Abstract: Cnaphalocrocic medinalis is one of the main pests in rice producing areas in China, and chemical control is usually used in practice. Chemical residues would have environmental consequences, particularly in the rice-crayfish symbiotic mode where chemical control increases the risk of healthy crayfish farming. It is necessary to explore and utilize biodiversity to control rice diseases and insect pests. Based on the rice-crayfish symbiosis mode and the traditional one-season medium rice mode, we conducted a field experiment of mixed cropping of different rice cultivars. During the experiment, we recorded the occurrence of Cnapalocrocis medinalis under single cropping of four rice cultivars (Y Liangyou 911, Huanghuazhan, Meixiangzhan 2 and Xiangyaxiangzhan) and mixed cropping of two rice cultivars (Y Liangyou 911 + Meixiangzhan 2, Meixiangzhan 2 + Xiangyaxiangzhan), and measured main indices of rice growth and metabolism. Compared with the rice-crayfish symbiotic mode, leaf rolling rate of rice was increased by 173.93% under the traditional medium rice mode. Plant height, tiller number, leaf area index (LAI), and aboveground dry matter weight (DW) were increased by 5.82%, 16.44%, 19.51% and 15.84%, respectively. Wax content, SPAD, and net photosynthetic rate (P_n) of leaves were increased by 11.09%, 3.36% and 6.50%, respectively. Effective panicle and rice yield were increased by 17.58% and 20.69%, respectively. Compared with rice monoculture, mixed cropping decreased leaf rolling rate, and increased tiller number, LAI, and DW. In mixed cropping of two rice cultivars that have great difference in silicon content, wax content, and P_n of the leaves, the aforementioned index values of the two mixed cropping cultivars were between their monoculture, but the SPAD value was usually lower than that of their monoculture. Under mixed cropping, the effective panicle number and grain number per panicle were between those of the two mixed cropping cultivars, but seed setting rate and 1000grain weight showed no difference. The effect of mixed cropping on yield varied with cultivar and environment. Our results suggested that mixed cropping of rice cultivars can be used as an effective means for green controlling of Cnaphalocrocis medinalis.

Key words: rice-crayfish symbiosis, mixed cropping of rice cultivars, Cnaphalocrocis medinalis, leaf rolling rate, rice yield.