R1 Growth Stage Research Articles

Genome-wide association analysis of sucrose and alanine contents in edamame beans.

The sucrose and Alanine (Ala) content in edamame beans significantly impacts the sweetness flavor of edamame-derived products as an important attribute to consumers' acceptance. Unlike grain-type soybeans, edamame beans are harvested as fresh beans at the R6 to R7 growth stages when beans are filled 80-90% of the pod capacity. The genetic basis of sucrose and Ala contents in fresh edamame beans may differ from those in dry seeds. To date, there is no report on the genetic basis of sucrose and Ala contents in the edamame beans. In this study, a genome-wide association study was conducted to identify single nucleotide polymorphisms (SNPs) related to sucrose and Ala levels in edamame beans using an association mapping panel of 189 edamame accessions genotyped with a SoySNP50K BeadChip. A total of 43 and 25 SNPs was associated with sucrose content and Ala content in the edamame beans, respectively. Four genes (Glyma.10g270800, Glyma.08g137500, Glyma.10g268500, and Glyma.18g193600) with known effects on the process of sucrose biosynthesis and 37 novel sucrose-related genes were characterized. Three genes (Gm17g070500, Glyma.14g201100 and Glyma.18g269600) with likely relevant effects in regulating Ala content and 22 novel Ala-related genes were identified. In addition, by summarizing the phenotypic data of edamame beans from three locations in two years, three PI accessions (PI 532469, PI 243551, and PI 407748) were selected as the high sucrose and high Ala parental lines for the perspective breeding of sweet edamame varieties. Thus, the beneficial alleles, candidate genes, and selected PI accessions identified in this study will be fundamental to develop edamame varieties with improved consumers' acceptance, and eventually promote edamame production as a specialty crop in the United States.

Split applications of molybdenum fertilizer on common bean increase molybdenum in seed

AbstractCommon bean (Phaseolus vulgaris L.) plants sprayed with molybdenum (Mo) fertilizer produce Mo‐enriched seeds, which may increase yield in Mo‐poor soils. The challenge has been to produce Mo‐enriched seeds with less fertilizer. Split applications of Mo increase seed Mo content (SMoC), but the number of splits that maximize SMoC has not been studied sufficiently. In three sprinkler‐irrigated field trials, we evaluated the effects of split‐applied Mo fertilizer on SMoC and seed physiological quality. All treatments received NPK fertilizer at sowing. In two treatments, 69 kg ha−1 of urea‐N was top‐dressed or not applied. In six treatments, Na2MoO4·2H2O was foliar‐sprayed once at either 90 or 600 g ha−1 of Mo at the 4th trifoliolate leaf (V4) growth stage, or 600 g ha−1 was split equally at V4 and bud initiation (R5); V4, R5, and full flowering (R6); V4, R5, R6, and early pod formation (R7); or V4, R5, R6, and early and late R7 growth stages. Seed yield for each trial ranged from 3723 to 4621 kg ha−1. Site‐treatment interaction was significant for SMoC and seed germination (p < 0.001). SMoC ranged from 0.11 to 0.23 (only NPK‐fertilized), 1.81 to 3.31 (600 g ha−1, no split), and 5.22 to 6.29 μg (four splits). Four and five splits did not differ significantly for any variable. In two trials, seeds from 600 g ha−1 of Mo had a 3.9% higher germination than seeds from 90 g ha−1. In conclusion, SMoC increases as the number of splits increase up to four times. Additionally, Mo applied at 600 g ha−1 may improve seed germination rate.

Soybean response to potassium, magnesium, and sulfur fertilization on Southeastern Coastal Plain soils

AbstractPotassium (K), magnesium (Mg), and sulfur (S) are susceptible to leaching in Southeastern Coastal Plain soils and can limit crop production if not properly managed. This study aimed to determine the effect of K, Mg, and S fertilization on soybean [Glycine max (L.) Merr.] yield, tissue nutrient concentrations, and soil K, Mg, and S concentrations. Treatments included three K, two Mg, and two S fertilizer rates arranged in a randomized complete block design with three replications. There was no significant main or interaction effect of K, Mg, and S on soybean yield, even when the initial soil‐test S level was below critical levels. Leaf K concentrations of control plots measured at the R2 growth stage were in the sufficiency range reported for soybean in southeastern states. However, leaf Mg and S concentrations were below the sufficiency ranges. Applying S fertilizer increased leaf Mg and S concentrations, but Mg fertilizer did not affect leaf Mg concentrations. Applying K fertilizer rates increased soil‐test K across three soil depths compared to the control K treatment. The application of Mg fertilizer increased soil‐test Mg more at 0–15 cm than at the other two depths (15–30 or 30–45 cm), whereas S fertilizer application increased soil‐test S more at 15–30 cm. The soil samples taken before experiment initiation showed that the lower two soil depths had greater soil‐test K and S concentrations than at the top layer. These findings indicate that more research is needed to appropriately credit subsoil nutrients while making fertilizer recommendations for soybean grown on Southeastern Coastal Plain soils.

Evaluation of soybean grain quality and yield across various row spacings, planting dates, and fungicide programs

AbstractOne of the major constraints to profitable soybean [Glycine max (L.) Merr.] production is yield losses caused by disease. The mid‐southern region of the United States typically experiences environmental conditions that are conducive to disease development, particularly during later reproductive growth stages. It is common for producers in this region to apply fungicides at the beginning of pod development (R3 growth stage; development of pods 3/16 inches long). Producers often question if establishing crops in different row patterns would alter the yield response to prophylactic fungicide applications. Producers also seek answers regarding the yield and grain quality responses to fungicide applications across different row patterns. However, limited data exist to determine if fungicide applications influence the responses of soybean's yield and grain quality between different row spacings. The objective of this research was to evaluate soybean's growth, development, yield, and grain quality across various row spacings, planting dates, and prophylactic fungicide application programs in the absence of disease. These data support that early‐planted soybean had greater yield than later‐planted soybean. No interactions were observed among row spacing, planting date, and fungicide product with respect to yield. Independently, no yield differences were observed regardless of the row spacing or the fungicide product. Regarding quality, soybean planted later resulted in fewer total damaged soybean kernels. These data suggest that row spacing and planting date may not influence soybean's yield response to prophylactic fungicide. Furthermore, these data also suggest that prophylactic fungicide during pod development may not influence the subsequent grain quality.

Normalized Difference Vegetation Index (NDVI) for soybean biomass and nutrient uptake estimation in response to production systems and fertilization strategies

The system fertilization approach emerged to improve nutrient use efficiency in croplands. This new fertilization concept aims at taking advantage of nutrient cycling within an agroecosystem to obtain maximum production from each nutrient unit. To monitor this effect, methodologies such as the Normalized Difference Vegetation Index (NDVI) are promising to evaluate plant biomass and nutrient content. We evaluated the use of NDVI as a predictor of shoot biomass, P and K uptake, and yield in soybean. Treatments consisted of two production systems [integrated crop-livestock system (ICLS) and cropping system (CS)] and two periods of phosphorus (P) and potassium (K) fertilization (crop fertilization—P and K applied at soybean sowing—and system fertilization—P and K applied in the pasture establishment). NDVI was evaluated weekly from the growth stage V2 up to growth stage R8, using the Greenseeker® canopy sensor. At the growth stages V4, V6, R2, and R4, plants were sampled after NDVI evaluation for chemical analysis. Soybean yield and K uptake were similar between production systems and fertilization strategies (P > 0.05). Soybean shoot biomass and P uptake were, respectively, 25.3% and 29.7% higher in ICLS compared to CS (P < 0.05). For NDVI, an interaction between the production system and days after sowing (P < 0.05) was observed. NDVI increased to 0.95 at 96 days after sowing in CS and to 0.92 at 92 days after sowing in ICLS. A significant relationship between NDVI and shoot biomass, and P and K uptake was observed (P < 0.05). Our results show that the vegetation index NDVI can be used for estimating shoot biomass and P and K uptake in the early growth stages of soybean crops, providing farmers with a new tool for evaluating the spatial variability of soybean growth and nutrition.

Continuous-cropping-tolerant soybean cultivars alleviate continuous cropping obstacles by improving structure and function of rhizosphere microorganisms.

Soybean continuous cropping will change soil microorganisms and cause continuous cropping obstacles, resulting in a significant yield decline. Different soybean cultivars have different tolerances to continuous cropping, but the relationship between continuous cropping tolerance and soil microorganisms is not clear. Two soybean cultivars with different tolerances to continuous cropping were used to study the effects of continuous cropping on soil physical and chemical properties, nitrogen and phosphorus cyclic enzyme activities, rhizosphere soil microbial community and function. The results showed that the yield reduction rate of a continuous-cropping-tolerant cultivar (L14) was lower than that of a continuous-cropping-sensitive cultivar (L10) under continuous cropping. At R1 and R6 growth stages, soil nutrient content (NH4 +-N, NO3 --N, AP, DOM, TK, and pH), nitrogen cycling enzyme (URE, NAG, LAP) activities, phosphorus cycling enzyme (ALP, NPA, ACP) activities, copy numbers of nitrogen functional genes (AOA, AOB, nirK, nirK) and phosphorus functional genes (phoA, phoB) in L14 were higher than those in L10. Soybean cultivar was an important factor affecting the structure and functional structure of bacterial community under continuous cropping. The relative abundances of Proteobacteria, Bacteroidota, Acidobacteriota and Verrucomicrobiota with L14 were significantly higher than those of L10. The complexity of the soil bacterial community co-occurrence network in L14 was higher than that in L10. The continuous-cropping-tolerant soybean cultivar recruited more beneficial bacteria, changed the structure and function of microbial community, improved soil nitrogen and phosphorus cycling, and reduced the impact of continuous cropping obstacles on grain yield.

Analysis of vegetative storage protein accumulation in soybean cultivars expressing different green stem disorder severity affected by soil moisture change

ABSTRACT Green stem disorder (GSD), characterized by delayed stem senescence during seed maturation, complicates harvesting in soybean production. Although GSD is associated with a sink – source imbalance, a rapid and precise evaluation of GSD has not been established. In sink-limited soybean plants, vegetative storage protein (VSP) accumulates. In this study, pot and field experiments were conducted to reevaluate the relationship between GSD, sink – source imbalance caused by soil moisture change, and VSP accumulation as a possible indicator of GSD in Kyoto, Japan over two years. Drought treatment for four weeks from R1 (beginning flowering), R3 (beginning pod), or R5 (beginning seed) growth stage in pots using the short growth-period cultivar Yukihomare reduced sink size in both years, but reduced relative sink mass (pod weight/shoot weight) and increased GSD severity only in 2017, suggesting that sink-source imbalance, affected by soil moisture, can induce GSD. Soil moisture change from around R3 or R5 to maturity in fields using trench-filled or unfilled water tended to change GSD severity but not VSP accumulation in the uppermost fully expanded leaves from R5 (2018) or 15 days before R5 (2019) to 28 days after R5. GSD and VSP responses, however, differed between the two contrasting cultivars, Tachinagaha and Touhoku 129, suggesting the potential usability of VSP for GSD evaluation.

Sowing date influence on the soybean tolerance to defoliation at the beginning of pod formation

Late sowings anticipate flowering and decrease the soybean vegetative plasticity. These changes may limit the ability of plants to tolerate leaf area losses. The objective of this research was to evaluate the sowing date effect on soybean tolerance to defoliation at the beginning of pod formation. The experiment was set in Lages (Santa Catarina State, Brazil) during the 2016/2017 growing season. Two sowing dates were tested: November 2, 2016 (preferential) and December 15, 2016 (late). Five levels of defoliation (0%, 17%, 33%, 50% and 67%) of cultivar NA 5909 RG were imposed at the R3 growth stage. Grain yield showed a quadratic response to defoliation, ranging from 4,313 to 6,478 kg ha-1 in the preferential sowing date and from 3,374 to 4,443 kg ha-1 in the late sowing date. The plants tolerated up to 45.6% of defoliation in early sowing and 55.8% in late sowing, without yield losses, in comparison to the control. The highest level of defoliation reduced grain yield by 26.9% and 13.4% in early and late sowings, respectively, compared to the control. The delay of sowing date did not increase the sensitivity of cultivar NA 5909 RG to defoliation at the beginning of pod formation.

Application of Pyraclostrobin Fungicide at Miniature Floral Head Development Growth Stage Is Efficacious Against Phomopsis Stem Canker Fungi in Sunflower (Helianthus annuus)

Phomopsis stem canker, caused by multiple species of Diaporthe, is a yield-limiting disease of sunflower ( Helianthus annuus L.) in the U.S. Northern Great Plains. To develop fungicide recommendations, we performed meta-analyses on data collected from 56 foliar fungicide efficacy trials conducted in Minnesota, Nebraska, North Dakota, and South Dakota between 2009 and 2021. The specific objectives were to compare the fungicide application timings and active ingredients with a nontreated control (NTC) and determine their impact on the disease severity index (DSI) and yield. Effect sizes, Cohen's f or Hedges’ g, were calculated as the difference in DSI or yield between the fungicide treatment and NTC. We observed that fungicide application timings (DSI [ f = 0.43] and yield [ f = 0.26]) and active ingredients (DSI [ f = 0.51] and yield [ f = 0.39]) had a significant effect on DSI and yield ( P < 0.0001). In addition, application of pyraclostrobin (DSI [ g = −0.65] and yield [ g = 0.43]), pyraclostrobin + fluxapyroxad (DSI [ g = −0.55] and yield [ g = 0.36]), and mefentrifluconazole + pyraclostrobin + fluxapyroxad (DSI [ g = −2.23] and yield [ g = 0.85]) at the R1 (miniature floral head formation) growth stage outperformed NTC. This study suggests that farmers can rely on a single application of pyraclostrobin at R1 for Phomopsis stem canker management. Future studies on the economic benefits from fungicide use are important to help enhance farmer decisions.

Non‐dicamba‐resistant soybean response to multiple dicamba applications

AbstractThe rapid adoption of dicamba (3,6‐dichloro‐2‐methoxybenzoic acid)‐resistant (DR) soybean [Glycine max (L.) Merr.] resulted in an increase of post‐emergent dicamba applications during the soybean‐growing season, resulting in off‐target movement and injury to non‐DR soybean. Field trials were established in Manhattan, KS, in 2018 and 2019 and in Ottawa, KS, in 2019 to characterize the response of non‐DR soybean to one, two, or three applications of reduced rates of dicamba at three application timings. Soybean were treated with 0.56, 1.12, and 5.6 g a.e. ha−1 of dicamba, which is equivalent to 1/1,000X, 1/500X, and 1/100X of a 1X field‐use rate (560 g a.e. ha−1), respectively. Soybean plants were treated at V3, R1, R3, V3 followed by (fb) R1, V3 fb R3, R1 fb R3, and V3 fb R1 fb R3 growth stages. Soybean injury from dicamba was less severe following application during the V3 than the R1 or R3 growth stages. In general soybean injury was the greatest 4 wk after application. The greatest soybean yield reduction (68%) followed dicamba applications of 5.6 g a.e. ha−1 at V3 fb R1 fb R3 in Manhattan, KS, 2018, where yield loss was generally greater and may be attributed to droughty conditions. Yield loss was minimal in Manhattan, KS, and Ottawa, KS, in 2019 following a single dicamba application at the V3 stage, regardless of application rate and following dicamba application at 0.56 g a.e. ha−1, regardless of number of applications. The greatest soybean yield losses from dicamba occurred with two or three applications at 1.12 or 5.6 g a.e. ha−1.

Effects of Soil Type, Temperature, and Moisture on Development of Fusarium Root Rot of Soybean by Fusarium solani (FSSC 11) and Fusarium tricinctum.

Fusarium solani FSSC 11 and F. tricinctum are important root rot pathogens of soybean in North Dakota. The roles of soil type, temperature, and moisture in disease development by both species are poorly documented. To assess the effect of soil type on disease, three types of soil (Glyndon sandy loam, La Prairie silt loam, and Fargo clay) that represent soils of the soybean production region in the Red River Valley were examined in greenhouse, microplot, and growth chamber studies. Disease incidence and lesion length on roots were evaluated at growth stages V3 and R6. Soil type significantly affected disease development, with higher severity in the lighter soils of Glyndon sandy loam and La Prairie silt loam compared with Fargo clay. Soil type also interacted with Fusarium species, in which the maximum severity was observed in Glyndon sandy loam for F. solani, and in La Prairie silt loam for F. tricinctum. In addition, the cumulative effects of soil type, temperature, and soil moisture were tested in a growth chamber. Emergence and disease on seedlings were evaluated at growth stage V3. Significant reductions in emergence occurred at 10°C in treatments with F. solani and F. tricinctum, but there was no significant difference among the three soils. Infection was visible at temperatures of 10 to 20°C for F. solani and 15 to 20°C for F. tricinctum. F. solani caused the greatest infection at 20°C in Glyndon sandy loam, while it was at 15°C in La Prairie silt loam for F. tricinctum. The isolates of the two Fusarium species caused root rot in soil moisture ranging from 20 to 100% water holding capacity (WHC). The greatest reduction in emergence caused by the Fusarium spp. was observed at 80% WHC in silt loam and clay soils and 40% WHC in sandy loam soil, when compared with the same WHC in noninfested soils. Ranges of soil moisture causing infection were negatively correlated with temperature. At the lower temperature there was a broader range of soil moistures resulting in infection compared with higher temperatures. At 18°C, most infection occurred at soil moistures of 20 to 80% WHC, while it was 40 to 80% WHC at 28°C. Disease caused by F. solani was favored by a temperature of 18°C with high soil moisture (60 to 80% WHC) or 28°C with low soil moisture (20 to 40% WHC), while F. tricinctum was favored by cooler temperature and lower soil moisture.

The effects on the root and plant development of soybean of organic fertilizer applications

Organic fertilizers increase soil aeration, water and nutrient holding capacity, improve seed germination and encourage the production of thicker roots, increase the yield and quality of the crop. This study was aimed to determine the effects of organic fertilizer (vermicompost, sheep manure, cattle manure, poultry manure and inorganic fertilizer as control) applications on the root and plant development of soybean during two growth stages, namely third trifoliate stage (V3) and beginning of flowering of the plants (R1) in the pot condition. The experiment was established with a two-factorial randomized plot design with four replications. The fertilizer applications had a significant effect (p<0.01) on the V3 and R1 growth stages of soybean. The highest plant height (36.78 cm) and root length (41.18 cm) were achieved with vermicompost, and the lowest plant height (21.73 cm) was recorded with inorganic fertilizer. The number of nodules was highest for vermicompost and cattle manure applications (17.16 plant-1 and 16.76 plant-1, respectively), and lowest for poultry manure (0.22 plant-1). In the R1 growth stage, poultry manure produced the highest biological fresh and dry weights, root dry weight at 25.08 g plant-1 and 5.67 g plant-1, 3.99 g plant-1 respectively. As a result, it was demonstrated that vermicompost and poultry manure applications promote strong root and plant development due to high organic matter and phosphorus and can be used successfully without inorganic fertilize application in soybean farming.

The impact of electrocution treatments on weed control and weed seed viability in soybean

AbstractField experiments were conducted in 2020 and 2021 to determine the effectiveness of electrocution on several weeds commonly encountered in Missouri soybean production using an implement known as The Weed Zapper™. In the first study, the effectiveness of electrocution on waterhemp, cocklebur, giant and common ragweed, horseweed, giant and yellow foxtail, and barnyardgrass was determined. Electrocution was applied when plants reached average heights and/or growth stages of 30 cm, 60 cm, flowering, pollination, and seed set. Electrocution was applied once or twice, at two different tractor speeds. Electrocution was more effective at the later plant growth stages. Pearson correlation coefficients indicated that control of weed species was most related to plant height and amount of plant moisture at the time of electrocution. When plants contained seed at the time of electrocution, viability was reduced from 54% to 80% among the species evaluated. A second study determined the effect of electrocution on late-season waterhemp plants, and also soybean injury and yield. Electrocution timings took place throughout reproductive soybean growth stages. The control of waterhemp escapes within the soybean trial ranged from 51% to 97%. Yield of soybean electrocuted at the R4 and R6 growth stages was similar to that of the nontreated control, but soybean yield was reduced by 11% to 26% following electrocution at all other timings. However, the visual injury and yield loss observed in these experiments likely represents a worst-case scenario because growers who maintain a clear height differential between waterhemp and the soybean canopy would not need to maintain contact with the soybean canopy. Overall, results from these experiments indicate that electrocution as part of an integrated weed-management program could eliminate late-season herbicide-resistant weed escapes in soybean, and reduce the number and viability of weed seed that return to the soil seedbank.

High source–sink ratio at and after sink capacity formation promotes green stem disorder in soybean

Green stem disorder (GSD) of soybean is characterized by delayed leaf and stem maturation despite normal pod maturation. Previous studies have suggested that GSD occurrence is promoted by a high source–sink ratio, which is produced by thinning or shade removal at the R5 growth stage (the beginning of seed filling). Here the effects of different times and durations of shade removal after the R5 stage on GSD severity were analyzed. First, shade removal for more than 28 days after R5 increased GSD severity by more than 0.4 point in GSD score. Thinning treatment at R5 increased specific leaf weight by 23%, suppressed stem dry weight reduction, and upregulated 19 genes including those encoding vegetative storage proteins at R5 + 28d, indicating excess source ability relative to sink size. On the contrary, shade removal for 14 days after R5 decreased GSD severity by 0.5 point in GSD score. In this treatment, seed size was smaller, while seed number was significantly larger than control, suggesting that shortage of source ability relative to sink size. These results implied that soybean plants regulate GSD occurrences either positively or negatively according to a source-sink ratio during the R5 to R5 + 28d growth stages.

Effects of nitrogen and water stress on the rehydration, endogenous hormonal regulation and yield of maize

AbstractWater scarcity is known to be a strong limiting factor affecting maize grown and yield in cold semi‐arid regions. Numerous studies have shown that rehydration improves maize growth. Our study aimed to explore the effects of rehydration treatments on maize growth and yield under water and nitrogen stress during different growth stages. We selected the drought‐tolerant maize variety Nendan 19 (ND19) and subjected it to water stress during the V6 (sixth‐leaf), R2 (filling) and R6 (maturity) growth stages and a rehydration treatment after each stress stage. Our results indicated that N1 (N100 kg N ha−1) and N3 (N300 kg N ha−1) treatments significantly increased the leaf moisture status relative to water content (RWC), bound water content (BWC), free water content (FWC) and water potential (WP)) at different growth stages. Similar trends were observed in the accumulation of plant leaf and root hormones (zeatin+zeatin riboside, indole‐3‐acetic acid, abscisic acid and gibberellic acid), photosynthetic pigments and chlorophyll fluorescence. However, under the same water stress conditions, they decreased as the N rate increased and reached a minimum value in the S3 (water stress for N3) treatments. In addition, with growth stage advancement and extension of the rehydration time, both showed a gradual upward trend. The results showed that to save water resources in the cold semi‐arid region, rehydration treatments (R2S1 and R2S3) significantly increased the photosynthetic pigments and chlorophyll fluorescence parameters, leaf moisture status, biomass, 100‐grain weight, hormone content, ear characteristics and grain yield of maize.

Soybean dose-response to 2,4-D and dicamba at vegetative and reproductive growth stages.

Field experiments were conducted across multiple sites in 2012 and 2013 to describe sensitivity of soybean to 2,4-D (six doses) and dicamba (seven doses) at V3 and R1 growth stages. Further experiments were conducted under greenhouse conditions in 2017 and 2018 to compare soybean response to several dicamba herbicides across a broader range of doses than those tested in the field. Soybean yield loss was 6.1-fold greater from 2,4-D exposure at V3 compared to R1 and 1.4 times greater from dicamba exposure at R1 than at V3. In V3 exposures, soybean was 15.4 times more sensitive to dicamba than 2,4-D and 134.4-fold more sensitive to dicamba when exposed at R1. Plant injury and height correlations to grain yield resulted in coefficients ranging from 0.65 to 0.91. In greenhouse experiments, five dicamba products were tested at up to 19 doses and as low as 0.002 g ae ha-1 (3.6 × 10-6 % of maximum single use-rate); however, no differences were observed among formulations used in dicamba-resistant crops versus traditional formulations. A no observable effects dose was not identified due to responses observed even at the lowest doses tested, although hormesis effects were observed in plant height. These data suggest that the sensitivity of soybean to dicamba is much greater than what has previously been reported. However, as has been indicated by previous work, that injury does not always result in yield loss. © 2022 Society of Chemical Industry.

Impact of Delaying Irrigation on Wilting, Seed Yield, and Other Agronomic Traits of Determinate MG5 Soybean

Soybean production in the U.S. Mid-South relies heavily on irrigation with 85% of soybean surfaces irrigated in Arkansas. Reduction in irrigation due to water quantity restrictions will significantly affect soybean seed yield, making variety selection increasingly important. The objective of the study was to assess if irrigation onsets at different reproductive stages affect wilting, seed yield, and key agronomic traits on determinate maturity group 5 (MG 5) soybean. One-hundred sixty-five F4-derived populations of recombinant inbred lines with determinate growth habit, similar maturity, and contrasting wilting potential were planted in an augmented strip-plot design in four environments as a single replicate. Four irrigation onsets were applied at R1 (initiation flower), R2 (full bloom), R3 (initiation pod), and R4 (full pod) using an atmometer. Results indicated significant differences in wilting and yield but no significant differences in maturity, protein, oil concentration, and 100-seed weight across different irrigation onsets. There was no significant difference between the fast and slow wilting genotypes across different irrigation onsets for each trait. Allowable depletions measured in this study indicated that both fast and slow wilting soybean genotype determinate MG5 can tolerate high allowable depletion with no significant yield penalty at R3 growth stage in silt loam soil.

First Report of Exserohilum rostratum Causing Leaf Spot on Maize (Zea mays) in Henan, China.

In August to September of 2019 and 2020, a leaf spot was observed on maize at growth stages R1 through R5 in Henan. Leaf samples (N = 63) were collected from 152 fields from 50 counties. Symptomatic plants had light-yellow to brown elliptic lesions (0.6 to 5.0 cm × 0.2 to 0.8 cm) with gray. Incidence rates were 1 to 15% in individual fields. Symptomatic leaf samples (3 to 5 cm2) were surface sterilized (75% ethanol, 30 s; 3% NaClO, 2 min), rinsed three times in sterile distilled water, and allowed to dry. Small sections from the samples were placed on potato dextrose agar (PDA) medium and incubated at 25°C for 4 days. Observed colonies were circular, taupe, pewter in color with light gray edging and many cottony aerial mycelia. Single spores (N = 45) were inoculated on water agar medium with wheat straw (TWA + W). Conidiophores on wheat straw were single, erect or slightly curved, in clusters, septate, sympodial, geniculate and 5 to 7 μm thick. The basal cell was slightly swollen and was dark brown. The basal septum was darker and thicker than other septa, with a distinctly protruding truncate hilum. The conidia belonged to two types (Lin et al. 2011). Type A were fusiform, cylindrical, pyriform to oval, dark brown, 2 to 7 septate, 16.5 to 70.5 µm × 10.2 to 24.7 µm (N = 50). Type C were straight or slightly bent, ellipsoidal or long ellipsoidal, light brown, 6 to 13 septate, 36.3 to 106.8 µm × 10.5 to 16.0 µm (N = 50). All single spore isolates were identified morphologically as Exserohilum rostratum (Drechs.) Leonard & Suggs (Ahmadpour et al. 2013; Sivanesan et al. 1987). Four isolates (ML154-1, ML300-2, ML598-4 and ML626-1) were arbitrarily selected for molecular identification and inoculation testing. The internal transcribed spacer (ITS) and glyceraldehyde-3-phosphate dehydrogenase-like (gpd) gene were amplified and sequenced using primer pairs ITS1/ITS4 (White et al. 1990) and Gpd1/Gpd2 (Berbee et al. 1999), respectively. Sequences MW440488, MW440489, MW440491 and MW440492 of ITS and MW448214, MW448215, MW448217 and MW448218 of gpd were submitted to GenBank. BLASTn analysis revealed a high match (ITS: 598/600 bp; gpd: 527/527 bp) to E. rostratum isolate BRIP11422 (ITS: LT837464; gpd: LT883541). A phylogenetic tree was constructed based on concatenated sequences of ITS and gpd gene in MEGA-X. All four isolates formed a single clade with E. rostratum reference isolates CBS732.96, BRIP11422 and BRIP11416. To test pathogenicity in the greenhouse, a conidial suspension of each of the four strains (1 × 104 conidia/ml) was sprayed on the leaves of the common maize hybrids, Zhengdan 958 and Xianyu 335 (V6- V7). Control plants were sprayed with sterile water. Plants were incubated in plastic bags to retain high relative humidity for 24 h at 25~27°C. Three days after inoculation, the leaves began to show symptoms, and 7 days later, symptoms of the leaves were identical to those observed in the field. Control plants developed no symptoms. The pathogen was re-isolated from the infected leaves and was confirmed to be E. rostratum. The first E. rostratum isolate was isolated from the leaves of Eragrostis in China (Jiang et al. 1959). Thereafter E. rostratum has been reported as the causal agent of leaf spot in Ananas comosus (He et al. 2011), Musa paradisiacal (Luo et al. 2012), Hevea brasiliensis (Zhang et al. 2016) and many gramineous grass weeds (Liu et al. 2016) in China. To our knowledge, this is the first report of E. rostratum causing leaf spot disease on maize in Henan, China. Since this is an economically important pathogen of maize throughout the world, disease management strategies are likely to be needed.

First Report of Pod and Stem Blight and Seed Decay Caused by Diaporthe longicolla on Soybean in Western Canada

In Oct. 2019, soybean plants (Glycine max) (cv. 24-10RY, R7 growth stage) with dry rot, necrosis, reddish-brown lesions, and small black fruiting bodies in linear rows were collected from fields in Manitoba (Carman, St. Adolph, Dauphin), Canada. The pods and seeds were shrivelled, small and some seeds were covered with whitish mycelium. Symptoms began as brown lesions, which darkened, elongated, causing wilt of the above stems then plant death. Microscopy showed that the fruiting bodies were pycnidia. Symptomatic stems were cut into 1-2 cm pieces and seeds surface-sterilized in 0.5% NaOCl, rinsed twice in sterilized H2O, air-dried on sterilized filter paper, and plated on PDA medium amended with 100 mg/L streptomycin sulfate at room temperature with 12-h fluorescent light/12-h dark for 3 days. The emerging hyphae were transferred using the hyphal tip method to new PDA petri dishes and incubated for 21 days (room T°). Mycelia of 20 isolates were dense, white and floccose with occasional green-yellow areas. Black stromata in concentric patterns or scattered as large masses were visible on the cultures' back. Pycnidia formed solely or aggregated after 4-5 weeks of incubation on PDA. Alpha conidia emanated from pycnidia in creamy-to-yellowish drops and were hyaline, non-septate, ellipsoid to fusiform, and biguttulate. The average length and width of Alpha conidia were 5.5 μm and 1.5 μm, respectively (n = 30). No perithecia were seen. The cultures' morphology was consistent with Phomopsis longicolla's description (Hobbs et al., 1985). Seven isolates were selected for molecular characterization to confirm their identity by amplifying the ITS region with universal primers ITS4/ITS5 (White et al. 1990). All PCR amplicons were analyzed by electrophoresis through 1.5 % agarose gels and the size of PCR amplicons estimated using 1-kb plus DNA ladder (Thermo Fisher Sci., ON, Canada). PCR amplicons (~650 bp) were purified and sequenced in two directions by Psomagen Inc. (Rockville, MD, USA). ITS sequences were identical for all isolates, and GenBank searches (BLASTn: Altschul et al. 1990) confirmed species identity. ITS sequences (accessions MW466183-MW466189) were deposited in GenBank and matched the type sequence of Diaporthe longicolla strain ATCC 60325 (accession NR_144924) from G. max in USA with identities = 473/475 (99.6%) and gaps = 0/475 (0%). To confirm the pathogenicity of the seven isolates, the stems of V4-stage (four open trifolilates) soybean plants (cv. 24-10RY) were excised using a sterile scalpel. Mycelial plugs (9 mm in diameter) from 1-week-old culture of each isolate were placed over the wounded stems (Abdelmagid et al., 2019). Sterile PDA plugs were used on control plants. Six plants were used per isolate and control. Plugs of both treatments were wrapped with parafilm to avoid drying. The plants were incubated in a humidity chamber for 4 days and then in a greenhouse at 24:16°C day/night, 13:11-h light/dark cycle, and 70-80% relative humidity, and were irrigated as needed. Symptoms similar to those observed in the field were seen on the stems and seeds of all artificially-infected plants approx. 8 weeks after inoculation. Pods and seeds of inoculated plants were shrivelled and small. No symptoms were observed on control plants. Diaporthe longicolla was re-isolated only from the diseased plants and seeds. To our knowledge, this is the first report following Koch's postulates to identify the causal pathogen of soybean pod and stem blight and seed decay in Western Canada. This will be instrumental in determining the causes of stem decay and contribute in properly dealing with soybean seed issues in Western Canada in the future.

Wheat Production Alters Soil Microbial Profiles and Enhances Beneficial Microbes in Double-Cropping Soybean

Plant-parasitic nematodes represent a substantial constraint on global food security by reducing the yield potential of all major crops. The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is widely distributed across important soybean production areas of the U.S., being the major soybean yield-limiting factor, especially in the Midwestern U.S. Double cropped (DC) soybean is commonly planted following winter wheat. We previously reported double-cropping soybean fields with reduced SCN counts compared to fallow at both R1 growth stage (beginning of flowering) (−31.8%) and after soybean harvest (−32.7%). To test if higher counts of beneficial and SCN antagonistic microorganisms could be correlated with the suppression of SCN in fields previously planted with wheat, three field locations with noted SCN suppression were selected for a metagenomics study. Ten subplots were selected (5 wheat and 5 fallow pre-soybean) from each location. A total of 90 soil samples were selected: 3 fields ×2 treatments × 3 timepoints × 5 replications. Three DNA markers targeted distinct microbial groups: bacteria (16S V4-V5), fungi (ITS2), and Fusarium (tef1). Amplicons were sequenced using an Illumina MiSeq platform (300 bp paired-end). Sequencing datasets were processed in R using the DADA2 pipeline. Fungal populations were affected by location in all sampling periods and differed significantly between DC and fallow plots at soybean planting and after harvest (P < 0.001). Several enriched fungal and bacterial taxa in wheat plots, including Mortierella, Exophiala, Conocybe, Rhizobacter spp., and others, were previously reported to parasitize SCN and other plant-parasitic nematodes, suggesting a potential role of beneficial microbes in suppression of SCN in soybean fields double-cropped with wheat.