by NGUYEN Thi Hue
The Meloidogyne graminicola (Mg) is a biotrophic plant-parasitic nematode that is considered as the major nematode affecting rice production in South East Asia. Using resistant plant germplasms expressing valuable resistant genes is a promising and essential strategy for controlling pests and diseases. Zhonghua 11 is an Oryza sativa (O. sativa) japonica rice variety resistant to this pathogen. This thesis thus aims to analyze the incompatible interaction at molecular and cellular between Zhonghua 11 and Mg.
In the first part of the thesis, the inheritance determinism of the resistant gene(s) in Zhonghua 11 was investigated using F2 progenies obtained from intraspecific (O. sativa japonica Zhonghua 11 x O. sativa japonica Nipponbare) and interspecific (O. sativa japonica Zhonghua 11 x O. sativa indica IR64) crosses. The results indicated that two unlinked dominant genes likely control resistance in Zhonghua 11. Using the histological approach, we found that the resistance in Zhonghua 11 is associated with a hypersensitivity response. We also studied the possible involvement in this incompatible interaction of several autophagy genes and of three classical defense hormone-related pathways (i.e., salicylic acid (SA), jasmonic acid (JA), and ethylene (ET)). The result showed that the salicylate signaling might be important in the resistance-mediated hypersensitive response in the Zhonghua 11. Notably, the expression of OsAtg4 and OsAtg7 significantly increases in the roots of the resistant plant in parallel with the cell death response, suggesting that autophagy is activated and may contribute to the resistance-mediated hypersensitive response.
The second objective was to survey potential virulent pathotypes and isolate them in naturally-infested fields. Indeed, the Zhonghua 11 resistance durability is potentially threatened by the evolution of Mg, which can bypass the resistance mechanism and become virulent. We surveyed a naturally infested field for endogenous Mg population and isolated an Mg pathotype virulent to Zhonghua 11. We confirmed that the virulent pathotype is Mg using morphology and molecular analysis. Comparison with an avirulent pathotype revealed few intraspecific variabilities in the virulent isolate. Reproduction factor measurement on different rice varieties showed that this virulent Mg pathotype could bypass the resistance of two other O. sativa-resistant rice varieties, namely LD24 and Khao Pao Maw, as well as Mi-1.2 tomato. Meanwhile, virulent Mg could not propagate on rice of Oryza glaberrima.
Finally, we examined the impact of Mg on several cover crop species and rice seeds. The Mg could significantly reproduce on those cover crop plants and reduce rice development, germination, and vigor.
Results obtained in this thesis can be found in the papers below.
[1] Nguyen H.T., Mantelin S., Ha C.V., Lorieux M., Jones J.T., Mai C.D. and Bellafiore S.. Insights into the genetics of the Zhonghua 11 resistance to Meloidogyne graminicola and its molecular determinism in rice. Front. Plant Sci. (2022) 13:854961.
[2] Nguyen Thi Hue, Tran Thi Thanh,, Masson Anne-Sophie, Mouline Lionel, Lebrun Michel, Bellafiore Stéphane, Ha Viet Cuong. Rice root knot nematode, Meloidogyne graminicola, a serious pathogen on rice in Northern Vietnam. Proceedings in Conference of Faculty of Agronomy, Vietnam National University of Agriculture. (2021), pp.16-17.
[3] Nguyen, T. H., Masson, A. S., Moulin, L., Trinh, Q. P., Ha, V. C., Bellafiore, S. Root knot nematode infections promoted by agricultural practice modifications in Vietnam and the impacts on rice production. Academia Journal of Biology, (2020). 42(3), 31–42.
[4] Masson A. S, Bich H. H., Simonin M., Thi, H. N., Czernic, P., Moulin, L., Bellafiore, S. Deep modifications of the microbiome of rice roots infected by the parasitic nematode Meloidogyne graminicola in highly infested fields in Vietnam. Fems Microbiol. Ecol. (2020), 96(7).
[5] Suong, M., Chapuis, E., Leng, V., Tivet, F., De Waele, D., Nguyen, T. H., Bellafiore S . Impact of a conservation agriculture system on soil characteristics, rice yield, and root- parasitic nematodes in a Cambodian lowland rice field. Journal of Nematology, (2019), 51, 1- 15.