The Involvement of Antioxidant Enzyme System, Nitrogen Metabolism and Osmoregulatory Substances in Alleviating Salt Stress in Inbred Maize Lines and Hormone Regulation Mechanisms.

Salt stress inhibited the growth of maize. B46 and NC236 were chosen as materials and NaCl concentrations (0, 55, 110, 165, and 220 mmol L-1) were set. We found the activities of SOD, POD, CAT, APX, GR, MDHAR, and DHAR decreased under NaCl stress. Compared with NC236, the contents of AsA and GSH, AsA/DHA and GSH/GSSG of B46 decreased. The content of O2-, H2O2, MDA, and EL of B46 increased. The contents of NO3- and NO2- decreased, while the content of NH4+ increased under high NaCl concentration. The activities of NR and NiR decreased, while the activities of GS and GOGAT increased first and then decreased. For B46 and NC236, the maximum of NADH-GDH and NAD-GDH appeared at 165 and 110 mmol L-1 NaCl concentration, respectively. Compared with B46, and the GOT and GPT activities of NC236 increased first and then decreased. With the increase of NaCl concentration, the contents of proline, soluble protein, and soluble sugar were increased. The Na+ content of B46 and NC236 increased, and the K+ content and K+/Na+ decreased. Compared with NC236, B46 had higher IAA content in leaf, higher Z + ZR content in leaf and root, and lower ABA content in leaf and root.

Planting models and mulching material strategies to reduce bundle sheath cell leakage and improve photosynthetic capacity and maize production in semi-arid climate.

Better understanding of soil water storage and photosynthetic regulation of maize production will be useful to develop a water-saving strategy in rain-fed conditions. Therefore, maize crop was grown under the different cultivation practices for analyzed light and CO2-response curves under various mulching strategies during 2017-2018 years. Six different treatments were used such as the following: PP, ridges and furrows zone covered with plastic film mulching; PS, ridges covered with plastic film and furrows zone with stalk mulching; PN, ridges covered with plastic film and furrows zone without mulching; TP, conventional flat planting with plastic film mulching; TS, conventional flat planting with stalk mulching; and TN, conventional flat planting without mulching. The PP treatment had considerable effects on rainwater collection, improved SWS, and maize productivity than that of TP treatment. Significantly increase of SWS was observed under the PP treatment as a result photosynthetic capacity (An) improved under light and CO2-response curves, apparent quantum efficiency (α), respiration rate, total chlorophyll ab content, and 13C-photosynthates distribution in different organs. Under the PP and TP treatments, the maize might keep a great photosynthetic capacity at the post-flowering stage through improving An, LAI, soluble protein, Rubisco contents, and grain yield. The CO2 and light-response curves were significantly enhanced at the PP treatment due to higher 13C carbon isotope (Δ‰) and Ci/Ca as a result lower bundle sheath to leakiness of CO2 (ɸ) compared with the rest of all treatments. The results suggested that PP cultivation practice was the best water-saving strategy because it reduced bundle sheath leakiness to CO2 (ɸ); as a result there's a significant improvement in soil water storage, LAI, 13C-photosynthates distribution, photosynthetic capacity parameters, and maize production.

First Report of Didymella americana causing corn stalk rot in China.

Corn (Zea mays L.) is an important food crop and feedstuff worldwide. However, Corn stalk rot, caused by multiple pathogens, is globally an economic soil-borne disease worldwide. In September 2019, a survey was carried out to characterize pathogenic fungi in corn stalks in Nehe city (48.48°N 124.88°E), Heilongjiang Province, China. Stalk rot incidence was approximately 5% in three of the fields sampled (5 ha/per field). Symptoms included wilting of whole plants, drooping ears or rapid death of the upper leaves or whole plant from blister stage to physiological maturity (growth stages R2- R6) stage with drooping ears or rapid death of the upper leaves or whole plant. A brown to black dry rot or necrosis was observed throughout the central pith and internal tissues of the stalk and crown were observed, which resulted in hollow and soft stalks. Fifteen tissue samples (0.25 cm2) from 15 individual diseased plants were surface disinfested with 75% ethanol for 2 s, followed by 0.5% NaOCl for 5 min, rinsed three times in sterile distilled water and cultured on potato dextrose agar (PDA) with 50 µg/mL streptomycin at 26°C in darkness. After 3 days, a total of eight fungal isolates with consistent characteristics were obtained from three sampling points and subcultured by transferring hyphal tips onto a new PDA plate. Single-conidium isolates were generated with methods reported previously (Leslie and Summerell 2006). Cultures on PDA were honey to olivaceous buff in the center with dense aerial mycelia and wide buff colored margins. The dimensions of conidia from 30-day-old PDA cultures were 4.5 to 15.3 µm × 1.5 to 4.3 µm (n = 50). Often, one to two oil bodies were present within the conidia. Based on these morphological features, the isolates were identified as Didymella americana (Aveskamp et al. 2010; Gorny et al. 2016). Genomic DNA was extracted from a representative isolate YJDA8 and the internal transcribed spacer regions (ITS) and translation elongation factor 1-alpha gene (TEF-1ɑ) were amplified and sequenced using the primers ITS1/ITS4 (Yin et al. 2012) and EF1-728F/EF1-986R (Carbone and Kohn 1999), respectively. The sequences of YJDA8 (accession nos. MT995077 for ITS and MW003707 for TEF-1a ) showed 99.6% (529/531 bp) and 97.6% (283/290 bp), identity to the sequences of D. americana isolate YSGYE6 (accession no. MK945663.1) and isolate K_INSO2_6_10 (MN554764.1) respectively. Pathogenicity tests were conducted by root injection of corn plants at the blister stage in the field. Conidia were obtained from 30-day-old PDA cultures grown at 20°C with a 12 h photoperiod. A conidial suspension (1.5 ml of 1×105 conidia/mL) was injected into the base of the maize stems using a 5 ml syringe. For each treatment, 5 plants were inoculated. Plants injected with 1.5 ml distilled sterile water served as the control. After inoculation, the plants were managed using conventional methods. All inoculated plants showed symptoms 25 days after inoculation that were similar to those observed in the field, while no symptoms were observed on the control plants. The fungus was re-isolated and confirmed to be D. americana. D. americana has previously been reported on corn roots and soybean pods in the USA (Aveskamp et al. 2009 as Peyronellaea americana), on lima bean in Delaware and Maryland (Everts et al. 2020). To our knowledge, this is the first report of D. americana causing stalk rot on corn in China. Therefore, its distribution needs to be investigated, monitored and managed with effective disease management strategies to protect corn.

Halomonas songnenensis sp. nov., a moderately halophilic bacterium isolated from saline and alkaline soils.

A moderately halophilic bacterium (strain NEAU-ST10-39T) was isolated from saline and alkaline soils in the oilfield of Daqing City, Heilongjiang Province, China. The strain was strictly aerobic, Gram-stain-negative, rod-shaped and motile by peritrichous flagella. Its colonies were yellow. It grew at NaCl concentrations of 0.2-15% (w/v) (optimum 4%, w/v), at temperatures of 4-40 °C (optimum 35 °C) and at pH 5-10 (optimum pH 7). It did not produce acids from sugars or alcohols. Its DNA G+C content was 57.4 mol%. Phylogenetic analyses based on 16S rRNA gene sequences and concatenated 16S rRNA, gyrB and rpoD gene sequences indicated that it belonged to the genus Halomonas in the class Gammaproteobacteria. The most phylogenetically related species were Halomonas axialensis, Halomonas meridiana and Halomonas aquamarina, whose types shared 98.3% (16S rRNA), 82.7% (gyrB) and 83.9-84.5% (rpoD) sequence similarity with strain NEAU-ST10-39T. The results of DNA-DNA hybridization assays showed 20±2%-50±1 % relatedness between strain NEAU-ST10-39T and the most closely related species including Halomonas axialensis DSM 15723T, Halomonas meridiana DSM 5425T, Halomonas aquamarina DSM 30161(T), Halomonas johnsoniae DSM 21197T, Halomonas stevensii DSM 21198T, Halomonas nanhaiensis CCTCC AB 2012911(T), Halomonas hamiltonii DSM 21196T and Halomonas arcis CGMCC 1.6494T. The major fatty acids were C18 : 1ω7c (47.2%), C16:1ω7c and/or C16:1ω6c (18.9%) and C16:0 (16.3%), the only respiratory quinone detected was ubiquinone 9 and polar lipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, two unknown phospholipids and three unknown lipids. The new isolate is proposed to represent a novel species with the name Halomonas songnenensis sp. nov., NEAU-ST10-39T (=CGMCC 1.12152T=DSM 25870T) being the type strain.

Halomonas zhaodongensis sp. nov., a slightly halophilic bacterium isolated from saline-alkaline soils in Zhaodong, China.

A slightly halophilic bacterium (strain NEAU-ST10-25(T)) was isolated from saline-alkaline soils in Zhaodong City, Heilongjiang Province, China. The strain is a Gram-negative, aerobic motile rod. It accumulates poly-ß-hydroxyalkanoate and produces exopolysaccharide. It produces beige-yellow colonies. Growth occurs at NaCl concentrations (w/v) of 0-15 % (optimum 3 %), at temperatures of 4-60 °C (optimum 35 °C) and at pH 6-12 (optimum pH 9). Its G+C content is 53.8 mol%. Phylogenetic analyses based on the separate 16S rRNA gene and concatenation of the 16S rRNA, gyrB and rpoD genes indicate that it belongs to the genus Halomonas in the class Gammaproteobacteria. The most phylogenetically related species is Halomonas alkaliphila DSM 16354(T), with which strain NEAU-ST10-25(T) showed 16S rRNA, gyrB and rpoD gene sequence similarities of 99.2, 82.3 and 88.2 %, respectively. The results of DNA-DNA hybridization assays showed 60.47 ± 0.69 % DNA relatedness between strain NEAU-ST10-25(T) and H. alkaliphila DSM 16354(T), 42.43 ± 0.37 % between strain NEAU-ST10-25(T) and Halomonas venusta DSM 4743(T) and 30.62 ± 0.43 % between strain NEAU-ST10-25(T) and Halomonas hydrothermalis DSM 15725(T). The major fatty acids are C18:1 ω7c (62.3 %), C16:0 (17.6 %), C16:1 ω7c/C16:1 ω6c (7.7 %), C14:0 (2.9 %), C12:0 3-OH (2.8 %), C10:0 (2.1 %) and C18:1 ω9c (1.6 %) and the predominant respiratory quinone is ubiquinone 9 (Q-9). The proposed name is Halomonas zhaodongensis, NEAU-ST10-25(T) (=CGMCC 1.12286(T) = DSM 25869(T)) being the type strain.