Greenhouse Experiment Research Articles

Drought Stress at Different Growth Stages Affects the Capacities of Sinks and Two Carbon Sources of Spring Wheat (Triticum aestivum L.)

ABSTRACTDrought stress reduces cereal crop growth and yield due to modifications to interactions between sink and source. However, little research has investigated multiple carbon sources and their relationships with sink capacities, especially in response to drought stress at different growth stages. The objective of this study was thus to examine two major carbon sources (i.e., photosynthetic assimilation in the flag leaf and remobilisation of pre‐anthesis reserves in stems) and their interactions with sink strength in response to drought stress at different phenological stages. A greenhouse experiment was conducted at five water regimes: well‐watered (WW), progressive drought (PD), and drought stress (DS) during vegetative growth (DS‐V), early reproductive growth (DS‐ER), and post‐anthesis (DS‐PA). Compared with the WW regime, the DS‐V treatment reduced shoot biomass, grain yield, number of grains per pot, grain weight, harvest index, and water‐soluble carbohydrates in stems despite the recovered photosynthesis after rehydration. Wheat plants subject to DS‐PA exhibited reduced shoot biomass, grain yield, grain weight, and post‐anthesis photosynthetic rate but greater depletion of water‐soluble carbohydrates in stems during grain filling relative to the WW regime. Grain yield positively correlated with residual water‐soluble carbohydrates in stems and late‐season photosynthetic rates. This study demonstrated yield losses associated with changes in sink and source capacities in response to drought stress at different phenological stages and showcased the predominant role of the two carbon sources in grain filling.

Coapplication of humic acid and gypsum affects soil chemical properties, rice yield, and phosphorus use efficiency in acidic paddy soils

This study investigated the effects of humic acid (HA), flue gas desulfurization gypsum (FG), and their combined application on soil chemical properties, rice yield, phosphorus use efficiency (PUE), and phosphorus agronomic efficiency (PAE) during rice production in acidic paddy soil, which has not been previously studied. A greenhouse experiment was conducted in a completely randomized block design with four treatments, including a control (no soil amendments), HA (975 kg ha−1), FG (636 kg ha−1), and HA plus FG. HA application increased the soil pH; cation exchange capacity (CEC); total concentrations of P, Ca, and S; and exchangeable Ca and S. Additionally, HA application maximized the rice yield, total P uptake, PUE, and PAE. FG application alone increased the soil total Ca, whereas coapplication of HA and FG increased the total organic carbon (TOC), CEC, available P, exchangeable Ca, exchangeable S, and total S. However, FG application, both alone and combined with HA, failed to increase the rice yield, PUE, and PAE owing to lower total P uptake by the plants. Therefore, HA application alone is a sustainable soil management practice for acidic paddy soils, whereas FG application must be carefully considered, as it produces disappointing agronomic effects.

Evaluation of Sinorhizobium meliloti strains and commercial rhizobial inoculants for fenugreek production in Canada

Fenugreek (Trigonella foenum-graecum L.) is a versatile annual legume valued for its nutritional, medicinal, and agricultural uses. Like other legumes, fenugreek can conduct biological nitrogen fixation (BNF). Because fenugreek lacks a dedicated commercial rhizobial inoculant, this study aimed to evaluate the effectiveness of six commercial rhizobial inoculants registered for alfalfa and sweet clover, alongside fifteen Sinorhizobium meliloti strains, on two fenugreek varieties, CDC Canafen and Fenucold. Using laboratory inoculation tests and greenhouse experiments, the symbiotic potential of these products and strains was assessed through nodule formation, BNF, dry matter yield, and the amount of nitrogen fixed. There was variability in symbiotic performance across the strain-variety combinations, with the commercial inoculant RIZOLIQ TOP-Alfalfa and the pure strains USDA1811 and USDA1150 demonstrating superior nodulation, % nitrogen derived from the atmosphere (%Ndfa), and dry matter production. CDC Canafen generally exhibited greater nitrogen fixation compared to Fenucold, and the varieties could fix up to 58% and 47% of their required nitrogen, respectively. The study identifies a registered commercial inoculant that can be used on common fenugreek varieties grown in Canada and shows the potential of other S. meliloti strains for future improvements to inoculant offerings.

New members of Alternaria (Pleosporales, Pleosporaceae) collected from Apiaceae in Algeria

Alternaria species have often been reported as plant pathogens and are commonly isolated from diseased plant hosts. During an investigation of this genus in Algeria, seven Embellisia-like isolates were collected from Apiaceae. Phylogenetic analysis using sequences at four loci, the internal transcribed spacer of the rDNA region (ITS), glyceraldehyde-3-phosphate dehydrogenase (gpd), translation elongation factor 1-alpha (tef1), and RNA polymerase second largest subunit (rpb2), revealed that these isolates grouped into three sections, namely Embellisia, Embellisioides, and Eureka. Four isolates had significant differences with their closest species and were determined to be new species, namely Alternaria longiformis and A. radicicolaspp. nov. The three other isolates of section Eureka were identified as A. eureka and A. hungarica, the latter species being described as a new record in Algeria. Detailed descriptions of new species are provided based on colony color, aspect, diameter, conidial size, septa, sporulation patterns and compared with other relevant Alternaria species within same sections. All these species were weakly pathogenic on carrot, coriander, and fennel under greenhouse experiments. Apiaceae may constitute a reservoir of Alternaria species that could represent potential pathogens for other plant families.

Plant-microbe interactions influence plant performance via boosting beneficial root-endophytic bacteria

BackgroundSalvia miltiorrhiza is a highly valuable medicinal plant and its cultivation is constrained by limited suitable land. Long-term continuous cropping practices alleviate limitations in planting area as well as causes the decline in plant yield and quality. Endophytic microorganisms colonize inside plant roots and are known to play important roles in improving the performance of model plants (such as Arabidopsis thaliana) and food crops (such as wheat, soybean, rice and maize). However, the understanding of how medicinal plants with different growth status (i.e., healthy and disease) shape the assembly of root-endophytic microorganisms and the functional importance of these microorganisms in improving plant performance remains largely unknown.ResultsHere, we investigated the assembly of root-endophytic microorganisms in medicinal plants with different growth status and its links with plant performance improvement. We found that medicinal plants with different growth status had distinct root-endophytic bacterial communities. Healthy plant roots recruited some potentially beneficial bacteria partners, particularly Pseudomonas into the endosphere. We further investigated the functional importance of these potentially beneficial bacteria on plant performance in subsequent greenhouse and field experiments. We found that root-endophytic Pseudomonas effectively increased medicinal plant seedling growth, crop yield, and the content of effective medicinal components.ConclusionsTaken together, we demonstrate that healthy medicinal plants can form a distinct root-endophytic bacterial community, leading to an increase in plant growth-promoting endophytic bacteria (PGPEB) that contribute to the improvement of crop growth and quality. Our research provides valuable insights into the significant role of PGPEB in enhancing crop growth and improving medicinal plants quality for human health development in the future.

Biochar from crop residues mitigates N2O emissions and increases carbon content in tropical soils

AbstractThe application of biochar may offer a cost‐effective solution to decrease nitrous oxide (N2O) emissions in agriculture soils while having the potential to enhance soil carbon (C) accumulation. Biochar can be produced primarily from a range of agricultural and woody residual biomass, potentially resulting in biochar types with distinct properties. This study evaluated the effects of four different biochar types on soil N2O emissions, C storage, and diversity of the soil microbial community in a tropical environment. A greenhouse experiment with sugarcane plants was conducted with six treatments: soil only (CTR); soil + N fertilizer (NF); NF + sugarcane straw biochar (NF+SB); NF + sugarcane bagasse biochar (NF+BB); NF + Pinus residue biochar (NF+PB); and NF + eucalyptus residue biochar (NF+EB). Regardless of the origin of the feedstock, all biochar reduced the cumulative N2O emissions by 25% to 50% in comparison with the nitrogen‐fertilized treatment. Only NF+EB registered higher N2O emissions than NF+SB. The feedstock material also influenced the chemical properties of biochar, showing a negative correlation between oxidized functional groups and N2O emissions. Variations in the physicochemical properties of biochar did not affect soil C levels or microbial diversity, as all treatments with biochar presented similar results. All biochar types increased soil C levels, but only those derived from wood residues showed higher C content than CTR and NF. Despite biochar having no effects on overall soil microbiome diversity, the amendment tended to increase the abundance of Bacteroidetes and Proteobacteria, while suppressing the ammonia‐oxidizing phylum Thaumarchaeota. Biochar application had no significant effect on ammonium availability; however, it exhibited the capacity to retain nitrate. The application of biochar in tropical soils can therefore be considered a nature‐based solution to decrease N2O emissions and increase C levels without changing microbial diversity.

Using a Soil Surfactant to Improve Kenaf Establishment under Deficit Irrigation

Kenaf (Hibiscus cannabinus) is a fiber crop that grows well in tropical climates and has numerous potential industrial and environmental benefits. However, like many crops, it may be limited by sensitivity to water stress, particularly at the seedling stage. Soil surfactants are frequently used as soil amendments to increase the volumetric water content (VWC), particularly under deficit irrigation. Two greenhouse experiments were conducted to determine the emergence and growth response of kenaf to three irrigation regimes and a one-time soil surfactant application. Kenaf seeds were planted in native Margate fine sand soil (siliceous, hyperthermic Mollic Psamnaquent) and sprayed with a nonionic surfactant at 3 quarts/acre (7.5 L/ha) (1×) and subjected to three irrigation regimes of 3.5 ounces (100 mL) of water applied every day (ED), every other day (EOD), or every 4 days (E4D). In Expt. 2, an additional surfactant treatment applied at 6 quarts/acre (15 L/ha) (2×) was included. The percent emergence, plant height, postexperiment biomass, and volumetric water content data were collected. During Expt. 1, kenaf emergence was significantly inhibited by ED irrigation with 1× when compared with E4D with 1×. In Expt. 2, seed treated with the 2× rate emerged faster and had better overall emergence under all irrigation regimes when compared with no soil surfactant. There was a trend for better kenaf emergence when less water was applied. The ED irrigation increased biomass in both experiments; however, in Expt. 2, the 2× rate doubled the biomass in the ED irrigation regime, and both 1× and 2× rates increased biomass in the EOD and E4D irrigation regimes. Soil surfactant treatment significantly increased the VWC in ED in Expt. 1 on four dates; however, in Expt. 2, both surfactant treatments increased the VWC in E4D irrigation until 35 days after planting. The results of this experiment suggest that a one-time soil surfactant treatment did not inhibit kenaf emergence under any irrigation regime. Kenaf emergence and biomass was greater and VWC was lower when a 2× rate of soil surfactant was applied to soil. In hydrophilic disturbed native sand soils, a one-time soil surfactant application increased kenaf emergence under deficit irrigation and the 2× rate of soil surfactant increased biomass under every irrigation regime. To maximize water savings, this study indicated that kenaf seed could withstand four-times less water to improve emergence. To maximize biomass, ED irrigation with a 2× soil surfactant treatment was significantly better.

Mean plant toxicity modulates the effects of plant defense variability.

Plant trait variation is thought to suppress herbivore performance, but experiments typically manipulate only a single mean level of the trait. We manipulated the mean and variation of the concentration of a plant toxin in a model plant-herbivore system across three field and greenhouse experiments. Plants with leaves painted with a higher mean toxin concentration exhibited increased fitness and resistance to herbivores; however, at high mean concentrations, variation reduced the defensive effect, while at lower mean concentrations, variation enhanced it. This reversal aligns with models that include herbivore food selectivity, but our simulations revealed that the benefits of food selectivity for herbivores were minimal. Instead, nonlinear averaging and physiological tracking effects likely drove patterns in plant fitness and resistance to herbivores. We suggest that high defense variation in plants may be a widespread defensive phenotype, but for well-defended plants, variation may inadvertently promote herbivore niche expansion.

Response of an obligate CAM plant to competition and increased watering intervals.

Climate change has exacerbated precipitation variability, profoundly impacting vegetation dynamics and community structures in arid ecosystems. There remains a notable knowledge gap regarding the ecological effects of altered precipitation on crassulacean acid metabolism (CAM) plants and their interactions with other photosynthetic types. This study investigated the response of the typical obligate CAM plant Orostachys fimbriata to extended watering intervals (WI4-WI8) and various competitive patterns (M1-M4) with the C3 grass Melilotus officinalis and the C4 grass Setaria viridis through greenhouse experiments. The results showed that: (1) In species mixtures, CAM plants had slightly reduced the total biomass (TB) compared to monocultures, yet maintained competitiveness by increasing the root-to-shoot biomass (R:S) ratio, stabilizing plant height, and sustaining their photosynthetic rates. (2) As watering intervals increased, CAM plants adapted by further elevating the R:S ratio, reducing height, and decreasing aboveground biomass. However, their height, CO2 assimilation rate, and above- and below-ground biomass were significantly suppressed, particularly when coexisting with C4 plants. More extreme watering regime caused a 47.6% decrease in TB of CAM plants in M4, while C3 and C4 grasses declined by 53.2% and 37.8%, respectively. (3) Given the predicted extension of drought intervals and the intensification of individual rainfall events under future climate conditions, the competitive pressure from C4 plants with high drought tolerance and resource acquisition advantages may limit the expansion potential of CAM plants in drylands. This study enhances the understanding of adaptive mechanisms of CAM plants competing and coexisting with grasses under variable environments, providing scientific bases for predicting arid ecosystem dynamics.

Commercial bioinoculants improve colonization but do not alter the arbuscular mycorrhizal fungal community of greenhouse-grown grapevine roots

BackgroundArbuscular mycorrhizal fungi (AMF) are beneficial root symbionts contributing to improved plant growth and development and resistance to abiotic and biotic stresses. Commercial bioinoculants containing AMF are widely considered as an alternative to agrochemicals in vineyards. However, their effects on grapevine plants grown in soil containing native communities of AMF are still poorly understood. In a greenhouse experiment, we evaluated the influence of five different bioinoculants on the composition of native AMF communities of young Cabernet Sauvignon vines grown in a non-sterile soil. Root colonization, leaf nitrogen concentration, plant biomass and root morphology were assessed, and AMF communities of inoculated and non-inoculated grapevine roots were profiled using high-throughput sequencing.ResultsContrary to our predictions, no differences in the microbiome of plants exposed to native AMF communities versus commercial AMF bioinoculants + native AMF communities were detected in roots. However, inoculation induced positive changes in root traits as well as increased AMF colonization, plant biomass, and leaf nitrogen. Most of these desirable functional traits were positively correlated with the relative abundance of operational taxonomic units identified as Glomus, Rhizophagus and Claroideoglomus genera.ConclusionThese results suggest synergistic interactions between commercial AMF bioinoculants and native AMF communities of roots to promote grapevine growth. Long-term studies with further genomics, metabolomics and physiological research are needed to provide a deeper understanding of the symbiotic interaction among grapevine roots, bioinoculants and natural AMF communities and their role to promote plant adaptation to current environmental concerns.

Resistance-breaking strains of tomato spotted wilt virus hamper photosynthesis and protein synthesis pathways in a virus accumulation-dependent manner in Sw5-carrying tomatoes

Tomato spotted wilt virus (TSWV; Orthotospovirus tomatomaculae) is one of the major horticultural threats due to its worldwide distribution and broad host range. In Italy, TSWV is widely spread in tomato (Solanum lycopersicum) crops and causes severe yield losses. In the last decades, several tomato varieties carrying the Sw-5b gene for resistance to TSWV have been released. We investigated the interaction between Sw-5b-carrying tomatoes and Sw5-Resistance-Breaking (SRB) TSWV to elucidate the molecular mechanisms underlying resistance breakage. Transcriptome sequencing (RNA-Seq) was used to analyze 18 tomato leaf samples collected from a field crop naturally infected by SRB TSWV in Italy. An increase in virus accumulation level in leaf tissues (titer) resulted in a higher number of differentially expressed genes (DEGs), ranging from 33 to 44% of the whole transcriptome, when the samples with the lowest and the highest virus titer were compared to the asymptomatic sample, respectively. Photosynthesis and protein biosynthesis were the main down-regulated biological processes, while enzyme families such as oxidoreductases and transferases, genes related to the response to biotic stimuli, solute transport, and vesicle trafficking were overall up-regulated. Remarkably, the expression of around 45% of genes (ca. 14000) of the whole transcriptome was significantly (P < 0.05) correlated (positively or negatively) to the virus titer, and in 6% of cases (about 2000 genes) the correlation was high (i.e., absolute value of R2 > 0.85). This phenomenon was also verified on 15 genes by a quantitative reverse transcription PCR assay on a greenhouse experiment with a different Sw-5b-tomato variety artificially inoculated with another SRB TSWV strain. In conclusion, the tomato transcriptome was considerably rearranged upon TSWV infection, with deregulation of photosynthesis, protein biosynthesis, and induction of defense pathways. Finally, this research demonstrated that the magnitude of transcriptional changes was proportional to the virus accumulation level in the leaves.

Effects of eucalypt and black wattle biochars from vacuum pyrolysis on sandy soil quality and cauliflower yield

Woody invasive alien plants (IAPs), including black wattle (Acacia mearnsii De Wild.) and eucalypt species (Eucalyptus camaldulensis Dehnh.), present significant environmental challenges in South Africa. Biochar from these plants can enhance soil carbon sequestration and fertility. This study examines the effect of biochars from different IAP feedstocks and pyrolysis temperatures on soil quality and crop production. Five biochars were produced at a range of temperatures (500–800 °C) from eucalypt and a single temperature (600 °C) from black wattle biomass using low-vacuum pyrolysis. Biochars were applied at 1.5% (wt.) to acidic sandy soil in which cauliflower was cultivated in a fertilised greenhouse experiment. Soil chemical, physical and microbiological properties were determined at planting and harvest. The 600 °C eucalypt biochar increased cauliflower yields by 53%, attributed to higher soil basic cation availability and N retention. In contrast, higher temperature eucalypt biochars and the black wattle biochar decreased curd yields by 26–79%, attributed to phytotoxicity, alkalinity, and reduced boron availability. Additionally, biochars reduced plant available water due to high porosity. These findings highlight the critical role of pyrolysis conditions and feedstock selection in determining biochar performance in soil and crop systems.

Effective Applications of Bacillus subtilis and B. amyloliquefaciens as Biocontrol Agents of Damping-Off Disease and Biostimulation of Tomato Plants

Using Bacillus species as bioagents for environmentally sustainable and economically viable plant disease management is a viable strategy. Thus, it is important to promote their use in agriculture. In this study, two Bacillus species were isolated from the rhizosphere of tomato plants, while three fungal species were isolated from samples of tomato plants that were infected with damping-off disease. The Bacillus strains were tested in vitro for their antagonistic activity against fungal species using a dual culture technique. In a greenhouse experiment, the effectiveness of applying antagonistic bacteria with soilborne fungal disease on induced damping-off of tomato (cv. Super Strain B) plants, their physiological attributes, antioxidant enzymes, mineral content, and yield under greenhouse conditions during the 2022 and 2023 seasons were determined. The fungal isolates were identified as Fusarium oxysporum KT224063, Pythium debaryanum OP823136, and Rhizoctonia solani OP823124, while the Bacillus isolates were identified as B. subtilis OP823140 and B. amyloliquefaciens OP823147 on the basis of the rRNA gene sequences. The dual culture test revealed that B. subtilis outperformed B. amyloliquefaciens in resistance to R. solani and F. oxysporum, which were recorded as 28.33 and 33.00 mm, respectivley. In contrast, B. amyloliquefaciens caused the highest antagonistic effect against tested P. debaryanum fungus. Additionally, in a greenhouse experiment, tomato plants treated with each of these antagonistic Bacillus strains significantly suppressed fungal disease, displayed improved plant growth parameters, had an increased content of photosynthetic pigments, antioxidants enzymes, and total phenols, and an increased macronutrient content and yield during the two growing seasons. In conclusion, effective applications of B. subtilis and B. amyloliquefaciens had the potential to mitigate damping-off disease, which is caused by F. oxysporum, P. debaryanum, and R. solani in tomato plants, while simultaneously promoting growth dynamics.

Varying effects of Vicia sativa and Vicia villosa on bacterial composition and enzyme activities in nutrient-deficient sugarcane soils under greenhouse conditions

Declining soil health and productivity are key challenges faced by sugarcane small-scale growers in South Africa. Incorporating Vicia sativa and Vicia villosa as cover crops can improve soil health by enhancing nutrient-cycling enzyme activities and nitrogen (N) contributions while promoting the presence of beneficial bacteria in the rhizosphere. A greenhouse experiment was conducted to evaluate the chemical and biological inputs of V. sativa and V. villosa in nutrient-deficient, KwaZulu-Natal (KZN) sugarcane plantation soils. The nutrient concentrations, N and phosphorus (P) cycling bacteria, and extracellular enzyme activities of 5 soils were determined pre-planting and post-V. sativa and V. villosa harvest. Post-harvesting soils had higher pH levels than pre-planting soils. The number of plant growth-promoting rhizobacteria increased post-V. sativa and V. villosa harvest, with Arthrobacter, Burkholderia, Paraburkholderia and Pseudomonas as the dominant genera. Acid phosphatase and glucosidase activities increased, with Mvutshini and Mzinto showing the most significant increases (phosphatase: 18.66 to 84.67 for V. villosa, 90.33 for V. sativa; glucosidase: 15.33 to 83 for V. villosa and 105 µmolh− 1g− 1 for V. sativa). In conclusion, V. sativa and V. villosa increased PGPR, pH and enzyme activities, making them viable cover crops for nutrient-deficient sugarcane soils.

Comparative Pathogenicity of Meloidogyne enterolobii and Meloidogyne incognita in Cotton Cultivars

Meloidogyne enterolobii (Me) is a nematode that has recently been observed in cotton. Initial observations indicate that cotton cultivars resistant to Meloidogyne incognita (Mi) are susceptible to Me, but the reproductive capacity and ability to cause damage by Me compared to Mi is unknown. The objective of this study was to assess the reproductive capacity and ability to cause damage by Mi and Me at different population densities in two cotton cultivars. The study included two greenhouse experiments in which two cotton cultivars, resistant and susceptible to Mi, were inoculated with six increasing population densities of Me and Mi. The genetic resistance of cotton to Mi given by quantitative trait loci of the q-Mi11 and q-Mi14 genes is ineffective against Me. The Mi-resistant cotton cultivar showed a similar gall index to the Mi-susceptible cultivar when inoculated with Me. The mean gall index with Me was significantly higher than that with Mi on the Mi-resistant cotton cultivar. Based on the number of nematodes per root mass and the reproductive factor, Me showed a higher reproductive capacity than Mi on cotton. Increasing Me population densities linearly reduced the height and dry matter production of aboveground biomass in the Mi-resistant cotton cultivar. However, neither Meloidogyne species affected leaf chlorophyll content and photosynthetic rate of the cotton plants.

Combined Solar Air Source Heat Pump and Ground Pipe Heating System for Chinese Assembled Solar Greenhouses in Gobi Desert Region

Chinese Assembled Solar Greenhouses (CASGs) in the Gobi Desert region face significant diurnal temperature variations, with excessively high temperatures during the day and low temperatures at night, which adversely affect crop growth. Traditional temperature regulation technologies are hindered by high energy consumption, high costs, and severe pollutants. To address these issues, this study designed a heating system suitable for CASGs in the Gobi Desert region, integrating solar air source heat pump technology with underground pipe systems. The power consumption and performance of the system were assessed by comparing temperature and humidity in an experimental greenhouse (with the system), a control greenhouse (without the system), and outdoor environments under various typical climate conditions. The results indicated that the system exhibited excellent performance in both daytime heat absorption and nighttime heat release. Specifically, during operation, the maximum daytime temperature in the experimental greenhouse was reduced by up to 5 °C, while the minimum nighttime temperature increased by up to 8 °C, effectively preventing crop frost damage. The system achieved heat absorption rates of 14 to 16 KJ s⁻1 and heat release rates of 36.5 to 37.5 KJ s⁻1, with average coefficients of performance (COP) of 4.33 and 4.81. Compared to traditional heating methods using coal, gas, and electricity, the system reduced energy consumption by 84.7%, 81.3%, and 79.1%, respectively, and decreased greenhouse gas emissions by 8.24 t, 6.52 t, and 5.67 t, respectively. This system exhibits outstanding thermal efficiency, energy savings, and environmental benefits, while also showing promising economic benefits with a payback period of four years, providing a reliable heating solution for CASGs in the Gobi Desert region.

Identification of Pratylenchus coffeae as a causal agent of root rot disease in Sorghum bicolor in China

Sorghum (Sorghum bicolor) is an important food and feed crop. Root-lesion nematodes (Pratylenchus spp.) are a group of pathogenic nematodes that cause severe economic losses in various food and cash crops. This study identified diseased sorghum plants with stunted growth and brown, rotting roots in sorghum fields in Shanxi Province, China. A species of root-lesion nematode was isolated by modified Baermann funnel method and named the GL-1 population. Afterward, the GL-1 population of root-lesion nematodes was identified as P. coffeae through a combination of morphological, rDNA-ITS and rDNA-28 S D2-D3 region techniques for molecular biological identification. We also conducted greenhouse experiments to assess the parasitism and pathogenicity of GL-1 and four other P. coffeae populations on sorghum through pot inoculation. At 60 days after inoculation, the results indicated that all five populations of P. coffeae were capable of infecting and causing damage to the sorghum plants. Sorghum is a suitable host for P. coffeae (with a reproduction factor > 1). Moreover, compared with those in the control group, the aboveground fresh weights and root fresh weights of sorghum in the five inoculation groups were significantly lower, and brown spots or even necrotic rot appeared on the roots. All five populations were highly pathogenic to sorghum, but there were significant differences in pathogenicity among the populations. This study provides a scientific basis for identifying and detecting root-lesion nematodes in sorghum.

Effects of cereal rye residue biomass and preemergence herbicide on the emergence of troublesome southeastern weed species

Cover crops are increasingly adopted to suppress weed growth and reduce reliance on chemical herbicides. A greenhouse experiment was conducted to evaluate the emergence and growth response of troublesome southeastern weeds to various cereal rye (Secale cereale L.) residue levels. Trays planted with Palmer amaranth (Amaranthus palmeri S. Watson), sicklepod (Senna obtusifolia L.), ivyleaf morningglory (Ipomoea hederacea), and large crabgrass (Digitaria sanguinalis L.) seeds mixed with soil were covered uniformly by four different levels of cereal rye biomass. The following field experiment was conducted at two locations in Alabama in a split-plot design, with the main plot factor being four seeding rates of cereal rye to obtain various cereal rye biomass. Subplot factors were preemergence herbicide flumioxazin and non-treated (NT) check. The greenhouse results demonstrated reduced seed emergence and lower weed biomass for Palmer amaranth, sicklepod, and large crabgrass in plots with higher cereal rye residue biomass compared to those with lower biomass. In both greenhouse and field conditions, the emergence of ivyleaf morningglory was not affected by the increasing biomass of cereal rye residue. Palmer amaranth seed emergence was the most sensitive to increasing biomass residue due to its small seed size. Cereal rye biomass and Palmer amaranth counts were strongly negatively correlated with a Pearson’s coefficient (r) of 0.83 while weakly negatively correlated for ivyleaf morningglory with 0.49. In conclusion, increasing the biomass of cereal rye residue is effective in suppressing Palmer amaranth seed emergence but not ivyleaf morningglory. The flumioxazin treatment demonstrated 95%–90% control for Palmer amaranth and ivyleaf morningglory, while the NT check exhibited 50% control of Palmer amaranth and 30% control of ivyleaf morningglory by cereal rye biomass alone. In conclusion, a sufficient amount of cereal rye biomass can effectively suppress the emergence and growth of weeds, particularly Palmer amaranth.

Mitigating negative impacts of drought on oak seedlings performances through plant growth-promoting rhizobacteria.

Drought stress during the plant's growing season is a serious constraint to plant establishment in arid and semiarid Mediterranean ecosystems. Plant growth promoting rhizobacteria (PGPR) as environmentally friendly and innovative management approach can be used to produce seedlings better adapted to these environments. We tested native PGPR strains isolated from drought-tolerant tree and shrub species originating from two climatically contrasting regions: hot-dry (Dehloran) and milder Mediterranean climate (Ilam). These strains were used as a biological input to improve the morphological and physiological traits of Brant's oak (Quercus brantii Lindl.) seedlings in a greenhouse experiment. Seedlings were inoculated with various drought-tolerant strains or a combination of all bacteria (Bmix) and their morpho-physiological traits were measured under three levels of water stress (80% field capacity, FC80: no stress; 60% FC, FC60: moderate water stress and 40% FC, FC40: severe water stress). Strains from Dehloran were the most performant (Bacillus anthracis, B. licheniformis, B. cereus) except Stenotrophomonas maltophilia which originated from Ilam. They demonstrated the ability to solubilize insoluble phosphates (except for the B. licheniformis). They were also all able to produce auxin and the ACC-deaminase enzyme (except S. maltophilia). PGPR application, water stress treatments, and their interaction significantly influenced all the morphological and physiological seedling traits. Most traits significantly (p<0.01) decreased under FC40, in particular average leaf area, shoot fresh weight, and shoot dry weight. This decrease was particularly marked for the control (no inoculation), as the leaf area was reduced by 60% in FC40. In FC40, all bacterial treatments, especially B. cereus and Bmix efficiently improved seedling morphological traits and seedling quality index. The highest amount of chlorophyll a in FC40 was recorded for Bmix and B. licheniformis isolates. Total phenolic content and malondialdehyde levels, as well as proline, showed an increase under water stress conditions, particularly at FC40, irrespective of inoculation conditions. The amounts of malondialdehyde without inoculation increased significantly under water stress and the content were 1.3 and 2 times higher in FC60 and FC40, respectively, compared to FC80 with no inoculation. Under water stress, seedling performances and quality were impacted and the production of substances associated with physiological defense mechanisms, increased. However, the application of PGPR was able to mitigate these effects (in particular for B. cereus and Bmix). We concluded that application of drought tolerant PGPRs can be a cost effective and ecologically sustainable method for producing oak seedlings better adapted to water-scarce environments.

Assessing foodborne pathogen survival in bird faeces to co‐manage farms for bird conservation, production, and food safety

Abstract Because birds can carry foodborne pathogens, widespread concern exists that birds impose food‐safety risks to farms. Growers are thus often encouraged to deter birds and forego harvesting crops near bird faeces (e.g., no‐harvest buffers). Developing a holistic understanding of the pathogen spillover process—from individual infection to pathogen persistence on crops—is essential to understand and manage food‐safety risks associated with birds. Here, we coupled field and greenhouse experiments to understand the relative risks associated with different bird species on California farms. We first compared E. coli survival in bird faeces on lettuce, soil, and plastic mulch to identify where pathogens are likely to persist. Next, we quantified pathogen survival in faeces from 10 bird species to identify higher‐risk species. Finally, we combined pathogen survival data with bird surveys and faecal transects to assess food‐safety risks across 29 California lettuce farms. E. coli abundance rapidly declined in bird faeces, but rates varied across substrates. E. coli survival was higher on lettuce compared to soil and plastic mulch, likely because of lettuce's cooler and wetter microclimate. E. coli persistence was also much higher in faeces from larger birds—which produce larger faeces—than small songbirds. Importantly, minimal differences in persistence among species were observed after all faeces were standardized to the same mass. Though bird faeces were common on farms, most birds entering farms, contacting crops, and defecating on crops were small songbirds that defecate small faeces. Coupled with our finding that ~90% of faeces were deposited on soil, these results suggest that most birds on farms present relatively low food‐safety risks. Synthesis and applications. Growers are often encouraged to deter all bird species and forego harvesting crops near all bird faeces, but our work suggests not all birds and faeces pose the same food‐safety risks. If growers ignored small bird faeces on soil, then we estimate that the area of California lettuce farms affected by no‐harvest buffers could decrease from ~10.3% to ~2.7%. More broadly, our results suggest farmers could promote small, insect‐eating birds by erecting nest boxes or preserving habitat without necessarily compromising food safety.