Occurrence Of False Smut Of Late Japonica Rice In Jiangxi Province And Its Control Techniques

Rice false smut [Ustilaginoidea virens(Cooke) Takahashi] is an important disease in the rice panicle and a significant threat to rice yield and quality. With the promotion of “japonica replace indica rice” in Jiangxi province, false smut has become the bottleneck which restricts its development. The objective of this study is to investigate the resistance of introduction varieties of late japonica rice to rice false smut in Jiangxi province, to test cultivation modes on the occurrence of rice false smut, to screen fungicides against rice false smut and its using technologies and to provide basis for the extension of resistance varieties of late japonica rice in Jiangxi province and integrated control against rice false smut. The resistance of 27 introduction varieties of late japonica rice to rice false smut in Jiangxi Province was identified by natural infection, the effect of different rice cultivation modes(rice sowing and transplanting period, transplanting density, nitrogen fertilizer amount and its application mode) on the occurrence degree of the rice false smut was studied by field trials, indoor toxicity of 10 fungicides against rice false smut was assayed by measuring mycelial growth rate, the efficacies of 10 fungicides against rice false smut and the effects of spray timing and times on the efficacies of 3 fungicides were conducted by field trials. The results are as follows:1. The results of field identification showed that there was a big difference among the resistances of different rice varieties to rice false smut, and the disease panicle rate of 27 late japonica rice varieties was 0.26~23.26%, and the disease index was 0.10~7.00%. There were 3 high resistance varieties, 14 resistance varieties, 7 middle resistance varieties and 3 middle susceptible varieties among 27 tested varieties according to disease panicle rate for resistance evaluation index. There were 25 high resistance varieties and two resistance varieties according to disease index for resistance evaluation index. From integrated evaluation of resistance according to diseased panicle rate and disease index, late japonica rice varieties, ‘Changjiang 32’, ‘Changyou 5’ and ‘Chishugeng 5’ were high resistant to rice false smut, suitable for the promotion of the rice area in Jiangxi province.2. The results of different rice cultivation modes showed that different sowing and transplanting timing, transplanting density, nitrogen fertilizer amount and its application mode had obvious differences on the occurrence of the rice false smut. Rice false smut occurred more heavily when sowing and transplanting periods was late, and more heavily when a higher transplanting density was present, and more heavily when more total nitrogen per hectare existed. Increasing nitrogen(panicle fertilizer) was benefit to the occurrence of rice false smut during the late rice growth period under using equal amount of nitrogen. Therefore, late japonica rice should be as far as possible in advance of sowing and transplanting under affecting no rice growth and yield. Under satisfying the basic requirement of rice nitrogen amount, the application of base fertilizer should be increased in the early stage in order to promote rice yield, and the application of panicle fertilizer should be decreased in the late stage in order to reduce occurrence of the disease.3. The results of indoor toxicity bioassay showed that relative toxicity index of 10 kinds of fungicides against mycelium growth of rice false smut were 168.49(fenbuconazole), 111.08(thifluzamide), 107.84(azoxystrobin, 91.68(epoxiconazole), 83.47(difenoconazole·propiconazole), 42.34(tebuconazole), 21.51(prochloraz), 12.92(hexaconazole), 1.32(triadimefon and 1(Jinggangmycin A) by the largest LC50 value of jinggangmycin A for pharmaceutical standard, respectively. The field tests revealed that the efficacy of thifluzamide(24% SC) against rice false smut was the highest among 10 tested fungicides according to spray with the recommended using dose in paddy field in heading, followed by azoxystrobin(25% SC), fenbuconazole(24% SC) and epoxiconazole(12.5% SC), again for tebuconazole(43% SC) and triadimefon(15% WP). The efficacies of hexaconazole(30% SC), prochloraz(25% EC), difenoconazole·propiconazole(300g/L EC) and jingangmycin A(5% SP) were poor. From integrated analysis of the indoor toxicity and field efficacy, thifluzamide 24%SC, fenbuconazole 24% SC, epoxiconazole 12.5% SC and azoxystrobin 25% SC were ideal fungicides for controlling rice false smut.4. The results of field trials on different spray timing and times showed that the efficacies of fenbuconazole(24% SC), epoxiconazole(12.5% SC) and thifluzamide(24% SC) against rice false smut decreased with delaying spray timing at 7 d before heading, heading and 7 d after heading, of which was the best with spray at 7 d before heading, and was the worst with spray at 7 d after heading. The efficacies of 3 fungicides against rice false smut rose with increasing spray times with spraying once(at 7 d before heading), 2 times(at 7 d before heading and heading) and 3 times(at 7 d before heading, heading and 7 d after heading), of which was the best with spraying 3 times. Therefore, fungicide for controlling rice false smut would be sprayed at 7 d before heading. Spraying times should be appropriately increased 1 application in order to improve the control effect when rice heading period met cloudy and rainy weather.