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Laboratory mutants of Sclerotinia sclerotiorum (Lib) de Bary, resistant to boscalid, have been extensively characterized. However, the resistance situation in the lettuce field remains largely elusive. In this study, among the 172 S. sclerotiorum isolates collected from asparagus lettuce field in Jiangsu Province, China, 132 isolates (76.74%) exhibited low-level resistance to boscalid (BosLR), with a discriminatory dose of 5 μg mL−1. In comparison to the boscalid-sensitive (BosS) isolates, most BosLR isolates demonstrated a slightly superior biological fitness, as evidenced by data on mycelial growth, sclerotium production and pathogenicity. Moreover, most BosLR isolates showed comparable levels of oxalic acid (OA) accumulation, increased exopolysaccharide (EPS) content and reduced membrane permeability when compared to the BosS isolates. Nevertheless, their responses to distinct stress factors diverged significantly. Furthermore, the effectiveness of boscalid in controlling BosLR isolates on radish was diminished compared to its efficacy on BosS isolates. Genetic mutations were identified in the SDH genes of BosLR isolates, revealing the existence of three resistant genotypes: I (A11V at SDHB, SDHBA11V), II (Q38R at SDHC, SDHCQ38R) and III (SDHBA11V+SDHCQ38R). Importantly, no cross-resistance was observed between boscalid and other fungicides such as thifluzamide, pydiflumetofen, fluazinam, or tebuconazole. Our molecular docking analysis indicated that the docking total score (DTS) of the type I resistant isolates (1.3993) was lower than that of the sensitive isolates (1.7499), implying a reduced affinity between SDHB and boscalid as a potential mechanism underlying the boscalid resistance in S. sclerotiorum. These findings contribute to an enhanced comprehension of boscalid’s mode of action and furnish valuable insights into the management of boscalid resistance.

WRKY transcription factors (TF) have been identified in many plant species and play critical roles in multiple stages of growth and development and under various stress conditions. As one of the most popular vegetable crops, asparagus lettuce has important medicinal and nutritional value. However, study of WRKY TFs family in asparagus lettuce is limited. With the lettuce (Lactuca sativa L.) genome publication, we identified 76 WRKY TFs and analyzed structural characteristics, phylogenetic relationships, chromosomal distribution, interaction network, and expression profiles. The 76 LsWRKY TFs were phylogenetically classified as Groups I, II (IIa-IIe), and III. Cis element analysis revealed complex regulatory relationships of LsWRKY genes in response to different biological progresses. Interaction network analysis indicated that LsWRKY TFs could interact with other proteins, such as SIB (sigma factor binding protein), WRKY TFs, and MPK. The WRKYIII subfamily genes showed different expression patterns during the progress of asparagus lettuce stem enlargement. According to qRT-PCR analysis, abiotic stresses (drought, salt, low temperature, and high temperature) and phytohormone treatment could induce specific LsWRKYIII gene expression. These results will provide systematic and comprehensive information on LsWRKY TFs and lay the foundation for further clarification of the regulatory mechanism of LsWRKY, especially LsWRKYIII TFs, involved in stress response and the progress of plant growth and development. [ABSTRACT FROM AUTHOR]

The utilization of wastewater for agricultural irrigation has been widely accepted in China and other arid and semi-arid regions around the world. Effects of lateral depth and irrigation frequency on inorganic nitrogen yield and quality of Lactuca sativa var. augustana (asparagus lettuce) under drip irrigation with sewage effluent was examined in a solar-heated greenhouse in North China Plain amid two growing seasons of 2014 and 2015. Three pan coefficients of 0.6, 0.8, and 1.0 and three lateral depths of 0, 10, and 20 cm were tested during the 2014 season. In contrast, three irrigation intervals of 4, 8, and 12 days and three lateral depths similar to the 2014 season were utilized in the 2015 season. The groundwater control experiment was applied for treatments with a pan coefficient of 0.8 (2014) and irrigation intervals of 8 days (2015). A higher irrigation frequency increased the yield of asparagus lettuce, while a lower frequency was favorable to the quality parameters of vitamin C and soluble sugar. Generally, compared with surface drip irrigation, subsurface drip irrigation increased inorganic nitrogen distribution in the subsurface soil layer, and also increased the yield, vitamin C, and soluble sugar of asparagus lettuce. When asparagus lettuce was buried laterally 10 cm below the soil surface, highest yield was observed. Sewage irrigation increases the accumulation of nitrogen in the soil, and asparagus lettuce yield is higher compared to groundwater irrigation. Additionally, compared with groundwater irrigation, no destructive effect of sewage irrigation on the quality of asparagus lettuce was found. [ABSTRACT FROM AUTHOR]

Evidence on mechanism of instantaneous pressure softening of asparagus lettuce under high pressure processing was explored with respect to pectin methylesterase activity, degree of methylation of pectin, degree of methylation patterns of pectin fractions, and pectin distribution in cell wall matrix. Instantaneous pressure softening was observed at 300 MPa, while texture recovery was obtained at 500 MPa. Pectin methylesterase activity was not significantly affected at 100 and 300 MPa, but dramatically activated at 500 MPa (p < 0.05). Correspondingly, the degree of methylation of pectin decreased as pressure rose. Results of in situ immuno-dot blotting and immunolabeling based on specific bindings of antipectin antibodies showed a significant reduction of chelator-soluble pectin at 300 MPa, in contrast to a remarkable increase at 500 MPa. High pressure processing-induced demethoxylation was further verified by the enhanced fluorescence intensity of LM19 (an antihomogalacturonan antibody specifically binds to nonmethoxylated pectin) immunolabeled pectin, which was mainly located in tricellular junctions at 300 MPa, but covered the full cell surface at 500 MPa. In conclusion, instantaneous pressure softening of asparagus lettuce is strongly associated with loss of chelator-soluble pectin at 300 MPa. [ABSTRACT FROM AUTHOR]

The two-year experiments presented in this paper aimed at investigating the effects of water management practices on transport of E. coli in soil and residuals in plants for drip irrigation while applying secondary domestic sewage effluent. In 2014, the experiments were designed with three lateral depth of 0 (S0), 10 (S1) and 20 cm (S2) below the soil surface along with three irrigation levels that were determined by pan coefficient of 0.6 (I1), 0.8 (I2) and 1.0 (I3). In 2015, three irrigation intervals of 4 days (F1), 8 days (F2) and 12 days (F3) along with three lateral depths similar to the 2014 experiments were used. Groundwater control experiments were applied for the treatments with pan coefficient of 0.8 (I2) in the 2014 and the irrigation intervals of 8 days in the 2015. The fate of E. coli in the soil was greatly influenced by lateral depth, and subsurface drip irrigation could avoid pathogen contamination when sewage effluent was applied. Surface drip irrigation more likely induced E. coli contamination on surface soil and the E. coli concentration demonstrated a decreasing trend after irrigation ceased. In general, a more frequent irrigation and a higher containing level of E. coli increased short term E. coli contamination of soil as it increased contacting opportunities between effluent and soil. However, the E. coli declined during an irrigation interval and was hardly detected three days after an irrigation ceased. On harvest, no E. coli was detected in the stems of asparagus lettuce and few counts of E. coli was detected on the leaves of the crop but a weak association between the irrigation management practices and E. coli contamination of leaves was found. Our study recommended that subsurface drip irrigation is a promising method to avoid E. coli contamination when applying sewage effluent. [ABSTRACT FROM AUTHOR]

To explore the mechanisms of texture change under high pressure (HP) processing, the effects of different pressures on cell microstructure and cell morphological behaviors of asparagus lettuce were investigated using different microscopy approaches. Pectin immunofluorescence labeling was adopted to analyze cell morphological change in vivo by in situ visualization of cell wall. Image analysis showed that cells in asparagus lettuce treated at lower pressures (100 MPa, 200 MPa and 300 MPa) exhibited rounder and smaller than the untreated samples. However, the shapes of cells in asparagus lettuce treated at 500 MPa were close to the control. The in situ analysis on pectin distribution by CLSM indicated that pectin was mainly restricted in the corners of tricellular junctions in the samples treated at 200 MPa and 300 MPa, whereas pectin uniformly distributed around the whole cell wall at 500 MPa. The results of cell activity staining were consistent with that of ultrastructure change of cell wall and membrane observed by TEM, which suggested that plasma membrane was ruptured at the pressure of 200 MPa, 300 MPa and 500 MPa. Meanwhile, the integrity of cell wall structure was retained under all HP conditions. Based on the above results, a 7-cell tissue model has been proposed to show the cell morphological behavior. On the one hand, moderate HP (100 MPa–300 MPa) caused an initial texture loss of asparagus lettuce tissue, probably due to the loss of turgor pressure and the loose skeleton of cell wall. On the other hand, HP (500 MPa) caused less apparent texture loss of asparagus lettuce due to the unchanged pectin distribution, which can maintain the rigid and flexible cell wall. [ABSTRACT FROM AUTHOR]

WRKY transcription factors (TF) have been identified in many plant species and play critical roles in multiple stages of growth and development and under various stress conditions. As one of the most popular vegetable crops, asparagus lettuce has important medicinal and nutritional value. However, study of WRKY TFs family in asparagus lettuce is limited. With the lettuce ( Lactuca sativa L.) genome publication, we identified 76 WRKY TFs and analyzed structural characteristics, phylogenetic relationships, chromosomal distribution, interaction network, and expression profiles. The 76 LsWRKY TFs were phylogenetically classified as Groups I, II (IIa-IIe), and III. Cis element analysis revealed complex regulatory relationships of LsWRKY genes in response to different biological progresses. Interaction network analysis indicated that LsWRKY TFs could interact with other proteins, such as SIB (sigma factor binding protein), WRKY TFs, and MPK. The WRKYIII subfamily genes showed different expression patterns during the progress of asparagus lettuce stem enlargement. According to qRT-PCR analysis, abiotic stresses (drought, salt, low temperature, and high temperature) and phytohormone treatment could induce specific LsWRKYIII gene expression. These results will provide systematic and comprehensive information on LsWRKY TFs and lay the foundation for further clarification of the regulatory mechanism of LsWRKY, especially LsWRKYIII TFs, involved in stress response and the progress of plant growth and development., Competing Interests: The authors declare there are no competing interests., (©2022 Du et al.)

Abstract: Effects of aqueous chlorine dioxide (ClO2) treatment on enzymatic browning and shelf-life of fresh-cut asparagus lettuce (Lactuca sativa L. var. angustana) were investigated. Fresh-cut asparagus lettuce was treated at different concentrations (10, 40, and 100mgL−1) for different times (5, 10, and 20min). Following treatments, lettuce slices were stored at 4°C for 14 d. The activities of polyphenol oxidase (PPO) and peroxidase (POD) in the lettuce were reduced by ClO2, and degradation of color was also delayed. Thus ClO2 concentration and treatment time were two significant factors affecting ClO2 treatment on enzymatic browning of fresh-cut asparagus lettuce. From the microbiological and sensory quality perspectives, the treatment with 100mgL−1 ClO2 for 20min could prolong the shelf-life to 14 d compared to 4 d for the control. These results indicated that ClO2 treatment was a promising approach to inhibit enzymatic browning and prolong shelf-life of fresh-cut asparagus lettuce. [ABSTRACT FROM AUTHOR]