Soil tillage is generally recognized as having a negative effect on soil health and weed seed predators. Recent advancements in conservation tillage practices allow for further comparison of how different levels of soil disturbances could influence soil food web communities. Field trials were conducted in 2017 and 2018 at two different sites to measure the effects of four cover crop termination treatments: conventional till (CT), no-till (NT), strip-till following roller-crimping (ST-RC), and strip-till with a living mulch between crop rows (ST-LM) on soil health using nematode community indices as soil health bioindicators. Following cover crop termination, the soil was monitored in the subsequent bell pepper (Capsicum annuum) crop over three sampling dates (June, August, and October). In the ST-RC treatment plots, soil nutrients were enriched (increased Enrichment Index, EI) and the soil food web structure was improved (higher Structure Index, SI) by the mid-season of the 2017 trial. In the 2018 trial, the ST-RC treatment enhanced fungal decomposition pathways (fungivore/fungivore + bacterivore ratio) throughout the bell pepper crop cycle and enhanced bacterial decomposition (abundance of bacterivorous nematodes) by the end of the cropping cycle compared to the no-till treatment, suggesting that the ST-RC treatment can further improve soil health conditions achieved by the NT treatment. Scatter plots of sampling points revealed that the treatments CT and NT had very distinct nematode-weed community assemblages in both trials, with the ST-RC and ST-LM treatments distributed closely with the NT treatment. Multivariate analysis among soil health bioindicators, weed pressure and weed seed predation explained 76.4 and 55.7% of the variance in the 2017 and 2018 trials, respectively. Weed pressure was consistently negatively related to (1) the SI, indicating soil disturbance would lead to more weed pressure; (2) the EI, indicating soil with higher weed pressure was linked to poor soil nutrient cycling, (3) cover crop residues left in the field from conservation tillage, or (4) how well the living mulch of red clover covered the ground. This study did not show that weed seed predation would lead to lower weed pressure but weed seed predation increased as weed biomass increased.
Taro, Colocasia esculenta, is one of the world's oldest root crops and is of particular economic and cultural significance in Hawai'i, where historically more than 150 different landraces were grown. We developed a genome-wide set of more than 2400 high-quality single nucleotide polymorphism (SNP) markers from 70 taro accessions of Hawaiian, South Pacific, Palauan, and mainland Asian origins, with several objectives: 1) uncover the phylogenetic relationships between Hawaiian and other Pacific landraces, 2) shed light on the history of taro cultivation in Hawai'i, and 3) develop a tool to discriminate among Hawaiian and other taros. We found that almost all existing Hawaiian landraces fall into 5 monophyletic groups that are largely consistent with the traditional Hawaiian classification based on morphological characters, for example, leaf shape and petiole color. Genetic diversity was low within these clades but considerably higher between them. Population structure analyses further indicated that the diversification of taro in Hawai'i most likely occurred by a combination of frequent somatic mutation and occasional hybridization. Unexpectedly, the South Pacific accessions were found nested within the clades mainly composed of Hawaiian accessions, rather than paraphyletic to them. This suggests that the origin of clades identified here preceded the colonization of Hawai'i and that early Polynesian settlers brought taro landraces from different clades with them. In the absence of a sequenced genome, this marker set provides a valuable resource towards obtaining a genetic linkage map and to study the genetic basis of phenotypic traits of interest to taro breeding such as disease resistance.
Black oat (Avena strigosa) is a cover crop with great potential for weed suppression and erosion control while conserving soil moisture. Little is known about the potential of black oat for enhancing the soil food web structure and the ecosystem services in tropical Oxisols. Two-year field trials were conducted in Hawaii to compare three pre-plant treatments: (1) black oat (BO) as a pre-plant cover crop followed by no-till practice (previously managed by cover crop and cash crop rotation and conservation tillage for 7 years); (2) bare ground (BG) followed by conventional tillage (previously managed by conventional tillage and cash crop planting for 7 years); (3) conventional tilling of bare ground followed by soil solarization (SOL) (previously fallow with weeds for 5 years then summer solarization and cash crop planting for 2 years). Various soil properties and the soil food web structure using nematodes as soil health indicators were monitored throughout the subsequent corn (Zea mays) crops. SOL served as a negative control pre-plant treatment known to manage plant-parasitic nematodes but be destructive to the soil food web. No-till cropping with BO resulted in higher levels of volumetric soil moisture, field capacity, and soil organic matter, and supported a fungal-dominated decomposition pathway in trial I and more structured nematode communities than BG and SOL in trial II. This study provides evidence that no-till cover cropping with black oat improves the soil water conservation and soil food web structure following a continuous conservation tillage system in tropical Oxisols if the black oat biomass is high (36 tons/ha). However, no-till cropping with BO in Oxisol decreased the soil macroporosity and increased the soil bulk density, which were not favorable outcomes for water infiltration. On the other hand, SOL following conventional tillage was successful in generating lethal temperatures to suppress plant-parasitic nematodes and increased water infiltration in both years but was destructive to the soil food web and reduced the soil organic matter and soil moisture in both years, even when solarization failed to generate lethal temperatures in the second year.
Avian pathogenic E. coli (APEC) is major bacterial pathogen causing the most prevalent colibacillosis with significant financial losses in the poultry industry and has the potential to adversely affect public health. The iron acquisition system encoding iutA and aerobactin encoding gene iucD gene are the most frequently detected in avian pathogenic E. coli and used as the marker gene. Our research on 105 broiler meat samples, including liver, thigh, and breast muscle in Chitwan, Nepal were examined the antibiotic resistance patterns, and the occurrence of virulence associated genes iutA and iucD from July to September 2021. The APEC were isolated and identified by culturing them on MacConkey’s Agar, Eosin-Methylene Blue (EMB) agar and different biochemical test. Following isolation, the molecular detection of APEC was performed using conventional Polymerase Chain Reaction (PCR). Antibiotic resistance patterns were determined through disc diffusion method using the Kirby-Bauer disc diffusion method. Among these samples, 58.1% were found to be positive for Avian pathogenic E. coli (APEC), resulting in the isolation of 61 APEC strains. Among the 61 confirmed APEC isolates, the presence of iutA was detected in 47 samples, accounting for 77.0% of the isolates. Similarly, iucD was found in 46 samples, representing 75.4% of the isolates. The antibiograms revealed that amikacin exhibited the largest zone of inhibition (20.0±0.42mm), followed by ciprofloxacin, tetracycline, ampicillin, and gentamicin. Gentamicin and tetracycline exhibited the highest resistance rates, with 90.2% and 67.2% respectively. Conversely, amikacin displayed sensitivity in 56% of the isolates, while ciprofloxacin showed sensitivity in 39% of the isolates. Notably, 29.4% of the isolates displayed multi-drug resistance. The APEC strains isolated from broiler meat found the highest prevalence of marker gene iutA and iucD with high resistance pattern for gentamicin and tetracycline. It is essential to screen APEC based on molecular marker gene iutA and iucD in large population to reduce antimicrobial misuse promoting control of APEC through safe broiler meat production.
Sorghum/sorghum–sudangrass hybrids (SSgH) have been used as a cover crop to improve soil health by adding soil organic matter, enhancing microbial activities, and suppressing soil-borne pathogens in various cropping systems. A series of SSgH were screened for (1) allelopathic suppression and (2) improvement of soil edaphic factors and soil microbial profile against plant-parasitic nematode (PPNs). The allelopathic potential of SSgH against PPNs is hypothesized to vary by variety and age. In two greenhouse bioassays, ‘NX-D-61′ sorghum and the ‘Latte’ SSgH amendment provided the most suppressive allelopathic effect against the female formation of Meloidogyne incognita on mustard green seedlings when using 1-, 2-, or 3-month-old SSgH tissue, though most varieties showed a decrease in allelopathic effect as SSgH mature. A field trial was conducted where seven SSgH varieties were grown for 2.5 months and terminated using a flail mower, and eggplant was planted in a no-till system. Multivariate analysis of measured parameters revealed that increase in soil moisture, microbial biomass, respiration rate, nematode enrichment index, and sorghum biomass were negatively related to the initial abundance of PPNs and the root-gall index at 5 months after planting eggplant in a no-till system. These results suggested that improvement of soil health by SSgH could lead to suppression of PPN infection.
Agriculture production emits significant amounts of nitrous oxide (N2O), a greenhouse gas with high global warming potential. The objectives of this study were to examine whether different husbandry practices (tillage and plasticulture) following winter cover cropping would influence soil food web structure and whether a change in the soil community could help mitigate N2O emission in vegetable plantings. Three consecutive field trials were conducted. A winter cover crop mix of forage radish (Raphanus sativus), crimson clover (Trifolium incarnatum) and cereal rye (Secale cereale) were planted in all plots. Winter cover crop was terminated by flail mowing followed by (1) conventional till without surface residues [Bare Ground (BG)], (2) conventional till with black plastic mulch (BP) without surface residues, (3) strip-till (ST) with partial surface residues, or (4) no-till (NT) with surface residues. The cash crop planted subsequently were eggplant (Solanum melongena) in 2012 and 2014 and sweet corn (Zea mays) in 2013. The soil food web structure was consistently disturbed in the BP compared to other treatments as indicated by a reduction in the abundance of predatory nematodes in 2012 and 2014, and nematode maturity index in 2013 in BP. Changes in soil food web structure in the conservation tillage (NT or ST) treatments based on the weight abundance of nematode community analysis were not consistent and did not improve over the 3-year study; but were consistently improved based on functional metabolic footprint calculation at termination of cover crops of 2013 and 2014. None-the-less, the N2O emissions increased as the abundance of fungivorous nematodes increased during all three trials. It was also found that improved soil food web structure [higher abundance of omnivorous in 2012 or predatory nematodes in 2013 and 2014, and structure index (SI) in all 3 years] reduced N2O emissions. These findings suggested that proper soil husbandry practices following winter cover cropping could mitigate N2O emissions over time.
Highlights•We reported avian pathogenic Escherichia coli (APEC) from 58.1 % from retail meat shops in Nepal.•Most prevalent virulence iss gene, iutA gene and iucD gene, and ompT gene were detected 86.8%, 77 %, 75.4 % and 63.9% of identified APEC.•The gentamicin and tetracycline antibiotics were most resistant (90.2 % and 67.2 % respectively).•The cent percent of APEC were the MAR index greater than 0.2, with 29.4 % multidrug resistant (MDR).AbstractAvian pathogenic Escherichia coli (APEC) is a major bacterial pathogen responsible for the most widespread form of colibacillosis, resulting in substantial economic losses within the poultry sector and posing a potential public health risk. From July to September 2021, our study investigated the antibiotic resistance pattern of Escherichia coli (E. coli) and the presence of virulence-associated genes (iucD, iutA, iss, and ompT) linked to APEC using 105 broiler meat samples comprising liver, thigh, and breast muscle, in Chitwan, Nepal. E. coli was isolated and identified by culturing samples on MacConkey's agar, Eosin-methylene blue (EMB) agar and performing different biochemical tests. Antibiotic resistance patterns of E. coli were determined by the Kirby-Bauer disc diffusion method. Following the isolation of E. coli, the molecular detection of APEC was performed using conventional polymerase chain reaction (PCR). Out of the 105 samples analyzed, 61 (58.1 %) tested positive for E. coli. In antibiotic susceptibility test (AST), gentamicin and tetracycline exhibited the highest resistance rates, with 90.2 % and 67.2 %, respectively and 29.5 % of the E. coli isolates displayed multidrug-drug resistance. Out of 61 confirmed E. coli isolates, iutA was detected in 47 (77.0 %) samples, iucD in 46 (75.4 %), iss in 53 (86.8 %), and ompT in 39 (63.9 %) samples. This study reports the occurrence of MDR E. coli in meat samples, together with virulence genes associated with APEC which poses a public health threat. Continuous surveillance is vital for monitoring APEC transmission within poultry farms, coupled with efforts to raise awareness of food safety among consumers of broiler meat.
A list of supplemental data and files associated with the manuscript "Exploiting the innate potential of Sorghum/Sorghum-Sudangrass cover crops to improve soil microbial profile that can lead to suppression of plant-parasitic nematodes"
A list of supplemental data and files associated with the manuscript "Exploiting the innate potential of Sorghum/Sorghum-Sudangrass cover crops to improve soil microbial profile that can lead to suppression of plant-parasitic nematodes"
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