Use of Genetically Improved Nitrogen-Fixing Cyanobacteria in Rice Paddy Fields: Prospects as a Source Material for Engineering Herbicide Sensitivity and Resistance in Plants

Cyanobacteria are the largest and most widely distributed group of photosynthetic prokaryotes on Earth, forming a prominent component of microbial populations in wetland soils, especially in rice paddy fields, and significantly contributing to fertility as a natural biofertilizer. Modern agricultural fields are generally treated with high doses of synthetic nitrogenous fertilizers and pesticides having adverse effects on the soil microflora of naturally occurring N₂-fixing cyanobacteria. This review deals with some of the advances made during the last few decades in the areas of developing ammonia derepressible pesticide-resistant cyanobacterial mutants for algalization of the wet agricultural fields as a viable and efficient N-photobiofertilizer.     

Source Analysis and Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Paddy Soils

Polycyclic aromatic hydrocarbons (PAHs) are typically persistent organic pollutants with hypertoxicity and widespreading, attracting increasing attention in recent years. Six paddy land sites soils irrigated from different rivers in the Nansi Lake area of Shandong Province, China, were studied to analyze and assess the source and risk of PAHs.Analysis revealed total PAHs (TPAHs) concentrations in topsoil ranging from 57.49 to 2046.47 μg kg^?1, meanwhile, Weishan County (WS) was highly contaminated primarily from coal combustion based on the Nemerow composite index and geochemical indices.Canonical correspondence analysis (CCA) suggested that bacterial species were affected by pH, TPAHs, and soil organic matter (SOM), while covariables analysis confirmed that most effects of PAHs on bacterial diversity were attributed to the PAHs effect alone rather than the combined effects of PAHs and soil properties. The average daily human exposure (ADE) in children was approximately 2 times higher than that in adults, and the exposure paths values followed a decreasing order, oral intake > skin contact > inhalation. Furthermore, the WS site and another rice test field (TF) presented potential cancer risks and required further investigation. Therefore, the study has important theoretical significance for the control of PAHs pollution in this field, providing a scientific basis for health assessment.     

Chironomids of Italian rice fields

Studies on chironomids of Italian rice fields began in 1914, but a comprehensive faunistic picture of Italian rice field chironomids was provided only by COCCHI in 1966. In 1988 and 1989 field research south of Verona (northern Italy) permitted us to confirm the results of COCCHI regardingC. sylvestris andChironomus spp., and to increase the number of known species of Italian rice field chironomids. The list of species which are injurious to rice is similar to that of other European countries, with the exception ofHarnischia falcata andTanytarsus sp. The type and period of damage is different for certain species (e.g. Cricotopus sylvestris) in Italy in comparison to other countries. A few agrotechnical steps are recommended to control pest species. The finding of the parthenogenetic speciesParatanytarsus grimmii in lab. aquaria used for rearing purposes is documented.     

Field spray abdominal gland secretions of rove beetles: Effects on the pest abundance and arthropod community

Alternative environmentally friendly methods for pest control are in high demand because of the environmental impacts of pesticides. Notably, predator-released kairomone is a natural compound released by natural enemies, which mediates non-consumptive effects between natural enemies and prey. However, this novel pest control agent is underutilized relative to pesticides and natural enemies. Additionally, the effects of spraying predator kairomone on the number and diversity of arthropods in fields and whether this method is environmental-friendly are poorly understood. In the present study, a predator kairomone, rove beetle (Paederus fuscipes Curtis) abdominal gland secretion (AGS), was sprayed in rice fields to investigate whether AGS can suppress pest populations or will affect the fields’ arthropod communities. After AGS spraying, the abundance of arthropods decreased throughout the first 12-d period, including arthropod pests such as hemipterans (small brown planthopper, Laodelphax striatellus (Fallén), brown planthopper, Nilaparvata lugens (Stål), white-backed planthopper, Sogatella furcifera (Horváth), and leafhoppers), and lepidopterans (rice leaf folder, Cnaphalocrocis medinalis Guenée). The abundance of arthropod predators was not affected, except for predatory spiders, which decreased, and rove beetles (P. fuscipes), which increased. In the terms of arthropod diversity, neither pests nor their natural enemies were changed by AGS application. This work highlights that predator kairomone can temporarily suppress pest populations in fields but has no adverse effects on arthropod diversity; thus, this approach is environmentally friendly and can be used in real-world applications. Broadly, present studies suggest that the application of predator kairomone may have synergistic or cumulative effects on pest suppression.