Conserving and Sharing Taro Genetic Resources for the Benefit of Global Taro Cultivation: A Core Contribution of the Centre for Pacific Crops and Trees

Establishment of discrete element flexible model of the tiller taro plant and clamping and pulling experiment

The taro harvesting process is affected by a complex system composed of particle mechanics system and multi-body dynamics system. The discrete element method(DEM) can effectively solve the nonlinear problem of the interaction between harvesting components and working materials. Therefore, the discrete element model of taro tiller plants is of great importance for taro harvesting. This paper proposes a simulation method to establish a discrete element flexible plant model and dynamic clamping and pulling process of taro tiller plant. Discrete Element models of taro corm and flexible tiller petiole and leaf were established using DEM method, and the discrete element flexible model of the taro plant was established. Taro clamping and pulling force testing platform was designed and built. The single factor and Plackett-Burman experiments were used to determine the simulation parameters and optimize the taro plant model by taking the correlation coefficient of clamping force and correlation coefficient of pulling force collected from the simulation and the bench experiment as the experiment index. The parameter calibration results of discrete element model of taro plant are as follows: petiole-petiole method/tangential contact stiffness was 8.15×10⁹ N·m^-3, and normal/tangential critical stress was 6.65×10⁶ Pa. The contact stiffness of pseudostem- corm method was 1.22×10⁹ N·m^-3, the critical stress of normal/tangential was 1.18×10⁵ Pa, and the energy of soil surface was 4.15×10⁶J·m^-3. When the pulling speed is 0.1, 0.2, 0.3, 0.4 and 0.5 m·s^-1, the correlation coefficients between the simulation experiment and the bench experiment are 0.812, 0.850, 0.770, 0.697 and 0.652, respectively. The average value of correlation coefficient is 0.756, indicating that the simulated discrete element plant model is close to the real plant model. The discrete element model of taro plant established in this paper has high reliability. The final purpose of this paper is to provide a model reference for the design and optimization of taro harvester by discrete element method.

Dissipation behavior, residue distribution, and dietary risk assessment of fluopimomide and dimethomorph in taro using HPLC-MS/MS

Dimethomorph is a morpholine broad-spectrum fungicide and effectively controls taro blight, cucumber downy mildew, rice blast disease, and others. Fluopimomide is a newly developed broad-spectrum fungicide to primarily control oomycetes and rhizoctonia diseases. Taro, one of the earliest cultivated crops, is a staple food in Africa, Oceania, and Asia. Recently, a commercial suspension concentrate formulation containing 15% fluopimomide and 25% dimethomorph has been registered in China, the second largest taro producer in the world. The objective of this study was to develop a high-performance liquid chromatography tandem mass spectrometry method to detect the residues of fluopimomide and dimethomorph concurrently in taro samples. The results showed that the average recoveries of fluopimomide and dimethomorph ranged from 83 to 108%, and relative standard deviations (RSD) ranged from 1 to 11%. The limit of quantitation (LOQ) was 0.01 mg kg^-1 for the two compounds. The dissipation results demonstrated that both fluopimomide and dimethomorph in taro degraded rapidly in taro fields, and the residues of the two fungicides were below the LOQ within 14 days post-application. The final residue levels of fluopimomide and dimethomorph in taro were lower than 0.066 mg kg^-1 28 days post-application. For dietary risk assessments, the dietary structure of different genders and age of people in China exposure risk assessment and whole diet exposure risk assessment shows that the risk quotient (RQ) values were substantially lower than 100%, suggesting that the long-term risks of fluopimomide/dimethomorph mixed formulation in taro at the recommended dosage were negligible. In summary, our combined results from the dissipation behaviors, terminal residues, and dietary risk assessments provide the critical empirical data for the establishment of the maximum residue levels (MRLs) of the two broad-spectrum fungicides in taro, a traditional food for African, Oceanic, and South Asian cultures.

Dry, rainfed or irrigated? Reevaluating the role and development of rice agriculture in Iron Age-Early Historic South India using archaeobotanical approaches

Domestic rice agriculture had spread across the mainland Indian subcontinent by c.500 BC. The initial spread of rice outside the core zone of the central Gangetic Plains is thought to have been limited by climatic constraints, particularly seasonal rainfall levels, and so the later spread of rice into the dry regions of South India is largely supposed to have relied on irrigation. This has been associated with the development of ritual water features in the Iron Age (c.1000-500 BC), and to the subsequent development of tanks (reservoirs) during the period of Early Historic state development (c.500 BC-500 AD). The identification of early irrigation systems within South Asia has largely relied on early historical texts, and not on direct archaeological evidence. This initial investigation attempts to identify irrigated rice cultivation in the Indian subcontinent by directly examining rice crop remains (phytolith and macrobotanical data) from four sites. The evidence presented here shows that, contrary to accepted narratives, rice agriculture in the Iron Age-Early Historic South India may not have been supported by irrigated paddy fields, but may have relied on seasonal rainfall as elsewhere in the subcontinent. More caution is urged, therefore, when using terms related to 'irrigation' and 'agricultural intensification' in discussions of the Iron Age and Early Historic South Asia and the related developments of urbanism and state polities.