by 8.4% compared to the control treatment. Higher doses can reduce productivity by up to 17% when 400 mg L−1 of Zn is applied. Foliar application of zinc is efficient in promoting an increase in the concentration and accumulation of Zn in the leaves in the stage R5, but at the harvest stage there is no influence of fertilization on the levels and accumulations of zinc in the plant.

Manganese sources and rates impact plant Mn concentrations and soil Mn fractions

AbstractManganese (Mn) is an essential micronutrient for all organisms. In plants, Mn plays a critical role in photosynthesis and as a structural component of enzymes. In soils, Mn exists as different fractions of varying availability to plants. Mn fertilizers can be used to increase Mn availability to plants but are easily converted from a plant‐available fraction (exchangeable Mn) to an unavailable fraction (Mn‐oxides). Little research has been done in agricultural settings on soil Mn fractions; thus, the objective of this experiment was to study the effect of Mn additions on soil Mn fractions and plant Mn concentration. A greenhouse experiment was conducted by growing soybean (Glycine max) treated with three Mn application rates (recommended or 1×, 10×, and 50×) of two sources (MnSO4 and Mn ethylenediamine tetraacetic acid [MnEDTA]). Soil Mn fractions (Mehlich‐1 extractable, exchangeable, organic‐bound, Mn‐oxide, residual) were quantified via sequential Mn extraction procedures. Bioavailability was evaluated by measuring soybean leaf Mn concentrations. Both fertilizer types increased available soil Mn fractions. Leaf Mn concentration increased with MnSO4 50× application at the V3 stage and decreased with MnEDTA addition at the V3 and R2 stages. Mn additions likely resulted in the conversion of Mn into unavailable fractions. This was amplified by higher application rates, where total Mn increased by 18.5%, but available Mn decreased by 4.3% relative to initial soil values. Thus, our study showed that adding Mn to soils does not necessarily increase plant‐available Mn.

Application periods against diceraeus (dichelops) melacanthus on maize and their significant response on damage and grain yield in the Brazilian Midwest

Diceraeus melacanthus (Dallas, 1851) (Heteroptera: Pentatomidae) remains one of the primary pests in maize nowadays in Brazil, causing significant losses in production. Different insecticide application periods against this pest were performed, and the following parameters were evaluated the plant damage, maize yield and an economic analysis was conducted using these two parameters. The experiment was performed in two growing seasons (2021 and 2022) in a two-factor scheme, with five insecticide application periods: zero (untreated); V1–V3; V1–V3 + V3–V4; V1–V3 + V3–V4 + V4–V6, and V1–V3 + V3–V4 + V4–V6 + V6–V7; and three insecticides: acephate (Perito - 970 g a. i./kg SG - 1,0 kg/ha), thiamethoxam + lambda-cyhalothrin (Engeo Pleno S - 141 + 106 g a. i./L ZC - 0,3 L/ha) and ethiprole (Curbix - 200 g a. i./L SC - 0,75 L/ha). There was a significant difference for the isolated factors of growing season, evaluation stages, application periods and insecticides for the number of plants with damage rating ≥2. Curbix, Engeo Pleno and Perito showed the maximum reduction of damage in maize plants with application periods at V1–V3 + V3–V4 + V4–V6 and V1–V3 + V3–V4 + V4–V6 + V6–V7, presenting 3.2 and 2.9 plants with damage rating ≥2, respectively. Evaluations between the V7 and V8 stages showed a negative correlation with maize yield (Cor = −0.712 at V7 and -0.537 at V8). Regardless of the insecticide used, the V1–V3 + V3–V4 + V4–V6 + V6–V7 application period had the highest productivity, with an average of 4660 kg/ha, differing 681.8 kg/ha and net income of $ 30,3/ha from the uncontrolled plots. Additionally, every 5 days of an application period increased the yield in 178,9 kg/ha or 35 kg/ha daily. Therefore, the use of control tactics from V1–V3 to V6–V7 of maize plants contributes significantly to the reduction of damage, the increase of productivity and a higher net income.

Spectral variables as criteria for selection of soybean genotypes at different vegetative stages

Understanding the association between variables obtained by multispectral imaging, such as plant canopy reflectance at different wavelengths and vegetation indices (VIs), and agronomic traits of interest for soybean is crucial for breeding programs. This approach, associated with the evaluation of the best stage for spectral data collection, can identify easier-to-measure variables to be used in the indirect selection of genotypes for more expensive-to-measure traits or those that are expressed later, resulting in a faster, labor-saving, and large-scale selection process. The hypothesis of this study is the possibility of identifying promising variables for the selection of soybean genotypes through the use of vis and that different times of collection of information regarding reflectance interfere in the selection responses. Thus, our objectives were: i) to estimate heritability (h2) for agronomic traits and VIs; ii) to estimate the gains with direct selection (DS) on the VIs and indirect selection (IS) for the agronomic traits selected by the higher heritability; iii) to estimate correlations between spectral variables, VIs, and agronomic traits; iv) to identify the most promising populations for the evaluated variables; and vi) to identify the most adequate phenological stage for spectral data collection. We installed a field experiment in a randomized block design with four repetitions, 28 F3 soybean populations, and four control treatments. Agronomic traits evaluated were: days to maturity (DM), plant height (PH), first pod insertion height (PIH), number of branches (NB), and grain yield (GY). Spectral collections were performed at the V8 (45 days after emergence), R1 (60 days after emergence) and R5 (80 days after emergence) stages. Correlations between agronomic traits, reflectance at 790 nm (near-infrared), 735 nm (RedEdge), 660 nm (red), 550 nm (green), and 450 nm (blue) wavelengths, and VIs were estimated. The heritability were estimated for agronomic traits and VIs. Our findings reveal that it is possible to select soybean genotypes using spectral variables based on heritability and phenotypic aspects. Enhanced vegetation index (EVI) and soil-adjusted vegetation index (SAVI) have high heritability values (>75%) at V8. It is possible to obtain satisfactory selection gains for agronomic traits, especially GY, based on selection on EVI and SAVI at V8 stage. By this approach, the F3 segregating populations that provided the highest selection gains were P7, P8, P9, P14, P27, and P28. Spectral data collection at V8 stage provided higher h2 for VIs and agronomic traits, while R5 is the most suitable stage for estimating associations between VIs and agronomic traits.

Sampling Methodology of a Key Pest: Technique and Sampling Unit for Evaluation of Leafhopper Dalbulus maidis Populations in Maize Crops

Maize (Zea mays) is the most consumed food in the world. The leafhopper, Dalbulus maidis, (Hemiptera: Cicadellidae) is one of the most important maize pests, and due to its direct and indirect damage, it can cause losses of up to 100%. Sampling plans are essential components for integrated pest management programs. The first two components to be determined in these plans are the sampling unit and the sampling technique. The sampling unit consists of determining the plant organ to be evaluated in the sampling and the techniques are the devices used to sample populations of pests in crops. Thus, the objective of this work was to select the unit and technique to be used in the sampling of D. maidis in maize crops. For this purpose, pest populations in plants at stages V4, V6, V8, and V10 were monitored in 16 commercial crops in the Atlantic Forest and Cerrado biomes over two years. The sample units studied were the leaves at different positions in the canopy of the plants. The techniques studied were direct counting, shaking the apex of the plants in a plastic tray and using a beating cloth. In the process of selecting the unit and technique to be used in sampling populations of pests in crops, adequate criteria must be used. These criteria include precision, representativeness, sampling time and that the use of these components in the sampling plans should not cause damage to the plants. The most suitable sampling unit for evaluating these pest populations was the whorl leaves and the best technique was the direct counting. Therefore, the unit and technique selected in this work can be used in sampling plans for D. maidis in maize crops.

First report of Curtobacterium flaccumfaciens pv. flaccumfaciens causing bacterial tan spot of soybean in Russia.

Curtobacterium flaccumfaciens pv. flaccumfaciens (H.) Collins & Jones is known as a pathogen of different legume crops, including soybean (Glycine max (L.) Merr.) (Hedges 1922; Dunleavy 1983). OEPP/EPPO (2011) considers C. flaccumfaciens pv. flaccumfaciens as present in Russia based on reports of the disease on common beans in two regions of Russia (North Caucasus and Far East) made without proper pathogen identification. During the summer of 2020 and the spring of 2021, soybean plants with tan spot disease (10-40% of plants) were reported during routine assays of several fields in Stavropol Krai (44.72°N, 43.29°E). After harvest in 2021, we inspected 48 soybean seed lots collected in different regions of Russia for the presence of C. flaccumfaciens pv. flaccumfaciens. Seed testing was performed using the OEPP/EPPO (2011) protocol. For bacteria isolation, seed extracts were spread on MSCFF agar plates (Maringoni et al. 2006). After 5 days of incubation at 28°C potential, C. flaccumfaciens pv. flaccumfaciens colonies were used for further tests on NSA and SSM agar (Tegli et al. 2017, Maringoni et al. 2016). Six seed lots produced in Stavropol, Ryazan (53.95°N, 40.62°E), Orel (52.39°N, 37.69°E) and Amur (51.31°N, 128.22°E) regions were suspect. Ten isolates (SB1 to SB4 from Stavropol, F-125-1 to F-125-3 from Ryazan, and F-30-1 to F-30-3 from Amur) were selected, and further identified by morphological, physiological, and biochemical properties, MALDI TOF MS, 16S rRNA sequences, and specific primers CffFOR2 and CffREV4 (Tegli et al. 2017). Isolates consistently formed yellow, circular, smooth colonies on agar, and were identical to C. flaccumfaciens pv. flaccumfaciens type strain DSM 20129T in diagnostic physiological properties (Tegli et al. 2017). DNA was isolated from the bacteria by the CytoSorb Kit (Sintol, Moscow). All tested strains were positive in the PCR assay (Fig. 1). 16S rRNA fragments were amplified using primers 27F/1492R (Marchesi et al. 1998) and PCR products were sequenced (Evrogen, Moscow, Russia). The obtained 16S rRNA sequences (1473 bp, Accession No. OL539808.1-OL539817.1) were 100% identical to DSM 20129T (AM410688.1) according to a BLAST NCBI search. A pathogenicity test was done by leaf-cutting with scissors wetted with inoculum (for soybeans) or by injecting 5 microliters of the bacterial suspension (108 CFU/ml) into the stem (for common beans). All ten isolates for the inoculum were grown on nutrient agar for 72 h at 28°C. Soybean cv. Kasatka plants (stage V1) were used for inoculation, and common bean (cv. Purpurnaya) plants were inoculated as well to confirm multi-host virulence. Sterile water served as a control. Ten plantlets were used as replicates for each treatment. The plants were incubated at 24°C, 80% RH, and a 14 hour light/10 hour dark cycle. Tan spots (soybean) and wilt (beans) have developed 7-21 d.p.i (Fig. 2.1-2.6). Control plants remained asymptomatic. Seed inoculation by soaking them in the same bacterial suspension repeatedly produced twisted primary root (Fig. 2.7-2.8), but typical disease symptoms on leaves developed in 4-5 weeks only. The pathogen was successfully reisolated from all infected plants and not from the controls, thus fulfilling Koch's postulates. The identity of the reisolated strains was confirmed using morphological and physiological characteristics and the DNA sequence data for the 16S rRNA. These results indicated that a causal agent of the tan spot is present on soybean in three important agricultural areas of Russia (South, Central, and the Far East). To the best of our knowledge, this is the first report of C. flaccumfaciens pv. flaccumfaciens causing a bacterial tan spot of soybean in Russia.

Exogenous melatonin mitigates saline-alkali stress by decreasing DNA oxidative damage and enhancing photosynthetic carbon metabolism in soybean (Glycine max [L.] Merr.) leaves.

Saline-alkali stress (SS) is a common abiotic stress affecting crop cultivation worldwide, seriously inhibiting plant growth and biomass accumulation. Melatonin has been proven to relieve the inhibition of multiple abiotic stresses on plant growth. Therefore, soybean cultivars Heihe 49 (HH49, SS-tolerant) and Henong 95 (HN95, SS-sensitive) were pot-cultured in SS soil and then treated with 300 μM melatonin at the V1 stage, when the first trifoliate leaves were fully unfolded, to investigate if melatonin has an effect on SS. SS increased reactive oxygen species (ROS) accumulation in soybean leaves and thereby induced DNA oxidative damage. In addition, SS retarded cell growth and decreased the mesophyll cell size, chloroplast number, photosynthetic pigment content, which further reduced the light energy capture and electron transport rate in soybean leaves, and affected carbohydrate accumulation and metabolism. However, melatonin treatment reduced SS-induced ROS accumulation in the soybean leaves by increasing antioxidant content and oxidase activity. Effective removal of ROS reduced SS-induced DNA oxidative damage in the soybean leaf genome, which was represented by decreased random-amplified polymorphic DNA polymorphism, 8-hydroxy-20-deoxyguanine content, and relative density of apurinic/apyrimidinic-sites. Melatonin treatment also increased the volume of mesophyll cells, the numbers of chloroplast and starch grains, the contents of chlorophyll a and b and carotenoids in soybean seedling leaves treated with SS, thereby increasing the efficiency of effective light capture and electron transfer and improving photosynthesis. Subsequently, carbohydrate accumulation and metabolism in soybean leaves under SS were improved by melatonin treatment, which contributes to providing basic substances and energy for cell growth and metabolism, ultimately improving soybean SS tolerance.

Influence of genotype and bacterization on growth, development, and soluble carbohydrate content in soybean E-genes isogenic lines

Photoperiod, which regulates the duration of vegetative and generative development, and the plant-microorganism interaction, which influences the metabolic status of plant organisms, are important factors in the regulating plant growth and development. The aim of the study was to determine the influence of Glycine max (L.) Merr. genotype and seed pre-bacterization with a virulent and active strain of Bradyrhizobium japonicum 634b on the plant growth and development, and on the soluble carbohydrate content in leaves of isogenic by E-genes lines under field conditions. Nearly isogenic lines (NILs) of soybean, in which the E1, E2, and E3 genes are located at different allelic loci, were used. Sterile seeds were pretreated with distilled water (control) and Bradyrhizobium japonicum 634b cell suspension (experiment). Plants were grown under natural long-day conditions (16 hours). The growth and development of the soybean were evaluated by phenological observations, morphometric indicators fixed at the V3 and V5 developmental stages, relative growth rate (RGR), and the content of soluble sugars ‒ mono- and oligosaccharides. The effect of the factors studied (genotype, bacterization, and their interaction) was calculated. The results of the experiment and the calculation of the effect of the factor showed that the isoline genotype has the greatest effect on seed germination, phenological development of the plant and duration of the VE-R1 phase, growth of the root system in the V3 and V5 phases, and the content of monosaccharides involved in forming the plant-microorganism interaction. The effect of bacterization is most evident in the RGR, shoot development, and the oligosaccharide content of the leaves of NILs in the V3 and V5 phases. Among the isolines studied, L 80-5879, which has the E1 gene (flowering repressor) in a dominant state, was characterized by minimal sensitivity to bacterization. It was found that bacterization and genotype interaction didn't influence the VE-R1 duration stage and the shoot and root length. The results obtained therefore prove that the E-series genes, which determine the photoperiodic sensitivity of soya beans, can also be indirectly involved in establishing plant-microorganism interactions.

Understanding the impact of fall armyworm (Spodoptera frugiperda J. E. Smith) leaf damage on maize yields.

Fall armyworm (Spodoptera frugiperda J. E. Smith), a serious pest of maize and other cereals, recently invaded the Old World potentially threatening the food security and incomes of millions of smallholder farmers. Being able to assess the impacts of a pest on yields is fundamental to developing Integrated Pest Management (IPM) approaches. Hence, working with an early maturing, medium maturing and late maturing variety, we inoculated maize plants with 2nd instar S. frugiperda larvae at V5, V8, V12, VT and R1 growth stages to investigate the effects of FAW induced damage on yield. Different plants were inoculated 0-3 times and larvae were removed after 1 or 2 weeks to generate a wide range of damage profiles. We scored plants for leaf damage at 3, 5 and 7 weeks after emergence (WAE) using the 9 point Davis scale. While at harvest we assessed ear damage (1-9 scale), and recorded plant height and grain yield per plant. We used Structural Equation Models to assess the direct effects of leaf damage on yield and indirect effects via plant height. For the early and medium maturing varieties leaf damage at 3 and 5 WAE, respectively, had significant negative linear effects on grain yield. In the late maturing variety, leaf damage at 7 WAE had an indirect effect on yield through a significant negative linear effect on plant height. However, despite the controlled screenhouse conditions, in all three varieties leaf damage explained less than 3% of the variation in yield at the plant level. Overall, these results indicate that S. frugiperda induced leaf damage has a slight but detectable impact on yield at a specific plant developmental stage, and our models will contribute to the development of decision-support tools for IPM. However, given the low average yields obtained by smallholders in sub-Saharan Africa and the relatively low levels of FAW induced leaf damage recorded in most areas, IPM strategies should focus on interventions aimed at improving plant vigour (e.g. through integrated soil fertility management) and the role of natural enemies, as these are likely to result in greater yield gains at lower cost than a focus on FAW control.

Root phenological and physiological response of maize (Zea mays L.) for adaptation under drought stress at vegetative and reproductive stages ​

Drought stress is known to negatively affect vegetative growth and biomass production, as well as the development of reproductive organs and yield characteristics in maize. The crop root systems are crucial for adaptability to various biotic and abiotic stresses, but studies addressing this are quite limited. The experiment was conducted simultaneously in both glasshouse and field condition during summer 2022 at TNAU, Coimbatore. The study was focussed to assess the root system architecture (RSA) of the drought tolerant and drought susceptible hybrids using PVC cylinders by imposing stress at V4 stage and root pulled out from the fieldby imposing stress at V14 stage. The results from the study showed that the significant variation was observed in both latter vegetative and mature root system under drought stress. Apart, the reduction in relative water content, SPAD values and increase of proline content were observed. The photosynthetic rate and gas exchange parameters were decreased upon exposure to drought stress. On considering, the hybrid N10-51 × DQL80 can accumulate osmolytes, maintaining tissue water potential and photosynthetic functionality for longer time when compared to other hybrids. This hybrid also exhibited the deep rooting ability with high yield under drought stress. Hence, it was identified as the drought tolerant hybrid and could be commercialized after testing their yield stability.

A single plant segmentation method of maize point cloud based on Euclidean clustering and K-means clustering

It is very important to study the correlation between phenotypic information and genetic information of population maize plants for breeding good maize varieties. How to separate single maize plants from population plants to more accurately measure maize phenotypic parameters is still a difficult problem. Therefore, we propose a single plant segmentation method based on Euclidean clustering and K-means clustering. First, three dimensional (3D) point cloud data of two planting density populations of maize (field 1 and field 2) at five-leaf stage (V5) and six-leaf stage (V6) were obtained by terrestrial laser scanning (TLS). Second, the point cloud data of maize plants were preprocessed to extract the point cloud data of the experimental area. Then, plane segmentation, point cloud filtering and Euclidean clustering were used to segment the population maize plants. Finally, the number of plants and center point of point cloud of maize plants after preliminary segmentation were obtained by voxel filtering, and then K-means clustering was used to achieve single segmentation of maize plants. When planting density was sparse, the segmentation results based on Euclidean clustering and K-means clustering showed that the Accuracy* F1 Score (A * F1) of V5 stage and V6 stage plants were 100.00 % and 99.87 %, respectively; and the A * F1 of V5 stage and V6 stage were 99.59 % and 85.69 %, respectively, when planting density was dense. Compared with the results of Euclidean clustering single plant segmentation, maize single plant segmentation A * F1 increased by 0.00 %, 6.02 %, 12.25 % and 73.41 % at V5 stage and V6 stage in field 1 and field 2, respectively. The results showed that the single plant segmentation based on Euclidean clustering and K-means clustering method could solve the problem that Euclidean clustering single plant segmentation method could not segment the cross-leaf plants. This study provides a simple and reliable method for plant segmentation of population maize for breeders and crop phenotypists.

Classification of soybean cultivars by means of artificial neural networks

The cultivation of soy has an economic importance for the Brazilian agricultural scenario. The aim of this study was to establish a network architecture for the classification of soybean genotypes, by means of morphological characters measured in the juvenile phase of the plant, and finally to compare the results obtained through Artificial Neural Network (ANN) and Anderson Discriminant Analysis. The study analyzed plants of 10 conventional cultivars in the initial stages of development (V1, V2 and V3 stages). The experiment was carried out in a randomized block design with 5 replications, and the experimental unit was represented by 9 plants. The data were submitted to the Anderson Discriminant Analysis and multilayer Perceptron ANN, with 1 or 2 hidden layers. To analyze the homogeneity of the variance and covariance matrix, the Box’s M-Test was adopted in the Program R, at 5% significance level. An input layer, one or two hidden layers, and an output layer formed the ANN architecture. The 5-fold cross validation was used to verify the efficiency of the discriminant functions and also in the ANN analysis. Subsequently, the apparent error rate (AER) was obtained. Box’s M-Test indicated inhomogeneity in the variance and covariance matrices, which indicated the need to perform Anderson's Quadratic Discriminant Analysis. The ANNs presented lower apparent error rate when compared to the Anderson's Quadratic Discriminant Analysis and the artificial neural network with 1 hidden layer was sufficient to perform the classification of soybean cultivars.

Rhizosphere and bulk soil bacterial community succession is influenced more by changes in soil properties than in rhizosphere metabolites across a maize growing season

The rhizosphere microbiome composition shifts across plant developmental stages. In addition, the bulk soil microbiome also changes during the growing season. However, the factors governing the rhizosphere and bulk soil microbiome succession across plant development are still not well identified. In this study we analyzed the changes in rhizosphere and bulk soil bacterial community structure through 16S rRNA amplicon sequencing across three maize growth stages (vegetative leaf 5 [V5], vegetative leaf 10 [V10] and reproductive stage 2 [R2]), as well as their correlations with temporal shifts in soil physicochemical properties and in root metabolites quantified in rhizosphere soils by LC/GC–MS. Twelve maize genotypes were used in a replicated field experiment for a comprehensive study. Results indicated significant correlations between the rhizosphere and bulk soil bacterial community succession with the temporal changes in rhizosphere metabolites and soil physicochemical properties. The changes in soil properties (mainly soil N and moisture) across stages explained more of the variation in the rhizosphere and bulk soil bacterial communities than the rhizosphere metabolites. However, shifts in rhizosphere metabolites (mainly sugars and gibberellins) across stages also strongly affected the rhizosphere bacterial community succession, but this effect was weaker on the bulk soil bacterial community. In addition to the changes in microbiome composition and diversity, we also detected changes in soil microbial respiration between plant developmental stages, with greater microbial activity at the V10 stage. In sum, our study showed that changes in soil properties have a great influence on both rhizosphere and bulk soil bacterial community succession across a growing season. The changes in plant root metabolites across the cropping season also affected the succession of the belowground bacterial communities, but the impact was much larger on the rhizosphere than on the bulk soil microbiome. Understanding the ecological processes shaping the belowground microbiomes through time is pivotal to develop future strategies for the most appropriate crop management across the whole growing season.

Yield Prediction of Four Bean (Phaseolus vulgaris) Cultivars Using Vegetation Indices Based on Multispectral Images from UAV in an Arid Zone of Peru

In Peru, common bean varieties adapt very well to arid zones, and it is essential to strengthen their evaluations accurately during their phenological stage by using remote sensors and UAV. However, this technology has not been widely adopted in the Peruvian agricultural system, causing a lack of information and precision data on this crop. Here, we predicted the yield of four beans cultivars by using multispectral images, vegetation indices (VIs) and multiple linear correlations (with 11 VIs) in 13 different periods of their phenological development. The multispectral images were analyzed with two methods: (1) a mask of only the crop canopy with supervised classification constructed with QGIS software; and (2) the grids corresponding to each plot (n = 48) without classification. The prediction models can be estimated with higher accuracy when bean plants reached maximum canopy cover (vegetative and reproductive stages), obtaining higher R2 for the c2000 cultivar (0.942) with the CIG, PCB, DVI, EVI and TVI indices with method 2. Similarly, with five VIs, the camanejo cultivar showed the highest R2 for both methods 1 and 2 (0.89 and 0.837) in the reproductive stage. The models better predicted the yield in the phenological stages V3–V4 and R6–R8 for all bean cultivars. This work demonstrated the utility of UAV tools and the use of multispectral images to predict yield before harvest under the Peruvian arid ecosystem.

Late-vegetative and reproductive-stage nitrogen determinants of kernel weight in maize

Differences in maize kernel weight (KW) due to soil N availability have usually been associated with the indirect role that N plays in the prevailing source-sink balance for carbon at the canopy level during reproductive development. Additionally, KW changes have also been described in response to N assimilate supply to the reproductive tissues (i.e., direct N role). Our objective was to determine the most important source factors driving KW gains with varying N and dry matter supply via the multivariate study of pertinent phenotypic relationships during late vegetative and reproductive growth. Maize responses to N rate plus N timing and(or) plant density treatments were followed in five field experiments. Principal component analyses (PCA) and partial least square (PLS) regressions explored the relationships between final KW, plant-component biomass (DM), plant-component N concentrations, N uptake at V12, R1, R3, and R6 stages, plus specific grain-filling parameters including effective grain-filling rate (EGFR), grain-filling duration (GFD), and the kernel N accumulation features of rate and duration (KNAR and KNAD, respectively). Across experimental sites, grain yields at the highest N rate were 93–196 % above those with zero N. These yield increases coincided with incremental gains in both kernel number and KW at maturity. Via PCA, final KW was more positively correlated with vegetative-tissue N concentrations (stem N % at V12 and R1, leaf N % at R1 and R3) than with biomass during the critical period. In addition, final KW was more correlated with stem biomass at R6 than at V12, R1 or R3 stages. Via PLS, the majority of KW variability was explained by critical-period N contents, either in leaf (V12 and R1) or stem (R3), while at R6 stem DM was more important in KW determination. Finally, when tested against its physiological determinants, KW at maturity was largely associated with KNAR (via PCA) and EGFR (via PLS) during the grain-filling period. Overall, these results suggest the dual importance of N in determining KW at maturity through both leaf and stem N supply during the critical period and through dry matter allocation during the effective grain filling period.

Grain yield and N uptake of maize in response to increased plant density under reduced water and nitrogen supply conditions

The development of modern agriculture requires the reduction of water and chemical N fertilizer inputs. Increasing the planting density can maintain higher yields, but also consumes more of these restrictive resources. However, whether an increased maize density can compensate for the negative effects of reduced water and N supply on grain yield and N uptake in the arid irrigated areas remains unknown. This study is part of a long-term positioning trial that started in 2016. A split-split plot field experiment of maize was implemented in the arid irrigated area of northwestern China in 2020 to 2021. The treatments included two irrigation levels: local conventional irrigation reduced by 20% (W1, 3,240 m3 ha–1) and local conventional irrigation (W2, 4,050 m3 ha–1); two N application rates: local conventional N reduced by 25% (N1, 270 kg ha–1) and local conventional N (360 kg ha–1); and three planting densities: local conventional density (D1, 75,000 plants ha–1), density increased by 30% (D2, 97,500 plants ha–1), and density increased by 60% (D3, 120,000 plants ha–1). Our results showed that the grain yield and aboveground N accumulation of maize were lower under the reduced water and N inputs, but increasing the maize density by 30% can compensate for the reductions of grain yield and aboveground N accumulation caused by the reduced water and N supply. When water was reduced while the N application rate remained unchanged, increasing the planting density by 30% enhanced grain yield by 13.9% and aboveground N accumulation by 15.3%. Under reduced water and N inputs, increasing the maize density by 30% enhanced N uptake efficiency and N partial factor productivity, and it also compensated for the N harvest index and N metabolic related enzyme activities. Compared with W2N2D1, the N uptake efficiency and N partial factor productivity increased by 28.6 and 17.6% under W1N1D2. W1N2D2 had 8.4% higher N uptake efficiency and 13.9% higher N partial factor productivity than W2N2D1. W1N2D2 improved urease activity and nitrate reductase activity by 5.4% at the R2 (blister) stage and 19.6% at the V6 (6th leaf) stage, and increased net income and the benefit:cost ratio by 22.1 and 16.7%, respectively. W1N1D2 and W1N2D2 reduced the nitrate nitrogen and ammoniacal nitrogen contents at the R6 stage in the 40–100 cm soil layer, compared with W2N2D1. In summary, increasing the planting density by 30% can compensate for the loss of grain yield and aboveground N accumulation under reduced water and N inputs. Meanwhile, increasing the maize density by 30% improved grain yield and aboveground N accumulation when water was reduced by 20% while the N application rate remained constant in arid irrigation areas.