Abstract: To clarify the effects of the mycotoxins of Ustilaginoidea virenson physiological0biochemical characteristics of different resistant rice varieties, the susceptible variety 9311 and the resistant variety IR28 were treated with the crude toxin ofU. virens. The effects of toxin on the growth of radicle, germ, seedling stem and leaf, hypersensitive reaction of leaves, defense enzyme activity, soluble protein (SP) and esterase (EST) isozyme of seedling were analyzed. The results showed that the crude toxin of U. virens inhibited the growth of radicle, germ, seedling stem and leaf of resistant and susceptible varieties, with higher inhibitory effect of toxin on susceptible cultivar 9311 than cultivar IR28. The toxin caused hypersensitive reaction in leaves and disease symptom. Under the stress of toxin, the enzyme activities of SOD, POD, PAL and PPO of resistant and susceptible varieties increased by different magnitude compared with the control, and the peak value increased by 8.79%-34.29%. The activities of POD and PAL increased slowly at first, reached the peak along with the extension of toxin treatment time, and then decreased gradually. The activities of SOD and PPO decreased sharply at first and then increased slowly, reached the peak, and then decreased gradually. The activities of four enzyme of the resistant cultivar IR28 were higher than that of the susceptible cultivar 9311, with peak values being 17.85% to 58.30% higher. After treated with mycotoxins, the content of SP in rice seedlings decreased to some extent. The content of SP in cultivar IR28 was higher than that in cultivar 9311, and reached the highest at the fifth day, which was 51.37% higher in cultivar IR28 than cultivar 9311, and the color of SP band of IR28 was darker than that of cultivar 9311. In addition, the EST isozyme bands of the two cultivars became lighter along with the prolongation of treatment time, but the EST isozyme bands of cultivar IR28 were darker than those of cultivar 9311. This study provided scientific basis for the application of mycotoxins ofU. virens in identification and breeding for disease resistance cultivar.

Key words: Ustilaginoidea virens, rice, cultivar resistance, defense enzyme, soluble protein.