Detecting fungal disease in the fresh produce supply chain

Ethylene produced by many fungi can cause disease in perishable fresh produce. Scientists found that this phytohormone can be used as a marker in non-destructive diagnosis for fruit disease detection of post-harvest fruits. A portable gas analyzer was used in an experiment to measure fungal ethylene in real-time. The findings from the experiment could help in reducing food loss. Methods of fungal fruit disease detectionAround 40-50% of fresh produce is lost in the post-harvest stage due to rotting. Fungi alone can account for the destruction of 22.5% of fruits and vegetables. Being able to detect fungal presence and damage early can limit the spread of diseases. Traditional fruit disease detection methods rely on microscopic examination, isolation, and culture to find pathogens. These methods are destructive, laborious, and time consuming. Being restricted to spot sampling, they introduce estimation error in disease burden. Hence, scientists have been trying to use physiological indices based on markers to find a better fruit disease detection method. Ethylene production had been noticed during disease occurrence, but researchers wanted to be sure of the cause, since stress can also trigger the production of this phytohormone. A group of Chinese scientists—Guo, Liu, Y. Wang, T.Wang, Zhang, Zhu, and Xu—knew that ethylene production in plants infected by fungus was often greater in high-light vs low-light conditions. However, they were not sure to what degree the presence and absence of light influenced ethylene production in diseased plants. In their experiment, the scientists tested the ethylene production of plant material infected by the fungus Botrytis cinerea (strain B05.10), expressing the GFP marker in both darkness and light. The fresh produce chosen for these tests were tomato (Solanum lycopersicum, the cherry tomato cultivar) and grapes (Vitis vinifera, the Shine-Muscat cultivar). Challenge: finding a non-destructive mode of ethylene measurementThe scientists conducted four different experiments to examine various aspects: 1) Besides B. cinerea, Colletotrichum gloeosporioides, Penicillium digitatum, Alternaria alternata, and Fusarium asiaticum fungi were cultured and the pelleted spores were mixed in water to check if they produced ethylene. 2) To test for the effect of light, invivo tests were created. Spores were added to a medium and grown in a petri dish for two days, after which they were subjected to two light treatments: dark and light from LEDs. 3) Arabidopsis thaliana seedlings were used to check for ethylene production as a result of B. cinerea fungal infection in plants, with uninfected plants as controls. After four days, plants were again divided and kept in both dark and light conditions. 4) Tomato and grape fruits were purchased from the market, and wounded, freeze treated, or injected with B. cinerea spores. After twenty-four hours, they were also kept in light and dark conditions for one hour and tested for ethylene in real-time. In the last three experiments, ethylene measurements were taken from samples kept in the light. Control samples kept in the dark were moved into the light for a short time. In all experiments, the fungal ethylene production was measured by gas chromatography and had to be measured in real-time by a non-destructive method. For the non-destructive measurements, the scientists needed a portable gas analyzer that was accurate, could measure low levels of ethylene, and was effective in a wide range of temperature and humidity conditions. There are several portable gas analyzers on the market. Micro gas chromatography systems are available, but a preconcentration step is necessary to improve sensitivity, so getting real-time readings is not possible. Optical gas detectors can give readings in real-time, but the accuracy depends on the price of the tool and sensors used. Solution: Felix F-950 Three Gas AnalyzerThe scientists decided to use an electrochemical sensor-based tool, the FELIX INSTRUMENTS F-950 Three Gas Analyzer. This gas analysis instrument has been designed to operate in a wide range of temperature and humidity conditions, unlike other electrochemical sensors, which can operate only within a narrow range of environmental conditions. To measure fungal ethylene production in real-time, as shown in Figure 2, the Petri dishes or fruit samples were kept in an airtight chamber and connected to the inlet and outlet of the portable gas analyzer F-950 with air-tight needles and tubes. A micropump created a circulating airflow, and ethylene levels were measured every second. Benefits of using the portable gas analyzerThe scientists had selected the F-950 due to its ability to measure ethylene levels ranging from 0.1 to 100 parts per million (ppm). Thus, they were certain they would get accurate results. Use of the instrument with a wide variety of fruits had already established, and the small, portable form factor made it a convenient tool for the researchers. Moreover, scientists needed only 30 seconds to record each reading, so the requirement of getting real-time measurements was also fulfilled. A battery with a charge lasting for eight hours allowed data collection of the various samples without interruption. A 16 GB SD card stored the data logged by the portable gas analyzer for statistical analysis without the hassle of data entry, saving them considerable time. This data was easily transferred to the scientists' computers for further use.