Study On Etiology And Preliminary Control Methods Of Watermelon Root Rot

Root rot of watermelon is a disease caused by deuteromycetes Amon fungal. Recently, it has become one of the major diseases in watermelon areas. According to reports, watermelon and grafted watermelon both are susceptible to the disease. It has caused serious economic losses.Watermelon grafting technique is an effective means to prevent and control soil-borne diseases and the current penetration of grafted watermelon has reached to40%. Currently related research is relatively small. Systematic research on the etiology and prevention methods of watermelon root rot is still blank. Through pathogens isolation and identification, biological characteristics and control methods, my research aimed to clear the pathogens and make scientific and rational control methods. Concrete findings are as follows:1. Using conventional organization separation and single spore purification method,53isolates were finally acquired. According to the taxonomic system of Nelson these isolates were classified into Fusarium solani(44.3%), Fusarium commune (28.5%), Fusarium verticillioide(15.1%), Fusarium proliferatum(13.2%) based on the morphologi-cal characteristics.2. Using spore suspension (106spore/mL) dipping inoculation method to test the pathogenic of isolates, and Fs-8was identified as the pathogen. The result was verified by the EF-la gene sequence analysis and found Fs-8exhibited100%similarity with F.solani (FN689821.1, FN689824.1, FN689827.1). Using MEGA5.0to draw the Neighbor-Joining tree, the result shows that Fs-8and F.solani were in the same cluster, which was consistent with the results of morphological identification.3. Using inoculation and specific primers methods to indentify the biotypes and physiological races of Fs-8. The results showed that Fs-8were pathogenic to watermelon,Gourd, pumpkin seedlings and watermelon fruits. The result was verified by the specific primer of Fusarium solani f. sp. cucurbitae race1and found a specific amplification product with size of505bp. Based on morphological characteristics, pathogenicity and molecular results, Fusarium solani f. sp. cucurbitae race1was identified as the pathogen casuing watermelom root rot.4. Using PDA media and fungal physiological media to clear the effects of different temperature, pH, carbon and nitrogen on the growth and sporulation of Fs-8. The results showed that the optimum temperature for Fs-8growth and sporulation is28℃～30℃; the optimum pH is5to10; Fs-8can well utilize many kinds of carbon sources; the suitable nitrogen is nitrate nitrogen such as KNO3, Ca (NO3, NaNO3, but ammonium-Nitrogen (NH4-N) such as (NH4)2SO4, NH4Cl is not favorable for Fs-8growth and sporulation.5. Using staining methods to study the Fs-8infection pathway. The results showed that after Fs-8enter the root of watermelon through wounds, mycelium expansion slowly in the gap of parenchyma cells and make the parenchyma cells disintegrated; chlamydo-spores were produced around the rupture site; chlamydospores transferred to a new site and germination to start another infection cycle.6. Using toxic media method to clear the inhibition ability of thiophanate-methyl, carbendazim, mancozeb, phenyl ether prochloraz, difenoconazole, hymexazol, trifloxystrobin-tebuconazole seven fungicide on Fs-8growth.The results showed that phenyl ether prochloraz, trifloxystrobin-tebuconazole and carbendazim with EC50of0.7261μg mL/-1,0.7529μg mL/-1and0.8774μg mL-1has the highest inhibitory effection.7. Using spore suspension(106spore/mL)dipping inoculation method to evaluate the resistance of76rootstocks. The result showed that RSH2、 RSN7. RSN1、RSN15、 RSN22、RSN30are resistant to Fs-8.