The Effect Of Different Nitrogen Fertilizers On The Incidence Of Bacterial Wilt In Tomato

Tomato(Solanum lycopersium)is one of the vegetables with the largest cultivated area in China,but various diseases have seriously affected their growth,yield and quality.Ralstonia solanacearum is the causal agent of bacterial wilt and causes the most serious harm in crops and economic loss.Bacterial wilt is a soil-borne disease.The high temperature and humidity is easy to cause the incidence of bacterial wilt.Tomato is a crop of high fertilizer requirement,which mainly extracts the nutrients needed for growth and development from the soil.Among all kinds of fertilizers,nitrogen fertilizer is used most widely.It has an important impact on the productivity and quality of crops,but over-application will cause the disease,such as Botytis cinerea,bacterial spot disease and so on.At present,the effect of nitrogen fertilizer on the incidence of bacterial wilt is still unclear.In this study,we used tomato as the experimental material to study the effects of different nitrogen fertilizers on the incidence of bacterial wilt.The results are as follows:1.The identification,isolation and preservation of R.solanacearumIn order to obtain highly pathogenic R.solanacearum strain,we used the medium to screen,and extracted from the stems as the separation source.Then we used the inoculation detection method to test the pathogenicity of R.solanacearum.After the identification and isolation,we preserved the R.solanacearum strain with high virulence to be used for the further research.2.The effect of different nitrogen fertilizers on the incidence of bacterial wilt in tomatoWe used the hydroponics cultivation and after the different treatments of 7 mM NO3--N/7 mM Mix-N[NO3--N/NH4+-N(concentration rate=7:3),the same as below]/1 mM NO3--N/1 mM Mix-N,we found that the NO3--N content and NR activity in tomato leaves decreased in vitro.And after the inoculation of R.solanacearum on the roots of tomato plants,7 mM Mix-N treated tomato plants had the most serious disease,while 1 mM NO3-N treated plants had the mildest incidence,indicating that low N concerntration of 1 mM compared with 7 mM can alleviate the occurrence of bacterial wilt in tomato,and high NO3--N content conditions at the same concerntration can also alleviate the incidence of bacterial wilt.We also found that the relative expression of NR/NiRl/NiR2/GS2/Fd-GOGAT were all in the level of 7 mM NO3--N>7 mM Mix-N>1 mM NO3--N>1 mM Mix-N.What's more,after inoculation by R.solanacearum,PR related genes were up-regulated;and the contents of SA and JA were also increased by 50%.It is indicated that high N fertilizer application and NH4+ content can aggravate the incidence of bacterial wilt in tomato;and different nitrogen fertilizers in the rhizosphere can affect the sensitivity of tomato plants to R.solanacearum by affecting the activity of key enzymes involved in the nitrogen metabolism.3.The effect on the incidence of bacterial wilt in tomato after nitrogen metabolism key genes silencingWe used the Virus-induced gene silencing technology to construct the key genes silencing plants with nitrogen metabolism.After the inoculation of R.solanacearum,the disease index of TRV:NR/TRV:NiRl&2/TRV:GS2/TRV:Fd-GOGAT decreased by 25%-40%compared with TRV:0.The relative expression of PR1 and PR5 was up-regulated significantly,and the up-regulation multiple of the gene silenced plants was significantly higher than TRV:0;the contents of SA and JA in roots were significantly up-regulated,and the content of SA in the gene-silenced plants was 1.5-2.25 times of TRV:0,while the content of JA was less than TRV:0.It is proved that after silencing the key genes of nitrogen metabolism,the resistance to bacterial wilt in tomato is improved,and at the same time,the content of SA which is relative to disease resistance is accumulated,but the regulatory mechanism is necessary to be researched in the future.