RESUMEN
Fluxapyroxad, a persistent fungicide in soil, was investigated for differences in residue dissipation in Chinese cabbage and spring scallion through the application methods of soil, foliar, and systemic treatment. Soil application of 0.4% granule fluxapyroxad resulted in residues up to 0.09 mg kg-1 in the scallion, while it did not contribute to the residues in the harvested cabbage. The 50% dissipation time (DT50) of fluxapyroxad in the scallion was 6.8 days. The residues from systemic treatment were highly correlated with foliar application in both the cabbage and the scallion, and the initial residue and DT50 values were similar for foliar and systemic treatments. In comparing the residues from the systemic treatments between the two crops, the initial residue was 3.11 and 0.22 mg kg-1 in the cabbage and the scallion after the systemic treatment, respectively. The DT50 values were 2.6 and 12.2 days in the cabbage and the scallion, respectively. The theoretical dilution effect due to crop growth was higher for the cabbage (4-fold) than for the scallion (1.2-fold), and the half-lives of fluxapyroxad without considering the dilution effect were 6.4 days in the cabbage and 17.8 days in the scallion. Thus, the residue difference was drastically reduced after 14 days from the last treatment.
RESUMEN
Lettuce (Lactuca sativa L.) is a vegetable belonging to the family Asteraceae, and one of the major leafy vegetables in Korea. Lettuce has long been consumed as a fresh vegetable. In 2020, 96,774 tons were produced in about 3,800 ha according to Statistics Korea, and various types of lettuce have been bred for year-round production in line with consumer needs (Jang 2007). In August 2020, symptoms of a disease on young leaves of green lettuce (cv. Cheongpungyeoreumchima) were observed in the commercial greenhouse, Jeongeup (35°37'17.5"N, 126°53'40.4"E), Korea. About 60% of plants in 500 m2 of the cultivation area were infected. The tips of infected leaves appeared water-soaked, with brown to black lesions and were covered with dark masses of sporangiophores. Two fungal isolates NC20860 and NC20861 were isolated from monosporous sporangiola in infected leaves. Two isolates produced fast-growing colonies on potato dextrose agar medium (PDA) with abundant white mycelium at the top and bright yellow pigmentation at the underside in only 2 days. Morphological characteristics of the two fungal isolates were investigated from 30 days after inoculation on PDA. Sporangiophores bearing sporangia were erect, non-septate, unbranched, hyaline, and straight. Sporangia were hyaline to brown, globose to subglobose, 28.4 to 33.6 µm diameter. Sporangiospores from sporangia were brown to dark brown, ellipsoid to ovoid, distinctly longitudinally striate, with hyaline appendages at each pole, 6.3 to 7.5 µm wide and 13.0 to 16.0 µm long. Sporangiophores bearing sporangiola were erect, unbranched, hyaline and sporangiola were fusiform, ellipsoid to broadly ellipsoid, 7.6 to 9.8 µm wide, 13.3 to 17.8 µm long. Based on the morphological and cultural characteristics, this fungus was identified as Choanephora cucurbitarum (Berk.&Ravenel) Thaxt (Kirk 1984). To identify the species of the two isolates, DNA was extracted by using the Maxwell® RSC PureFood GMO and Authentication Kit (Promega). The internal transcribed spacer (ITS) region of ribosomal DNA was amplified using nTaq-Tenuto polymerase chain reaction (PCR) kit and therein specified protocol (Enzynomics). The primers ITS1F and ITS4 were used for PCR and sequencing (Gardes 1991). The ITS sequences of the isolates NC20860 and NC20861 from Korea (NCBI GenBank accession no.MZ960299, MZ960300) and the sequences of C. cucurbitarum strains CBS 150.51 (MH856791.1), and KUS-F29113 (KU316934.1) were compared. The sequences of the isolates were identical to those of the reference strains of C. cucurbitarum CBS 150.51 (reference/isolates base pairs, 566/566) and KUS-F29113 (572/572) at the 100% of sequence similarity. Pathogenicity test was conducted using seedlings of 8-week-old green lettuce (cv. Cheongsimchima) by spraying spore suspension (2â¨104 spores/ml). The plants were covered with plastic bags and incubated at 25 â and 70 to 90% RH with a 12-h photoperiod for 20 days. The symptoms were observed only on the inoculated plants within 20 days after inoculation. The inner leaves of the inoculated lettuces had water-soaked lesions. No symptoms were observed in controls. C. cucurbitarum was reisolated from inoculated lettuce, fulfilling Koch's postulates. This fungus has been reported as the causal pathogen of fruit and blossom rot in cucurbits and other plants (Akwaji 2014). However, to our knowledge, occurrence of this pathogen on lettuce has not been reported as yet. This disease is crucial for producers because infected leaves directly results in yield loss of lettuce. This is the first report of Choanephora rot on lettuce caused by C. cucurbitarum in Korea and worldwide.
RESUMEN
Tenebrio molitor larvae (mealworm) is an edible insect and is considered a future food. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), a novel method for simultaneous analysis of 353 target analytes was developed and validated. Various sample preparation steps including "quick, easy, cheap, effective, rugged, and safe" (QuEChERS) extraction conditions, number of acetonitrile-hexane partitions, and dispersive-solid phase extraction (dSPE) sorbents were compared, and the optimal conditions were determined. In the established method, 5 g of homogenized mealworms was extracted with acetonitrile and treated with QuEChERS EN 15662 salts. The crude extract was subjected to three rounds of acetonitrile-hexane partitioning, and the acetonitrile layer was cleaned with C18 dSPE. The final solution was matrix-matched and injected into LC-MS/MS (2 µL). For target analytes, the limits of quantitation (LOQs) were ≤10 µg/kg, and the correlation coefficient (r2) of calibration was >0.990. In recovery tests, more than 90% of the pesticides showed an excellent recovery range (70-120%) with relative standard deviation (RSD) ≤20%. For more than 94% of pesticides, a negligible matrix effect (within ±20%) was observed. The analytical method was successfully applied and used for the detection of three urea pesticides in 4 of 11 mealworm samples.