Effect Of Ryegrass-rice Rotation On Rice Sheath Blight And Rice Blast

Rice sheath blight and rice blast are the two most important and common diseases in rice production,which brought huge losses to the yield of rice every single year,now have become the key factors that restrict the high-stable yield of rice in rice production.At present,chemical fungicides are the main approaches that farmers can count on to fulfill the control and the prevention of rice sheath blight and rice blast,however,long-term usage of fungicides has brought many negative effects while preventing diseases,such as the destruction of environment and the “3R” problems(known as residue,resurgence and resistance)and so on.Ryegrass-rice rotation,one of the forage-crop rotation systems,had been developed among rice fields of southern China in the 1990 s.It has been proven practically that this rotation system,which is a sustainable process that combine plantation and aquaculture,has the advantages of high yield,excellent quality and high efficiency,now is regarded as an agricultural coupling system that synchronize the development of grain and livestock production.However,with the uncertainty of how this rotation system affects rice diseases,not a report relating to this has been reported to date.In view of this,the study of effect of winter cropping ryegrass on the survival rates of pathogens overwintering in paddy field and on the occurrence degrees of two diseases were conducted to verify if the ryegrass-rice rotation has a satisfactory control effect to this two main rice diseases,so that it can provide some more powerful theoretical backgrounds for the futher promotion of ryegrass-rice rotation in the rice districts of southern China.The main results of this study are as follows:1.Effect of winter cropping ryegrass on the survival rate of Rhizoctonia solani overwintering in paddy fieldIn this research,the amounts and germination rates of Rhizoctonia solani sclerotium,as well as rice sheath blight incidences and mycelium survival rates of rice stubble were surveyed three times in December 2015,March and May 2016,respectively.Results of this research indicated that,regarding to the amounts of sclerotium and incidences of rice stubble,no significant differences between the ryegrass area and the control area were seen in every single survey,meanwhile,both the two results did not change significantly in the ryegrass area or the control area among different surveys.As for germination rates of sclerotium and mycelium survival rates,at the very beginning of the whole overwintering process,compared with the control area,both sclerotium germination rate and mycelium survival rate of the ryegrass area were slightly lower,even though no significant differences between them were observed.With the survey time went by,however,results of another two surveys suggested that,there were significant differences between the two areas in clerotium germination rates as well as mycelium survival rates.Here are the differences: sclerotium germination rates of the ryegrass area were 10.25% and 21.69% lower than the control area,respectively.In terms of mycelium survival rates,its values in the ryegrass area were lower than the control area,too,the gaps between them were 22.00% and 25.00%,respectively.The results above show that,winter cropping ryegrass has no influence on the overall amount of Rhizoctonia solani in paddy field,but affect its sclerotium germination rate and mycelium survival rate,so that the amount of living Rhizoctonia solani decline at the end of the overwintering process,which means the initial infection sources of rice sheath blight for subsequent rice decrease.2.Effect of ryegrass-rice rotation on the occurrence degree of rice sheath blightIn this research,the occurrence degree of rice sheath blight were examined three times altogether by doing the sampling surveys in both ryegrass area and control areain July,August and September 2016,when rice plants were in their different cultivation periods.Results of this research revealed that,at the same survey time,both disease incidences and disease indexes of the ryegrass area were significantly lower than the control area.For instance,compared with the control area,disease incidences in the ryegrass area were 3.60%,14.04% and 24.17% lower,respectively.Disease indexes were quite similar to disease incidences,which were 1.25,3.06 and 6.42 lower in the ryegrass area when compared with the control area.By analyzing the results above,it is clear that the occurrence degree of rice sheath blight in the ryegrass area are slighter than the control area during the same period of time.So this give the evidence that rice sheath blight could be restrained by implementing ryegrass-rice rotation in paddy fields.3.Effect of winter cropping ryegrass on the survival rate and sporulation capacity of Magnaporthe oryzae overwintering in paddy fieldRice blast incidences as well as mycelium survival rates of rice stubble,together with sporulation capacities of Magnaporthe oryzae were examined by further research on the rice stubbles collected from both the ryegrass area and the control area in December 2016,February and April 2017.Results of this research suggested that,every survey there were no significant differences observed when the incidences of rice stubble of this two areas are concerned,also,no significant differences were seen in the ryegrass area or the control area at different survey times.However,the survival rate of mycelium in the control area were higher than the ryegrass area in significant ways,its differences of this two areas were 10.40%,19.20% and 24.00%,respectively.When it comes to the sporulation capacity,significant differences were also seen in the amounts of spores in every single vision of microscope of this two areas,compared with the control area,the amounts of spores in the ryegrass area were 2.39,3.70 and 5.73 less,respectively.The results above indicate that,winter cropping ryegrass do not affect the overall amount of Magnaporthe oryzae,but considerably reduce its survival rate as well as its sporulation capacity,making the amount of the living Magnaporthe oryzae dropped off when the overwintering process finish,so that the initial infection sources of riceblast for subsequent rice decrease accordingly.4.Effect of ryegrass-rice rotation on occurrence degree of rice blastThrough the method of sampling Investigation,the occurrence degrees of rice blast(leaf blast and panicle blast)were examined when rice plants were at different stages of growth and development.The results showed that,through all the three investigations,the incidences of rice blast in the ryegrass area were significantly different from those of the control area.The first investigation,which was an investigation on leaf blast taken in July 2017,showed that the incidence of leaf blast in the ryegrass area was 5.60% lower than the control area.Another two investigations on panicle blast taken in August and September 2017 revealed this similar inferior positions of the ryegrass area in disease incidence,the incidences of panicle blast in the ryegrass area were 10.00% and 9.94% lower respectively when compared with the control area.This big differences were also seen in disease indexes of this two areas,among all three investigations,disease indexes of the ryegrass area were lower than the control area all the way,the gaps between them were 1.47,2.97 and 3.45,respectively.It is obvious that,during the same investigation time,both disease incidences and disease indexes of the ryegrass area are lower than those of the control area,remarkably.So,by implementing ryegrass-rice rotation in paddy fields,the spread of rice blast could be inhibited at a certain extent.