Impact of Genetic Divergence between Intercropped Rice Varieties on Their Efficiency of Resistance to Rice Blast Diseases

The utilization of varietal diversity of rice under an intercropping mode is proven to be effective for control rice blast diseases. However, the underlying mechanisms of such blast control from varietal intercropping are still not clear. Among the other hypotheses, we propose one that genetic divergence of intercropped rice varieties plays a roles in enhancing resistance rice varieties to blast diseases. To test this hypothesis, we developed a rapid, accurate and effective method to determine the level of genetic divergence between rice varieties using neutral molecular markers (InDel). This method can quantitatively determine the level of genetic divergence index (GDI), ranged hypothetically between 0.00~1.00, between the intercropped varieties. A large number of widely used rice varieties for intercropping in Yunnan were examined for their GDI using the InDel markers. We selected 19 varietal combinations with either high or low GDI for field experiments to determine the correlation between genetic divergence of intercropped rice varieties and their efficiency of resistance to rice blast diseases in the field. Results from field experiments indicated significant positive correlation (R20.92, P0.01) between GDI of intercropped varieties (major and minor) and their efficiency of blast control. Rice varieties under the intercropping mode with higher genetic divergence level demonstrated a significant impact on their efficiency of resistance to rice blast in the field. This finding has its significant implications not only for understanding the underlying mechanisms of varietal diversity for blast control in rice, but also for predicting the possible field performance of resistance to rice blast in the field.