Non-inoculated Plots Research Articles

Effects of Hybrids, Foliar Treatments, and Infection Conditions on Bacterial Leaf Streak of Sweet Corn.

Bacterial leaf streak (BLS) of corn caused by Xanthomonas vasicola pv. vasculorum was first reported in the United States in 2017. The biology and management of BLS are poorly understood. The objective of this work was to determine the effects of hybrids, foliar treatments, and infection conditions (timing, temperature, and inoculation site) on BLS of sweet corn. Field studies were conducted to determine if hybrid or foliar disease management treatments influenced BLS development and yield. Corn leaves were inoculated in plots with X. vasicola pv. vasculorum, and noninoculated plots were used for comparison. The leaf incidence and severity of BLS differed significantly among sweet corn hybrids, suggesting different levels of susceptibility to BLS. Grain yield was significantly reduced (14.7%) by BLS for one hybrid. The corn growth stage at the time of infection influenced BLS, with incidence and severity significantly greater after inoculation at stage V6 than at V9. Foliar application of Kocide, LifeGard, and Kocide and LifeGard significantly reduced leaf severity compared with nontreated controls in field studies. Kocide significantly reduced leaf incidence, but no treatments significantly increased yield versus controls. In comparisons of inoculation methods in a growth chamber, lesion length on leaves was significantly greater on stalk-inoculated than leaf-inoculated plants. Lesions developed on leaf-inoculated plants only at inoculation sites, whereas lesions developed on stalk-inoculated plants on multiple leaves. In controlled environments, lesion length on leaves was significantly greater at 21°C than at 27 and 32°C. This study expands our understanding of factors that influence the development and management of BLS of sweet corn.

Evaluation of exotic soybean accessions and their use in developing improved soybean lines with resistance to Phomopsis seed decay.

Poor seed quality of soybean is often associated with Phomopsis seed decay (PSD), which is one of the most economically important seed diseases. Diaporthe longicolla (syn. Phomopsis longicolla) is the primary cause of PSD. Control of PSD is best accomplished by planting PSD-resistant cultivars. Sixteen exotic soybean accessions from the USDA soybean germplasm collection were screened for reaction to PSD at Stoneville, Mississippi. They consisted of maturity groups (MG) II, III and IV. Seeds from inoculated and non-inoculated plots harvested either promptly at maturity, or after a two-week delay in harvest, were assessed for infection by D. longicolla. Seed infection ranged from 0 to 36.7%. Overall, PI 417050 (MG II), PI 417017 (MG III), and PI 594692 (MG IV) had significantly (P ≤ 0.05) lower percentages of seed infected by D. longicolla and higher seed germinations than other genotypes in the same maturity groups. PI 587982A also performed well. As a result of these findings, these resistant accessions were used over multiple cycles of breeding to develop improved breeding lines with resistance to PSD and low seed damage. Breeding line 11043-225-72, with combined resistance from both PIs 417050 and 587982A, had low scores for PSD (6.7%) and seed damage (3.4%), while DS65-1, deriving resistance from PI 587982A, had the lowest seed damage score (1.1%) and the highest seed germination (85.6%) among all lines tested in 2017. DS65-1 and 11043-225-72, along with five other improved breeding lines, were provided to public soybean breeders for developing improved cultivars and germplasm lines. DS31-243 (PI 700941), derived from PI 587982A, was publicly released by the USDA in 2022. This research will lead to future releases of improved germplasm lines and cultivars with PSD resistance and high seed quality. It will also aid in disease management and be a benefit to soybean producers and the industry at large.

Effect of arbuscular mycorrhizal fungi inoculation on revegetation at Nukui Dam site, Japan

The establishment of the surviving arbuscular mycorrhizal (AM) fungi, Gigaspora margarita Becker & Hall, inoculated in revegetation at the Nukui Dam was studied. The population of AM fungi and AM colonization of three plant species Japanese hill cherry (Prunus jamasakura Sieb. ex Koidz, yamazakura-inoculated plant), eulalia (Miscanthus sinensis Anderss, susuki), and mugwort (Artemisia vulgaris Pampan, yomogi) were investigated to compare inoculated and non-inoculated treatments. The AM colonisation was enhanced in inoculated plots although natural or accidental AM fungi were involved in non-inoculated plots and successfully colonised. Coverage of soil surface was more than 80% and even reached nearly 100% in summer regardless of the soil amendment type.The number of spores and the percentage of colonisation of investigated plant roots, as well as the density of typical AM structures such as arbuscules, auxiliary cells, vesicles, and coiling hyphae by AM fungi in inoculated plots were higher than those in non-inoculated ones. Some spores were Gigaspora andGlomus-inoculated species and were relatively rich in inoculated plots of Yamazakura. There was a significant increase in the number of AM spores in inoculated treatments at a 5% confidence level (ANOVA, p<0.05) in Susuki and Yamazakura. Much more spores of Gigaspora sp.occurred in the rhizosphere soil of Yamazakura and Susuki plants in inoculated plots than in non-inoculated plots (2.33 and 3.73 times, respectively).The colonisation intensity and spore number in the rhizosphere were positively correlated. Therefore, inoculation at an early establishment should be important for the successive development of AM-plant symbiosis formation.

Canola Growth Stage at Time of Infection Determines Magnitude of White Leaf Spot (Neopseudocercosporella capsellae) Impact.

White leaf spot (Neopseudocercosporella capsellae) is a persistent and increasingly important foliar disease for canola (Brassica napus) across southern Australia. To define the role of plant growth stage in the development of disease epidemics, we first investigated the response of different canola cultivars (Scoop and Charlton) at five Sylvester-Bradley growth stages against N. capsellae. White leaf spot disease incidence and severity was dependent on plant growth stage and cultivar (both P < 0.001), with plants being most susceptible at plant growth stage 1.00 (cotyledon stage) followed by plant growth stage 1.04 (fourth leaf stage). Then, to quantify the impact of this disease on canola yield, we investigated the in-field relationship of white leaf spot disease incidence and severity with seed yield loss following artificial inoculation commencing at growth stage 1.04 (fourth leaf stage). White leaf spot significantly (P < 0.001) reduced seed yield by 24% in N. capsellae inoculated field plots compared with noninoculated field plots. To our knowledge, this is the first time that serious seed yield losses from this disease have been quantified in the field. The current study demonstrates that N. capsellae disease incidence and severity on canola is determined by host growth stage at which pathogen infestation occurs. Emerging seedling cotyledons were highly susceptible, followed by less susceptibility in first true leaves to emerge, but then increasing susceptibility as plants subsequently aged toward the fourth leaf stage. This explains field observances where white leaf spot readily establishes on emerging seedlings and subsequently becomes more prevalent and severe as plants age.

Genetic variation for fusarium crown rot tolerance in durum wheat.

Tolerance to the cereal disease Fusarium crown rot (FCR) was investigated in a set of 34 durum wheat genotypes, with Suntop, (bread wheat) and EGA Bellaroi (durum) as tolerant and intolerant controls, in a series of replicated field trials over four years with inoculated (FCR-i) and non-inoculated (FCR-n) plots of the genotypes. The genotypes included conventional durum lines and lines derived from crossing durum with 2-49, a bread wheat genotype with the highest level of partial resistance to FCR. A split plot trial design was chosen to optimize the efficiency for the prediction of FCR tolerance for each genotype. A multi-environment trial (MET) analysis was undertaken which indicated that there was good repeatability of FCR tolerance across years. Based on an FCR tolerance index, Suntop was the most tolerant genotype and EGA Bellaroi was very intolerant, but some durum wheats had FCR tolerance indices which were comparable to Suntop. These included some conventional durum genotypes, V101030, TD1702, V11TD013*3X-63 and DBA Bindaroi, as well as genotypes from crosses with 2-49 (V114916 and V114942). The correlation between FCR tolerance and FCR-n yield predictions was moderately negative indicating it could be somewhat difficult to develop FCR-tolerant genotypes that are high yielding under low disease pressure. However, FCR tolerance showed a positive correlation with FCR-i yield predictions in seasons of high disease expression indicating it could be possible to screen for FCR tolerance using only FCR-i treatments. These results are the first demonstration of genetic diversity in durum germplasm for FCR tolerance and they provide a basis for breeding for this trait.

Can silicon applied to correct soil acidity in combination with Azospirillum brasilense inoculation improve nitrogen use efficiency in maize?

Alternative management practices are needed to minimize the need for chemical fertilizer use in non-leguminous cropping systems. The use of biological agents that can fix atmospheric N has shown potential to improve nutrient availability in grass crops. This research was developed to investigate if inoculation with Azospirillum brasilense in combination with silicon (Si) can enhance N use efficiency (NUE) in maize. The study was set up in a Rhodic Hapludox under a no-till system, in a completely randomized block design with four replicates. Treatments were tested in a full factorial design and included: i) five side dress N rates (0 to 200 kg ha-1); ii) two liming sources (Ca and Mg silicate and dolomitic limestone); and iii) with and without seed inoculation with A. brasilense. Inoculation with A. brasilense was found to increase grain yield by 15% when N was omitted and up to 10% when N was applied. Inoculation also increased N accumulation in plant tissue. Inoculation and limestone application were found to increase leaf chlorophyll index, number of grains per ear, harvest index, and NUE. Inoculation increased harvest index and NUE by 9.5 and 19.3%, respectively, compared with non-inoculated plots. Silicon application increased leaf chlorophyll index and N-leaf concentration. The combination of Si and inoculation provided greater Si-shoot accumulation. This study showed positive improvements in maize growth production parameters as a result of inoculation, but the potential benefits of Si use were less evident. Further research should be conducted under growing conditions that provide some level of biotic or abiotic stress to study the true potential of Si application.

Can NBPT urease inhibitor in combination with Azospirillum brasilense inoculation improve wheat development?

This research was developed to investigate the use of Azospirillum brasilense to enhance N use in wheat cropping systems and to assess the potential interactions between inoculation and urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT). The study was set up under a no-till system in a Rhodic Hapludox. The experimental design was a randomized completely block design with four replicates arranged in a two N source (urea with and without NBPT) × five N rate applied as side dress (0–200 kg ha−1) × two inoculation (with and without A. brasilense) factorial scheme. Inoculation with A. brasilense in combination with application of 100 and 150 kg N ha−1 was found to increase grain yield by 19.6 and 18.8%, respectively. Inoculation also increased biomass N uptake by 66.9% when N was omitted. Inoculation and NBPT application were found to increase NUE by 23.7% compared to inoculation in combination with conventional urea and by 140% compared to NBPT without inoculation. In addition, inoculation increased plant height and NUE by 13.2 and 49%, respectively, compared with non-inoculated plots. Conventional urea and urea with NBPT had a similar effect on nutrient concentration, N uptake, leaf chlorophyll index, biomass weight and wheat grain yield. This study showed positive improvements in wheat production parameters as a result of inoculation, but the potential benefits of NBPT use were less evident. Further research should be conducted under growing conditions that provide increased N volatilization to better study the potential of NBPT application.

Inoculation with Rhizophagus Irregularis Does Not Alter Arbuscular Mycorrhizal Fungal Community Structure within the Roots of Corn, Wheat, and Soybean Crops.

Little is known about establishment success of the arbuscular mycorrhizal fungal (AMF) inocula and their effects on a soil-indigenous community of AMF. In this study, we assessed the effect of introducing Rhizophagus irregularis DAOM-197198 in soil under field condition on the community composition of indigenous AMF in the roots of corn (Zea mays), soybean (Glycine max), and wheat (Triticum aestivum). Three field trials were conducted with inoculated and non-inoculated plots. Four to ten roots and their rhizosphere soil samples of two growth stages for corn and wheat, and one growing stage of soybean, were collected, totalling 122 root and soil samples. Root colonization was measured microscopically, and the fungal communities were determined by paired-end Illumina MiSeq amplicon sequencing using 18S rDNA marker. After quality trimming and merging of paired ends, 6.7 million sequences could be assigned to 414 different operational taxonomic units. These could be assigned to 68 virtual taxa (VT) using the AMF reference sequence database MaarjAM. The most abundant VT corresponded to R. irregularis. The inoculation treatment did not influence the presence of R. irregularis, or AMF community diversity in roots. This seems to indicate that inoculation with R. irregularis DAOM-197198 does not change the indigenous AMF community composition, probably because it is already present in high abundance naturally.

Fusarium Crown Rot of Winter Wheat Influenced by Resource Competition Near a Tree Windbreak.

Fusarium crown rot becomes most severe when wheat is stressed for water near the time of anthesis. This research examined the potential to study crown rot in the gradient of resource competition near a tree windbreak. Winter wheat was planted for 2 years into a field infested by Fusarium pseudograminearum and bordered by 17-m-high Austrian pines. Crown rot, plant growth and yield, and soil water content were evaluated at six distances (5 to 46 m) perpendicular to the tree line in strip plots inoculated or not inoculated with the pathogen. Crown rot was minor (<5% whiteheads) in noninoculated strips and greater in inoculated strips (26 to 35%) in a 21-m zone from 9 to 30 m from the tree line (0.5-1.8 times the tree height; 0.5-1.8H). At 46 m (2.7H), crown rot was similar in noninoculated and inoculated strips (2 to 5% whiteheads). Whiteheads and culm browning were roughly the reverse of soil water depletion by tree roots. Grain yield at 23 m compared with 46 m was reduced by 33 to 35% in noninoculated plots and by 43 to 49% in inoculated plots. It is possible to study associations between water stress and Fusarium crown rot in the zone of resource competition near windbreaks.

Responses of earthworm communities to crop residue management after inoculation of the earthworm Lumbricus terrestris (Linnaeus, 1758)

Earthworms are important for soil functioning in arable cropping systems and earthworm species differ in their response to soil tillage and crop residue management. Lumbricus terrestris (Linnaeus, 1758) are rare in intensively tilled arable fields. In two parallel field trials with either non-inversion (NIT) or conventional tillage (CT), we investigated the feasibility of inoculating L. terrestris under different crop residue management (amounts and placement). Simultaneously, we monitored the response of the existing earthworm communities to L. terrestris inoculation and to crop residue treatments in terms of earthworm density, species diversity and composition, ecological groups and functional diversity. L. terrestris densities were not affected by residue management. We were not able to infer effects of the inoculation on the existing earthworm communities since L. terrestris also colonized non-inoculated plots. In NIT and two years after trial establishment, the overall native earthworm density was 1.4 and 1.6 times higher, and the epigeic density 2.5 times higher, in treatments with highest residue application (S100) compared to 25% (S25) or no (S0) crop residues, respectively. Residue management did not affect earthworm species composition, nor the functional trait diversity and composition, except for an increase of the community weighted means of bifide typhlosolis in S0 compared to S100. In CT, however, crop residues did have a strong effect on species composition, ecological groups and functional traits. Without crop residues (S0), epigeic density was respectively 20 and 30% lower than with crop residues placed on the soil surface (S100) or incorporated (I100). Community composition was clearly affected by crop residues. Trait diversity was 2.6 to 3 times larger when crop residues were provided, irrespective of placement. Crop residues in CT also resulted in heavier earthworms and in a shift in the community towards species with a thicker epidermis and cuticle, a feather typhlosolis shape, and a higher average cocoon production rate. We conclude that earthworm communities under conventional tillage respond more strongly to the amount of crop residue than to its placement. Under non-inversion tillage, crop residue amounts affected earthworm communities, but to a smaller degree than under conventional tillage.

Chemical Weed Control in Paddy Fields Inoculated with Azospirillum lipoferum

ABSTRACT: Herbicides, as a major part of weed control strategy in paddy fields, have different impact on growth and activity of soil-beneficial bacteria such as Azospirillum species. A field experiment was conducted at Sefid Rood Livestock and Agricultural Company, northern Iran, to investigate the possibility of chemical weed control in paddy fields inoculated with Azospirillum lipoferum. The experiment was designed in a factorial arrangement based on a randomized complete block with three replicates. The factors were Azospirillum application (inoculation with or without Azospirillum lipoferum) and weed management regime (butachlor application with supplementary hand-weeding, bensulfuron methyl application with supplementary hand-weeding, combination of butachlor and bensulfuron methyl application with supplementary hand-weeding, hand-weeding at 15, 30, and 45 days after transplanting, and no weeding [not weeded during the rice-growing period). The results showed that plants inoculated with A. lipoferum produced 19% higher grain yield compared to plants that were not inoculated. The highest grain yields were recorded for plots treated with butachlor with supplementary hand-weeding (4,512 kg ha-1) and for those treated with a combination of butachlor and bensulfuron methyl with supplementary hand-weeding (4500.5 kg ha-1). The lowest yield (3494.3 kg ha-1) was recorded for weedy plots. No significant interaction was detected between A. lipoferum application and weed management regime for grain yield, indicating that the herbicides had no adverse effect on the efficiency of A. lipoferum in promoting growth and grain yield of rice. There was no significant difference in the dry weights of weed between inoculated and non-inoculated plots. The dry weights of weed in hand-weeded and herbicide-treated plots were significantly lower than that of the weedy plot. In conclusion, the result of this experiment confirms the possibility of chemical weed control in paddy fields inoculated with A. lipoferum.

Response of winter wheat to arbuscular mycorrhizal fungal inoculation under farm conditions

The effect of arbuscular mycorrhizal (AM) fungi inoculation was investigated on two winter wheat cultivars (Triticum aestivum var. Mv Nádor and var. Genius) grown under farm conditions in the neighbourhood of Nagyhörcsök in 2016. The soil was a chernozem with lime deposits (WBR classification: Calcic chernozem) with a mean humus content of 2.73%, AL-soluble P2O5 and K2O concentrations of 181 mg kg-1 and 149 mg kg-1 and a pH(KCl) value of 7.27. The AM inoculum contained reproductive units of Rhizophagus irregularis (previously Glomus intraradices) and Glomus mosseae (syn. Funneliformis mosseae). In addition to soil inoculation, some of the treatments were also given mineral fertiliser treatment (130 kg N ha-1, 78 kg P2O5 ha-1, 60 kg K2O ha-1). Both AM inoculation and mineral fertiliser treatment were found to have a significant effect on the yield (at the p&lt;0.05 level). The yield of plots with mycorrhizal inoculation averaged 8.17 t ha-1, which was higher than that of non-inoculated plots (7.52 t ha-1), while the yield of plots with fertiliser treatment averaged 8.31 t ha-1, as compared with 7.38 t ha-1 for non-fertilised plots. The yield-enhancing effect of AM inoculation was only manifested in plots given no mineral fertiliser. Plant protection measures were the same in all the treatments. The results and the conclusions drawn from them were based on the data of a single year (2016). Data from experiments performed in several years with more cultivars and soils with diverse properties will be required to obtain better grounded, more reliable recommendations for farmers.

Evaluation of Commercial Soybean Cultivars for Reaction to Phomopsis Seed Decay.

Phomopsis seed decay (PSD), caused by Phomopsis longicolla (syn. Diaporthe longicolla), is an economically important soybean disease causing poor seed quality. Planting resistant cultivars is one of the most effective means to control PSD. In this study, 16 commercially available maturity groups IV and V soybean cultivars, including two previously identified PSD-resistant and two PSD-susceptible checks, were evaluated for seed infection by P. longicolla in inoculated and noninoculated plots, and harvested promptly or with a 2-week delay in harvest. The test was conducted at Stoneville, Mississippi, in 2012 and 2013. Seed infection by P. longicolla ranged from 0.5 to 76%, and seed germination ranged from 18 to 97%. One MG IV cultivar (Morsoy R2 491) and five MG V cultivars (Progeny 5650, Progeny 5706, Asgrow 5606, Asgrow 5831, and Dyna-Gro33C59) had significantly (P ≤ 0.05) lower percent seed infected by P. longicolla than their respective susceptible checks and other cultivars in the same tests. Information obtained from this study will be useful for soybean growers and breeders for selection of cultivars for planting or breeding and future genetic studies in the development of cultivars with improved resistance to PSD.

Grain Chemical Composition as Affected by Genetic Backgrounds and Toxigenic Aspergillus flavus Inoculation in Corn Hybrids

Mycotoxins are toxic secondary metabolites commonly found in corn and known to cause health issues to human and animals. Information on the relationship between corn grain inoculated with mycotoxins and grain nutrients (protein, oil, fatty acids, sugars, and amino acids) in corn hybrids, especially stacked-gene hybrids is very limited. The objective of this study was to investigate the nutritional advantage of stacked-gene hybrids (Stgene) over non-genetically modified organisms (non-GMO) corn or glyphosate-resistant corn (RR). The experiment was conducted in two locations (clay and sandy soils) in 2011, irrigated, and inoculated with toxigenic Aspergillus flavus using four hybrids of stacked-gene, four of RR, and two non-GMO (conventional). Non-inoculated plots were used as control. The results showed that stacked-gene hybrids had no observable nutritional advantage over RR or non-GMO as all hybrid classes accumulated adequate nutrients in their grains; this effect could be due to adequate concentrations of nutrients in the soil. Higher levels of grain protein, carbohydrates (glucose, reducing sugars, and starch), oleic acid, total amino acids, and some minerals were observed under inoculated conditions in clay and sandy soils indicated a possible osmotic adjustment role of these compounds as stress indicators and osmoprotectants under inoculated conditions. Grain nutrients in clay soil were higher than those in sandy soils; nutrient differences could be due to sandy soil possibly suffering drier conditions, especially inoculated soil, reducing nutrient uptake and nutrients mobility to the grain. This study provides advanced knowledge on the relationship between grain nutrients and mycotoxins in corn hybrids. It is also useful to the corn breeders to understand the responses of grain nutrients to fungal diseases in corn hybrids.

Plant Growth Promotion and Suppression of Bacterial Leaf Blight in Rice by Inoculated Bacteria

The present study was conducted to evaluate the potential of rice rhizosphere associated antagonistic bacteria for growth promotion and disease suppression of bacterial leaf blight (BLB). A total of 811 rhizospheric bacteria were isolated and screened against 3 prevalent strains of BLB pathogen Xanthomonas oryzae pv. oryzae (Xoo) of which five antagonistic bacteria, i.e., Pseudomonas spp. E227, E233, Rh323, Serratia sp. Rh269 and Bacillus sp. Rh219 showed antagonistic potential (zone of inhibition 1–19 mm). Production of siderophores was found to be the common biocontrol determinant and all the strains solubilized inorganic phosphate (82–116 μg mL-1) and produced indole acetic acid (0.48–1.85 mg L-1) in vitro. All antagonistic bacteria were non-pathogenic to rice, and their co-inoculation significantly improved plant health in terms of reduced diseased leaf area (80%), improved shoot length (31%), root length (41%) and plant dry weight (60%) as compared to infected control plants. Furthermore, under pathogen pressure, bacterial inoculation resulted in increased activity of defense related enzymes including phenylalanine ammonia-lyase and polyphenol oxidase, along with 86% increase in peroxidase and 53% increase in catalase enzyme activities in plants inoculated with Pseudomonas sp. Rh323 as well as co-inoculated plants. Bacterial strains showed good colonization potential in the rice rhizosphere up to 21 days after seed inoculation. Application of bacterial consortia in the field resulted in an increase of 31% in grain yield and 10% in straw yield over non-inoculated plots. Although, yield increase was statistically non-significant but was accomplished with overall saving of 20% chemical fertilizers. The study showed that Pseudomonas sp. Rh323 can be used to develop dual-purpose inoculum which can serve not only to suppress BLB but also to promote plant growth in rice.

Effects of arbuscular mycorrhizal fungi on CH4 emissions from rice paddies

ABSTRACT Arbuscular mycorrhizal fungi (AMF) play a key role in soil carbon storage and release; however, they have never been considered as a factor affecting methane (CH4) emissions from rice paddies. To reveal the role of AMF, the diurnal variations of CH4 emissions from the noninoculated and inoculated rice field plots were compared at midseason drainage, reflooding stage, and end-of-season drainage. The results showed that the diurnal variation patterns in the two treatments both closely tracked soil water content at midseason drainage and end-of-season drainage, while correlated very well with the stomatal conductance of rice at reflooding stage. There were no significant differences between treatments in soil water content and stomatal conductance. However, the diurnal CH4 emission fluxes at the three stages ranged from 4.8 to 39.3, 0.9 to 12.4, and 0.2 to 2.3 mg m−2 h−1 in the noninoculated plots, and those in the inoculated plots ranged from 2.1 to 18.7, 0.9 to 5.0, and 0.3 to 1.2 mg m−2 h−1. The significant differences resulted from carbon-to-nitrogen ratios (C:N) of the noninoculated and inoculated soil, which had a negative linear correlation with maximum diurnal CH4 fluxes. Compared with the noninoculated treatment, inoculating with AMF significantly increased soil C:N by improving the dry matter of rice, which intensified N limit for CH4 production.

Dissemination of Goss's Wilt of Corn and Epiphytic Clavibacter michiganensis subsp. nebraskensis from Inoculum Point Sources.

Goss's wilt of corn, caused by Clavibacter michiganensis subsp. nebraskensis, has reemerged since 2006 as an economically important disease of corn in in the Midwestern United States. In 2012 and 2013, field plot studies were conducted with a pathogenic, rifampicin-resistant C. michiganensis subsp. nebraskensis isolate and a Goss's wilt-susceptible corn hybrid to monitor epiphytic C. michiganensis subsp. nebraskensis population densities and the temporal and spatial spread of Goss's wilt incidence originating from inoculum point sources. The randomized complete block trial included three treatments: noninoculated control, inoculum point sources established by wound inoculation, and inoculum point sources consisting of C. michiganensis subsp. nebraskensis-infested corn residue. Epiphytic C. michiganensis subsp. nebraskensis was detected on asymptomatic corn leaves collected up to 2.5 m away from inoculum sources at 15 days after inoculation in both years. The percentage of asymptomatic leaf samples on which epiphytic C. michiganensis subsp. nebraskensis was detected increased until mid-August in both years, and reached 90, 55, and 35% in wound-, residue-, and noninoculated plots, respectively, in 2012; and 50, 11, and 2%, respectively, in 2013. Although both growing seasons were drier than normal, Goss's wilt incidence increased over time and space from all C. michiganensis subsp. nebraskensis point sources. Plots infested with C. michiganensis subsp. nebraskensis residue had final Goss's wilt incidence of 7.5 and 1.8% in 2012 and 2013, respectively; plots with a wound-inoculated source had final Goss's wilt incidence of 16.6 and 14.0% in 2012 and 2013, respectively. Our findings suggest that relatively recent outbreaks of Goss's wilt in new regions of the United States may be the result of a gradual, nondetected buildup of C. michiganensis subsp. nebraskensis inoculum in fields.

Evaluation of foliar-applied copper hydroxide and citric acid for control of Goss’s wilt and leaf blight of corn

Goss’s wilt and leaf blight, caused by Clavibacter michiganensis subsp. nebraskensis (Cmn), is a re-emerging disease of corn (Zea mays) in portions of the midwestern USA. Although resistant corn hybrids have been developed for some regions, the availability of adapted resistant hybrids may be limited in other areas; therefore, chemical control could potentially serve as an interim control measure while resistant hybrids are being developed. A field experiment was initiated to evaluate the effect of copper hydroxide and citric acid on Goss’s wilt severity and yield of corn. Chemicals were applied relative to inoculation with Cmn, and non-inoculated plots also were included. Treatments not inoculated with Cmn had significantly (P ≤ 0.05) lower Goss’s wilt severity values compared with those that were inoculated, but no significant differences among treatments within Cmn-inoculated or within non-inoculated plots were observed. Neither Cmn-inoculation nor chemicals applied had a significant effect on corn yield. Overall, corn yields were reduced by approximately 9% in Cmn-inoculated plots compared with non-inoculated plots. From our research, application of copper hydroxide or citric acid was not a viable Goss’s wilt management practice. Therefore, corn growers should continue to rely on cultural practices such as crop rotation and tillage to limit Cmn inoculum in fields, and grow resistant hybrids if they are available.

Timing and Efficacy of Fungicide Applications for Diplodia Ear Rot Management in Corn

Diplodia ear rot, a corn (Zea mays L.) disease caused by the fungus Stenocarpella maydis (Berk.) B. Sutton, has been a persistent ear rot across the United States. Management options are currently limited. Field trials conducted under inoculated and non-inoculated conditions were established at two locations in Indiana from 2011 to 2013 to test the fungicides azoxystrobin plus propiconazole and prothioconazole against Diplodia ear rot. Fungicides were applied at three individual growth stages during each year. Fungicides did not consistently reduce Diplodia ear rot compared to non-fungicide-treated controls in any year. Applications also did not consistently increase yield at any timing under inoculated and non-inoculated plots compared with the non-fungicidetreated control. Fungicides were tested in an in vitro assay to determine the effective fungicide concentration at which 50% of mycelial growth or conidial germination of S. maydis was inhibited (EC50). Propiconazole and prothioconazole EC50 values indicated efficacy in reducing fungal growth under controlled conditions; however, current fungicide application methods and plant barriers to fungicide contact with the pathogen may prevent these products from effectively reducing Diplodia ear rot in a field setting. Accepted for publication 23 August 2015. Published 1 September 2015

Diversity and persistence of ectomycorrhizal fungi and their effect on nursery-inoculated Pinus pinaster in a post-fire plantation in Northern Portugal.

Ectomycorrhizal fungi (ECMF) play an important role in forest ecosystems, often mitigating stress factors and increasing seedling performance. The aim of this study was to investigate the effects of a nursery inoculation on Pinus pinaster growth and on the fungal communities established when reforesting burned areas. Inoculated P. pinaster saplings showed 1.5-fold higher stem height than the non-inoculated controls after a 5 year growth period, suggesting that fungal inoculation could potentiate tree growth in the field. Ordination analysis revealed the presence of different ECMF communities on both plots. Among the nursery-inoculated fungi, Laccaria sp., Rhizopogon sp., Suillus bovinus and Pisolithus sp. were detected on inoculated Pinus saplings on both sampling periods, indicating that they persisted after field establishment. Other fungi were also detected in the inoculated plants. Phialocephala sp. was found on the first assessment, while Terfezia sp. was detected on both sampling periods. Laccaria sp. and Rhizopogon sp. were identified in the control saplings, belonging however to different species than those found in the inoculated plot. Inocybe sp., Thelephora sp. and Paxillus involutus were present on both sampling periods in the non-inoculated plots. The results suggest that ECMF inoculation at nursery stage can benefit plant growth after transplantation to a post-fire site and that the inoculated fungi can persist in the field. This approach has great potential as a biotechnological tool to aid in the reforestation of burned areas.