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The filamentous fungus Paecilomyces is currently being developed as a biocontrol agent against plant parasitic nematodes, which often cause black leaf disease in pepper and coffee trees. Nematode eggs and cuticles are the infection sites for biocontrol agents that penetrate those areas by the production of lytic enzymes. Paecilomyces variotii NV01 was isolated from pepper soil from the Dak Lak province. The purpose of this work is to study the activity of protease and chitinase in the strain Paecilomyces variotii NV01. The protease activity was determined to be 82.3 U/ml in a 0.65% casein substrate concentration after 84 hours of culture, which was 6 folds higher than with a basal medium (12.7 U/ml). Exo-chitinase activity was found to be 37.28 U/ml after 84 hours of culture in a chitin substrate concentration of 0.75%, which is 4 folds greater than the basal medium. It was found that adding Ca2+ to the medium drastically altered chitinase activity, increasing it by 10.5%. A 5 mM concentration of Ca2+ was found to affect chitinase activity but not protease activity. Furthermore, the percentage of Meloidogyne sp. nematodes killed by Paecilomyces variotii NV01 after 96 hours of culture was 50.4%. Further study should be carried out in order to use this fungal strain to control plant parasitic nematodes.

Vietnam possesses an abundant and highly diverse resource of plants. Therefore, the search and evaluation of bioactive compounds extracted from these plants are a potential research direction to support developing products that improve human health. The purpose of this study is to assess the antifungal activity of some essential oils produced by materials harvested in Vietnam such as King orange peel (Citrus sinensis), lemongrass (Cymbopogon flexuosus), peppermint (Mentha arvensis), and betel leaf (Piper betle). The antifungal effect of these essential oils was determined by the Kirby-Bauer disc diffusion technique. In addition, the antifungal properties of the essential oils were also assessed through their effects on the reproduction of C. albicans and the spore germination, mycelium elongation, and sporulation of A. fumigatus. The results demonstrated that all peppermint, lemongrass, and betel leaf essential oils showed antifungal activity against C. albicans and A. fumigatus. Especially, betel leaf essential oil could perform antifungal activity at a low dilution concentration of 10% and could also inhibit the reproduction of C. albicans and the spore germination, mycelium elongation, and sporulation of A. fumigatus. Meanwhile, orange peel essential oil did not exhibit any antifungal properties.

Our study made a comparative analysis of the different drying practices used in Vietnam, Cambodia, the Philippines, and Myanmar. Quantification of energy efficiency, greenhouse gas (GHG) emissions, and cost-benefits generated the implications for selecting the optimal drying practice corresponding to various techno-economic indicators, environments, scales of operations, and market demands. Using a reversible airflow flatbed dryer with a capacity of 20 tons of paddy per batch was found to be the best option in terms of cost-benefit, labor operation, and energy efficiency. On the other hand, a recirculating columnar dryer requires 15% higher energy consumption but only needs 20–50% of the floor area; while a solar bubble dryer still needs optimization in terms of reduced investment cost and labor requirement. A two-stage drying system including a fluidized-bed and ten recirculating columnar dryers is an optimal option with the lowest drying cost and labor use when aiming at an industrial capacity of greater than 200 t/day. Nevertheless, the energy consumption and GHG emission of the solar bubble dryer are lower by more than 50% than that of other practices. In addition to the comparative analysis of these techno-economic factors, this research also identified the trajectories of developing paddy drying technologies that are aligned with different postharvest systems identified as subsistence farming for own consumption, surplus farming for local markets, and surplus farming for premium and export markets. The study recommends paddy drying strategies in Southeast Asian countries that could be applied in other rice-production regions as well. Abbreviation: GHG: greenhouse gas

This research developed a computer-based simulation model applicable for conventional and reversible airflow flatbed dryers, which can be used to predict the optimized time for mixing paddy (for the conventional flatbed dryer) and reversing the drying air (for the reversible air flatbed dryer). The developed software has the ability of simulating the paddy moisture content and temperature based on the input parameters of ambient (temperature and relative humidity) and drying air (temperature and airflow rate), dimensions of the dryers, and input grain properties and weight. The model was verified based on data collected from actual paddy drying practices in Vietnam from 1994 to 2015. Relative errors between modeled and measured moisture content of paddy varied for different stages of the drying process and different dryer capacities. On average, the error was highest at the middle stage of the drying processes. This error increased gradually during the early two-thirds stage of the drying process and reached 19% and 14% for the conventional and reversible air flatbed dryers, respectively. On the other hand, these errors decreased to less than 10% at the end of the drying process. Accurate prediction of optimized machine operating time determines the uniformity of the final moisture content of paddy between top and bottom layers, improving energy efficiency, and reducing postharvest losses and drying cost.