Responses of Phosphate-Solubilizing Microorganisms Mediated Phosphorus Cycling to Drought-Flood Abrupt Alternation in Summer Maize Field Soil

Soil microbial communities are essential to phosphorus (P) cycling, especially in the process of insoluble phosphorus solubilization for plant P uptake. Phosphate-solubilizing microorganisms (PSM) are the dominant driving forces. The PSM mediated soil P cycling is easily affected by water condition changes due to extreme hydrological events. Previous studies basically focused on the effects of droughts, floods, or drying-rewetting on P cycling, while few focused on drought-flood abrupt alternation (DFAA), especially through microbial activities. This study explored the DFAA effects on P cycling mediated by PSM and P metabolism-related genes in summer maize field soil. Field control experiments were conducted to simulate two levels of DFAA (light drought-moderate flood, moderate drought-moderate flood) during two summer maize growing periods (seeding-jointing stage, tasseling-grain filling stage). Results showed that the relative abundance of phosphate-solubilizing bacteria (PSB) and phosphate-solubilizing fungi (PSF) increased after DFAA compared to the control system (CS), and PSF has lower resistance but higher resilience to DFAA than PSB. Significant differences can be found on the genera Pseudomonas, Arthrobacter, and Penicillium, and the P metabolism-related gene K21195 under DFAA. The DFAA also led to unstable and dispersed structure of the farmland ecosystem network related to P cycling, with persistent influences until the mature stage of summer maize. This study provides references for understanding the micro process on P cycling under DFAA in topsoil, which could further guide the DFAA regulations.

Research on Maize Disease Recognition Method Based on Improved ResNet50

In order to solve the problem of accuracy and speed of disease identification in real-time spraying operation in maize field, an improved ResNet50 maize disease identification model was proposed. Firstly, this paper uses the Adam algorithm to optimize the model, adjusts the learning strategy through the inclined triangle learning rate, increases L2 regularization to reduce over fitting, and adopts exit strategy and ReLU incentive function. Then, the first convolution kernel of the ResNet50 model is modified into three 3 x 3 small convolution kernels. Finally, the ratio of training set to verification set is 3 : 1. Through experimental comparison, the recognition accuracy of the maize disease recognition model proposed in this paper is higher than that of other models. The image recognition accuracy in the data set is 98.52%, the image recognition accuracy in the farmland is 97.826%, and the average recognition speed is 204 ms, which meets the accuracy and speed requirements of maize field spraying operation and provides technical support for the research of maize field spraying equipment.

Sphingosinicella flava sp. nov., indole acetic acid producing bacteria isolated from maize field soil

A novel isolated yellow-pigmented bacterial designated strain UDD2T was isolated from a maize field soil sample collected in Ilsan, Republic of Korea. Cells of strain UDD2T were Gram-stain-negative, non-sporulating, long rod-shaped and exhibited flagellar motility. Cells could grow at 15–42 °C and pH 5.5–11.0. Strain UDD2T was sensitive to NaCl and barely tolerated up to 1 % NaCl (w/v). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain UDD2T formed a separate clade with the members of genus Sphingosinicella within the family Sphingomonadaceae . Strain UDD2T showed the highest 16S rRNA gene sequence similarity to Sphingosinicella vermicomposti KCTC 224446T (98.5 %) and Sphingosinicella humi KCTC 62519T (96.7 %), followed by members of the genus Sphingomonas (96.4–94.5 %) and Sphingobium (96.1–94.9 %), but they were located in other phylogenetic clusters. Average nucleotide identity and digital DNA–DNA hybridization values between strain UDD2T and S. vermicomposti KCTC 224446T and S. humi KCTC 62519T were 80.2/24.2 and 75.6/20.4 %, respectively. The total size of the genome was 2 421 697 bp and composed of one circular chromosome, with a G+C content of 63.7 mol%. Strain UDD2T produced indole acetic acid (IAA) in the presence of l-tryptophan. Bacterial IAA is a crucial phytohormone in plant growth and development. Gene clusters for indole-3-glycerol phosphate synthase and tryptophan synthase were found in the genome of strain UDD2T. To the best of our knowledge, no member of the genus Sphingosinicella has been reported to produce IAA to date. The major cellular fatty acids (>10 %) were found to be C16 : 0, C14 : 0 2OH and summed feature 3 (comprising C16 : 1 ω7c and/or iso-C15 : 0 2-OH). Strain UDD2T had ubiquinone Q-10 as the major respiratory quinone and homospermidine as the major polyamine. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid, phosphatidylglycerol, phosphatidylcholine, three unidentified phosphoglycolipids, one unidentified phospholipid, one unidentified aminoglycophospholipid, one unidentified glycolipid and one unidentified polar lipid. Based on the phylogenetic, phenotypic, chemotaxonomic and genotypic data, strain UDD2T represents a novel species of the genus Sphingosinicella , for which the name Sphingosinicella flava is proposed. The type strain is UDD2T (=KCTC 82357T=NBRC 114507T).

A Promising Predator-In-First Strategy to Control Western Corn Rootworm Population in Maize Fields

Western Corn Rootworm is a pest of maize that mostly damages roots. Many alternative strategies have been explored to control this species, with little or non-lasting success, and it remains a threat to maize production worldwide. Gaeolaelaps aculeifer, a soil-dwelling predatory mite that inhabits the first few centimeters of the soil, showed high predatory potential against WCR larvae in the laboratory. In this study, we explored the efficiency of G. aculeifer against WCR in more realistic contexts. First, we infested maize plants isolated in pots in a greenhouse with WCR, and tested the impact of different densities of mites on plant protection. Using standard indicators of WCR population presence and impact, we confirmed that G. aculeifer has the potential to control WCR at densities starting from 100 mites/plant. Then, considering that the release of a large amount of biocontrol agents at WCR emergence might be too costly and constraining for large-scale implementation, we tested the efficiency of a predator-in-first strategy in a maize field infested by WCR. The goal was to introduce fewer G. aculeifer combined with Aleuroglyphus ovatus eggs as an alternative food source in order to let the mite population grow in the field and reach sufficient density at the critical stage for protection. This strategy gave comparable results to pesticide on all indicators examined in our field trial, highlighting the potential to sustainably manage this pest.