Investigation of pathogenesis-related genes expression in rice symbiont with Trichoderma harzianum after inoculation with Magnaporthe oryzae fungus

Rice is one of the most important crops in the world, which occupies a large area of arable land. Blast disease is one of the most important and destructive rice diseases, which reduces production of this product. Due to environmental pollution caused by overuse of fungicides to control this disease and on the other hand, the pathogen resistance to these chemicals, development of better and healthier strategies to control this pathogen is necessary. Biological control of plant diseases using antagonists can be a promising alternative method.

In this study, indirect effect of Trichoderma harzianum fungus on pathogenic fungus, Magnaporthe oryzae, under greenhouse conditions was investigated by induction of systemic resistance in susceptible Tarom cultivar. For this purpose, expression of several important defense genes was investigated using real-time qPCR technique in plants symbiont with Trichoderma compared to control plants (without Trichoderma) at different times after infection with pathogenic fungi.

The results showed increasing expression level of NPR1, PR2 and PR3 genes after pathogen inoculation in plants symbiont with Trichoderma compared to the control plants that there was statistically significat difference about PR2 and PR3 genes. Nevertheles in a number of times, there was no significant difference in expression level of the evaluated genes between two treatments. Examination of various morphological traits such as root, stem and leaf dry weight, root length, stem diameter and plant height showed an increase in plants symbiont with Trichoderma compared to control plants (without Trichoderma), although this difference was not significant about these traits except for plant height. Chlorophyll a and b levels were also measured as physiological traits in both treatments. Although amount of chlorophyll a was higher in plants symbiont with Trichoderma than control plants, but no significant difference was observed. Phenotypic study of interaction of rice plant and pathogen in presence of Trichoderma showed a significant difference about disease severity in plants symbiont with Trichoderma compared to control plants.

These results could somewhat indicate the systemic protection of the rice plant against M. oryzae due to symbiosis of the plant root with Trichoderma harzianum and induction of resistance and increase in pathogenesis-related genes, but this is not enough. Therefore, it is necessary to repeat greenhouse experiment to ensure that there is a significant difference in expression of the studied genes between symbiotic and control plants.