Outbreak of Rice Blast Disease at Yeoju of Korea in 2020

Dynamics of spatial and temporal population structure of Pyricularia oryzae in Taiwan

BACKGROUND

To gain a better understanding of how Pyricularia oryzae population shifts is important for selecting suitable resistance genes for rice breeding programs. However, the relationships between P. oryzae pathogenic dynamics, geographic distribution, rice varieties, and timeline are not well studied.

RESULTS

Resistance genes Piz-5, Pi9(t), Pi12(t), Pi20(t), Pita-2, and Pi11 showed stable resistance to the Taiwan rice blast fungus over 8 years of observations. Furthermore, 1749 rice blast isolates were collected from 2014 to 2021 and categorized into five pathotype clusters based on their correlation analysis between the geographic sources and virulence of Lijiangxintuanheigu monogenic lines. A detailed map of their distributions in Taiwan is presented. Isolates collected from the western region of Taiwan had greater pathotype diversity than those from the east region. Isolates collected from the subtropical region had greater diversity than those from the tropical region. Rice cultivars carrying Pik alleles were highly susceptible to pathotype L4. Cultivars with Piz-t were highly susceptible to pathotype L5, and those with Pish were highly susceptible to pathotype L1. The geographical distribution of each pathotype was distinct, and the population size of each pathotype fluctuated significantly each year.

CONCLUSION

The regional mega cultivars significantly impact the evolution of Pyricularia oryzae in Taiwan within the span of 8 years. However, the annual fluctuation of pathotype populations likely correlate to the rising annual temperatures that selected pathotype clusters by their optimal growth temperature. The results will provide useful information for effective disease management, and enable the R-genes to prolong their function in the fields. © 2023 Society of Chemical Industry.

Identification of paddy blast disease field images using multi-layer CNN models

Farmers and agricultural experts can take action on many areas of paddy crop handling and management practices with the use of actionable information from the in-field diagnosis of paddy blast disease. To successfully diagnose the blast disease affecting fifteen different paddy crop varieties, three transfer learning multi-layer convolutional neural network (CNN) models, such as CapsNet, EfficientNet-B7, and ResNet-50, are presented in this paper. The field images of blast disease are captured and classified based on disease severity levels, such as low, medium, high, and severe. The study employing the CapsNet model with a dataset consisting of a total of 20,000 labeled images demonstrated significant results with a testing efficiency of 90.79% and a validation efficiency of 93.29%. The ResNet-50 and EfficientNet-B7 models have yielded average testing efficiencies of 85.10% and 88.72%, respectively. On the held out blast disease affected paddy field image dataset, the CapsNet model outperformed the EfficientNet-B7 and ResNet-50 CNN models in terms of both classification efficiency and computational efficiency.

Natural Product Citronellal can Significantly Disturb Chitin Synthesis and Cell Wall Integrity in Magnaporthe oryzae

BACKGROUND

Natural products are often favored in the study of crop pests and diseases. Previous studies have shown that citronellal has a strong inhibition effect on Magnaporthe oryzae. The objective of this study was to clarify its mechanism of action against M. oryzae.

RESULTS

Firstly, the biological activity of citronellal against M. oryzae was determined by direct and indirect methods, and the results show that citronellal had a strong inhibition effect on M. oryzae with EC₅₀ values of 134.00 mg/L and 70.48 μL/L air, respectively. Additionally, a preliminary study on its mechanism of action was studied. After citronellal treatment, electron microscopy revealed that the mycelium became thin and broken; scanning electron microscopy revealed that the mycelium was wrinkled and distorted; and transmission electron microscopy revealed that the mycelium cell wall was invaginated, the mass wall of mycelium was separated, and the organelles were blurred. The mycelium was further stained with CFW, and the nodes were blurred, while the mycelium was almost non-fluorescent after PI staining, and there was no significant difference in the relative conductivity of mycelium. In addition, chitinase was significantly enhanced, and the expression of chitin synthesis-related genes was 17.47-fold upregulated. Finally, we found that the efficacy of citronellal against the rice blast was as high as 82.14% according to indoor efficacy tests.

CONCLUSION

These results indicate that citronellal can affect the synthesis of chitin in M. oryzae and damage its cell wall, thereby inhibiting the growth of mycelium and effectively protecting rice from rice blasts.

Comparison of projected rice blast epidemics in the Korean Peninsula between the CMIP5 and CMIP6 scenarios

Recently, the International Panel for Climate Change released the 6th Coupled Model Intercomparison Project (CMIP6) climate change scenarios with shared socioeconomic pathways (SSPs). The SSP scenarios result in significant changes to climate variables in climate projections compared to their predecessor, the representative concentration pathways from the CMIP5. Therefore, it is necessary to examine whether the CMIP6 scenarios differentially impact plant-disease ecosystems compared to the CMIP5 scenarios. In this study, we used the EPIRICE-LB model to simulate and compare projected rice blast disease epidemics in the Korean Peninsula using five selected family global climate models (GCMs) of the CMIP5 and CMIP6 for two forcing scenarios. We found a similar decrease in rice blast epidemics in both CMIP scenarios; however, this decrease was greater in the CMIP6 scenarios. In addition, distinctive epidemic trends were found in North Korea, where the rice blast epidemics increase until the mid-2040s but decrease thereafter until 2100, with different spatial patterns of varying magnitudes. Controlling devastating rice blast diseases will remain important during the next decades in North Korea, where appropriate chemical controls are unavailable due to chronic economic and political issues. Overall, our analyses using the new CMIP6 scenarios reemphasized the importance of developing effective control measures against rice blast for specific high-risk areas and the need for a universal impact and vulnerability assessment platform for plant-disease ecosystems that can be used with new climate change scenarios in the future.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10584-022-03410-2.