Improvement Of Culture Medium For Sclerotium Rolfsii And Evaluation Of Field Efficacy And Safety Of Its Granules

Sclerotium rolfsii strain SC64 "junkekuo" granules is a kind of bio-herbicide,which can be used to control most of the broad-leaved weeds and some of the sedges in rice fields.It is necessary to systematically evaluate the field efficacy of the product.Previously,the field efficacy test has been carried out in seven provinces,but the rice planting area in China is widely distributed,and the test scope needs to be further expanded.The safety of subsequent crops after application has not been clear and the cost of liquid fermentation still can be reduced.According to the climate characteristics of different rice regions in China,10 experimental sites were selected for the field efficacy test to evaluate the control effect in different climate conditions and different regions.At the same time,different rice areas were selected to plant local crops,in order to evaluate the safety of S.rolfsii to different crops.In addition to the field experiment,the liquid fermentation medium was further improved to reduce the cost.The results of each experiment are as follows:First of all,according to the climatic characteristics of rice growing areas in China and the new pesticide registration regulation,10 test sites were selected in the lower and middle reaches of the Yangtze River rice zone,the South China rice zone and the southwest rice zone,including Hunan,Hubei,Jiangxi,Henan,Zhejiang,Jiangsu,Shanghai,Guangdong,Guangxi and Sichuan provinces,which were used to systematically carry out the field efficacy evaluation,so as to understand the adaptability and control effect of the bio-herbicide under different climatic conditions.In this experiment,7 different treatments were designed,including 4 different doses of the S.rolfsii granules(120 kg/ha,180 kg/ha,240 kg/ha,360 kg/ha),at the same time,10%bensulfuron methyl wettable powder,mannual weeding and blank control were used as the control.The effect of plant mortality 15 DAT,the plant mortality and fresh weight reduction 30 DAT were investigated.Based on the analysis of control effect of different test points,the results are as follows:except for a few test sites affected by the weather,the average control effect on broad-leaved weeds(Monochoria vaginalis,Lindernia procumbens,Rotala indica)and Cyperus difformis in most of the field trial sites obtained more than 76%,and the control effect was dose-dependent.Pearson’s correlation analysis between the control effect and environmental factors showed that,temperature and latitude were significantly correlated with the control effect of fresh weight.Secondly,because of its wide host range,S.rolfsii may cause a variety of sensitive crops diseases so that its application may bring potential safety risks.By observing the incidence of the symptoms of southern blight in rice growing process and measuring its yield,the safety of the bioherbicide to rice was comprehensively evaluated.The results showed that there was not the symptoms of southern blight during rice growing process of 10 indica and japonica rice varieties.At the same time,the rice yield of the treatment plots was significantly higher than that of the blank plot and the rice yield increased with the increase of the application dose.The results indicated that the S.rolfsii granules were safe to rice.The mycelium will form sclerotia and remain in the soil after infecting the target weeds and the sclerotia may germinate and infect the sensitive crops during the growth of the next crop under the suitable conditions.At present the safety test of the bioherbicide has been conducted on the following crops of winter wheat and rape in Jiangsu Province,but the safety to other following crops is not clear yet.Therefore,a test site was selected in different rice growing zones to plant the local conventional following crops and observe the emergence rate of crops,the occurrence of the symptoms of southern blight and the impact of yield,comprehensively evaluate the safety of the S.rolfsii granules to different crops.The results showed that there was no significant difference in the emergence rate,growth and yield of four kinds of crops,including green vegetables,radish,celery and potato,between the plots with and without the application of S.rolfsii granules and the growth stage was normal without the symptoms of southern blight.Therefore,it is safe for the following crops after the application of S.rolfsii granules.Finally,on the premise of the growth quality of S.rolfsii,by measuring the dry weight of mycelia,oxalic acid content and infection diameter,the more optimized culture medium was selected to further to reduce the production cost of S.rolfsii and provide technical basis for promoting its commercial development.In this experiment,Solanaceae plants and potato components were mainly used to replace the potatoes in the original improved culture medium.Through the determination and analysis of three detection indexes of different improved medium,the results showed that 30 g tomato,2.2 g potato protein powder,30 g tomato plus 8 g potato starch and 20 g tomato plus 1.1 g potato protein powder can effectively replace the potatoes in the original improved culture medium,but 12g potato starch medium was the cheapest among all the tested media but the price of potato will fluctuate with different seasons in different regions.Therefore,with substition of 40g potato in the original improved medium,12g potato starch medium may be the best improved medium for submerged culture of S.rolfsii.In conclusion,the results showed that the S.rolfsii granule had significant control effect on broad-leaved weeds and Cyperus difformis in main rice zones of China under different climate and environmental conditions,and it was safe for the rice itself and succeeding crops in different rice zones.The improved medium is cheaper which reduced the production cost of the granule.This may lead the product to be in practical use.