Controlled-release granules for the delivery of pymetrozine to roots of transplanted rice seedlings with decreased phytotoxicity and enhanced control efficacy against paddy planthoppers

BACKGROUND

Seedling transplanting is widely used in rice cultivation. Systemic insecticides can be delivered to seedling roots by application through rice seedling boxes before transplanting. The most challenging aspect is to provide long-term control of rice pests and overcome transplanting shock. Precise control of the release rate of insecticide can meet these requirements. Pymetrozine is a promising insecticide used for the control of rice planthoppers resistant to neonicotinoid insecticides.

RESULTS

In this study, four controlled-release granular formulations of pymetrozine were prepared based on a mixture of cost-effective and biodegradable kaolin and xanthan gum or a mixture of calcined kaolin and xanthan gum. Fluorescence images showed that different 3D networks were formed in the four granular formulations. The four granular formulations showed different water uptake rates and release rates of pymetrozine in water. Pymetrozine release rate was positively correlated with the water uptake capacity, rather than the water uptake rate of granules. Diffusion was the dominant mechanism for the release of pymetrozine from granules. Pymetrozine was found to reduce the survival of transplanted rice seedlings suffering from transplanting shock. Incorporating pymetrozine in controlled-release granules alleviated this phytotoxicity. The survival rate of rice seedlings in granular pymetrozine treatments ranged 68.8-85.0%, whereas the survival rate was <50% for powdered pymetrozine treatments. Additionally, four prepared granule formulations had a significant control effect on rice planthopper with efficacies ranging from 76.7% to 98.0% 40 days after seedling box treatment.

CONCLUSIONS

The granule with an intermediate release rate of pymetrozine was shown to be more suitable for seedling box treatment than field application and traditional liquid spraying for the long-term control of paddy planthoppers. © 2021 Society of Chemical Industry.

Triacontanol Reduces Transplanting Shock in Machine-Transplanted Rice by Improving the Growth and Antioxidant Systems

Machine transplantation results in serious transplant shock in seedlings and results in a longer recover stage, which negatively impacts the growth of low-position tillers and the yield of machine-transplanted rice. A barrel experiment was conducted to examine the effect of the foliar application of triacontanol (TRIA) on machine-transplanted rice during the recovery stage. TRIA (0, 1, 5, and 10 μM) was sprayed over leaves 2 days before transplanting. The chlorophyll content, sucrose content, oxidative damage, antioxidant enzyme levels, glutathione (GSH), and ascorbate (ASA) redox states, tiller dynamics and yield components of the plants were investigated. The results show that foliar-applied TRIA significantly alleviates the growth inhibition and oxidative damage caused by transplant shock. Furthermore, the application of TRIA increased the chlorophyll and sucrose contents of the plants. Importantly, TRIA not only significantly improved the activity of catalase (CAT) and guaiacol peroxidase (POD), demonstrating that POD can play an important role in scavenging H2O2 during the recovery stage, but it also enhanced the redox states of ASA and GSH by regulating the activities of enzymes involved in the ASA-GSH cycle, such as ascorbate peroxidase (APX) and glutathione reductase (GR). A dose of 10 μM TRIA was the most efficient in reducing the negative effects of transplant shock, increasing the panicles, grain filling, and grain yield per hill by 17.80, 5.86, and 16.49%, respectively. These results suggest that TRIA acts to reduce transplant shock in association with the regulation of the redox states of ASA and GSH and antioxidant enzymes and serves as an effective antioxidant to maintain photosynthetic capacity and promote the occurrence of low tillers.